DAYLIGHTING AND ELECTRIC LIGHTING
Introduction
A good visual environment is an essential part of learning. Prior to the mid-20th century and the advent of fluorescent lighting, all school buildings were designed to operate with daylight rather than electric light.
"Daylighting" is the practice of using windows, skylights, and other means to bring daylight into a building interior with the intention of reducing energy use and creating a high quality indoor environment. Daylight for this purpose must be controlled light from the sky, which in most instances limits the use of direct sun. If uncontrolled sunlight strikes students, their desks, or surfaces used for instruction, a teacher will close the shades and turn on electric lights. Uncontrolled sunlight also brings heat, requiring air conditioning or leading to a lack of comfort. Thus it is important to understand that good daylighting does not mean just adding a lot of windows or skylights.
Well daylighted "finger-plan" schools, with rows of single classrooms with glass on both sides were common in California during the 1950s and early 1960s. Then, with the belief, that air conditioning and electric lighting could produce an 'ideal' or at least 'standard' environment, classrooms were designed with less glass and lower ceilings. School facilities were sited without solar orientation in mind. Eventually, in some schools windows were eliminated completely in a misguided effort to improve energy efficiency and out of a belief that outside views distracted students from learning.
In the interim since the windowless schools of the 1970s and 1980s, researchers have begun to provide evidence supporting a human biological need for exposure to daylight. Research also supports the contribution windows make to visual comfort and mental stimulation. At the same time, research on energy issues has shown windows and skylights can provide a net positive impact on building energy use.
The keys to good energy performance are:
- correctly orienting the building to the sun
- proper location and sizing of daylight openings
- appropriate shading or dispersion of direct sun
- selection of appropriate glass.
Integrated Design Approach
Well-designed daylighting will deliver abundant, well-distributed light, without producing discomfort or much glare or strong shadows. Poorly designed daylighting will deliver either inadequate amounts of light, so that electric lighting has to be used, poorly distributed light, or abundant light with discomfort, glare, and strong shadows. To ensure that teachers and students do not use blinds to block all sources of daylight, it is vital that some daylight enter high in a room and that building elements reflect, redirect, or filter direct sun so it does not enter in a way that causes discomfort for the occupants. Blinds are needed to darken the room for projection and to control glare at view windows during part of the day. However, if blinds come down and stay down because the daylight openings are poorly designed, little has been achieved.
Because fundamental architectural design decisions are critical to success, the goal of daylighting the building must be recognized by all members of the design team and the owner's representative from the early stages of the project. 'Greening' a project that has already been designed without proper consideration of daylight requirements adds cost and may fail to achieve the goal. Integrating daylighting as part of fundamental architectural decisions about orientation, building form, and finish materials, and coordinating those decisions with other building systems and components, helps control first cost and improves ongoing building operations.
For example, electric lighting produces heat, increasing the need for cooling during warm months. Because daylight produces less heat per a given quantity of light than even the most energy-efficient electric lighting, properly sizing daylight openings such as roof monitors, high windows, and skylights, makes it possible to reduce the designed capacity of the air conditioning system. Similarly, daylighting only results in energy savings if electric lights are dimmed or turned off when adequate daylight is available. Electric lighting controls that respond to the amount of daylight are essential. Shading devices reduce direct sun during warmest months but also help reduce glare year round. Because the individual components of a daylighting system work together, eliminating any one of them will compromise performance. It is essential that the entire design/construction team understand the synergistic effects of individual components.
Impact on Student Performance
A set of studies conducted by the Heschong Mahone Group (HMG) found that well daylighted classrooms had a consistently positive impact on student performance. In the first study , undertaken for Pacific Gas & Electric Company, performance data from three elementary school districts, Capistrano, California; Seattle, Washington; and Ft. Collins, Colorado were analyzed. In the Capistrano school district, student performance in math and reading was tested at the start and end of the school year, providing the best data set. Students in classrooms with the highest degree of well-designed daylighting progressed 20% faster on math tests and 26% faster on reading tests in one year than those in classrooms with the least daylighting, controlling for all other factors. The impact of different types of daylighting was also examined. Students in classrooms with the largest window areas were found to progress 15% faster in math and 23% faster in reading than students in those with the least. Students with a well-designed skylight in their classroom, one that diffused the daylight and allowed teachers to adjust the amount of daylight, improved 19-20% faster than those without a skylight. However, students in classrooms with poorly designed skylights that allowed beams of direct sun to penetrate the room demonstrated a 21% decrease in the rate of learning for reading compared to students in classrooms with no skylight, though the students did make progress. All the effects were reported with 99% statistical certainty.
Because the students in the daylighted classrooms advanced more quickly, up to one month of instruction time in reading and math could be saved or used for other subject areas. In addition, it was found that the effect of moving a student from a classroom with the least daylighting to one with the most daylighting could be of the same magnitude as moving the student from an average school in the district to one of the highest-performing schools in the district.
In Seattle and Ft. Collins, students were given math and reading tests at the end of the year only. In Seattle, students in classrooms with the largest window area, or in this case the most daylight, tested 9% to 15% higher than students with the least window area. The Fort Collins results show a 7% improvement in test scores in the classrooms with the most daylighting, with a 14% to 18% improvement for students in classrooms with the largest window area.
Because results of these studies indicated that the way in which the classroom was daylighted, especially with skylights, had a significant impact on student performance, a more detailed study was conducted for the California Energy Commission's Public Interest Energy Research (PIER) program. The second study focused on which attributes of a daylighted classroom were significant contributors to student performance and also examined how other aspects of the indoor environment affected student performance. The study found that a pleasant view out of a window had a positive impact on student learning, but sources of glare and direct sun penetration associated with poorly designed windows and skylights had a negative impact. These findings suggest school planners should pay careful attention to the physical characteristics of classrooms.
Integration of Electric Lighting
Because operating hours typically extend beyond daylight hours for at least some part of the year, electric lighting is needed. For these reasons, design of electric lighting should be both efficient and produce a high quality visual environment. Two or three rows of suspended linear light fixtures can meet recommended lighting levels with properly chosen fixtures, lamps, and ballasts. These fixtures should include at least some indirect light that reflects off the ceiling and is scattered throughout the room. High performance T-8, T-5, or T5-HO lamps with good color rendering (>80) should be used. Additional lighting may be needed for the white board.
In order to save energy, electric lighting must be controlled in response to daylight. Electric lighting and associated control circuits should parallel daylight contours. As an example, in a classroom with no skylights, daylight levels will likely be higher closer to the windows. The linear light fixtures should parallel the windows in this case. If there are three rows of lights in the room, they should be controlled as independent zones so electric lights operate only where necessary. Where roof monitors or skylights are used, daylight should be evenly distributed across the space. In that case, lighting in the entire classroom may be controlled as one zone. However, both manual and automatic controls should make three different levels of illumination available to the occupants.
Dimming electric lights to maintain even light levels is preferable in a classroom setting. However, dimming ballasts have a significant cost premium over non-dimming ballasts. If first cost is critical, a switching system that turns off individual lamps can be used. In either case, provide users with a means to override the automatic.
Other Facilities
A gymnasium, locker rooms, cafeteria, and multi-purpose rooms have different lighting requirements than classrooms but also lend themselves well to daylighting. Daylight should still enter high in the space and be evenly diffused. Direct sun should generally be blocked, although limited admission of direct sun to a cafeteria can enliven the space. These rooms may have different electric lighting requirements. However, electric lighting should still follow daylight contours and be automatically controlled to assure energy savings.
Conclusion
Daylight is an essential part of a good learning environment. The careful introduction of daylight in a building reduces operating costs, improves human vision and perception, and contributes to occupant health, comfort, and productivity.
- Bill Burke
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