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A Literature Review of the

Effects of Natural Light on

Building Occupants

July 2002 ï NREL/TP-550-

L. Edwards and P. Torcellini

National Renewable Energy Laboratory

1617 Cole Boulevard Golden, Colorado 80401- NREL is a U.S. Department of Energy Laboratory Operated by Midwest Research Institute • ••• Battelle • ••• Bechtel Contract No. DE-AC36-99-GO

National Renewable Energy Laboratory

1617 Cole Boulevard Golden, Colorado 80401- NREL is a U.S. Department of Energy Laboratory Operated by Midwest Research Institute • ••• Battelle • ••• Bechtel Contract No. DE-AC36-99-GO

July 2002 ï NREL/TP-550-

A Literature Review of the

Effects of Natural Light on

Building Occupants

L. Edwards and P. Torcellini

Prepared under Task No. BEC2.

NOTICE

This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.

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Table of Contents

• 1. Background
• 2. Introduction.................................................................................................................................
• 3. Wavelengths of Light..................................................................................................................
• 4. Affects of Light on the Body
  • How the Eye Works
  • Affects of Light on Internal Body Systems
  • Nervous and Endocrine System
  • Circadian Cycles
  • Medical Cures from Light...........................................................................................................
  • Rickets and Osteomalacia
• 5. Daylighting in the Office
  • Health in the Office.....................................................................................................................
  • Productivity in the Office..........................................................................................................
  • Absenteeism in the Office.........................................................................................................
  • Employee Turnover
  • Financial Savings
  • Employee Preferences and Perspectives...................................................................................
  • Improper Daylighting................................................................................................................
• 6. Daylighting in Schools..............................................................................................................
  • Health........................................................................................................................................
  • Attendance
  • Achievement
  • Perspectives...............................................................................................................................
  • Financial Benefits: Costs of Absence/Student/Day Breakdown...............................................
  • Windowless Classrooms
    • Testimonials from Windowless Classrooms.........................................................................
• 7. Daylighting in Retail.................................................................................................................
  • Problems for Retail Daylighting
• 8. Daylighting in Health Care Facilities
  • Benefits for Patients and Workers
  • Post-Surgical Results
  • Healing Environment
• 9. Daylighting Industrial Environments........................................................................................
  • Physiological Effects
  • Psychological Health
  • Productivity and Safety.............................................................................................................
• 10. Conclusion
• References and Bibliography........................................................................................................
• Additional Articles of Interest
• APPENDIX...................................................................................................................................

1. Background

This paper presents summary information from a noncritical literature review on daylighting in buildings. It is by no means exhaustive, and no attempt has been made to determine the scientific nature of the studies that are cited. It was the goal of this document to compile a listing of the literature that is commonly cited for showing the impacts of daylighting in buildings. NREL does not endorse any of the findings as the citations have not been critically reviewed.

Many building owners and architects have reported energy savings received from daylighting. Looking at the energy consumption of commercial buildings in the United States demonstrates the importance of saving energy. According to the Department of Energy’s Office of Building Technology, State and Community Programs (BTS) 2000 Databook, commercial buildings consumed 32% of United States electricity in 1998, of which 33% went to lighting. Not only is electrical lighting responsible for a significant amount of the electrical load on a commercial building, but it can also cause excessive cooling loads. Utility costs for a building can be decreased when daylighting is properly designed to replace electrical lighting.

Along with the importance of energy, studies have demonstrated the nonenergy related benefits of daylighting. Quantitative studies and qualitative statements are used to summarize the use of daylighting in buildings, its effects on occupants, and its potential economic benefits. Data have been compiled from books, periodicals, Internet articles, and interviews. The books, periodicals and Internet articles provided the background information necessary to identify the main subjects of the paper. Interviews provided details related to specific buildings and companies that have integrated daylighting into their building.

Daylighting data have been divided into Wavelengths of Light, The Affects of Light on the Body, and the following building sections: offices, schools, retail, health care, and industrial. The sections Wavelengths of Lights and The Affects of Light on the Body help describe the impact daylight has on building occupants. Each building section includes the effect daylight has on the building occupants psychologically and physiologically. Economic data have been cited in the categories in which information was found.

2. Introduction

Before the 1940s, daylight was the primary light source in buildings; artificial lights supplemented the natural light. In the short span of 20 years, electric lighting had transformed the workplace by meeting most or all of the occupants’ lighting requirements. Recently, energy and environmental concerns have made daylighting a rediscovered aspect of building lighting design. The physics of daylighting has not changed since its original use, but the building design to use it has. Daylighting is often integrated into a building as an architectural statement and for energy savings. However, benefits from daylighting extend beyond architecture and energy. The psychological and physiological aspects of natural light should also be considered. The comforting space and connection to the environment provided to building occupants provide benefits as significant as the energy savings to building owners and managers.

This paper summarizes the benefits that different wavelengths of light have on building occupants. Daylighting has been associated with higher productivity, lower absenteeism, fewer errors or defects in products, positive attitudes, reduced fatigue, and reduced eyestrain.

3. Wavelengths of Light

Electrical light sources include cool white fluorescent, incandescent, energy-efficient fluorescent, and full-spectrum fluorescent lighting. Each type has a different level of energy consumption. However, the most important factor affecting building occupants is the different spectrums of light that each source produces (see Appendix).

Different wavelengths or spectral distributions of light have different effects on the human body. Most electrical light sources lack the spectral distribution needed for complete biological functions, although full-spectrum fluorescent lighting does come close to that of natural light (Hathaway, et al. 1992).

Cool white fluorescent lights are concentrated in the yellow to red end of the visible light spectrum. Incandescent lamps, similarly, are concentrated in the orange to red end of the spectrum. In comparison, energy-efficient fluorescent lighting is typically concentrated in the yellow to green portion of the spectrum. These three light sources lack the blue portion of the color spectrum (Liberman 1991), which is the most important part for humans and is best provided by natural light. Full-spectrum fluorescent lighting is the electrical light source that has a spectrum of light most similar to natural light because it provides light in the blue portion of the spectrum.

Daylight provides a better lighting environment than cool white or energy-efficient fluorescent electrical light sources because “daylight…most closely matches the visual response that, through evolution, humans have come to compare with all other light” (Franta and Anstead 1994). The majority of humans prefer a daylit environment because sunlight consists of a balanced spectrum of color, with its energy peaking slightly in the blue-green area of the visible spectrum (Liberman 1991). According to Hathaway, et al. (1992), natural light also has the highest levels of light needed for biological functions:

The photobiologic action spectra of greatest importance to humans ranges from 290 to 770 nanometers. Skin reddening and vitamin D synthesis occurs in the range of 290 to 315 nanometers. Tanning or pigmentation of the skin and reduction of dental…[cavities] occurs in response to band light in the band from 280 to 400 nanometers. Vision is the most sensitive to light in the 500- to 650- nanometer range (yellow-green light). Billirubin degradation occurs in response to light in the 400- to 500-nanometer range (blue light) (Hathway, et al. 1992).

4. Effects of Light on the Body

Humans are affected both psychologically and physiologically by the different spectrums provided by the various types of light. These effects are the less quantifiable and easily overlooked benefits of daylighting. Daylighting has been associated with improved mood, enhanced morale, lower fatigue, and reduced eyestrain. One of the important psychological aspects from daylighting is meeting a need for contact with the outside living environment (Robbins 1986).

According to Dr. Ott (Ott Biolight Systems, Inc. 1997a), the body uses light as a nutrient for metabolic processes similar to water or food. Natural light stimulates essential biological functions in the brain and is divided into colors that are vital to our health. On a cloudy day or under poor lighting conditions, the inability to perceive the colors from light can affect our mood and energy level. Dr. Liberman (1994) also mentioned that light plays a role in maintaining health:

When we speak about health, balance, and physiological regulation, we are referring to the function of the body’s major health keepers; the nervous system and the endocrine system. These major control centers of the body are directly stimulated and regulated by light, to an extent far beyond what modern science…has been willing to accept.

A 1986 study by West as cited by Heerwagen (1986) evaluated the effects of light on health by evaluating prison inmates with different window views. He found that inmates with windows facing a meadow or mountains had significantly lower rates of stress-related sick calls than inmates with a view of the prison courtyard and buildings. Furthermore, inmates on the second floor had lower rates of stress-related sick calls compared with inmates on the first floor. Reasons for the differences in sick calls included a more expansive view from the second floor, which provided increased positive psychological benefits. Inmates on the first floor had added stress from lack of privacy because of visibility to passersby.

Because natural views tend to produce positive responses, they may be more effective in reducing stress, decreasing anxiety, holding attention, and improving mood. Studies in 1979, 1981, and 1986 by Ulrich (Heerwagen 1986) support the effectiveness of natural views. Ulrich found that viewing vegetation and water through slides or movies is more effective in creating psycho-physiological recovery from stress than built scenes without water or vegetation. Also, individuals recovered faster and more completely from a stressful event when exposed to films of natural settings as opposed to urban scenes. Nature group subjects also had lower muscle tension, lower skin conductance, and higher pulse transit along with possibly lower blood pressure from these health differences. Furthermore, Ulrich reported more positive emotional states and wakeful relaxation states for people exposed to natural scenes.

How the Eye Works

The human eye functions at its best when it receives the full-spectrum of light provided by daylight (A Closer Look at Daylighted Schools 1998). Many fluorescent lights are concentrated in the yellow-green portion of the spectrum to obtain the most lumens per watt; this unbalanced, narrow spectrum limits the blue in the source, which leads to improper functioning of the eye. Therefore, the superior spectral content of natural light makes it the best light for the eye (Ott Biolight Systems, Inc. 1997a). Looking at what parts of the eye are affected by light helps to understand how it functions in different light sources:

The human eye is a light-sensing system with a pupil and a photoreceptive medium called the retina. The retina contains two photoreceptors: rods and cones. Cones (which see photopic lumens or bright light) are responsible for day vision. Rods (which see scotopic lumens or dim light) are associated with night vision…Studies at UC Berkeley Laboratories by Dr. Sam Berman, senior scientist, have proven that pupil size and brightness perception at typical office levels are, in fact, strongly affected by rod activity within the retina of the eye.

Light reaching the retina of the eye is converted into electrical signals that are transmitted by the optic nerve. Most of these signals end up in the visual cortex of the brain and produce our sense of vision. However, some of the nerve fibers split off from the optic nerve soon after leaving the eye and send signals to the suprachiasmatic nucleus, which is the area of the brain where the main clock for the human body resides (Light, Sight, and Photobiology 1998).

Affects of Light on Internal Body Systems

Wavelengths of light help control the human body’s chemistry (Ott Biolight Systems, Inc. 1997a). Many functions, including the nervous system, circadian rhythms, pituitary gland, endocrine system, and the pineal gland are affected by different wavelengths of light.

Nervous and Endocrine System

Both the central nervous system and the neuroendocrine hormonal system are influenced by the powerful stimulus of light (Ott 1982; Brody 1981; Wurtman 1975; Kotzsch 1988 ). Wurtman (A Summary of Light-Related Studies 1992) claimed that light has biological effects important to health and that some of these effects could be measured in a laboratory. The effects of light fall into two categories: those modifying individual endocrine, hormone, and metabolic state by light reaching the retina and those resulting from light on the skin. Some effects of light on the skin are vitamin D production, skin tanning, and dissociation of bilirubin. Other studies have also supported the possibility of physiological benefits from light.

Danzig, Lazarev, and Sokolov…contend that physiological disorders may occur in the human system if the human skin does not receive some exposure to solar radiation, either direct or diffused, for long periods of time. They believe there will be a vitamin D deficiency followed by weakened body defenses and an

aggravation of chronic diseases. Wurtman and Neer (1975) suggest that non- visual retinal responses to light mediate a number of neuroendocrine hormonal functions, which, in turn, regulate such mechanisms as pubescence, ovulation and a wide variety of daily rhythms. Faber Birren has been quoted as saying that ultraviolet radiation intensifies the enzymatic processes of metabolisms, increases hormone system activity, and improves the tone of the central nervous and muscular systems (A Summary of Light-Related Studies 1992).

Circadian Cycles

Light falling on the retina and being transmitted to the hypothalamus controls our circadian rhythms (Samuels 1990), which are responsible for synchronizing our internal clock to 24 hours (Light, Sight, and Photobiology 1998). The effects of light on circadian rhythms can be studied using physiological variables such as the daily patterns of core body temperature, levels of melatonin, urine production, cortex activity, and alertness (Light, Sight, and Photobiology 1998). In 1980, Bickford noted that prolonged exposure to cool white fluorescent lights might induce abnormal circadian rhythms because the hypothalamic pacemaking mechanism is thought to react to all the color frequencies. Other lighting studies have shown that the light absorbed by the eye controls the production of the hormone melatonin, which affects sleep, mood, body temperature, puberty onset, and tumor development (Salares and Russell 1996). By looking at the purpose of an internal 24-hour clock, the significance of circadian rhythms can also be seen.

The circadian system is organized neurologically to drive bodily functions up and down every day and is a pervasive physiological regulatory mechanism. The timing of such circadian rhythms as body temperature is independent of an explicit knowledge of external clock time—and, indeed, in the absence of periodic environmental cues, the internal clock produces a “subjective” day length that differs reliably from 24 hours. Humans living under experimental isolation conditions may cycle at lengths greater than 24 hours. This kind of deviation would pose the risk of continual lack of synchrony with the external world were it not for the ability of light to force a daily correction in the internal clock and a strict match to 24.00 hours (Terman, et al. 1986).

Among the hormone activities that closely follow 24-hour cycles, the secretion of melatonin from the pineal gland (which induces sleep, modifies mood and mental agility, and plays a role in the activities of the reproduction system) is the most notable. Secretion of melatonin is closely followed by cortisol secretion from the adrenal cortex (which affects the breaking down of carbohydrates, protein and fat; the development of white blood cells; the activity of the nervous system; and the regulation of blood pressure)(Bryan 1998).

Pineal and Pituitary Glands

Wurtman linked light entering the eye with responses of the pineal gland and secretion of the hormone melatonin in 1968; this hormone also influences the functions of other glands from direct action on specific areas of the brain (A Summary of Light-Related Studies 1992). Studies have shown how melatonin production affects human health.

Photoelectric energy influences the functioning of the pituitary gland which controls the hormonal system (Hollwich and Dieckhues 1980) and hence our coping mechanisms, emotional and stress relations…Melatonin is normally secreted by the gland in the absence of light and where daylight and artificial lighting in the interior of buildings are inadequate the natural suppression of melatonin production during the day fails and is accompanied by feelings of depression (Wurtman 1975; Liberman 1985; Lewy 1985).

Recognized scientific research inspired by full-spectrum advocates has contributed to the understanding of how the human endocrine system, triggered by light entering the eye, regulates body chemistry, and in particular, the secretion or suppression of melatonin. Melatonin levels in the body determine a person’s activity and energy level. High melatonin levels cause drowsiness, while low melatonin levels correspond to an alert state of consciousness (Ott Biolight Systems 1997a).

Medical Cures from Light

By affecting the human body’s chemistry, light can improve health and help cure medical ailments. Terman, et al. (1986) claimed that improved interior lighting could alleviate the common subclinical problems in the population at large such as oversleeping, overeating, energy loss, and work disturbance. Dr. Ott (1982) used kinesiology tests to prove that better light could increase muscle strength, but Jewett, et al. (1985) argued that light does not have this effect. Jewett, et al. concluded that the tests Dr. Ott used altered the experimental results and the true effect of lighting was so small that psychological effects would obscure any results. However, studies have shown that light can help cure rickets, osteomalacia, and Seasonal Affective Disorder (SAD).

Rickets and Osteomalacia

In 1919, sunlight was determined to be the key to curing rickets. Independent studies by Neer and Hollick in 1985 (A Summary of Light-Related Studies 1992) claimed that the ultraviolet radiation derived from sunlight in the region of 290–315 nanometers triggers the development of vitamin D in the skin that in turn can prevent or cure rickets (A Summary of Light-Related Studies 1992). Liberman (1991) explained the role of light in the cure for rickets.

One of the most important phototherapeutic discoveries of the 1890s was that rickets, a disease characterized by a deformation in the developing bones of young children, could be cured by sunlight. Although the reason for sunlight’s

effectiveness was not immediately understood, it was later discovered that sunlight striking the skin initiated a series of reactions in the body leading to the production of vitamin D, a necessary ingredient for the absorption of calcium and other minerals from the diet. If vitamin D is absent, the body will not absorb the amount of calcium required for normal growth and development of the bones. This deficiency leads to the condition called rickets in children and osteomalacia in adults, which is characterized by a weak, porous, and malformed skeleton. It is known that both the development and maintenance of healthy bones is dependent upon the body’s ability to absorb calcium and phosphorus.

Seasonal Affective Disorder (SAD)

SAD has been one of the most researched areas in the illnesses that light affects. SAD is attributed to a variety of recurring events, but has been clearly attributed to the amount of light available for individuals. Without the proper amount of light available, our circadian rhythms are affected and susceptibility to SAD is increased. SAD occurrences are dependent on the availability of outdoor light in the winter and latitude.

The farther north people live, the more likely they are to experience winter depression. For example, while SAD affects only 8.9% of the residents of Sarasota, Florida, more than 30% of those living in Nashua, New Hampshire, are affected. Although this condition is seen primarily in adults between the ages of 20 and 40, children have also been found to suffer from this affliction. For them, the irritability, fatigue, and sadness are frequently accompanied by a decline in concentration and school performance (Liberman 1991).

Even under unrestricted exposure, naturally occurring seasonal variations in the availability of outdoor light may have serious consequences. With increasing distance from the equator, annual contractions in the photoperiod during fall and winter can precipitate a recurring syndrome of clinical depression, Seasonal Affective Disorder (SAD) (Terman, et al. 1986)…We all experience one or another of these problems occasionally, for varying reasons, for varying durations, and with varying severity. But in SAD they appear as a highly reliable cluster of complaints every year in late fall or early winter, and they persist unrelentingly for several months. The symptoms divide into two clinical categories: (1) melancholic, which are also common in non-seasonal depressive syndromes, and (2) atypical/vegetative, marked by sluggishness and overeating. In severe cases the winter weight gain can reach 30 pounds, and the pressure for extra sleep (sometimes until afternoon) is so great that a normal workday schedule is impossible. In springtime, SAD patients show spontaneous remissions and most often their summers are problem-free (Terman, et al. 1986).

Because the availability of outdoor light affects SAD occurrences, light can play a vital role in preventing and curing SAD. Terman, et al. (1986) explained the importance of light in curing SAD.

Appropriate administration of light therapy clears the symptoms within a few days. This is a remarkable achievement, considering the clinical severity, and makes us think we are close to the mechanism of pathogenesis. By comparison, antidepressant medications often take several weeks to work. Upon withdrawal from light therapy, as we have observed in mid-winter experiments, the typical patient relapses in two to four days. Thus, during the dark months of the year, the SAD patient must establish a regular maintenance regimen in order to obtain consistent relief.

5. Daylighting in the Office

Occupants in daylit and full-spectrum office buildings reported an increase in general well being. Specific benefits in these types of office environments include better health, reduced absenteeism, increased productivity, financial savings, and preference of workers. Benefits to the office worker are so great that many countries in Europe require that workers be within 27 feet of a window (Franta and Anstead 1994).

In buildings where daylighting is not or cannot be integrated, using full-spectrum bright lights has been shown to positively affect the workers in the buildings. Full-spectrum bright lights allow day and night workers to adjust their internal clocks or circadian cycles (see section: Affects of Light on the Body) to match their work cycles. Improvements in productivity, a decrease in accidents, an increased level of mental performance, improvements in sleep quality, and an increase in morale among night shift workers have also been attributed to better lighting (Luo 1998).

Health in the Office

Studies show that the proper use of daylighting decreases the occurrence of headaches, SAD, and eyestrain (Franta and Anstead 1994). Headaches and SAD are related to insufficient light levels. These ailments are reduced when the lighting level is improved by using proper spectral light. However, the number one health problem in offices is eyestrain (Ott Biolight Systems, Inc. 1997a).

Eyestrain is related to the spectrum of light present in a workspace and the ability of the eye to refocus. The proper integration and management of daylighting in an office building provides the best spectrum of light for the eye. When the eye is not allowed to refocus to different distances over long periods of time, the dilating muscles are conditioned to a limited range of perspective, promoting near or far sightedness. Eyestrain is diminished with landscape views through windows because the combination of short- and long-range views allows the eye to refocus (Franta and Anstead 1994).

Stress reduction and attentional focus can also be increased by the presence of natural vegetation in the workspace or through windows. One study found that subjects had lower blood pressure readings and felt more attentive in a windowless room that had plants as opposed to one without (Heerwagen, et al. 1998).

Another important yet simple effect from daylighting could be a more positive mood for employees. Increased job satisfaction, work involvement, motivation, organizational attachment, and lowered absenteeism could result from an improved mood (Heerwagen, et al. 1998). In 1988, Clark and Watson found that negative moods are associated with discomfort and distraction, whereas positive moods are associated with the physical setting at work and daily activities such as social interactions among employees. Owen Bailey (Bruening), research associate at the Rocky Mountain Institute, said, “If you improve the space that employees work in, then they are likely to be happier, healthier, and more productive.”

Productivity in the Office

Studies show that office worker productivity can increase with the quality of light. Studies of the effects of light on productivity date back to the 1920s when studies were conducted on silk weavers. No change has occurred in the workplace from then until now; a relationship between work output and the amount of daylight still exists. On tests of direct attention, Tennesen and Cimprick (Heerwagen, et al. 1998) found that people with views of natural vegetation scored higher. The view from windows is not the only important part of daylighting techniques. Natural light increases attention and alertness during the post-lunch dip and has shown to be helpful in increasing alertness for boring or monotonous work (Light, Sight, and Photobiology 1998). Lockheed Martin, VeriFone, West Bend Mutual Insurance, Pennsylvania Power and Light, and the Reno Post Office reported increased worker productivity when improved lighting conditions were implemented.

In 1983, Lockheed Martin designers successfully increased interaction among the engineers by using an open office layout with integrated daylighting in their offices in Sunnyvale, California (Romm and Browning 1994). This increase helped boost contract productivity by 15%. Lockheed officials believe that the higher productivity levels pertaining to daylighting helped them win a $1.5 billion defense contract (Pierson 1995).

Located near Los Angeles, California, VeriFone, Inc., constructed a new daylit Worldwide Distribution Center and reported increased productivity a year and a half after they started using their new building. Productivity at VeriFone increased by more than 5% and total product output increased 25%–28%, making the new building more cost effective than first predicted (Pape 1998).

Employees of West Bend Mutual Insurance moved into a new building that gave them personal control over their workstation (temperature, task lighting) in the early 1990s. This building has artificial lighting on at all times, but the building is designed so that more employees will be close to windows. From the old building to the new one, the number of employees having a perimeter workstation with a window view increased from 30% to 96% (Heerwagen, et al. 1998). West Bend has determined that they had a 16% increase in claims processing productivity in the new building compared to the old building (Romm and Browning 1994). Having employees closer to windows may have contributed to the productivity increase. The new workstations with employee control alone were determined to be responsible for a 2.8% increase in productivity over the old building (Lovins 1995). The senior vice president at the time, Ronald W. Lauret, was also convinced that he could pay his employees $1,000 less a year and they

would stay at his company because his environment was superior to other places they could work (Drews 2001).

Pennsylvania Power and Light installed high-efficiency lamps and ballasts in the early 1980s to reduce glare for drafting engineers. The effects from the low-quality lights previously used were not only causing glare, but also morale problems, eye strain, headaches, and increased sick leave for employees (Lovins 1995). With improved lighting, productivity for the drafting engineers increased by 13.2% (Lovins 1995). Previously, the drafters took 6.93 hours on average to complete one drawing, which results in 0.144 drawings per hour. The upgrade decreased the time to complete one drawing to 6.15 hours, which increased productivity to 0.163 drawings per hour (Lovins 1995). The lighting retrofit also resulted in a decrease in sick leave from 72 hours to 54 hours per year, a difference of 25% (Lovins 1995).

In 1996, the Reno Post Office in Nevada was renovated to include a better quality of light in the building. Indirect light was enhanced and better quality electric lighting was installed. The quality of light helped the mail sorters become more productive. Reports from the first 20 weeks in the new building show productivity increasing more than 8% and leveling to 6% above the old numbers a year later (Romm and Browning 1994). The postal workers operating the mechanized sorting machine sorted 1,060 pieces of mail in the time it used to take to sort 1,000. The rate of sorting errors decreased to one mistake in every 1,000 letters (one-tenth of a percent). With the increased efficiency of the workers, the Reno Post Office had the most productive sorters from Colorado to Hawaii, the entire western region of the United States.

Absenteeism in the Office

Some companies have seen a reduction in office worker absenteeism after moving to new office buildings that integrated daylight. Lockheed Martin, the International Netherlands Group (ING) Bank, and VeriFone, Inc. are a few of these companies.

In 1983, when Lockheed Martin moved some of its California employees into a daylit building, a 15% decrease in absenteeism from the old building was witnessed (Romm and Browning 1994).

VeriFone Worldwide Distribution Center reported a reduction in absenteeism of 6.8 hours per person per year (Sundaram and Croxton 1998), an approximate attendance increase of 47% (Ander 1998).

The International Netherlands Group (ING) Bank has no desk farther than 23 feet from a window in its building constructed in 1987. ING reported a 15% decrease in absenteeism (Romm and Browning 1994) and a dramatic growth in business (Browning 1992). Also, as a result of the new building, a “progressive, creative bank image” was created (Browning 1992).

Employee Turnover

Story County Human Services in Iowa moved into a daylit building in 1999. The three social service groups in the building have attributed many of their non-energy-related benefits to their daylighting. Brent Shipper of Wells Woodburn O’Neil (2001) stated, “…without an increase in

staff, one social service group tripled the amount of people seen and served.” Another group doubled the amount of people that came through their office. Also, one group experienced a 200% decrease in the turnover of their staff. Furthermore, that group also received a record number of job applicants as well as a high number of people wanting to transfer into their building from other counties.

Financial Savings

In 1998, the average commercial building’s construction cost was $150/ft^2 (McHugh, et al. 1998). This was the largest initial cost incurred, making construction a primary concern. By cost comparison, the 1998 average annual utility cost of office buildings is about $1/ft^2 (McHugh, et al. 1998). The energy and operating costs of a building are small when compared to the cost of employees and initial construction. For daylighting to pay for itself, the dollar value associated with office worker productivity must increase beyond the added cost of implementing daylighting technology. Many companies have found that the increased dollar value of productivity does indeed outweigh the increased cost of technology, as is illustrated by the following examples.

Productivity gains of $400,000 to $500,000 per annum at the Reno Post Office paid for the building renovation in less than a year (Romm and Browning 1994).

West Bend Mutual Insurance saw increased profit levels due to improved productivity in their enhanced work environment. West Bend realized that its 2.8% gain in productivity is worth approximately $364,000, with its annual salary base of $13 million (Romm and Browning 1994). This calculation demonstrates the impact of employee productivity on company profits.

Lockheed Martin reported financial savings due to increased productivity by moving some of its offices to a daylit building. Lockheed calculated that “every minute less of wasted time per hour represents a 1.67% gain in productivity… where a 2% increase in productivity equates to $ million saved (per year)” (Thayer 1995). Construction costs of the new daylit building represented 2% of the total building cost (Thayer 1995). After that expenditure, 6% of the costs are dedicated to maintenance, and the remaining 92% goes toward employee salaries (Thayer 1995). Lockheed also reports that it has saved half a million dollars on energy bills and reduced absenteeism (Thayer 1995). Lockheed officials commented on their increased productivity and financial savings in an article by Burke Miller Thayer (1995).

…The energy savings…are overshadowed by the rewards of improved employee productivity. To illustrate this point, we’ll assume the average salary of the Lockheed engineers and staff is $50,000/year and that absenteeism (a simple measure of productivity) is down 15% (an unofficial figure attributed to company officials) from a level of 7% (14 days per year). A 15% improvement on 7% absenteeism yields a 1% improvement in productivity. Every 1% gain in productivity in Building 157 is worth $500 per employee ($50,000 salary times 1%), or $1.5 million ($500 times 3,000 employees) per year. This is three times the energy saving. And although these numbers are merely illustrative, Lockheed

officials have privately acknowledged that their gains in productivity offset the $ million extra cost for the building in the first year of occupancy.

In the following excerpt and in Figure 1, Romm and Browning (1994) illustrated the relationship between cost per employee and average cost per square foot by estimating the savings for any commercial building lighting retrofit.

…A three-year payback, typical in lighting retrofits, is equal to an internal rate of return in excess of 30%. This type of return is well beyond the “hurdle rate” of most financial managers. In addition, the same retrofit may cut energy use by $0.50 or more per square foot, which has significant positive effects on the Net Operating Income of a building. However, the energy and operating costs of a building are small when compared to the cost of employees.

Based on a national survey of the stock of offices for 1990…electricity typically costs ~$1.53 [per square foot] (85% of the total energy bill); repairs and maintenance typically add another ~$1.37 [per square foot]; both contribute to the gross office-space rent (including all utilities and support services) of $21 per square foot. Yet paying the office workers costs ~$130 [per square foot]. Thus the office workers’ salaries cost ~72 times as much as the energy costs. Or, an approximately 1% gain in productivity is equivalent to the entire annual energy cost.

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officeworkers'

salariesgross office

rent total energy

electricityrepair & maintenance

$/ft

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Figure 1. Approximate operating costs for an office building with 1990 data in $/rentable ft^2 /yr (Romm and Browning 1994)

Employee Preferences and Perspectives

Studies show that windows are highly valued by office workers in the workplace. A survey of office workers (Collins 1975) found that 35% of employees responded instantly that the lack of windows was their biggest difficulty with their office space. The specific reasons given for the dislike of the windowless offices were: “no daylight, poor ventilation, inability to know about the weather, inability to see out and have a view, feelings of being cooped-up, feelings of isolation and claustrophobia, and feelings of depression and tension.” Another study on the affects of windowless offices supports the findings of the Collins study by stating that employees in windowless buildings had much less job satisfaction and were substantially less positive (Finnegan and Solomon 1981).

Wotton and Barkow (1983) found that employees highly value any size of window that they can have access to and value it more than privacy in their office. The tolerance of windowless areas is lowered by “the workers’ knowledge that the executives have large offices upstairs with splendid views of the city… [whereas] the lower level personnel are left without windows and highly dislike their location” (Collins 1975). Wotton and Barkow (1983) also found that 74% of the surveyed employees prefer having a window close to their workspace. If offered a window, 57% of surveyed employees would like the window to be beside their workspace rather than in front or behind their workspace.

Markus (1967) used a questionnaire to determine how satisfied office workers were with their workspaces. Ten environmental factors, including sunshine and view, were presented to employees for a satisfaction analysis. The survey lacked the ability to portray how strongly each employee felt about issues, but it did provide an understanding of their overall satisfaction. From the questionnaire, approximately 96% of respondents preferred to work under natural light as opposed to electric lighting (Markus 1967). Furthermore, approximately 86% of the respondents preferred having sunshine in their office year round as opposed to only one season of the year or not at all. Also noted by the study was that employees sitting near windows were more content, whereas those sitting further away from the windows complained more. Therefore, workers with daylight and a view may suggest having a window is not important, but workers without either believe having more light and a view is very important.

In a 1983 study, Kit Cuttle examined England and New Zealand office workers on their attitudes toward their workplaces. Cuttle concluded that office workers believe large windows are important for an office environment. The workers preferred sitting close to a window, although in many office environments people of lower status are denied this privilege. Also, four out of five office workers preferred working in natural light because they believe working by electric lighting caused discomfort (Cuttle 1983). The employees believed that short-term discomfort from the electric lighting was more of a concern than the long-term deleterious effects. Furthermore, employees did not believe working by electric lighting resulted in poor work output; they believed that their work output was achieved at greater personal stress levels (Cuttle 1983).

Employees in daylit office buildings have expressed their feelings about their workspaces. The employees in the Lockheed Martin building had quite favorable responses to their workspace.

[Ben Kimura, staff engineer, said] “My workspace is 15 feet from the literium (a central area in the building which has daylight streaming in from skylights), and the lighting is great. The office décor, arrangement, and temperature are ideal. There are many people working on this floor, but the feeling is not one of crowding, but of spaciousness. Interface with other departments is greatly facilitated because we’re finally all in one building. By nature I’m very cynical, but the conditions in this building are far superior to any I’ve experienced in 30 years in the aerospace industry” (Romm and Browning 1994).

[Joanne Navarini, financial controller, said] “I love my work space. I think the building itself is very functional. I am five workstations from the window and the light is fine. I use my task light and could order an additional desk lamp if I felt like I needed to. I like the daylight” (Romm and Browning 1994).

Employees in the VeriFone building have also shown greater satisfaction with their daylit workspace. One employee stated, “Working in this building is like working outdoors–the light streaming into my workstation is wonderful…”(Sundaram and Croxton 1998). Another employee also enjoyed the building and stated, “In my previous office, it felt cooped in, always artificially lit…but here, if I look up, I can see glimpses of the sky outside and that makes me feel good…”(Sundaram and Croxton 1998).

Another building that integrated daylighting was the Iowa Association of Municipal Utilities, which was occupied in February 2000. This building was designed to have an inviting feeling and set an example of energy efficiency techniques. Daylighting fit the design goals of the building. According to Patti Cale (2001), Energy Services Coordinator for the building, “When people walk into the building they say wow and comment on how the building is nice, light, and airy. The building does not divide the occupants from the outside environment; the employees can watch what is going on in the world outside the window.” Cale (2001) said she would “choose to be in this building over a traditional building” because she can “see what is happening outdoors.”

Even integrating a central atrium that brings in natural light can affect the attitudes of office workers. The 3M Austin Center used a daylit atrium as the central point of its building complex. Task lighting is used in workspaces, but windows close to the ceiling let natural light deep into the building. David Wilson (2001), Director of Human Relations and Head of Corporate Services for the 3M Austin Center, said, “Visitors comment on how nice it is to have natural sunlight and they find the building bright, airy, open, and spacious.” Wilson had an office on the outside of the building with floor-to-ceiling windows on two walls. He said, “I couldn’t have a better office. I have a stressful job and the view of hills and distant skyscrapers through my windows help me to relax. I wouldn’t work anywhere else.” Some employees had windows opening to the atrium as opposed to the outside.

Nick Lampe (2001), an employee of the 3M Austin Center, said, “The atrium creates a more welcoming, relaxed, and comforting environment because artificial lights are not clicking overhead.” Part of his day was spent in an office one workspace away from a window and the other part was spent in an office with windows opening to the atrium on two walls. Lampe (2001) said that in the office with more window space he “does not feel as drowsy and is more

alert.” He did note, however, that for part of the morning, direct sunlight entered the windowed office space and his eyes had to adjust to the direct light. Even with the direct glare, Lampe preferred working in the office setting with more windows because of the natural light. The fact that the 3M Austin Center was built more recently than his previous working environments also affected his attitude toward the center. However, Lampe (2001) noted that the natural light is the most effective part of changing his attitude toward his working environment. He found taking breaks in the daylit atrium to be “refreshing.” Overall, Lampe (2001) prefers having the more natural environment in the center and said “it is motivating, calming, and puts me in a better mood.”

However, integrating natural light into all parts of an office has the greatest impact on building occupants. In the Story County Human Services building, visitors comment that the building has a friendly environment. Employees said that they “love the windows” and “the building is wonderful” (Shipper 2001). Although more notable was the employee who stated that “you’ll never be able to put into numbers what the windows do for us” (Shipper 2001).

Improper Daylighting

Studies show that daylighting can provide substantial benefits to staff and employers alike, but improper usage can lead to unpleasant conditions within the structure. The benefits of daylighting will only be realized if it is implemented correctly. Improper use of daylighting can reduce productivity and increase employee absenteeism due to the possibility of extremely high lighting levels, excessive glare, and high temperatures.

A 1992 study of energy efficient buildings investigated the tactics office workers used to reduce discomfort. All the tactics distracted employees from their work and were not effective. To improve comfort, some employees changed clothing, walked around, went for a break, complained, got something to drink, or added a heater or fan to their workspace (Heerwagen, Loveland, and Diamond 1992). With these ineffective coping methods, dissatisfaction, loss of work efficiency, reduced motivation, and fatigue were possible results. If employees tried to ignore the problem, mental energy would be absorbed that could have been focused on their work. To aid in keeping employees on task, a comfortable work environment is necessary.

The Iowa Association of Municipal Utilities building also had problems with glare, even though it was designed for indirect lighting. To alleviate the problem of high glare on the east side of the building, semi-opaque fabric was hung about six feet away from the windows for two to three months of the year (Cale 2001). Venetian blinds were also installed on another portion of the east side of the building. These blinds aid in darkening a room for multimedia presentations as well as reducing glare. To prevent other glare issues, new employees to the building were trained on how to orient their computer monitors in their workspaces to minimize glare. This building was a good example of how to overcome some glare issues.

The VeriFone building had some problems with glare in the afternoon and one employee stated, “…I get direct sunlight towards my workstation and must take a break because of the glare on computer and cannot work (cannot see at all)…” (Sundaram and Croxton 1998).

The Hughes Corporate Headquarters building also demonstrates potential problems if daylighting in buildings is not properly designed and managed. The Hughes Corporate Headquarters building, occupied in 1986, was designed to use daylighting, but its implementation was not planned properly. The initial positive perceptions of the building by employees became negative when the lighting levels and glare became too much to tolerate. The employees wore sunglasses at their desks, added temporary shades around their desk, and tried to match the high level of lighting with additional desk lamps to reduce eye fatigue. While one employee considered becoming a vitamin D donor, another employee stated that, “It is a beautiful building, management needs only to put down sand, beach umbrellas, and hand out piña coladas.”

Occupants of both daylit and nondaylit buildings that are improperly designed have had complaints. One problem was that “office staff seem much less ready to accept what they are given and much more prone to criticize” (Collins 1975). Lighting-level criticism could also result from the simulated or real daylight dimming systems keeping a constant workplace illumination. A study by Begemann, vad den Beld, and Tener (1996) concluded that these dimming systems are too simplistic to meet human preference and response. However, a different study found that employees in one daylit building are willing to accept the glare because of the overall building quality (Bryan 1998).

6. Daylighting in Schools

School children and teachers can benefit from integrating and managing daylight properly. Reported benefits include reduced utility costs for school districts, improved student attendance and academic performance, and a less stressful environment for students.

A Daystar article, “Benefits of Natural Daylighting” (1998), states that there is increased student and teacher attendance, increased achievement rates, reduced fatigue factors, improved student health, and enhancement of general development. Furthermore, natural lighting eliminates noise and flickering from electric light sources and provides the best quality of light available in classrooms, gymnasiums, and corridors. Other research has shown that students in windowless classrooms are more hostile, hesitant, and maladjusted. Also, students in windowless classrooms tend to be less interested in their work and complain more.

Health

Daylight has physiological and psychological benefits for teachers and students. Thomas Benton, principal of the daylit Durant Road Middle School in Wake County, North Carolina, claims that teachers who have been at his school for more than a year mentioned that they feel better mentally and physically (Bailey 1998). Physiological benefits due to daylight on school children are less dental decay (cavities), improved eyesight, increased growth, and improved immune system.

The sun is a primary source of vitamin D, and increasing vitamin D intake stimulates calcium metabolism (see also Affects of Light on Internal Body Systems). There is a strong correlation

between the amount of sunlight a child is exposed to and the level of dental decay, making daylighting a very important element for cavity prevention in children. Reports show that students’ rates of dental decay have decreased in fluorescent full-spectrum and daylit schools.

Research in the 1930s (Liberman 1991) provided evidence of the effects daylighting in school buildings has on students. McBeath and Zuker (Liberman 1991) conducted a study showing children are more prone to dental cavities in the winter and spring when they spend more time inside a school and less prone during the summer months when they are outside in the sun. These results are supported by a study that compared full-spectrum lit schools in Canada to traditional schools with fluorescent lighting (Hathaway, et al. 1992). Full-spectrum fluorescent light closely resembles daylight, but it does not provide the same spectral content. The full-spectrum fluorescent schools reported that student dental decay decreased nine times [compared to schools with fluorescent lights] as a result of the increase in vitamin D.

Studies supporting full-spectrum lighting effects on dental decay include research on golden hamsters by Sharon, Feller, and Burney in 1971(Liberman 1991). Two groups of hamsters were fed the same cavity-producing diet for 15 weeks but were raised in different spectrums of light. One group of hamsters was raised under cool-white fluorescent lights; the other group was raised under full-spectrum fluorescent lights. The hamsters that were raised under cool-white lights had five-times more severe dental cavities than the hamsters raised under full-spectrum fluorescent lighting.

Quality of light is also important for students’ eyes. Eyes collect and convert visible light into electrical impulses called photocurrents (Ott Biolight Systems, Inc. 1997b). These photocurrents flow through the optic nerves to the brain. Studies at University of California–Berkley Laboratories suggest that light sources with richer spectral content provide more usable light to the eye. Daylight provides the richest spectral, usable light, and it eases some of the stress to the eye. Research shows that reading is the most visually stressful task for students (Liberman 1991). Stress causes a contracted visual field in the eye that can lead to a decrease in information processing and learning ability (Liberman 1991). The direct affect of eye strain can be seen from a 1975 study showing that 88% of postgraduate students in the United States are nearsighted, although only 45% of the general population are nearsighted (Liberman 1991). Being nearsighted can be attributed to the high amounts of reading done by these students; poor lighting may also be a contributing factor.

A school with insufficient light can also reduce a student’s ability to learn due to the effect lighting has on physiology. Poor spectral light can create strain on students’ eyes, leading to a decrease in information processing and learning ability, causing higher stress levels (Liberman 1991). Dr. Walker (1998) found that stress impacts certain growth hormones. He determined that “persistent stress stunts bodily growth in children” because the activity of the growth-inhibiting hormones cortisol and ACTH increase under stress. Students in the Canadian full-spectrum fluorescent schools grew 2.1 cm more in two years (Hathaway, et al. 1992) compared to students who attended traditional fluorescent-lit schools. The increased activity of these hormones supports researchers’ observations that children under electric lights all day have decreased mental capabilities, agitated physical behavior, and fatigue.

Daylight also produces ultraviolet radiation. Dr. Ott claims, “trace amounts of certain wavelengths of light…can have a staggering affect on your health” (Liberman 1991). Ott also said that the trace amounts of UV light, measured as parts per trillion, are important because “we need a basic amount [of UV light] to support life and maintain a healthy immune system” (Liberman 1991). Faber Birren states that this basic amount of UV light needed has been demonstrated to “intensify the enzymatic process of metabolism, increase hormone system activity, and improve the tone of the central nervous and muscular systems” (A Summary of Light-Related Studies 1992).

Attendance

Schools that have integrated full-spectrum fluorescent or natural light show an increase in student and teacher attendance when compared to traditionally lit schools. A study of the full- spectrum fluorescent Canadian schools reported that students had an attendance increase of 3.2 to 3.8 more days per year than the students in traditional fluorescent lighting schools (Hathaway, et al. 1992). Durant Road Middle School is a daylit school in the Wake County, North Carolina, school system. Durant reported the best health and attendance in the entire school system, an attendance rate above 98% (Bailey 1998). Teachers also have lower absenteeism rates, claiming the lowest number of faculty health absences in the area.

Achievement

A study on the North Carolina Johnston County schools specifically analyzed the academic benefits of daylighting (Nicklas and Bailey 1997). The Johnston County school study compared the scores of students from newly constructed daylit schools to schools that were artificially lit. Students in the daylit schools had higher reading and math achievement scores.

Four Oaks Elementary is a daylit school in Johnston County and is a unique case because fire destroyed the original school and students were temporarily placed in mobile classrooms for two school years. During this time, a new daylit building was constructed. In Figure 2, test scores are compared between the old, temporary, and new school buildings in order to gauge the academic performance affects of daylighting (see Table 1 for timeline of school building occupancy).

Before the original building was destroyed in December 1988, California Achievement Test (CAT) scores of Four Oaks students were 7% above the average. When the students moved to the mobile classrooms, scores dropped to 10% below the average. Results from the new daylit building showed substantial improvement in test scores. First year test scores increased to 9% above the county average. Between 1988 (the last year in the old building) and 1992 (the last year of the study), Four Oaks had a 15% increase in test scores. The Four Oaks increase was 3% higher than the county’s 12% average for the period.

Figure 2. California Achievement Test scores for Four Oaks School vs. Johnston County (Nicklas and Bailey 1997)

Table 1. Timeline of Events for Four Oaks School

Date Event December 1988 School burns 1989 and 1990 Students placed in temporary classrooms June 1990 End of temporary facilities August 1990 Occupy new school April 1991 First CAT in new school April 1992 Last CAT test

Other daylit schools that were built in Johnston County after the Four Oaks school were the Clayton Middle School and the Selma Middle School. Also, the North Johnston Middle School was built after Four Oaks, but did not incorporate daylighting. Table 2 compares the average reading and math scores for multiple grades between these schools and the county average.

0

10

20

30

40

50

60

70

80

1988 1989 1990 1991 1992 S ch o o l Y ear

CAT Test Score

F our O aks S chool Johnston C ounty

Clayton’s daylit school building had a 7% test score improvement that was above the county’s 5% improvement. Selma Middle School also showed signs of benefiting from their daylit building with an 18% increase in test scores. The North Johnston Middle School, built without daylighting, only had a 5% increase in test scores, the same as the average for the county.

Table 2. Average of Reading/Math for Multiple Grades (Nicklas and Bailey 1997) School and Grade 1992/93 Base Year Average Scores

1993/95 Average Scores

% Improvement Base- Average Clayton 6–8 68.4 73.2 +7% Selma 6–7 46.3 54.8 +18% N. Johnston 6–8 62.5 64.2 +5% County Avg. 6–8 62.1 65.4 +5% County Avg. 6–7 61.3 64.6 +5%

Reports of the End-Of-Grade (EOG) testing scores for the daylit schools are also much better than North Johnston Middle School (Table 2). Clayton reported an EOG scoring of 1.5% above the county average, and Selma was 5.2% above the county average. North Johnston, the non- daylit school, was 1.6% below the average. The North Johnston test scores indicate that a new building does not necessarily correlate to positive affects on student performance.

Table 3. EOG Score Percentage Relative to Norm (Nicklas and Bailey 1997)

School 1992/93 Base Year Average 1993/95 Improvement Base- Average Clayton +6.3 +7.8 +1.5 Selma -15.00 -9.8 +5.2 N. Johnston +.4 -1.2 -1.6

Average reading and math test score results between 1992 and 1995 are included in Table 3. The eighth graders at Clayton had a 21% increase in their scores, which was well above the 10% increase of the average. The Selma seventh graders also had improvements and reported a 32% increase, exceeding the 15% increase of the county average.

Table 4. Average of Reading/Math for Specific Grades (Nicklas and Bailey 1997)

1992/93 1993/94 1994/95 % Improvement Base to 1994/95 Average Score Clayton 8th^ 69.2 67.8 83.8 +21% County Avg. 8th^ 63.8 64.3 70.2 +10% Selma 7th^ 45.6 51.8 60.3 +32% County Avg. 7th^ 61.4 59.7 70.4 +15%

Other studies on schools report the effects of full-spectrum fluorescent lighting on academic achievement. One study reported that learning-disabled children with extreme hyperactivity problems are calmer and overcome some of their learning problems in classrooms that use full- spectrum fluorescent lighting (Walker 1998). The benefits are not limited to learning disabled children. Students have shown better behavior in properly lit libraries than traditional fluorescent-lit schools (Nicklas and Bailey 1997).

The Heschong Mahone Group also showed improvements in student academic rates in a 1999 study for Pacific Gas and Electric in California. For this study, test scores for students in grades two through five were evaluated in Orange County, California; Seattle, Washington; and Fort Collins, Colorado. For the California schools, data were collected during the school year to produce a learning rate. This analysis provided information with the highest confidence of the three school districts because only a few variables influencing the students were involved in the data. For the Washington and Colorado schools, end-of-year data were evaluated. Variables were added in these studies due to the nature of the data collection.

The Capistrano Unified School District in Orange County, California, had different building plans to bring in natural light. Results for these schools were divided into groups but were also evaluated collectively. Overall, the classrooms with the most amount of daylighting had a 20% faster learning rate in math and a 26% faster learning rate in reading during one school year when compared to classrooms with the least amount of daylighting (Heschong Mahone Group 1999a). These results can also be evaluated by looking at the learning rate of an average child in the Capistrano district. Students in classrooms with the most daylighting are progressing on the order of one to two points above the average rate in reading and math over the time span between fall and spring testing. By advancing more quickly, the Heschong Mahone Group stated that schools “could be saving up to one month of instructional time for the reading and math curriculum that could be used for other areas of learning.” Also determined from the study on Capistrano schools was that the variable of daylighting had larger effects than the window variable. Therefore, the presence of natural light was responsible for the positive results of student performance, not the view from the windows.

As previously mentioned, the studies on the Seattle and Fort Collins schools used the absolute value of students’ final scores on EOG tests. From this data, more variables were introduced, creating less confidence in the study results. The Seattle Public School district, in Seattle, Washington, had 9% higher math scores and 13% higher reading scores for students in classrooms with the most daylight compared to students in the least daylit rooms. In Fort Collins, Colorado, the Poudre School district had 7% higher test scores in reading and in math for students in daylit rooms compared to those with the least daylighting. The difference in scores from each district could be due to the difference in daylight exposure in the different locations. Children in Seattle and Fort Collins might show greater effects from daylighting because they see less sun in their geographical location compared to California, which makes them more sensitive to the light.

The Heschong Mahone Group summarized its study by stating that it “found the positive effect of daylighting was distinct from all other attributes of windows.” Also, a positive correlation was found between daylighting and better test scores for all three school districts. The Heschong Mahone Group also noted that daylighting is complex and its study cannot prove why daylighting causes the positive affects on students. Reasons that were cited as possible causes for the good performance from students was the better distribution of light, improved visibility from improved light, better color rendering, and the absence of flickering from electrical lighting.