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These can save energy and reduce peak demand in offices and other facilities. Controls save money while providing user convenience and an improved lighting environment. There are several different kinds of controls. The choice of control type should be based on lighting usage patterns and the type of space served. Areas with intermittent occupancy are well-suited to occupancy sensors. In large, open office areas with many occupants, scheduled switching, “time scheduling” is often an effective energy-saving strategy. In day lit offices, properly adjusted daylight sensors with dimming ballasts make sense. Because some workers prefer lower lighting levels, bi-level manual switching is another option. Advanced lighting controls can be used for demand limiting to allow building managers to reduce lighting loads when electricity demand costs are high.
Occupancy Sensors - Occupancy sensors are the most common lighting control used in buildings today. Two technologies dominate: infrared and ultrasonic. Infrared sensors detect temperature changes in a room, and work well where the entire room is within the sensor’s field of view. Ultrasonic sensors use high frequency sound, much like bats do, to detect motion (even around corners). Dual-technology sensors use both methods, increasing accuracy and flexibility, but at a higher price. Even though lamp running life may be somewhat shortened by increased switching due to occupancy sensors, the overall chronological life of lamps is usually extended by the reduced daily burn hours.
Time Scheduling - Large open office areas work well with simple time scheduling – automatic switching at fixed hours of the day. Overrides allow users to turn on the lights after hours (using wall switches or telephone dial-up codes). Time scheduling can be accomplished with simple time clocks or more sophisticated computer controls. To save more energy, time scheduling systems can be designed so that lights are turned on manually rather than automatically at the beginning of the day, but are turned off automatically at 1- or 2-hour intervals after close of business.
Bi-level Switching - Some people prefer lower overhead lighting levels (especially if daylight is available). Lower light levels are often preferred for computer use, meetings or tasks that are not visually demanding. Bi-level switching can provide simple manual control. For example, in a typical 3-lamp fluorescent fixture, the outer lamps are switched separately from the middle lamp, allowing the user to switch on one, two, or all three lamps. This low-cost measure is a minimum control requirement in some state energy codes, and can provide a simple means of load-shedding during peak hours if the bi-level lighting circuits are remotely controllable.
Manual Dimming - In rooms where different light levels are needed at different times, such as conference rooms and some private offices, the use of manually-operated dimming controls is a common solution. These controls can be either wall-mounted or, for convenience, use wireless remote controls (like the controls for a TV or VCR).
Automatic Daylight Dimming - Automatic daylight dimming, or “daylighting,” uses a light sensor to measure the amount of illumination in a space. Then, light output from a dimming ballast is adjusted to maintain the desired level of illumination. The combination of daylight dimming with appropriate task lighting is often very effective. Corridors and open cubicles near windows, particularly those with task lighting, are good candidates for daylighting controls. Private offices with windows can also be equipped with individual daylight sensors. Initial commissioning and calibration of light sensors and controls is critical for effective daylighting, however; poorly calibrated daylight sensors can result in little or no savings, and may annoy occupants.
Demand Limiting - During peak demand periods utilities often charge significantly higher prices for electricity. Remote operation of dimming ballasts or bi-level switching helps operators to respond to price signals or utility requests to shed load to help avoid power outages. Characteristics of the most common lighting controls for offices and other public buildings are outlined below:
Selection of Lighting Controls for Offices and Public Buildings
- Proper installation and adjustment of lighting controls are essential to both occupant satisfaction and energy savings.
- Properly adjusted occupancy sensors reliably save energy.
- In areas with available daylight, well-designed and adjusted automatic daylight dimming systems can save a substantial amount of energy.
- The choice between time-scheduling and occupancy sensing controls for a given open-plan space depends on several factors, including budget, variations in occupancy patterns, and the frequency of after-hours use. Time scheduled controls (with overrides for those working late) may be as effective in some cases, especially where the primary savings comes from assuring that lights are turned off after normal business hours.
- In private offices whose occupants travel a lot or who move from place to place within the building frequently, occupancy sensors tend to save more than day lighting, but in window offices where the occupants work most of the day at their desks automatic day lighting provides greater savings.
- Occupant preferences vary: Some occupants with bi-level switching choose partial light levels consistently, while others always choose full lighting.
- For new construction or major renovation, designing lighting circuits to be switched in smaller “zones” has many advantages, especially where these zones conform to similar usage patterns and similar levels of daylight availability. Small lighting zones with dimming controls can also allow individual workers to adjust lighting levels to their own preferences, and to switch on only a few lights when they work late.
Light Pollution: is a growing problem in reaction to excess light being given off by numerous signs, houses, and buildings. Polluting light is often wasted light involving unnecessary energy costs and carbon dioxide emissions. Light pollution is describing as artificial light that is excessive or intrudes where it is not wanted. Well-designed lighting sends light only where it is needed without scattering it elsewhere. Poorly designed lighting can also compromise safety. For example, glare creates safety issues around buildings by causing very sharp shadows, temporarily blinding passerbys making them vulnerable to would-be assailants
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