Lighting
Apr 1, 2009 12:00 PM, By Mike Kennedy (mkennedy@asumag.com)
Tips for illuminating classrooms and other educational spaces.
For nearly a decade, schools and universities have been inundated with information on the benefits of incorporating daylight into their facility designs.
But even the most ingeniously designed educational spaces will need electric lights to supplement daylight or to illuminate interiors after the sun sets.
The Advanced Energy Design Guide for K-12 School Buildings, developed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), offers school planners several recommendations on good lighting design:
Interior finishes: For electrical lighting to be used efficiently, the guide says, spaces must have light-colored finishes. The ceiling reflectance should be at least 70 percent (preferably 80 to 90 percent). In most cases, that will mean smooth white acoustical tile or ceiling paint. The average reflectance of the walls should be at least 50 percent. In general, that will mean light tints or off-whites for the wall surface.
For ceilings, a flat painted surface or acoustical tile is the most efficient. Sloping ceilings and exposed roof structures may significantly reduce the effective ceiling reflectivity, so make sure the ceiling and all components are painted a high-reflectance white.
Sensors: Schools should use occupancy sensors in all classrooms, offices, mechanical rooms, restrooms and special-use spaces. "The greatest energy savings are achieved with manual-on/automatic-off occupancy sensors if daylight is present," the guide says. "This avoids unnecessary operation when electric lights are not needed and greatly reduces the frequency of switching."
The two primary types of occupancy sensors are passive infrared (PIR) and ultrasonic. PIR sensors should not be used in rooms where a user cannot see the sensor (e.g., storage areas with multiple aisles, restrooms with stalls). High airflow can disrupt ultrasonic sensors, so they should not be used near air duct outlets.
Circuiting and switching: As instruction relies more on technology, lighting and controls in classrooms now must take into account the requirements of video images. "New schools should be designed with the anticipation of substantial daily classroom time with the lights dimmed and video replacing the whiteboard as the principal teaching medium," the guide says.
That means a classroom will need two distinctly different lighting setups: a "bright" classroom with light levels of 30 to 70 footcandles throughout the room, and an "audiovisual" scenario that limits light on the screen to 7 to 15 footcandles. Adapting the lighting to accommodate both can be difficult.
"There is the distinct chance that once shades are put in place for (audiovisual), they will be left there all day, effectively preventing daylighting," the guide says. "The preferred solution is to educate teachers about the importance of daylighting. An alternative and more foolproof solution is to use electrically operated shades that automatically retract when lights are turned on …. Unfortunately, this is considered too expensive for most projects."
NOTABLE
26
Percentage of electricity consumption in a typical school that goes for lighting.
30 to 50
Percentage of lighting energy in a school that can be conserved through retrofitting.
25
Number of years that an Energy Star-rated LED exit sign can last without lamp replacement.
Source: U.S. Environmental Protection Agency, "Energy Star Building Upgrade Manual"
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