Lighting Considerations in Green Building
James Armstrong, CPE, CEM
Lighting uses between 20%–25% of electricity in the U.S.—5%–10% of it in households, and 20%–30% in commercial facilities. In most of these buildings, at least 50% of this energy is wasted because of inefficient fixtures or equipment, poor maintenance, or inappropriate use.
One of the best ways to understand your lighting requirements is using the IES guidelines (Illuminating Engineers Society). As part of lighting design they are encouraging engineers to run a photometric analysis of the design before it is built. In many cases the light level may be higher or lower than what was expected. This allows modifications to the design to meet the ideal light level. Many design changes are as simple as changing the selection of lamps and ballasts.
There are several approaches to saving energy expended on lighting. They include:
- Daylighting: Designing buildings for optimum use of natural light. Daylighting can save 40%–60% of energy costs compared to conventional design practices. It involves strategies to avoid glare and excess heat gain, while reflecting light into the building.
- Using lower wattage lamps in existing or new fixtures, providing the illumination is adequate for the task, purpose, and users. Replacing lamps with new ones of a more appropriate (lower) wattage, smaller tungsten halogen lamps, or CFLs (compact fluorescent lamps) is one method. New fixtures with lower wattage lamps can be a better solution, since they are likely to be more efficient and reliable over time.
- Controlling the amount of light and the time lights are on through devices such as dimmers, occupancy sensors, photocells, or timers (clock or crank timers), or encouraging users to turn lights off when they are not needed. Occupancy timers are well-suited to spaces used infrequently and are effective as a security measure. Dimmers can be used with both incandescent and fluorescent lamps. They prolong the life of incandescent lamps, but reduce their lumen output, making them less effi cient. Fluorescent lamps must have dimming ballasts and lamp holders that accommodate dimmers, but are no less efficient with dimming.
- Proper maintenance: Keeping fixtures dusted and cleaned, and replacing yellowed lenses. Maintaining wall and ceiling finishes also increases light efficiency, since dirt decreases light reflection on the walls.
Both the IES (Illuminating Engineering Society) and ASHRAE advocate for proper lighting power density calculations to provide adequate light for the type of space and not “over lighting.” Lighting design just 10 years ago averaged 2 watts per square foot; current technology and design can provide the proper light evenly displaced at less than 1 watt per square foot. There are three key design components:
- The space itself, including the reflectivity of the walls, ceiling, and furniture within it. The reflectivity of these items may require a designer to increase and or decrease the lighting levels.
- The fixture’s photometrics (how well will it distribute the light to where it is needed, evenly and without glare). Photometrics are often overlooked, and buildings end up with hot spots and cold spots or uneven light distribution. Look around your space —is the light evenly distributed, or do you have areas that are brighter than others (other than task lighting that is intended to focus on a certain area)?
- Lamp technology: Fluorescent fixtures are the most prevalent type of lamp. For the same light output, you can use 2 T-12 4' lamps with an electronic ballast that will use 85 watts, or 2 T-8 4' lamps with electronic ballasts that will use 65 watts—or the new technology called “high performance T-8 4' lamps” that use 47 watts. Close to half the power, yet these new lamps put out the same (approximate) 3100 lumens per lamp as the other two types.
This article is an excerpt from the book Green Building: Project Planning & Estimating which can be purchased through the RSMeans Bookstore.
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