2011 Energy Saving Potential and Strategies for Electric Lighting in Future North European, Low Energy Office Buildings a Literature Review

Energy and Buildings 43 (2011) 2572–2582Contents lists available at ScienceDirect Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild Review Energy saving potential and strategies for electric lighting in future North European, low energy office buildings: A literature review Marie-Claude Dubois ∗ , Åke Blomsterberg Inst. of Architecture and Built Environment, Div. of Energy and Building Design, Lund University, P.O. Box 118, SE-221 00 Lund, Sweden a r t i c l e i n f o a b s t r a c t This article presents key energy use figures and explores the energy saving potential for electric lighting in office buildings based on a review of relevant literature, with special emphasis on a North European context. The review reveals that theoretical calculations, measurements in full-scale rooms and simulations with validated lighting programs indicate that an energy intensity of around 10 kWh/m2 yr is a realistic target for office electric lighting in future low energy office buildings. This target would yield a significant reduction in energy intensity of at least 50% compared to the actual average electricity use for lighting (21 kWh/m2 yr in Sweden). Strategies for reducing energy use for electric lighting are presented and discussed, which include: improvements in lamp, ballast and luminaire technology, use of task/ambient lighting, improvement in maintenance and utilization factor, reduction of maintained illuminance levels and total switch-on time, use of manual dimming and switch-off occupancy sensors. Strategies based on daylight harvesting are also presented and the relevant design aspects such as effects of window characteristics, properties of shading devices, reflectance of inner surfaces, ceiling and partition height are discussed. © 2011 Elsevier B.V. All rights reserved. Article history: Received 28 January 2011 Received in revised form 10 June 2011 Accepted 3 July 2011 Keywords: Office Lighting Daylight harvesting Occupancy controls Manual or automatic dimming Potential electricity savings Illuminance Windows Shading devices Reflectance Contents 1. 2. Introduction: energy use in office buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Energy saving potential and strategies for office lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Actual energy use for office lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Energy saving potential for office lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Strategies to reduce energy use for lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1. Strategies related to electric lighting installations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2. Strategies related to daylight harvesting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2572 2573 2573 2573 2574 2574 2577 2580 2580 2580 3. 1. Introduction: energy use in office buildings Commercial buildings, and primarily office buildings, are classified among the buildings presenting the highest energy Abbreviations: CFL, compact fluorescent lamp; DLQ, designer’s lighting quality; EEG, electroencephalography; HF, high frequency; LCD, liquid crystal display; LED, light emitting diodes; LENI, lighting energy numeric indicator (kWh/m2 yr); LOR, light output ratio; LPD, lighting power density (W/m2 ); MF, maintenance factor; NPD, normalised power density (W/m2 100 lx); U, utilance; WWR, window-to-wall ratio. ∗ Corresponding author. Tel.: +46 46 222 7629. E-mail address: [email protected] (M.-C. Dubois). 0378-7788/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2011.07.001 consumption. The total annual energy use in office buildings varies in the range 100–1000 kWh/m2 yr, depending on the geographic location, use and type of office equipment, operational schedules, type of envelope, use of HVAC systems, type of lighting, etc. [1]. In Northern Europe, office energy intensity lies in the range 269–350 kWh/m2 yr and for offices all over Europe, it is about 306 kWh/m2 yr, with mean electric index 150 kWh/m2 yr and mean fuel index 158 kWh/m2 yr [2]. Recently, an inventory of energy use in 123 Swedish office buildings of different age revealed that office buildings have an energy intensity of 210 kWh/m2 yr in average, with a high electricity use by square meter (93 kWh/m2 yr excluding heating) [3,4]. 6].5 W/m2 . lighting normally accounts for 25–30% of electricity use in non-residential premises [4. annual electricity use for lighting was calculated to be 28 kWh/m2 yr if the lights were switched on 9 h/day. which is × 500 lx = 9. which varies according room type: 13. and 8. for example. a reduction of around 9 kWh/m2 yr has thus occurred in 20 years [3]. through simulations using the validated programs Rayfront/RADIANCE and DAYSIM. Å. 60 and 100% ¸ window-to-wall ratios). we obtain: LPD = NPD × Etask = 1.3 W/(m2 100 lx) The recent 2010 Energy Performance of Buildings Directive (EPBD) places a high demand on building professionals to produce (and eventually retrofit) office buildings to near-zero energy use levels.5 W/m2 (1) These values are in line with the values measured in the recent Swedish inventory reported earlier [4]. with a mix of active and passive users. The data for electric lighting showed average energy use ranging from 15 to 25 kWh/m2 yr depending on type of building. Blomsterberg / Energy and Buildings 43 (2011) 2572–2582 2573 Nomenclature Etask Swindow Sfloor illuminance on the task area (lx) window area (m) floor area (m) Greek letters ˚lum luminous flux emitted by the luminaire (lm) luminous flux emitted by the lamp (lm) ˚lamp ˚TA Luminous flux reaching the task area (lm) calculated as the power density divided by the mean maintained illuminance on a reference plane is a more interesting metric since it allows a simple and straightforward comparison between different spaces with different illuminance requirements. the calculated annual energy use ranges from 20 to 7 kWh/m2 yr. Assuming a LPD of 12 W/m2 . Assuming.9]. The study included single-cell and open-plan offices with three different facades (30. the consumption was less than 20 kWh/m2 yr. actual target NPD-values for efficient lighting installations with fluorescent lamps and a high degree of installation maintenance should be 1.13]. Assuming manual light switching. lighting is an important issue in minimizing overall energy consumption [10]. Santamouris et al. as well as the consumption for office equipment were monitored. modern office buildings have a high energy savings potential [5. and in comparison to a case with manual on/off switch near the door. This article explores the potential and strategies for energy savings in office lighting including control systems mainly in Northern Europe with some specific information from Sweden.1 W/m2 for individual office rooms. With a perfectly commissioned photosensor dimming system. A combination of occupancy sensors and daylight dimming provides the lowest energy intensity values.6 W/m2 for common rooms (including corridors). 5 days/week. lighting constitutes generally 20–45% of electricity demand [6] but it varies a lot from one building to another and the consumption of electric lighting can sometimes be as much as 40% of the gross energy consumption in some buildings [8]. cooling. Regarding the average LPD. Average LPDs of 7–11 W/m2 is achievable using efficient lamp circuits (based on T8 i. a task illuminance (Etask ) target of 500 lx. Electric lighting is one area where energy savings are possible at reasonable cost in new buildings as well as in retrofit projects. room surface reflectance. light source and the application.-C. Dubois. and mixed users. Sweden. Note that in 1990. and lighting purposes. In Sweden. Taking into consideration a reference annual time of use (2500 h) and various lighting control strategies.4 W/m2 for landscape offices.5–11. Bülow-Hübe [9] investigated the daylight availability and electricity use for lights in offices located in Gothenburg. The article is based on a literature review carried out as part of the Swedish project ‘Energy-efficient office buildings with low internal gains: simulations and design guidelines’. In commercial buildings. Hanselear et al. which results in annual energy use in the range 30–17 kWh/m2 yr depending on the selected lighting control strategy (see Table 1). Depending on room size. 2. for example.M. expressed in W/m2 100 lx). lighting accounts for around 10% of total energy consumption in the country. If occupancy and daylight sensors are integrated in the installation. the annual energy consumption for lights may come down to as low as 5 kWh/m2 yr. This study thus demonstrated by simulation that it is possible to cut down electricity use for office lighting by about 50% (from 23 to 11 kWh/m2 yr) using existing technology.e. this standard recommends an installed LPD under 12 W/m2 with preferable target under 10 W/m2 . 26 mm fluorescent tubes and standard electronic high frequency ballasts) for general office lighting of 300–500 lx [see 14]. Energy saving potential and strategies for office lighting 2. 12. lighting electricity use obtained was in the range 11–18 kWh/m2 yr. Recently.2.1. the electricity use obtained dropped to 20–23 kWh/m2 yr.9–2.12. [10] noted that this widely used indicator does not take into account the requirement for the mean illuminance. 2. Around 50% of the buildings presented a lighting consumption inferior to 11 kWh/m2 yr while for the majority of buildings (86%). The most significant environmental impact (80–90%) of lighting is generated during the operation of the lighting system. Energy saving potential for office lighting According to Borg [15]. while electricity use during operation represents around 70% of total costs [12]. the cost of an electric lighting installation typically represents only 15% of total costs. where the specific energy consumption of the buildings for heating. The recent inventory of 123 office buildings of varying age by the Swedish Energy Agency [4] revealed an average energy intensity of 21 kWh/m2 yr for office lighting and an average installed lighting power density (LPD) of 10. the normalized power density (NPD. office electric lighting was 30 kWh/m2 yr in Sweden. In Sweden.3 W/(m2 100 lx) [14]. In other countries. One recent study [7] indicated that investments in energy-efficient lighting is one of the most cost-effective ways to reduce CO2 emissions and many studies show that electricity use for lighting could be reduced by 50% using existing technology [8. For large office rooms (>12 m2 ). . According to these authors. The good news is that according to previous research. which shows the large potential for energy savings through control strategies (up to 65% reduction). an existing office (in Sweden) uses around 23 kWh/m2 yr for electric lighting whereas a modern advanced installation may only use 11 kWh/m2 yr.9–2. The European standard EN-15193 [17] presents LENI (Lighting Energy Numeric Indicators) prescribing installed LPD for small individual office rooms of 10 W/m2 with preferable target around 8 W/m2 (for ‘normal’ illuminance levels for offices). and this area offers considerable potential for energy savings [11]. [16] reported the findings of a large monitoring campaign in 186 office buildings in Greece. Actual energy use for office lighting Globally. In the past. Occupancy sensors and/or manual/automatic dimming. Use of task/ambient lighting. Also.1. which means that it will be developments in the design and control of lighting installations that are likely to provide substantial energy saving opportunities in the immediate future [22]. An overview of the related energy savings is presented at the end (see Table 2).-C.75 0. 12 Pref.19]. Reduction of switch-on time. Improvement in ballast technology. today’s most energy-efficient practice scenarios use modern technologies available on the market.90 0.3. Improvement in maintenance factor. Recent statistics for Sweden show that fluorescent lamps with conventional ballasts represent nearly half (46%) of the installed electric lighting power density in offices [6]. which implies that it takes about 33 years to replace old lighting installations with new. Effect of window characteristics. older T12 lamps. The light efficacy of LEDs is increasing very quickly. The next sections discuss each strategy in detail. energyefficient ones [13]. The research by Santamouris et al. there might be an increase in energy use for heating. traditional incandescent lamps represent 12% of total installed lighting power density [4]. he also demonstrated with simple calculations that it is likely that greater savings are achievable. T5 or metal halide light sources and efficient luminaires. and this. 2. Improvement in lamp technology.75 Daylight control LENI (kWh/m2 yr) Manual control + Absence/presence control 15 12 27 23 15 11 + Daylight control 0. Effect of reflectance of inner surfaces. about half the savings were due to the task/ambient lighting approach and about half to the controls applied to the task/ambient lighting system. which means that fewer lamps need to be disposed of in time [15]. Dubois. Note that the replacement rate of lighting systems is low.4 kWh/m2 yr respectively.2574 M. 2. Newer T5 16 mm lamps have even higher efficacies (90–104 lm/W) achieving a 40% reduction in energy use (compared to T12 lamps of 60 lm/W with magnetic ballasts) but these lamps need different fittings [13. especially the T5 lamps.77 0. about 3% per year in Sweden. . Reduction of maintained illuminance levels.5 and 1. Changing a conventional fluorescent tube with a T5 tube can allow saving electricity use by up to 80% (including savings from the HF ballast.18]. [16] in Greece.g. in cold climates. Strategies related to electric lighting installations 2. Also. Type of room LPD (W/m2 ) Reduction factor Manual control Individual office rooms (>10 m2 ) Obl. Å.1. recent statistics (for Sweden) [4] indicate that many existing lighting installations still use T8 or even. better luminaire and occupancy + daylight dimming) and at the same time obtain flicker-free light. However. which have a much lower luminous efficacy (lm/W). that light emitting diodes (LEDs) should provide the majority of light sources by 2035 [20].8 0.56 0. contain less mercury than older lamps and have a longer lamp life. Blomsterberg / Energy and Buildings 43 (2011) 2572–2582 Table 1 Guidelines for installed LPD (W/m2 ). Improvement in ballast technology. indirect energy savings can also be obtained because of the reduced heat production and cooling needs [10. Effect of ceiling height.1. it has nearly doubled every other year. Strategies related to daylight harvesting: Effect of latitude and orientation. Current predictions reveal.3.57 0. Effect of partition height. not even 40% of lighting installations have been changed and it will take another 20 years before the potential for energy savings is fully exploited [13].3. 10 Pref. 2. 6 Absence/presence control 0. would reduce the total energy requirements for lighting by up to 35%.90 0. According to Borg [15]. reduction factors and LENI (kWh/m2 yr).2. Also worth noting: besides direct electricity savings due to reduced use of lights. which consisted of a large monitoring campaign in 186 office buildings. ballasts were relatively simple wire-wound devices and consumed an apprecia- 1 In his calculations.56 0. Although T5 fluorescent lamps have existed for 15 years. A theoretical calculation [3] has shown that changing all fluorescent tubes to T5 tubes and all incandescent light bulbs to compact fluorescent lamps (CFL) in Sweden would reduce the energy intensity for electric lighting in offices by 5. which means extensive use of occupancy and daylight sensors. Loe [14] also presented detailed calculations showing that 50% savings are possible when an installation has a task and building lighting approach and is controlled to provide illumination only when needed1 . with existing technology.1.75 0. The next section examines the strategies to implement in order to reach such low energy intensities. e. Replacing T12 with T8 lamps can save up to 10% of the energy consumption while giving 10% more light [19]. white LEDs with a light efficacy of 100 lm/W were available [21]. Since 1995. new lamps. which is likely to be smaller than the electricity savings. showed that the replacement of the existing lamps with fluorescent lamps with an efficacy of 80 lm/W.57 20 16 30 25 20 15 8 7 21 17 9 6 These various sources indicate that it is possible to achieve energy savings of the order of 45–65% depending on room type and control strategy. In 2009. Strategies to reduce energy use for lighting Strategies to reduce energy use for electric lighting in offices include: 1) • • • • • • • • • 2) • • • • • • Strategies directly related to the electric lighting installation: Improvement in lamp technology.75 0. Effect of shading devices. Incandescent lamps which are changed for a CFL are directly economical and provide up to 15 times increase in durability for these types of lamps [4]. 8 Large office rooms (>12 m2 ) Obl. Improvement in utilance or utilization factor.8 1 1 1 1 0. However. however.77 0. 8 Pref. the use of very high efficacy lamps (117 lm/W) provided a reduction of up to 55%.3. 10 Corridor Obl. it is expected that more traditional light sources will have a major role to play for some time yet. Improvement in luminaire technology. According to him. Energy saving strategy 1 2 3 4 5 6 7 8 9 10 11 a b 2575 Relative saving potential 10% (T12 to T8) 40% (T12 to T5) 4–8% 40%b 22–25% 5%c Depends on application and context 20% (500 to 400 lx) 6%d 7–25% 20–35% 25–60%e a References [19][13. Dubois. d By reducing average existing total switch-on time to only 2600 h/year. and never as the sole light source. New lighting fixtures reflect light in such a way that more light can be used where needed and less light gets lost in the light fixture itself [14]. with T8 and T5-tubes. The efficiency of the luminaire is defined by light output ratio (LOR): LOR = ˚lum ˚lamp (2) where ˚lum is the initial luminous flux released by the luminaire and ˚lamp is the initial luminous flux released by the lamp. has an influence on visual. However. because illuminance is only provided when and where needed [24]. In addition to better integration with daylight. a task/ambient system often yields lower LPDs. Rogers [24] also suggested using task/ambient electric lighting system where daylight could provide an ambient level of light adequate for circulation and general tasks. the savings appear to be much higher than a more realistic case with e. High frequency (HF) electronic control ballasts. which can be used with both T8.4 W/m2 including the task lamp and respecting the Danish code DS700 (500 lx on task. resulting in a greater base level of energy savings. and a luminaire. represent so far only 27% of the total installed lighting power density in offices in spite of the fact that HF ballasts have existed for 20 years. Modern ballasts however often use electronic circuits. Inefficient ballasts are being steadily phased out across the European Union following the adoption of the Ballast Directive 2000/55/EC [23]. this number also includes dimming (occupancy and daylight) and improved (HF) ballasts. the shading strategy and the base line for comparison (if compared to a case where lights are on 100% of the time. [28] showed that the level of background luminance. Lighting equipment essentially consists of a lamp.). In recent experiments in Denmark [25]. particularly lamps. While the introduction of T5 lamps in 1995 allowed a 40% reduction in energy use compared to T12 lamps. In experiments achieved by Veitch and Newsham [26] in the nineties where nine light conditions including three levels of LPDs (9. and illumination on the task (500 lx) is achieved with individual task lamps. Worth noting that the Danish system is based on previous research which has shown that more uniform (monotonous) lighting normally demands higher illuminance levels and that users are normally more satisfied with control over their own task lamp [25]. both in terms of the electricity it consumed and the cost of equipment. They . 2005. 200 lx in immediate surroundings. the quality of the optical materials (reflectors. and reduction in power demand. However.1.1. measured LPD including task lighting) were rated as providing better quality lighting than systems without task lighting (14 W/m2 ).g. Its value is determined by the optical layout.46] [33. and especially the amount of daylight. The LOR describes the efficiency of the luminaire in emitting lamp flux in lumens into the interior space. Å. it was shown that lighting systems incorporating both task and ambient lighting (9 W/m2 .48.25] [12] [34] [3] [33. The use of new materials. and electric task lighting could provide higher localized illumination.23]. These improvements combined mean that modern lighting installations may use only about one fifth (20%) of the energy used by older installations [13]. etc. compatibility with occupation sensing and daylight control. where relatively low general illuminance levels (50–100–200 lx) required in the office are often provided by a combination of electric light and daylight.3. was too low [25]. Use of task/ambient lighting. better controllability and longer life [20]. allows LOR values of 75% and higher to be obtained [10]. installations combining low level general daylighting/lighting levels with task lighting achieved total LPDs of 5. e This number is highly dependent on the climate. 2.49] [54. this is not a new approach as it was used in the early part of the 20th century when lighting was extremely expensive. use less than half the energy required by the conventional wire-wound types [19]. this number also includes improvements due to HF ballast and improvement in luminaire. 100 lx in remote surroundings and 50 lx for general lighting). This installation resulted in 25% reduction in electricity use compared to a standard energyefficient installation.4. Loe [14] also presented calculations showing energy savings of around 22% (compared to fixed general lighting solution) by simply using a combination of general lighting level (200 lx) combined with task lighting. emotional and even biological aspects. Improvement in luminaires. only low loss magnetic ballasts with typical efficiencies of 85% (depending on the lamp power) and high frequency electronic control gear with efficiency values more than 92% are allowed [10. filters. HF lighting has many advantages: an improved lighting quality. such as coated reflectors and holographic diffusers. c About 5% of light output would be lost each year without a proper maintenance programme.45. Recent statistics [4] for Sweden indicate that fluorescent tubes with HF-ballasts. 2. flicker-free lighting.22] suggested an alternative approach to lighting design which consists of separating the elements of task lighting and building or amenity lighting and to control them both independently. 14. Loe [14. each contributing to the overall efficiency [19]. and particularly the luminance of the walls. diffusers. the combination of new reflector material in lighting fixtures with dimming (daylight and occupancy) allows achieving another 40% energy reduction.19] [19] [13] [14. ble amount of energy – typically 10–20% of the lamp wattage [14].M. Blomsterberg / Energy and Buildings 43 (2011) 2572–2582 Table 2 Overview of energy saving strategies and relative energy saving potential. desktop lamps should not be used for prolonged periods of time. controls and control gear if needed. manual on/off switch at the door). 25 W/m2 ) and three levels of designers’ lighting quality (DLQ) were evaluated by temporary office workers.-C. some researchers [27] expressed reserves about the use of task lighting: because of the increased risk of visual fatigue. Govén et al.and T5-tubes. This approach is already used in Denmark.3. but in an integrated way. Since November 21.74] Improvement in lamp technology Improvement in ballast technology Improvement in luminaire technology Use of task/ambient lighting Improvement in maintenance factor Improvement in utilization factor Reduction of maintained illuminance levels Reduction of total switch-on time Use of manual dimming Use of switch-off occupancy sensors Use of daylight dimming However. the ambient temperature of the lamp and the requirements for preventing glare.3. This was also an important result of the Danish study reported earlier: users complained that the general light level. Tregenza et al. Improvement in maintenance factor. as usually considered.6. first. A high degree of installation maintenance involves cleaning of the luminaires every year.3 kWh/m2 yr thus going from the actual 21 kWh/m2 yr to 19. some specifiers recognize that the most effective lamp and luminaire combination for a given application is often not the one with the highest lamp luminous efficacy.6 kWh/m2 yr for electric lighting using daylight-responsive dimming and assuming normal work hours i. Reduction of maintained illuminance levels.7 kWh/m2 yr [3]. several other studies [40–41] have indicated a preference for very high illuminance levels (including daylight) ranging from 0 to 3000 lx. and that occupants tend to select the middle point of the range available. It depends on: lum efficiency targets and target utilance values for efficient interior lighting have been recently proposed in the literature (see [10]). which is feasible even taking into consideration flextime. schools and shops. the lighting output can be reduced by up to 5% per year [12]. • the arrangement of the luminaires in the room in relation to the position of the task area. 2. Also. walls and ceiling. According to Borg [15]. suggests that lamp luminous efficacy is only partially related to the effectiveness of a lighting installation. Technologies using 6 W and less have been demonstrated with integrated LEDs in Swedish tests and are now being offered by several manufacturers [15]. The rate of reduction of illuminance is influenced by the equipment choice. In Sweden.000 h [14]. which resulted in total annual energy use of 9. [43] claimed that a universally preferred illuminance does not exist since they found that in both seasons the range of illuminance deemed acceptable is greater than the range considered as unacceptable.3. the lower limit being recommended for mainly computer-based work and the upper limit for mainly paper-based work [32]. and energy consumption will be reduced. Boyce et al. which do not normally become very dirty.e.-C. The value of the utilance is even more important than the LOR in reaching energy . one extensive study under office conditions has shown that people prefer artificial lighting in addition to the normal daylighting present in an office environment: average 800 lx on top of the prevailing daylight contribution [39]. meaning they will be satisfied with their environment despite an illuminance less than 500 lx. In the UK.5. In the Danish study [25]. the working plane illuminances recommended for offices are in the range 300–500 lx. as well as bulk lamp replacement every 10. Recently. • the reflectance of the surroundings. this range being chosen so that the expected preferred illuminance will be less than the standard 500 lx. an illuminance of 500 lx on the work plane is recommended for office work [30.31]. Rea [29] introduced the term ‘application efficacy’ that is. it was 5–6 W/m2 . They concluded that studies with different stimulus range will lead to different estimates of preferred illuminance. based upon the lamp and luminaire combination rather than.7. from 8:00 to 17:00. [34] also claimed that lighting practice that uses 500 lx as the target for maintained illuminance is excessive. and room surfaces and the environmental and operating conditions. for example. This reduction in light output depends on the fact that lighting fixtures. The maintenance factor takes into account lamp burnouts. An annual time budget of 2500 h corresponds to about 48 h per week and thus 9. Boyce [44] noted a lack of association between illuminances and their subjectively viewed suitability when subjects were carrying out realistic tasks. tasks for which visibility requirements were satisfied at relatively low levels of illuminance. The widespread use of tungsten halogen sources in display and downlighting applications.14]):(4)U = ˚ TA where ˚TA is the initial luminous flux reaching the task area and ˚lum is the luminous flux released from the luminaire.3. an illuminance of 500 lx is also recommended on the task area for individual office rooms while 300 lx are normally accepted as general lighting level for landscape offices [12].1. Loe [22] suggested recommending a band of adjustable task illuminance for particular situations rather than a minimum level. However. Many studies indicate that office workers generally prefer illuminance levels which are lower than recommended by the standards [33–38]. 2. become dirtier and also some lamps get older or burn.3.6 h per day (5 days/week) of total switchon time. By using 400 lx as a design criterion. and of room surfaces every three years. A high maintenance factor (cleaning) together with an effective maintenance programme promotes energy efficient design and limits the installed lighting power requirements [10]. The maintenance factor (MF) is the ratio of the average illuminance on the working plane after a certain period of use of a lighting installation to the initial average illuminance obtained under the same conditions for the installation. In offices. in architectural lighting.1. Reduction of switch-on time.2576 M. which determines the indirect contribution. luminaire. vertical or inclined. light sources. The application efficacy is related to the utilance factor U defined ˚ as (from [10. five days a week. In the Swedish context.1. 2. i. routine cleaning of the lamp.8. For example. including the electricity consumption of the ballast. a 20% decrease in energy consumption could be gained together with a likely increase in the percentage of office workers who are within 100 lx of their preferred illuminance. which would probably be more appropriate and yield higher energy savings as some individuals would probably select lower illuminance levels than the recommended levels.e. recent calculations have shown that reducing time of use of electric lighting in offices to 2600 h/yr would reduce energy intensity for electric lighting by 1. Recommended maintained illuminance levels are prescribed over the task area on the reference surface which may be horizontal. the recommended energy intensity of task lamps was 1–2 W/m2 and for the general lighting. These authors thus proposed to give occupants a restricted range of illuminances to choose from. 2. with studies with large range resulting in higher preferred illuminance selected. The European standard EN 15193 [17] recommends a total utilization time for electric lighting in offices of 2500 h (2250 daytime hours + 250 nighttime hours). solely on lamp luminous efficacy. Dubois. The total number of units of electricity consumed by the lighting installation will also obviously be affected by the length of time the lighting is switched on. no more than 20 W should be allowed for one task lamp to reach the recommended 500 lx in the task area. Fotios and Cheal [42] demonstrated that the preferred illuminance is significantly influenced by the range of illuminances available to the research participant (the stimulus range). In the USA and Canada for example. Improvement in utilance and utilization factor. The LOR and the utilance U are combined in what is called the utilization factor UF defined as UF = ˚TA /˚lamp . The utilance U relates the luminous flux from the luminaires to the luminous flux on the target area. Å. Blomsterberg / Energy and Buildings 43 (2011) 2572–2582 recommended wall luminance of around 100 cd/m2 for future lighting applications (office context with 500 lx on task). lamp lumen maintenance.1.3. despite the low lamp luminous efficacy of these technologies relative to others. An important principle of energy efficient lighting design is to make the most of any light sources available by directing the light to where it is needed [22]. • the luminous intensity distribution of the luminaires and the spacing to height ratio. luminaire dirt depreciation and room surface reflectance maintenance. where dimming is only useful during the early morning and late afternoon [52]. research has also shown that in spite of few promising laboratory test results and computer predictions. show energy savings of about 25% in private offices with a sensor time delay setting of 20 min. For a given quantity of illumination. [50]. 2.48. Note that Moore et al. the resulting annual energy use is 25 kWh/m2 yr. 2. Use of manual/automatic dimming and occupancy sensors. the phenomenon could be caused by occupant adaptation to exterior conditions prior to entering the building. Å. In parallel to this. most daylight-linked systems do not provide the anticipated energy savings when installed in real buildings [54]. For office buildings with classical windows (no specific daylight system).9. Sutter et al. given the general dislike of photoelectric control reported in the literature. [61] proposed two possible explanations to this phenomenon. Glare studies have shown that glare is tolerated much more from a daylight source than from its artificial equivalent [69]. dimming is not really necessary in areas with high levels of daylight. some form of automatic control must be provided either as automatic switchoff or photoelectric dimming. research has identified the benefits of daylight and sunlight in buildings for the health and well-being of occupants. daylight remains a predominant factor in how a space is revealed and perceived by its users. they found previous research indicating electricity savings for lights ranging from 20% to 77%. Bodart and De Herde [55] examined previous literature on the subject and concluded that it is difficult to evaluate the energy savings coming from light dimming as a function of daylight availability. room width as well as reflectance of interior walls. Research has shown that daylight-linked lighting control systems such as automatic on/off and continuous dimming have the potential to reduce the electrical energy consumption in office buildings by as much as 30–60% [54]. Studies comparing energy use after installation of occupancy sensors with manual switching on as the baseline. which is the lower bound for manufacturer claims [50]. Several studies have generated promising results showing that electrical energy use can be substantially reduced by using lighting control systems such as manual dimming and occupancy sensors. we have to consider the fact that daylight utilization is just one of the many arguments for admitting daylight in buildings. [52] claimed that to date.46]. [47] also claimed that there is little merit in equipping locally dimmable systems with photoelectric controls. Strategies related to daylight harvesting Most commercial spaces have enough daylight next to windows to eliminate the need for electric lighting [52] (apart for buildings located in the far north of Scandinavia where there is hardly any daylight in the winter). In general. but differences between observed savings and industry estimated savings that result from the application of these systems are often observed [50. facade configuration. For manual dimming.47. . Despite all these arguments. even with a maximum switch-on time of 2500 h and a LPD of 10 W/m2 . Therefore. by using control systems such as manual dimming. While useful in low daylight areas. Moreover. This shows that daylight harvesting cannot rely purely on occupant behavior. Daylight utilization may allow energy savings compared to electric lighting due to its higher luminous efficacy. switching will generally only occur twice a day. For switchoff occupancy sensors. light from clear blue skies delivers the least amount of heat gain [53]. the literature reveals a number of reports of switching behavior being related to daylight availability [45. [71] showed that high luminance contrasts were more tolerated when the window occupied a large portion of the visual field. Moore et al. [47] reported on a survey of user attitudes toward control systems and the luminous conditions they produce in 14 similar UK office buildings. orientation of ¸ opening.67]. Dubois. they obtained electricity savings for lights (with the window system and controllable highly reflective venetian blinds plus light dimming) reaching 76% on overcast days and 92% on clear days. Significant among the various reasons for this is the inability of the standard predictive methods to account for realistic conditions [56]. Also. the electric lighting energy savings obtained range between 7–25% [33. Significantly less incidents of eyestrain are reported by people whose workstations received large proportions of natural light [70]. considering a glazing type normally used in offices. automated control systems save energy compared to manual switching. in order to reach a total energy intensity for lighting of around 10 kWh/m2 yr. Most importantly for office environments. Post-occupancy studies carried out in real buildings have shown that the actual energy performance of daylit buildings is invariably markedly worse than that predicted at the design stage [53]. commonly referred to as ‘daylight utilization’ or ‘daylight harvesting’. Begemann et al. lighting electricity savings range from 20 to 35% [33. including its necessity for the regulation of circadian rhythms [66. Secondly. a practice which is unfortunately still not implemented in many countries. a number of studies have indicated no relationship between daylight availability and electric lighting use [35. However.M. In recent years.2. is recognized as an effective means to reduce the artificial lighting requirements of nondomestic buildings. Dimming electric lights based on available daylight is also expensive with significant equipment (dimming ballasts) and commissioning costs. it is necessary to either reduce the LPD to around 4 W/m2 or to switch-off lights at least 60% of the time. Comparing with an office space where lights are on 100% during all working hours. which would yield primary energy savings for the building of up to 40%. They found that the savings obtained depended on the glazing visual transmittance.1. In Canada. According to Guo et al. Daylight presence has a significantly positive contribution to lighting quality and makes an interior space look more attractive. during early morning and late afternoon or early evening hours. occupants could be attempting to balance the brightness of window areas with those of the interior. Blomsterberg / Energy and Buildings 43 (2011) 2572–2582 2577 Limiting the range of total switch-on time implies in practice that lighting systems must be switched-off after work hours. A number of studies have stressed the importance of daylight and windows and have demonstrated their numerous positive effects on building occupants. occupancy switch-off and/or daylight dimming. daylight is generally preferred to electric lighting [68].51]. First.-C.45.62–65] and even higher levels of electric light with higher external illuminances [61]. They observed that controllable systems were typically operated at 50% of maximum output but they did not specify the exact corresponding electricity savings. Papamichael et al. dimming ballasts are less efficient than non-dimming ballasts and consume 10–20% power even at the lowest possible light output [52]. and too short a period elapsing to allow full adaptation to interior conditions prior to switching. Also.57–61]. In addition. They achieved a study by computer simulations with ADELINE and TRNSYS for the Belgian climate and showed that daylight harvesting allows reductions of electric lighting consumption of 50–80%. The exploitation of daylight.3. otherwise there is a risk that more energy will be used.3. Athienitis and Tzempelikos [18] developed a simulation methodology and carried out simulations for a typical office room (5 m × 5 m × 3 m) located in Montreal with a Vision Control window measuring 2 m × 4 m on the facade facing 10◦ east of south with no ¸ obstructions.49]. While it is true that occupants might be more distracted by the dramatic changes in light levels caused by switching (as opposed to a smooth dimming function). only a small fraction of side-lit dimming applications operate satisfactorily. The next sections examine the effect of some design parameters on daylight utilization potential.3. His results indicated that energy savings were falling with rising latitude and total annual solar radiation. the 30% WWR was identified by the authors as the daylighting saturation region for south-facing facades in Montreal. the reduction in thickness of the exterior walls and the increased use of . The author mentioned. Therefore. In his simulations. Bodart and De Herde [55] found that north oriented room consumption was always higher than for other orientations but they did not use solar shading devices in their research so the savings obtained for the south. because of its variability and intensity. For these five climatic centers.73]. Boyce [72] argued that daylight offers no guarantees of a better work experience. have a lower impact than those facing other directions. over 1000 office settings were investigated which feature varying external shading situations. In their simulation study. any daylight availability had no more influence on the artificial light consumption. Tzempelikos and Athienitis [73] warned that large fenestration areas often result in excessive solar gains and highly varying heating and cooling loads. highly glazed facades. A user assessment survey by Osterhaus [75] in real daylit office spaces achieved in 1992–1994 in nine office buildings in the USA and Germany where 250 questionnaires were distributed to individual office workers indicated that north-facing windows (all survey sites were located in the northern hemisphere). however. In the ‘best’ case. together with the extra heat gains from the electric lighting made necessary by deep floor plans. orientation and number of windows influence the daylight indoors. An analysis of the monthly energy savings for the five sites studied in the United States and Canada showed that most differences appear in the winter months due to shorter day lengths in the North. 2. including the solar component) exceeds the energy saved due to reduced electric lighting. these numbers did not include the additional energy use for heating and cooling caused by the larger window. Five climatic centers which represent the ambient daylight conditions of 186 North American Metropolitan Areas were identified. 30% window to external wall area). In fact. They concluded that a high visible transmittance is beneficial for the lighting energy consumption but that beyond a certain value. Bodart and De Herde [55] performed a simulation study where they observed that the electricity consumption did not vary linearly with the glazing transmittance. due to the high latitudes and restricted daylight availability in the winter. an increase in the ratio Swindow /Sfloor from 16 to 32% reduced the electric lighting consumption by 12% for glazing with 20% visible transmittance and by 36% for glazing with 81% visible transmittance. the Vancouver region was characterized by dark overcast winter skies. electricity for pumps. the additional energy use of the 100% glazed building was 15% higher compared to the energy use of the 30% glazed building. The potential for daylighting during winter is limited in the Nordic countries.-C. 2. at some point. Therefore. However. the benefits decrease. Effect of latitude and orientation. The daylight performance of the offices was expressed in terms of their daylight autonomy distributions and energy savings for an ideally dimmed lighting system. [5] showed that office buildings in Sweden with fully glazed facades are likely to have a higher energy use for heating and cooling than buildings with conventional facades (e. that the beautiful view over certain landscape elements may have mitigated the effect of daylight glare for some orientations. fans and office equipment) of the 30% glazed building ranged from 123 to 136 kWh/m2 yr and that of the 100% glazed building ranged from 143. They showed that in an office room. he suggested that an ‘adequate’ blind control strategy had to be chosen.2578 M.2. Concerning orientation. Gratia and De Herde [76] provided some recommendations regarding windows: (1) Generally. Poirazis et al. Fortunately. 2. Reinhart [74] found that changing from a high (75%) to a low (35%) transmittance glazing reduced energy savings by about 20 percentage points for the peripheral office. and the wider use of false ceilings. Effect of shading devices. the author was surprised that east and west-facing windows showed no higher levels than south-facing windows.2. They showed that increasing the WWR above 30% did not result in significant increase in useful daylight in the room (9% more for 80% WWR). However. The authors also outlined that one of the main arguments for using increased glazed areas in buildings is the provision of better indoor environment due to daylight. or if the net heat gains and losses through the fenestration do not compensate for the lighting energy saved [53]. position. the higher the window is. cooling.55. glazing types. He outlined. In Belgium. many recent studies indicate that daylight harvesting can provide electric lighting savings with ‘reasonable’ fenestration areas (around 30–40% of facade area) including the use of shading devices when needed ¸ [9. (2) The area of the window plays a primordial role.2. increased window area does not necessarily lead to a reduction in energy use for lighting the building properly.1. shape.3. an all too common scenario in overglazed buildings is where the blinds are down to control glare and the lights are on [73]. that care has to be taken that such energy savings on the electric lighting side are not compromised by additional cooling loads. A full consideration of the potential for daylighting to save energy should. They observed that when an illuminance level of 500 lx was reached. According to Küller [27]. daylight provides peripheral offices in Montreal with 500 lx on the work plane 76% of the working time in a year. account also for the thermal effects of daylight [53]. Respondents in offices with northern orientation reported presence of daylight glare somewhat less frequently. often with poor shading.2.3. however. have become very common. facade orientations. In general. ¸ Tzempelikos and Athienitis [73] showed that for 30% windowto-wall ratio (WWR) and a south orientation. the total energy use (heating. the better the lowest part of the room is lit and the deeper the naturally lit zone is. Å. as does the framing and transmittance of glazing [27]. This.3. They explained this by the fact that daylighting availability was so important that the diffuse and the external reflected lighting portions added to the internal reflected daylight were sufficient to reach the minimum lighting requirement.0 to 176 kWh/m2 yr. Reinhart [74] studied the influence of various design variables on the daylight availability and electric lighting requirements in open plan office spaces using DAYSIM. daylight. While it can reasonably be expected that north-facing windows create fewer concerns for glare discomfort.e. there was no evidence that windows facing other directions created higher levels of glare. poses additional challenges and needs to be carefully considered to realize its potential to provide healthy and comfortable office environments. In particular. However. Daylighting could lead to a net increase in energy consumption if the additional cooling load due to daylight (i.g. The size. Dubois. Glare problems that can be caused by the large amount of daylight entering a highly glazed working space often reduce the quality of visual comfort and shading devices are used more frequently in highly glazed buildings often maintaining the same levels of daylight used in a building with a conventional facade (see also [9]). They also noted that the influence of orientation was minor and even nonexistent. ceiling designs and partition arrangements. east and west orientations may not be realistic given the fact that shading devices would probably be used in reality for these orientations. increase the risk of overheating [76]. Blomsterberg / Energy and Buildings 43 (2011) 2572–2582 However. Effect of window characteristics. rather than primarily in response to current conditions [81.85]. Other research has suggested that when sky luminance is maintained under 2500 cd/m2 . Å. 6) Once closed.0 (Superlite).3. 7617 and 7127 lx with ceiling reflectances of 70. which allows to conclude the following: 4) Below 50–60 W/m2 . The savings in lighting energy were more significant when the lighting control systems were used with photocontrolled blinds. He also pointed out that increasing the ceiling reflectivity has a positive effect on energy savings and leads to a more uniform distribution of daylight throughout the space. latitude. season. 80 and 0% respectively.m. however.3–0. especially when a light shelf is used because the light shelf redirects daylight toward the ceiling. For walls. occupants most certainly do not use shading devices [81. 5) Most people operate the blinds based on perceptions formed over long periods of time.86]. Effect of inner surface reflectances. Galasiu and Veitch [68] presented an exhaustive review of these researches. the blind will remain closed the entire day [78. Gratia and De Herde [76] presented general guidelines for the design of low energy office buildings in Belgium.5 1) Some research indicates no relation between exterior environmental conditions and use of shading devices [78]. He observed. ¸ 3) Solar radiation levels above 250–300 W/m2 normally induce a significant percentage of blind utilization [81. For the floors. This was due to the capability of the blinds to adjust their position automatically in direct response to the variable daylight levels. They explained that it is thus essential to raise the slats when not needed to provide natural light in the space. but the occupants were dissatisfied because the room appeared gloomy. based on the assumptions that the primary task involved a LCD computer monitor with an average luminance of 200 cd/m2 . According to Reinhart [74]. Under overcast sky. In his open-plan office study. The simulations were carried out for a rectangular. the simulation results revealed that the daylight availability in peripheral offices allowed for electric lighting energy savings between 25% and 60% for an ideally commissioned. They showed that under clear sky and without blinds. OPTI and ADELINE 2. continuous dimming and automatic on/off. they obtained average horizontal task illuminance values of 7552. one error source for overoptimistic energy savings predictions in office buildings is the treatment of blinds. 80 and 0% respectively.4. if these patterns are dependent on factors such as window orientation. light comes mainly from the ground and thus reduces illuminance levels by 75–90% in the case of white venetian blinds and by slightly less in the case of venetian blinds with reflective slats. where the performance of two commercial photocontrolled lighting systems. The use of brighter colours for inner walls is necessary to maximize the reflection of natural light in the space and even the reflection of electric lights on walls. based on a series of parametric simulations using the programs TAS. lat 45.-C. Shading devices generally reduce the amount of daylight available in a space. Often the problem was caused by low reflectance wall finishes in combination with luminaires which provided little light on vertical surfaces. that electric lighting energy savings for a dimmed lighting system in an open plan office decisively depended on the underlying blind control strategy.84]. and hence the room did not appear ‘light’ and was deemed to be under-lit and therefore unsatisfactory. they recommended keeping wall reflectances above 50% to maximize reflection of daylight in the space. They also showed that for light shelves. glare from windows is usually a considerable concern and needs to be carefully controlled [75].2–0. This surface and the surface of desks in . for a situation with a clear sky on March 15th. the best utilization of daylight is achieved with horizontal slats. 2.86]. a threshold value of 2000 cd/m2 was used. where the normal line of sight is more horizontal than for reading or handwriting tasks. They recommended high reflectance values (70–80%) for the ceiling. dimmed lighting system. 3041 m2 office building with five floors and 60% WWR. and by 5–80% for the automatic on/off system with the introduction of various static window blind configurations.89]. proposed ranges of useful reflectances for the major interior surfaces are: • • • • ceiling 0. the light shelf reduces the illuminance level on the working plane because it directly cuts off part of the view to the sky. These savings. 8149 and 7105 lx with wall reflectances of 45.81. the simulations showed that reducing partition reflectance seriously reduced the amount of daylight at second row offices (for landscape office layouts) and should be avoided if daylighting is desired. [77] noted that for venetian blinds. both lighting control systems reduced the lighting energy consumption on average by 50–60% when compared to lights fully on from 6 a. Christoffersen et al. They explained that if the slats are tilted downwards (+45◦ ). to 6 p.M. sky condition. It is often assumed that blinds are retracted all year round (maximum daylight availability) while the lighting is always activated during office hours. 80 and 0% respectively. Dubois. Galasiu et al. was evaluated as a function of various configurations of manual and photocontrolled automatic venetian blinds.84. The window was within the occupant’s peripheral field of view so that a maximum luminance ratio of 10:1 between window and task was just acceptable. and that the average background luminance was 50–100 cd/m2 . For computer tasks.6–0. they obtained average horizontal task illuminance values of 7552. 2) Sunlight entering the space (especially more than 2 m from the facade) triggers the use of shading devices [79–83]. because this evens out the big differences in luminances between the window zone and the rear wall zone.88].2. According to the European Standard EN 12464 [90]. Loe [22] noted that there have been examples when the correct horizontal task illuminance has been provided.9 walls 0. Therefore.8 working planes 0. only a minority of occupants would want to lower the window blinds [87. and workstation position. Blomsterberg / Energy and Buildings 43 (2011) 2572–2582 2579 glazing in the facades of modern architecture has made the design of good daylighting more difficult.80.24◦ N). In a more recent study about daylighting of the New York Times Headquarters building [89]. dropped by 5–45% for the dimming system. [54] achieved a field experiment in Ottawa (Canada. however. Results of their simulations indicated average horizontal task illuminance values of 7552. 9080 and 7314 lx with floor reflectances of 15. He explained that various kinds of shading devices might be necessary not only to avoid overheating but also to control the interior lighting and avoid glare from windows. A number of researchers have attempted to investigate whether occupants of office buildings use the shading devices according to predictable patterns and if so. In Reinhart’s open-plan office study [74].m. the only situation in which the light shelf increases the illuminance level is when it is specularly reflecting and hits direct sunlight from a relative azimuth angle so small that most of the reflected light hits the ceiling.1–0. time of day. It was also based on subjective survey results that found that there was a 50% probability that blinds would be lowered when the average window luminance was 2100 cd/m2 [88.6 floor 0. Asimakopoulos.-C. [3] L. too bright surfaces can yield disturbing reflections and glare.67. improvement in maintenance and utilization factor. M.25]. On the other hand. task/ambient lighting. Energy simulations for glazed office buildings in Sweden. theoretical calculations [14. 3.248/Global/Energifakta/F%C3%B6rb%C3%A4ttrad%20energistatistik/ Festis/STIL2-belysning-stengard.3. Statens energimyndigheten http:// 195. 2. Energy and Buildings 24 (1996) 237–243. lower installed illuminance levels (500 to 400 lx) and task/ambient lighting using very energy-efficient task lamps (6 W available). however. Finally.15] as well as simulations [9. ballast and luminaire technology. occupancy switch-off and daylight dimming. . [2] A. For the furniture. by replacing or planning the electric lighting installation with energy-efficient T5 fluorescent lamps-luminaires and CFL (or even LED lamps) for task lighting and a combination of task/ambient lighting design. Daylight harvesting based on photoelectric dimming can provide additional energy savings but at a higher commissioning cost. Another benefit of reduced partition heights between peripheral and second row offices was that the latter get a partial view outside. with associated reduced daylight benefits.se/stil2. last accessed 11 January 2009. These barriers may be related to the difficulty to switch-off lights at night due to extended office hours and flextime. Few studies have been found about the effect of ceiling height. (162. www. [6] Statens energimyndigheten.74 m) to 8 ft (2.e.5. that this figure may vary according to room type (i. Stengård. 2010.44 m) cuts energy savings for electric lighting in half. The review revealed also that a number of studies have indicated that daylight harvesting can be achieved in peripheral spaces with ‘reasonable’ window-to-wall ratios (WWR) of no more than 30–40%. D. [5] H. Acknowledgements The authors thank SBUF (the development fund of the Swedish Building trade). Reinhart [74] found that the ceiling was a crucial design element for daylighting as the majority of daylight that penetrates into a building beyond the 1st work station is reflected from the ceiling at least once.76. Strategies based on daylight harvesting were also addressed and some design aspects such as latitude and orientation. Wall. with a special emphasis on a North European context. Another solution might be to use transparent or semi-transparent partitions. 2. a simple daylight-sensitive switch-off system may be more cost-effective than continuous daylight dimming. a reflectance value between 25 and 45% has been recommended [91]. On the other hand. use of manual dimming and occupancy sensors. manual or automatic dimming. reflectance of inner surfaces. the difficulty to use daylight in core areas in deep building plans and glare problems related to the excessive exposure to daylight in peripheral office spaces are important issues which will demand attention. Blomsterberg / Energy and Buildings 43 (2011) 2572–2582 the office play a major role in light distribution due to geometrical considerations (exposure to skylight) and therefore. which assumes typical illuminance levels for office rooms. the authors noted that the floors are often relatively dark in order to facilitate maintenance and a compromise has to be made in order to simultaneously meet the requirements of visual comfort and maintenance.2580 M. etc. automatic switchoff occupancy sensors. Poirazis. they mention that light colours of desks also allow a reduction of contrast between the paper and the desk surface. Too dark desk and/or furniture surfaces may give rise to high contrasts and unacceptable luminance ratios in the direct field of view. Lagoudi. Symptoms experienced. The review reveals that the replacement of older lighting installations (T12 fluorescent lamps) with modern energy-efficient T5 lamps with HF ballasts could provide up to 40% energy savings. Å.energimyndigheten. Effect of ceiling height. A smart design option might be to group work places that require intense communication between co-workers in peripheral and second row offices and reserve inner spaces with higher partitions for more noise sensitive tasks. [4] Statens energimyndighetenen. Moreover. 2006. M. ceiling and partition height were discussed. An additional 40% energy savings could be obtained by using a combination of more energy-efficient luminaires. individual office rooms versus landscape rooms and common rooms). window characteristics. lower partitions reduce the acoustical separation between two work spaces.9 cm) nearly doubled energy savings for the automated and manually controlled blind scenario. He also noted that reducing the ceiling height from 9 ft (2. Passive retrofitting of office buildings to improve their energy performance and indoor environment: the OFFICE project.2.6.g.3. However. Building and Environment 37 (2002) 575–578. Förbättrad energistatistik för lokaler – “Stegvis STIL” Rapport år 1: Inventeringar av kontor och förvaltningsbyggnader. (121. Effect of partition height. Santamouris. E. He found that second row offices receive considerably less daylight even though a reduced partition height and increased ceiling reflectances can double electric lighting energy savings up to 40%. The review also indicates that lower energy intensities are even achievable by accepting e. reduction of maintained illuminance levels and total switch-on time. making it possible to achieve totally 80% energy savings compared to older T12 fixed lighting installations. Some barriers to the proposed energy saving strategies in a real context also need to be addressed in future research. Dubois. would yield a significant reduction in energy intensity of at least 50% compared to the actual average electric lighting use (21 kWh/m2 yr in Sweden).2. Dascalaki. Energy and Buildings 40 (2008) 1161–1170. Blomsterberg. CERBOF (Centre for energy and resource efficient construction and management of buildings) and NCC Construction Sweden for funding this research project. In his open-plan office study. shading devices. For peripheral office spaces where plenty of daylight is available. Delrapport från Energimyndighetens projekt Förbättrad energistatistik i samhället. M. which include: improvements in lamp. An increase in WWR does not provide substantial additional lighting energy savings and creates risks for overheating. References [1] M. Conclusions Key figures for energy consumption and energy saving potential for office lighting were presented based on a review of relevant literature. This review generally shows that cost-effective energy savings may be achieved by simply improving the electric lighting system i. use of task/ambient lighting. Global Energifakta. Osterhaus [75] also advised to select light monitor screen borders and lighter desktop surfaces to keep luminance ratios low. it was also shown that lowering partition heights from 64 in.pdf. Å.17] with validated lighting programs indicate that an energy intensity of around 10 kWh/m2 yr is a realistic target for electric lighting in future low energy office buildings as well as in office building retrofits. The review reveals that measurements in full-scale rooms [16.6 cm) to 48 in. Strategies for reducing energy use for electric lighting were also presented and discussed. as proposed by the author. Energi i våra lokaler: Resultat från Energimyndighetens STIL2-projekt. environmental factors and energy consumption in office buildings. glare and a consequent abusive use of shading devices. Note. ISSN 1403-1892. Loizidou. This target. last accessed 27 January 2011. In Reinhart’s open-plan office study [74].e. they recommended selecting floor and desk reflectances above 50%. user-acceptance issues related to the proposed low light levels or to the occupancy switch-off and daylight dimming control systems. which contributes to visual comfort. Santamouris. overview of visual and biological responses. [23] Official journal of the European Communities. Lighting Research Technology 5 (1973) 125–144.2. Energy and Buildings 38 (7) (2006) 728–742. Stockholm (Sweden). Occupant preferences and satisfaction with the luminous environment and control systems in daylit offices: a literature review.K. W. Blanc. Lighting Research and Technology 30 (1998) 45–50.). in: Proceedings of the CIBSE National Lighting Conference.D. overview of visual and biological responses. D.A. A. Bodart. also published in Leukos. van Bommel. Hunter. K. London.A. T.M. A. Blomsterberg / Energy and Buildings 43 (2011) 2572–2582 [7] P. Scholz. A. Newsham. IESNA Lighting Handbook (9th edition). J. W. The use of artificial lighting in relation to daylight levels and occupancy. illuminance. Rombauts. Butterworths. 1997. Energy saving lighting control systems for open-plan offices: a field study. L. New York. Galasiu. Power density targets for efficient lighting of interior task areas. vol. Solar Energy 72 (4) (2002) 271–281. 2007. Ashley. A.K.G. Light Research and Technology 34 (3) (2002) 207–219. S. Ottawa. Lighting Research and Technology 36 (4) (2004) 255–269. in: Proceedings of Right Light 5.V. Lighting Research and Technology 32 (2000) 199–212. [38] G.D. National Research Council of Canada. Mardaljevic. 2008.J. Mancini. M. Dascalaki. Hørsholm. Tregenza. A. Lighting Research and Technology 42 (2010) 399–414. Hunt. EN 15193:2007. M. G.P.J. January 2004. Report NRCC- 2581 [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60] [61] [62] [63] [64] [65] [66] [67] [68] [69] 50324. J. C. 2007. [24] Z. Institute for Research in Construction.C. Manual control of artificial lighting in a daylit space. October 2009. Veitch. 2003. K. Sander. Slater. Swedish Energy Agency. Impact of window blinds on daylightlinked dimming and automatic on/off lighting controls. Wouters. Age. visual performance and preference. [35] T.R. Faye. S.A. artificial light and people in an office environment. Heerwagen. Solar Energy 52 (1) (1994) 75–83. M. 2008. M. 2010. Begemann. P. J. Anaesthesia 62 (2007) 163–168. Carter. The performance of occupancy-based lighting control systems: a review. Statens Byggeforskningsintitut. G. 208–218.J.H.A. Lighting Research and Technology 42 (2010) 415–431. Katrineholm (Sweden). Department of Architecture and Built Environment. Lighting Research and Technology 42 (2010) 433–447. 2005. Boulder. Tiller. Institute for Research in Construction. Borg. Andra utgåvan. Tiller. P.D. G. [10] P. Acceptance and preference of illuminances in offices. Office Lighting Guide LG7. Guo. Ottawa. Boyce. M. Moore. 1998. J. 87–92. 234–241. Daylight. pp. A.S. [27] R.R. pp.R. Laurentin. Planning for good indoor lighting. Aries. Galasiu. 2008. D. Daylight. Boyce. En undersøgelse in ni kontorbygninger. Fontoynont. Energy performance of buildings – Energy requirements for lighting. Lighting Research and Technology 39 (2) (2007) 171–184.R. [11] T. G. Traberg-Borup. J. . in: Proceedings of the 3rd International Conference of Indoor Air Quality. B. Lund University. Rutledge. Minimum and optimum light output of Macintosh size 3 laryngoscopy blades: a manikin study. K.belysningsbranschen. A. Observations of the manual switching of lighting. Society of Light and Lighting.se. Housing Development and Management. Lootens. Tenner. S. Fischer. Newsham. Daylight metrics and energy savings. Journal of the Illuminating Engineering Society 28 (2) (1999) 42–56.se/files/Pressrum/ pressmeddelanden/UPPLYS SVERIGE En rapport fran Belysningsbranschen. [16] M. 1999.R.C. [13] Belysningsbranschen. P. [18] A. London. S. Colorado.J. Architectural Energy Corporation. Ventilation and Energy Conservation in Buildings. Govén. D. Halonen. Tuck. Society of Light and Lighting. Persson.D. P. [21] Belysningsbranschen. Begemann. Statens Byggeforskningsinstitut. last accessed 27 January 2011. J.M. Newsham. [19] Energy efficient lighting – guidance for installers and specifiers. pp.M. Lighting Research and Technology 38 (4) (2006) 358–378. Tenner. Dubois. [8] S. G. Lighting Research Technology 6 (1974) 205–211. Johnsen. Building issues 14 (2004). Manual switching patterns in private offices. A. Bath. Examples of Climate-Based Daylight Modelling. Lighting Research and Technology 41 (2009) 261–283. Lighting Research and Technology 35 (1) (2003) 43–59. vol.H. L. D.E. Hørsholm. Kontorbelysning baseret på energieffektive arbejdslamper. Considerations for lighting in the built environment: Non-visual effects of light. Lighting for work: a review of visual and biological effects. Romaya. V. S. H. 4 (3).T. 175–180. Newsham. [17] European Committee for Standardization (CEN).F. part 3: visual and biological processes. Graeber. Maniccia. Van Den Beld.E. 8 (22).R. 448–456. Svensson (Ed. 3. B.I. Brussels. M. Figueiro. Hall.J. 139–156. P. Veitch.R. ISBN 0-87995-150-8.A. [34] P. Athienitis. D. A. Küller. Energy and Buildings 34 (2002) 421–429. Veitch. Lund University.M. McKinsey Quarterly: the online journal of McKinsey & Co 1 (2007). DiBartolomeo. Loe. New Delhi (India). Nauclér. 141–146.D.belysningsbranschen. International Journal of Industrial Ergonomics 20 (3) (1997) 231–239. Begemann. Institute for Research in Construction. CIBSE National Conference: Engineering the Future. A comparative study of user opinion in offices with and without individually controlled lighting. Reykjavik. N. Deconinck. G. Keep cool program. D. 2000. [36] T. Rubinstein. Tzempelikos. 1991. Henze. S. Balaras. Directive 2000/55/EC.G. Bångens. G. 1996. 2006. A.H. Daylight in glazed office buildings: a comparative study of daylight availability. R. National Research Council of Canada. Newsham. Rasmussen. A. Van Den Beld. pp. 18–20 June. Tenner. Ljus och rum: Planeringsguide för belysning inomhus. Detection and acceptance of demand-responsive lighting in offices with and without daylight. Newsletter 1/99. Ballast for fluorescent lamps. also published in Lighting Research and Technology 40 (1) (2008) 25–41. ISBN 91-631-4675-4. The background luminance and colour temperatures influence on alertness and mental health. Rogers. Energy efficiency in lighting – an overview. H. J. Mancini. pp. pp.I. Waters. [9] H. Nice. E. Global energy savings in offices buildings by the use of daylighting. International Journal of Industrial Ergonomics (1997) 231–239. L. artificial light. Individual control of electric lighting in a daylit space. 2007. G. Daylight.J. A. D. C.R. Report SBI 2005:06. Ljuskultur. Report NRCC-49498. J. 2006. Farnum.A Love. Berrutto. S. Guidelines for integrating sustainable summer comfort into public procurement schemes for office equipment and lighting. D6-8-11. Upplys Sverige! Rapport om landets övergang till energisnål belysning. A. Good lighting with less energy: where next? Lighting Research and Technology 41 (2009) 285–286.E. Rosander. [25] K. 2001. pp. Discomfort glare from daylight in computer offices: how much do we really know? in: Proceedings of LUX Europa 2001. C. G. Dawe. 18–19 August 2010. [33] A. vol. Hampson. C. Moore. Cheal. [15] N. C. [28] T. A cost curve for greenhouse gas reduction: a global study of size and cost of measures to reduce greenhouse gas emissions yields important insights for businesses and policy makers. Larsen. Amsterdam (the Netherlands). Ceebel (Centrum för energieffektiv belysning). Energy and Buildings 14 (1979) 21–33. [14] D. Henze. Wilkes. C. Need of individual control to improve daylight utilization and user satisfaction in integrated lighting systems.D. M. Govén.D.L.P. Richards. 2006. Lighting Design + Application (LD + A). Solar Energy 52 (1) (1994) 59–66. [31] Illuminating Engineering Society of North America. and people. Comparison of control options in private offices in an advanced controls testbed. 4–6. Lighting Research and Technology 12 (1980) 195–205.K. Denmark. in: Proceedings of Lux Europa.J. in: Proceedings of the 23rd Session of the CIE. Preferred luminance distribution in working areas.A. User attitude toward occupant controlled office lighting.H. S. Iceland. Lighting Research and Technology 37 (2005) 219–233.-C. Preferred task-lighting levels in an industrial work area without daylight. Journal of the Illuminating Engineering Society 29 (2) (2000) 39–60. Papamichael. G. Report SBI 2009:09.I. Guo. TrabergBorup. Enkvist. CE61.A. Slater. B. Galasiu. X. Lyon (France). E. Conference Energy efficient lighting in a human perspective.J. Hanselaer.D. Suvagau.M. Reykjavik (Iceland). van den Beld. R. van den Beld. Veitch. Begemann. F. Tenner. Report NRCC-49453. London. Tenner. Osterhaus. Energy efficiency in lighting – considerations and possibilities. Cost effective simplified controls for daylight harvesting ACEEE Summer Study on Energy Efficiency in Buildings. Laike. Rea. MacDonald. Daylight Metric Development Using Daylight Autonomy Calculations in the Sensor Placement Optimization Tool. S. D. D. Ottawa.A. Effektiv belysning i kontor-og erhvervbyggeri.E. [20] M. Energy characteristics and savings potential in office buildings.A. Johnsen. Jones. in: Proceedings of the 9th European Lighting Conference (Lux Europa). [26] J. Webb.R. Energy saving trust. A. C. G. in: Proceedings of the 26th Session of the CIE. Energy and Buildings 38 (7) (2006) 721–727. Jennings.M. Division of Energy and Building Design. S. W. Rea. artificial light and people in an office environment. W. [22] D. Report EBD-R—08/17.-A.D. Solar Energy 76 (5) (2004) 523–544. Carter. L. A. Lund (Sweden). Myer. K. K. T. van den Beld. G. International Association for Energy-efficient Lighting (IAEEL). Juslén.S. J.P. A methodology for simulation of daylight room illuminance distribution and light dimming for a room with a controlled shading device. Pendse. Part II: Occupational Safety & Health. Occupant use of manual lighting controls in private offices. Heschong. Preferred luminous conditions in open-plan offices: research and practice recommendations. A. [30] Canadian Labor Code. T.G. Overall and zonal energy end use in an energy conscious office building. last accessed 27 January 2011. C. Mardaljevic. 2009. [12] R. Occupant use of switching and dimming controls in offices. A. J. A. National Research Council of Canada. Santamouris. Grau. Lighting that Benefits People and the Environment. [37] J. J. Reynolds. Carter. 1995. 5. M. Heap. Moore. Sjöberg. luminance and illunance distribution for an office room with three different glass areas. C. Morrow.R. S.H. Validating the application of occupancy sensor networks for lighting control. D.R. Long-term patterns of use of occupant controlled office lighting.R. 9th European Lighting Conference. www. 2001. Slater. Page. Deliverable 3. pp. vol. Gaglia. Å. C. G. Carter. Bülow-Hübe. Consistency and variation in preferences for office lighting.R. G. C. 2002. M. http://www. Waters.K. De Herde. 200–203. [32] Chartered Institution of Building Services Engineers (CIBSE). Newsham. Boyce. Atif. Action Energy GIR092.A. X. Occupancy Sensors: are there reliable estimates of the energy savings?. Energy-efficient lighting. B. pdf. 2005. Marchand. 2000. Fotios. R. Girault. Lee. Ryckaert. Denmark.R. pp. E. [29] M. Stimulus range bias explains the outcome of preferredilluminance adjustments. ISSN 110-9446. Argiriou. Lehtovaara. Iversen. Lighting Research and Technology 41 (2009) 209–218. Loe. 215–222. The use of shading systems in VDU task offices: a pilot study Energy and Buildings 38 (7) (2006) 780–789. [86] C. Inoue. [76] E. 2007. Building Research Establishment.T. The development of an optimal control system for window shading devices based on investigations in office buildings. Blomsterberg / Energy and Buildings 43 (2011) 2572–2582 [82] C. Selkowitz. [79] M. D. R. Monitoring procedure for assessment of user reaction to glare. Lighting Research and Technology 35 (3) (2003) 243–260. [90] Swedish Standards Institute (SSI). 2005. 11–13 May 1998. Osterhaus. D. Solar Energy 81 (2007) 369–382.L. B. distributed through the Canadian Mortgage & Housing Corporation. Tzempelikos. Kiliccote. S. Fontoynont. Reinhart. G. Rubinstein. Occupancy data for thermal calculations in nondomestic buildings. Inkarojrit. pp. 1–12. [91] K. [70] I. Subject responses to electrochromic windows. Matsuo. [87] J.K. E. [84] Farber Associates. vol. Monitoring manual control of electric lighting and blinds. Solar Energy 79 (2) (2005) 140–158. [77] J.D. 245–254. UK. in: Proceedings of Right Light 4. Watford. B. August. Division of Energy and Building Design. 112. 2005. 1990. Pacific Grove. Centre for Medical and Health Physics.R. in: Proceedings of the Daylighting ’98 Conference. Takakusa.-C. pp. Ottawa (Canada). Dubois. Department of Construction and Architecture.M. Dumortier. Piette. 2. 1978. USA. vol. 1997. Christoffersen.2582 M. Coyne. ASHRAE Transactions 94 (1988) 1049. [88] R. M. M. European standard SS-EN 12464-1. Sutter. Research Report. Rutledge. Building and Environment 19 (2) (1984) 133–137. Ljus och belysning – Belysning av arbetsplatser – Del 1: Arbetsplatser inomhus. [73] A. Wienold. final report LBNL-57602. in: Proceedings of the ACEEE Summer study on energy efficient buildings. [85] G. ENK6-CT-2002-00656. contract PD233/92. Athienitis. Ibamoto.I. [71] Y. K. K. Daylighting Guide for Buildings.J. Lund University. E. 1992. PhD thesis. Johnsen. Window blind occlusion: a pilot study. A. [72] P. [75] W. Christoffersen. Maniccia. Rea. Ottawa (Canada). Department of Physics. The impact of shading design and control on building cooling and lighting demand. Manual control of window blinds and electric lighting: implications for comfort and energy consumption. design of low energy office buildings. MA. R. Discomfort glare assessment and prevention for daylight applications in office environments.K. Collins. Gratia. De Herde. L. [83] H. Contract no. National Institute for Standards and Technology. Å. Window blinds as potential energy saver – a case study NBS Building Science Series. Energy and Comfort Control for Building Management Systems (ECCO-Build). Cowling. BRE Garston Library. pp. BRE Garston Library. Effects of interior design on the daylight availability in open plan offices. Ottawa (Canada). Gaithersburg. 359–366.R. Robertson. Energy-Efficient Window Systems: Effects on Energy Use and Daylight in Buildings. pp. Lawrence Berkeley National Laboratory. 2001. Fernandes. Daylighting the New York Times Headquarters Building. T. S. CA (USA). Lindsay. Kawase. S. 1992. EU Commission. Energy and Buildings 35 (2003) 473–491. An experimental evaluation of daylight systems and lighting control. 2002. Indoor Environment 3 (3) (1994) 135–144.L.S. Rubin. Rea. Bradley. Report ECCO-DBUR-0303-01.S. F.A. S. Boyce. Clear. Tibbott. P. Contract F3/31158. [78] A. 1998. .R. Littlefair. Watford. Lund (Sweden). Lee. J. 2002. Voss.F. Light in Brisbane Office Buildings: A Survey. Reinhart. Brisbane (Australia). Newsham.F. Clear. [81] T. Petersen. V. Building Research Establishment. Why daylight? Proceedings of Daylighting 98: An International Conference on Daylighting Technologies for Energy Efficiency in Buildings.E. [80] M. Energy and Buildings 38 (7) (2006) 758–779. [74] C. Occupant use of venetian blinds in offices.S.L. Lee. Y. Queensland University of Technology. Beyond daylight dogma. Bülow-Hübe. T. UK.S. [89] E. A.D.