Lighting and Human Performance
For purposes of learning, performance, and productivity, lighting in a school building should allow people to see to read, to see others with whom they are communicating, and to perform other visual tasks associated with learning, teaching, and school administration. Lighting can be provided by electric systems or by daylight through windows, clerestories, and skylights. Typically, school buildings use a combination of electric lighting and daylight.
When evaluating the performance of any lighting system, electric or daylight, its impact on two biological systems—the visual and the circadian—needs to be considered, together with the physical attributes of light that differentially affect these systems (Figure 5.1).
LIGHTING FOR VISUAL PERFORMANCE
The visual system functions as a very quick remote-sensing mechanism that alerts us to environmental changes and enables us to identify nearby threats and opportunities. The visual system is fairly well understood for adult populations in regard to the effects of light on both appearance (what things look like) and visual performance (how well visual information is processed). For example, there is a complete model of visual performance available for predicting the impact of background luminance (light level), target contrast, target size, and observer age from 18 to 65 years (Rea and Ouellette, 1991). Presumably, most school-age students should behave like 18-year-olds in regard to visual performance, but this has not been systematically studied. In general, given the characteristics
of the visual response functions, it can probably be concluded that most lighting and task conditions are adequate for most students. Going the next step, however, is more tenuous because there is no evidence that the quality or quantity of light directly affects student learning (Larson, 1965; Demos et al., 1967; Boyce et al., 2003).
For a large majority of the people working in buildings, lighting for vision during the day is quite adequate, in part because people have very flexible visual systems and adjust their posture in response to the available lighting conditions. For example, the dimmer the light, the closer one holds the reading materials to maintain a constant ability to read. Laboratory experiments show that young people with normal eyesight will systematically adjust the eye-to-task spacing to maintain good task visibility, either by moving closer to the visual task or shifting posture to avoid reflected glare (Rea et al., 1985). A flexible visual system combined with a flexible body provides most people with the ability to adapt to less than ideal lighting environments.
A significant minority of the school-age population may not have properly corrected eyesight, however, and may not be able to take full advantage of adaptive strategies to see educational materials in the classroom. In a large study using the 1996-1997 National Health Interview Survey, Kemper et al. (2004) determined that approximately 25 percent of U.S. school-age children have corrective lenses (eyeglasses or contact lenses). They showed that the prevalence of corrective lenses is related to several population factors such as age (older children are more likely to wear corrective lenses), ethnicity (black and Hispanic children are less likely to wear corrective lenses), income (poorer children are less likely to wear corrective lenses), and gender (girls are more likely to wear corrective lenses than boys). Of particular note, insurance coverage appears to be a major factor in the prevalence of corrective lenses in school-age children. The actual percentage of corrective lens wearers is probably smaller than the percentage of children who need them. Moreover, it is unknown whether students’ corrective lenses actually provide the proper refraction. Because lighting and task variables as well as proper corrective lenses determine visual performance, it seems likely that at least some students are not able to adequately see educational materials in the classroom.
Within the context of the school environment, then, what constitutes adequate lighting for the majority of the students may be inadequate for others. It could be hypothesized that for those students who need but do not have corrective lenses, supplemental daylight may offer a significant advantage by providing higher light levels and better distribution of light (side light) to minimize shadows than would be provided by electric lighting alone. However, the potential for daylight in classrooms to improve the visual performance of children with or without properly corrected eyesight has not been systematically studied.
Some portion of the adult population (teachers, administrators, support staff) will likely also have visual problems. Normal aging involves a continuous loss of visual accommodative ability, known as presbyopia, from about 20 years of age to about 65 (Weale, 1992). Until about age 45 the gradual loss in ability to focus on close objects is hardly noticed, but after this age nearly everyone begins to adopt new strategies to see small objects. Instead of getting closer to an object to see it as they did when they were younger, people with presbyopia actually move the object farther away from their eyes, or they place it under a bright light, usually provided by a window or skylight. Eventually, everyone needs optical aids, such as bifocals, reading glasses, or contact lenses to read normal print, but the use of bright light from the right direction will continue to be a strategy employed by older people to see small objects. Thus, the visual performance of adults older than 45 in a school building is likely to be negatively affected by poor lighting.
Glare and Visual Performance
There is much less certainty in predicting visual comfort in regard to glare, even in adults, than in predicting visual performance (Rea, 2000; Boyce, 2003). A clear distinction is made between glare that reduces visual performance (disability glare) and glare that does not (discomfort glare). Disability glare can be precisely predicted for a given individual and for the general population. As would be expected, disability glare becomes more problematic with age owing to physical changes of the eye, particularly from the scattering of light within the eye by the crystalline lens (Weale, 1963).
Formulas exist for calculating discomfort glare, and these are often used to characterize the lighting layout for a space using commonly available lighting software. However, collective understanding of the mechanisms underlying discomfort glare is rather poor (Boyce, 2003). Psychological phenomena appear to contribute significantly to discomfort glare, so that, for example, bright flashing lights in an office are highly uncomfortable, but the same lights can be highly desirable in a nightclub for dancing. Therefore, although disability glare is the same in both applications, discomfort glare is not. In this context, and given the strong psychological component to discomfort glare, predicting visual comfort in school-age children is an area that requires more research.
Daylighting and Student Achievement
Several studies investigating the effect of daylighting on student achievement were conducted by the Heschong-Mahone Group between 1999 and 2003. In the 1999 study, data were obtained from elementary school districts in three locations: Orange County, California; Seattle, Washington; and Fort Collins, Colorado (Heschong-Mahone Group, 1999). The study looked for a correlation between the amount of daylight provided by a student’s classroom environment and test scores. Test results for more than 21,000 students in these districts were analyzed. Demographic data sets, architectural plans, aerial photographs, the presence of skylights, maintenance records, and daylighting conditions for more than 2,000 classrooms were among the factors reviewed.
The study developed a regression model for approximately 150 independent variables (e.g., teacher salaries, grade level, attendance), including available daylight, which was represented by one of five different levels, or “daylight codes.” Although the regression analysis leads to a prediction that an increase in the value of the daylight code can increase scores in both math and English by more than 20 percent, a closer examination of the results shows that only 0.3 percent of the variance in the regression model is explained by daylight code (Boyce, 2004). This is a very small
effect and one that cannot be considered statistically significant. As noted below, these results could not be replicated in a subsequent study.
A reanalysis of the Orange County and Seattle data was undertaken in 2001 to evaluate additional variables that might have a confounding influence, including teacher assignments (Heschong-Mahone Group, 2001). In 2003 a third study was undertaken to see whether the original methodology and findings would hold up when data came from a school district (Fresno, California) with a different climate and curriculum. The preliminary statistical analyses used the same models as the previous studies. In the Fresno study, the holistic variable “daylight code” was found to be “not significant in predicting student performance. It had the least explanatory power of the variables considered, and the lowest significance level” (Heschong-Mahone Group, 2003, p. viii).
The authors proceeded with more detailed multilinear regression (statistical) analysis to see whether they could gain some insight into why the daylight code was not significant in Fresno as it had been in the earlier studies. Among the authors’ conclusions were that sources of glare negatively affect student learning; direct sun penetration into classrooms, especially through unshaded east- or south-facing windows, negatively affects student performance, likely causing both glare and thermal discomfort; blinds or curtains allow teachers to control the intermittent sources of glare or visual distraction through the windows; absence of teacher control of windows negatively affects student performance (Heschong-Mahone Group, 2003, p. ix). They summarized their results as follows:
Characteristics describing windows were generally quite stable in their association with better or worse student performance. Variables describing a better view out of windows always entered the equations as positive and highly significant, while variables describing glare, sun penetration, and lack of visual control always entered the models as negative (Heschong-Mahone Group, 2003, p. viii).
Because of the inconsistent results of this limited number of studies, there is insufficient evidence at this time to determine whether or not an association exists between daylight and student learning.
Views and Performance
Windows can be a major source of light in school buildings. Despite the greater thermal energy losses and higher initial costs they incur relative to insulated walls, people universally prefer having windows. First and foremost, windows provide a view to the outside. Depending on the context, views can be beneficial or distracting. Windows can also
provide high light levels, and, when properly located, they can provide ideal distribution of light for performing visual tasks that do not involve self-luminous displays, such as computer screens, or audiovisual presentations. Skylights and clerestories can also be good sources of illumination even though they do not provide a view.
Studies conducted using subjective ratings from adults show that people like views from windows (Markus, 1965; Jackson and Holmes, 1973; Ne’eman and Longmore, 1973; Collins, 1975; Ludlow, 1976; Cuttle, 1983; Heerwagen and Heerwagen, 1986; Leslie and Hartleb, 1990, 1991; Boubekri et al., 1991) and that architectural spaces with views from windows command higher prices (Boyce et al., 2003). Although these findings for adult populations are interesting, the relationship between view and performance of students remains largely undocumented, with the exception of one study that attempted to relate children’s hormone levels to behavior in classrooms with and without windows.
Kuller and Lindsten (1992) studied children’s health and behavior in classrooms with and without windows for an entire academic year. They concluded that work in classrooms without windows affected the basic pattern of the hormone cortisol, which is associated with stress, and could therefore have a negative effect on children’s health and concentration. This finding is strictly suggestive, however, because no direct relationship between cortisol levels and student performance and health was established (Rusak et al., 1997).
LIGHTING AND THE CIRCADIAN SYSTEM
The circadian system involves biological rhythms that repeat at approximately 24-hour intervals. The behavior of all terrestrial species, including humans, is driven by an internal clock synchronized to the solar light-dark cycle. Indeed, light is the primary stimulus for the internal clock. The circadian system regulates not only overt patterns of behavior such as activity and rest, but also bodily function at the cellular level, such as the cell cycle (Moore, 1997).
Current lighting technologies and lighting standards are designed exclusively for providing visual sensation. However, light affects the visual system very differently than it affects the circadian system. Relative to the visual system that underlies conventional photometry and all lighting standards, the circadian system needs a much higher light level on the retina for activation (McIntyre et al., 1989a,b); it has a peak spectral sensitivity to much shorter wavelengths (Brainard et al., 2001; Thapan et al., 2001); it has greater sensitivity to light in the inferior retina (such as would be involved when a person looks at the sky) than in the superior retina (Glickman et al., 2003); it requires much longer exposures for acti-
vation (McIntyre et al., 1989a,b; Rea et al., 2002); and, most important, its sensitivity to light depends on the time of day (Jewett et al., 1997).
There is a growing body of literature indicating that the effect of light on circadian rhythms can affect productivity as well as health. Seasonal affective disorder (SAD), or the “winter blues,” is recognized by the medical community as a psychiatric disorder. Apparently, seasonal reductions in the amount of daylight available in the winter at extreme northern and southern latitudes can induce depression (Rosenthal, 1998). Light treatment, typically provided as bright light from electric lighting systems, is recognized by the medical community as the preferred method of treating SAD (Rosenthal et al., 1985).
The incidence of SAD in school-age children is poorly documented, although it has been reported that adults who experience SAD also experienced it as a child. It seems, too, that postpubescent young women are more likely to experience SAD (Rosenthal, 1998). Depending on latitude, between 4 and 30 percent of the adult population, usually women, experience some symptoms of seasonal depression (Rosenthal, 1998), and this might also be true for teachers. Less learning might be expected on the part of children who experience symptoms of seasonal depression, so lighting might play a very important role in the design of a green school at northern latitudes. Systematic attempts to alleviate seasonal depression in children through lighting design have not been undertaken, but these early findings suggest a reconsideration of the role that light, particularly daylight, plays in the classroom.
Nearly half the population experiences some form of sleep disorder (National Sleep Foundation, 2005). Poor sleep directly affects a person’s ability to perform tasks and learn new tasks (Jennings et al., 2003; Heuer et al., 2004). Light and dark have a dramatic impact on sleep quality (Turek and Zee, 1999; Reid and Zee, 2004). Adolescents in particular commonly go to sleep late (after midnight) and have difficulty getting up early (before 7:00 a.m.) to go to school (Carskadon et al., 1998). In extreme cases this difficulty in falling asleep late and getting up early is diagnosed as delayed sleep phase syndrome (DSPS). Many school age children with DSPS must get special training or even repeat grades because of poor attendance and performance. Light is a recognized treatment for this disorder, and a regular light-dark cycle may have broader implications for sleep quality in a larger group of children.
Recent research at the other end of the age spectrum shows that light treatment can consolidate sleep and increase sleep efficiency during the night in older people (Satlin et al., 1992; Fetveit et al., 2003; van Someren et al., 1997; Figueiro and Rea, 2005). A regimen of bright light at school during the day, together with dark nights at home, may increase the atten-
dance and performance of school age children; however, there have been no systematic studies for this age group.
SOLUTIONS/DESIGN REQUIREMENTS FOR VISUAL PERFORMANCE
Sources of Light
Electric lighting systems have a number of components: luminaires, lamps (incandescent, fluorescent, high-intensity discharge [HID]), ballasts (except when using incandescent lamps), and controls. Electric lighting systems differ in the amount of power they require to operate and in the amount and direction of light they are able to generate to meet design objectives. They also vary in their initial cost, ease of maintenance and commissioning, and expected life. Also important, electric lighting systems vary in their ability to provide good color rendering and low levels of glare, flicker, and noise.
Fluorescent lighting systems are the most prevalent sources of general illumination in schools. Modern fluorescent systems (T8 and T5 lamps with electronic ballasts) can provide low cost, long life, high efficacy, good color, low levels of noise, and flicker. Other sources of illumination, including incandescent and HID lamps, can be specified to best accomplish specific design objectives, from outdoor applications such as sports fields to illuminating pictures or works of art (Rea and Bullough, 2001).
Windows are an important part of a school’s design as they relate to lighting. They allow for high light levels and, when properly located, ideal lighting configurations for visual tasks not involving self-luminous displays, such as computer screens, or audiovisual presentations. Windows are also the largest sources of glare in a classroom. However, glare can be controlled with fixed overhangs and blinds or window treatments that can be manually operated. Methods to control light from skylights and clerestories are also needed because the distribution and level of light changes as the day progresses.
A key difference between electric light and daylight is that electric light is almost always static, whereas daylight is ever-changing over the course of a day, with weather conditions, and with season. Daylight will also be different from one school to another, depending on building orientation and site, climate, and latitude, so that a cookie-cutter building design will rarely provide ideal lighting.
The dynamic nature of daylight, together with the wide range of intensities and distributions, demands a sophisticated understanding of its interactions with a building and the building’s spaces: A much more sophisticated understanding is required for using daylight effectively
than for using electric lighting effectively in school design. In some circumstances it may be desirable to conduct detailed lighting, heating, and cooling simulations in order to gain such an understanding.
Lighting Criteria for Schools
Light levels in school buildings are strongly influenced by the expected visual performance requirements for a given task. In general, higher illuminance levels are recommended for specialized tasks such as reading and writing than for less demanding visual tasks such as eating or walking. Lower illuminance levels are also recommended for public spaces where reading and visual inspection are only occasionally performed or where there is no time pressure to complete the task. For these reasons, lighting should be designed not just with respect to the source of illumination or the individual components needed to create the entire lighting system but should instead be designed with respect to the integrated system of enclosure design and controls, space configurations and surface finishes, and fixture components, all of them in relation to the task requirements: In schools, it is inappropriate to require specific types of luminaires and lamps without consideration of the space layout. This is true for new construction, significant renovation, or retrofit of school buildings.
Illumination on horizontal work surfaces from any type of electric luminaire will be equally satisfactory with regard to occupant visual performance. Among the recommended illuminance levels are these:
Desks (300-500 lux on a desktop),
Chalkboard (500 lux on a vertical surface),
Corridors (100 lux on the floor), and
Art rooms (500 lux on a desktop, 300 lux in the vertical plane) (Rea, 2000).
Lighting for chalkboards and whiteboards should be directed from a fixture to the specific surface to be illuminated (rather than coming from general illumination). Application efficacy (lumens per solid angle of the surface area per watt) is the correct photometric for determining the most energy efficient lighting for these uses (Rea and Bullough, 2001; Bullough and Rea, 2004).
Color rendering index (CRI) is commonly used by the industry as a measure of a lamp’s ability to make objects appear “natural.” A CRI of 80 for fluorescent lighting systems is probably appropriate, although a CRI as low as 70 can also provide satisfactory color rendering in most cases. It should be pointed out, however, that as new lighting technologies (e.g., LEDs) become more prevalent, CRI may not be a useful measure of source
color rendering. Indeed, industry and government are presently examining the utility of CRI for LEDs. In the meantime, CRI should be supplemented with two other measures of color rendering—gamut area (GA), which is related to the saturation or vividness of hues, and full spectrum color index (FSCI), which is related to fine color discrimination. All three measures are useful for specifying lighting sources (Rea et al., 2004).
Various lamp and luminaire combinations can be equally effective at producing energy-efficient, long-life, low-glare lighting systems. As noted previously, windows can be the main source of glare in classrooms. The easiest and most cost-effective method for controlling glare from windows is to provide manual blinds or other window treatments that can be adjusted by teachers as the need arises. The current technologies for automatic “daylight harvesting”1 require specialized expertise to design, operate, and maintain them. Although some manufacturers will be able to ensure proper performance, these systems are invariably expensive and can rarely be justified economically (Bullough and Wolsey, 1998; Bierman and Conway, 2000).
CURRENT GREEN SCHOOL GUIDELINES
Current guidelines for green schools usually focus on energy-efficient lighting technologies and components and the use of daylight to further conserve energy when addressing lighting requirements. They do not give guidance for lighting design that supports the visual performance of children and adults in various tasks and for different school room configurations, layouts, and surface finishes. Excellent resources for developing such guidance in the future include the current consensus-based lighting design guidelines from the Illuminating Engineering Society of North America.
FINDINGS AND RECOMMENDATIONS
Finding 5a: The research findings from studies of adult populations seem to indicate clearly that the visual conditions in schools resulting from both electric lighting and natural light (daylighting) should be adequate for most children and adults, although this supposition cannot be supported by direct evidence.
Finding 5b: There is concern that a significant percentage of students in classrooms do not have properly corrected eyesight, and so the general lighting conditions suitable for visual functioning by most students may be inadequate for those students who need but do not have corrective lenses. It could be hypothesized that daylight might benefit these children by providing higher light levels and better light distribution (side light) than would electric lighting alone. However, the potential advantages of daylight in classrooms for improving the visual performance of children without properly corrected eyesight has not been systematically studied.
Finding 5c: Current green school guidelines typically focus on energy-efficient lighting technologies and components and the use of daylight to further conserve energy when addressing lighting requirements. Guidance for lighting design that supports the visual performance of children and adults, based on task, school room configurations, layout, and surface finishes, is not provided.
Finding 5d: Windows and clerestories can supplement electric light sources, providing high light levels, and good color rendering. Light from these sources is ever-changing and can cause glare unless appropriately managed. Currently, there is insufficient scientific evidence to determine whether or not an association exists between daylight and student achievement.
Finding 5e: A growing body of evidence suggests that lighting may play an important nonvisual role in human health and well-being through the circadian system. However, little is known about the effects of lighting in schools on student achievement or health through the circadian system.
Recommendation 5a: Future green school guidelines should seek to support the visual performance of students, teachers, and other adults by encouraging the design of lighting systems based on task, school room configurations, layout, and surface finishes. Lighting system performance should be evaluated in its entirety, not solely on the source of illumination or on individual components.
Recommendation 5b: Future green school guidelines for the design and application of electric lighting systems should conform to the latest published engineering practices, such as the consensus lighting recommendations of the Illuminating Engineering Society of North America.
Recommendation 5c: Green school guidelines that encourage the extensive use of daylight should address electric control systems and specify
easily operated manual blinds or other types of window treatments to control excessive sunlight or glare.
Recommendation 5d: Because light is important in regulating daily biological cycles, both acute effects on learning and lifelong effects on children’s health should be researched, particularly the role that lighting in school environments plays in regulating sleep and wakefulness in children.