Lighting

In many buildings, lighting systems were designed within the restrictions of initial cost economies. Designers often aren't aware of final space use and subdivision, and are unfamiliar with recent developments in lighting. Today, there is significant potential for energy savings through lighting system modification. You can reduce the energy consumed by your building's lighting system while still providing building occupants with the quality and quantity of illumination. A lighting system may include lamp(s), ballast(s), a lighting fixture with a lens, louver, or diffuser, and a control (on/off switch, motion sensor, timer, etc.) These elements are interrelated. While energy can be conserved by properly removing lamps and luminaires, this action should be taken only after the entire system has been analyzed and all options evaluated. While energy conservation is important, keep in mind other demands, including those of productivity and visual comfort; aesthetics; and federal, state and local codes and ordinances. Also remember that alterations to your lighting system can have a significant effect on heating and cooling systems, which usually are designed to consider the heat emitted by the original lighting system. Before making significant modifications to your lighting system, be sure to consider all these factors.

Set Up a Schedule

Determine an lighting schedule for your indoor system. Don't forget that maintenance and clean-up personnel generally work after hours. Work with these people to determine how they can get their jobs done in an orderly fashion, using the least amount of lighting. Develop a schedule for their use and keep track of their performance to ensure they follow the schedule. A schedule for outdoor lighting also can be beneficial. You waste energy by putting lights on earlier than needed or turning them off long after they are no longer needed. Consider the use of automatic lighting controls for outdoor lighting. These ensure that lights are turned off and on in a cost-effective manner.

Use Lighting Switch Stickers

Put pre-printed, paste-on stickers on lighting switch plates. These tell people to turn off lights when they leave the room. Also consider signs on the door, so people cannot help but notice the request to turn off the lights.

Reduce Lighting Levels

With careful planning, you can reduce lighting levels and associated energy costs without affecting the productivity of the building's occupants. You will need to perform a lighting survey.

Conduct Lighting Survey

You can use a portable light meter to perform a lighting survey. The light meter should be accurate to about ±15 over a range of 30 to 500 foot-candles and ±20 for 15 to 30 footcandles. The meter should be color corrected and cosine corrected. Measurements should be made at any representative point between and under fixtures. An average of several readings may be necessary. Daylight should be excluded during illumination-level readings for a true determination of illumination level without light contribution from daylight. Compare your findings with the recommendations of the Illuminating Engineering Society. If the readings indicate conformance with IES Lighting Book, Application Volume (Volume II) [J.E. Kaufman, New York, Illuminating Engineering Society of North America, pp. 2-5 to 2-20 recommendations], no adjustment to the lighting level should be made. If readings indicate that the illumination level exceeds what is needed, the possibility exists that lighting levels can be reduced without causing any difficulty.

Reducing Lighting Levels

Perhaps the most effective way to reduce lighting levels is to install smaller wattage high-efficiency lamps. Another alternative is to replace two small bulbs with a larger one, e.g., replace two 60-watt incandescent lamps with one 75-watt lamp. When removing fluorescent lamps from a luminaire, all lamps controlled by a single ballast should be removed to prevent premature failure of the ballast or the remaining lamps. Except in the case of instant start lamps or luminaires with circuit interrupting lamp holders, unused ballasts should be disconnected to prevent them from consuming energy.

Improve Lighting Maintenance

Most often, lighting maintenance is limited to replacing a lamp when it burns out, i.e., spot relamping. Consider adopting cleaning and group relamping. You should have a regular program of cleaning lamps, lenses and fixture components to assure that dirt does not reduce light levels. The frequency of cleaning depends on the amount of contaminants in the air and the type of fixture involved. Group relamping involves replacing all lamps used for area illumination after they have been in service for a substantial portion of rated life. Many maintenance supervisors are reluctant to rely on group relamping because it seems wasteful to discard lamps while they appear to be functioning properly. There are, however, two very good reasons for doing this. First, the light output of lamps declines with use while energy consumption stays the same. Second, the cost of labor to replace all lamps at once is much less than that involved when lamps are replaced one-at-a-time. It generally takes about one-half hour to replace a single lamp. When all lamps are replaced at the same time, with a crew assembled for the purpose, it only takes about three minutes per lamp. Group relamping should take place when all or most all the lamps in a large area have been used to that point where the cost per footcandle can no longer justify their continued use. For fluorescent lamps, this usually occurs at about 70% of rated lamp life. Thus, if the lamps are rated at 28,000 hours of life at ten hours per start, they should be replaced after approximately 20,000 hours of use.