Section IV- Lighting
a.) Summary:
There are several lighting strategies that can be implemented fairly easily
while also saving a great deal of energy. SEDAC recommends the following:
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Lighting power density
o Reduce ASHRAE numbers (0.9 W/sf for schools, offices)
Occupancy and vacancy sensors
o Manual On/Auto Off (after less than 30 minutes)
Multi-level switching or dimming
o Now required in the codes
Daylighting controls
Solar tubes
o Natural light for interior rooms
o Better insulated than skylights
Outdoor Lighting
o Reduce by 50% after closing
o Turn off 30 minutes after sunrise
b.) Technical Information:
Lighting Power Density (LPD):
LPD is the amount of watts for square foot, is a useful way to measure the
amount of lighting necessary within a space. It is recommended that the number
of watts be kept as low as possible while still maintaining enough light to
complete essential tasks. SEDAC generally recommends under 1 watt per
square foot for any type of building. Many buildings have been able to manage
0.5-0.7 watts per square foot. Newer lighting systems have the capacity to
produce high quality lighting with even lower power draw. Lighting designers are
available for building occupants who may need assistance lowering their LPD.
Lighting occupancy sensors:
Occupancy sensors prevent lights from being on when nobody is occupying the
space. Occupancy sensors can be applied to any hallway, office, or restroom;
however, they save the most energy and money when placed in rooms that are
infrequently occupied, or in rooms where the light is often left on and forgotten.
An E Source® study estimates potential energy savings from occupancy sensors
at 13-50% for private offices, 40-46% for classrooms, 22-65% for conference
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rooms, and 30-90% savings for restrooms.
(http://www.esource.com/BEA/demo/PDF/P PA 10.pdf)
Sensors in all spaces are recommended to have manual-on/ auto-off settings
and a delay timer setting of 15 minutes. Requiring staff to turn on lights manually
reinforces the concept that lights do not always have to be on and also prevents
unintended movements from turning on the lights. Restrooms may be an
exception and require bi-level or auto-on settings. Many occupancy sensor
manufacturers provide guides for picking the right sensor for a specific location.
Multi-level switching:
Multi-level switching allows building owners to decide how many lamps should be
turned on in any particular fixture, providing options for different lighting levels
within a room. This saves energy by allowing lamps to remain off in day-lit areas
of the building. In office settings, some employees prefer to work under lower
lighting levels. Multi-level switching also allows for work environments to have
varying levels of lighting based on the preferences of the employees. This
strategy is now required by the Illinois Energy Conservation Code.
Daylighting controls:
Daylighting controls are a useful strategy for taking advantage of natural light, but
doing this well and in a way that will last can be difficult. Digital photosensors
detect daylight levels and adjust the output of electric light based on the amount
of natural light already illuminating the inside of a building.
Solar tubes:
Solar tubes save energy by providing natural light inside buildings. These
devices bring daylight into areas where skylights or traditional windows cannot
reach. Solar tubes also decrease some of the unpleasant effects of natural
daylight, such as glare, overheating and inconsistent lighting patterns.
Outdoor lighting:
For outdoor pole lights with metal halide (MH) fixtures, SEDAC recommends
replacing these with LED fixtures. Although metal halides have comparable color
temperature and color rendering index (CRI), LEDs produce a white light that is
generally perceived as being brighter despite the decreased energy
consumption. Since the area lit by LEDs appears brighter, a reduction in lamp
lumen output and lamp wattage can be considered during the design process,
which also saves energy. LED lamps also have a much longer lifetime,
approximately 100,000 hours, while the estimated lifetime of MH lamps is 10,000
hours. It is recommended that outdoor lighting be decreased 50 percent after a
building is closed, and turned off 30 minutes after sunrise.
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c.) Case Study: School Lighting
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LPD = 0.9 W/sf
o Reduce ASHRAE
numbers 0.9 W/sf
Daylighting controls on
perimeter windows
Vacancy sensors and
occupancy sensors throughout
Controllable solar tubes
In this art classroom, open solar tubes provide six foot-candles with the lights
turned off. When the lights are turned on, this increases to 50 foot-candles. This
instructor is able to keep the lights off because she only requires six foot-candles
to teach her lessons. Although the former standard was 50 foot-candles, this is
being decreased to 30 to 50 foot-candles because people are realizing they can
effectively function without as much light, especially in classroom environments
in which computers are now being used. Since the solar tubes are able to open
and close, the lighting can be reduced to 1 foot-candle by closing the dampers.
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