Lighting Controls

Dimmers

Manual dimming controls allow occupants of a space to adjust the light output or illuminance. This can result in energy savings through reductions in input power, as well as reductions in peak power demand, and enhanced lighting flexibility.

Slider switches allow the occupant to change the lighting over the complete output range. They're the simplest of the manual controls. Preset scene controls change the dimming settings for various lights all at once with the press of a button. You could also have different settings for the morning, afternoon, and evening. Remote control dimming is also available. This type of technology is well suited for retrofit projects, where it is useful to minimize rewiring.

Fluorescent lighting fixtures require special dimming ballasts and compatible control devices. Some dimming systems for high-intensity discharge lamps also require special dimming ballasts.

Dimming Systems

Compared to on-off controls, dimming controls generally increase energy savings, better align lighting with human needs, and extend lamp life. Dimming controls are also useful for spaces that have more artificial (electric) lighting than is currently needed, and have the added benefit of dimming lights further when natural light from outside is available. Such systems can also be used to dim lights for other reasons, such as for presentations. Dimming fixtures by as much as 50% may be barely noticeable to building occupants, unless they are involved in tasks requiring visual acuity.

Programmable Control Systems

Centralized building controls or building automation systems can be used to automatically turn on, turn off, or dim electric lights around a building. In the morning, the centralized control system can be used to turn on the lights before employees arrive. During the day, a central control system can be used to dim the lights during periods of high power demand. And, at the end of the day, the lights can be turned off automatically. A centralized lighting control system can significantly reduce energy use in buildings where lights are left on when not needed.

Sensors

Photo sensors automatically adjust the light output of a lighting system based on detected illuminance. The technology behind photo sensors is the photocell. A photocell is a light-responding silicon chip that converts incident radiant energy into electrical current.

While some photo sensors just turn lights off and on, others can also dim lights. Automatic dimming can help with lumen maintenance. Lumen maintenance involves dimming luminaries when they are new, which minimizes the wasteful effects of over-design. The power supplied to them is gradually increased to compensate for light loss over the life of the lamp.

Nearly all photo sensors are used to decrease the electric power demand for lighting. In addition to lowering the electric power demand, dimming the lights also reduces the thermal load on a building's cooling system. Any solar heat gain that occurs in a building during the day must be taken into account for a whole building energy usage analysis.

Occupancy sensors turn lights on and off based on their detection of motion within a space.

Some sensors can be also be used in conjunction with dimming controls to keep the lights from turning completely off when a space is unoccupied. This control scheme may be appropriate when occupancy sensors control separate zones in a large space, such as in a laboratory or in an open office area. In these situations, the lights can be dimmed to a predetermined level when the space is unoccupied. Sensors can also be used to enhance the efficiency of centralized controls by switching off lights in unoccupied areas during normal working hours as well as after hours.

There are three basic types of occupancy sensors:
Passive infrared
Ultrasonic
Dual-technology (hybrid)

Passive infrared (PIR) sensors react to the movement of a heat-emitting body through their field of view. Wall box-type PIR occupancy sensors are best suited for small, enclosed spaces such as private offices, where the sensor replaces the light switch on the wall and no extra wiring is required. They should not be used where walls, partitions, or other objects might block the sensors' ability to detect motion.

Ultrasonic sensors emit an inaudible sound pattern and re-read the reflection. They react to changes in the reflected sound pattern. These sensors detect very minor motion better than most infrared sensors. Therefore, they're good to use in spaces such as restrooms with stalls, which can block the field of view, since the hard surfaces will reflect the sound pattern.

Dual-technology occupancy sensors use both passive infrared and ultrasonic technologies to minimize the risk of false triggering (lights coming on when the space is unoccupied). They also tend to be more expensive.

Switches

Passive Infrared (PIR) wall switch occupancy sensors detect when a room becomes occupied, and turn on the controlled lighting automatically. If no occupancy is detected for five additional minutes, lighting automatically switches off.

Passive Infrared (PIR) vacancy sensors detect when a space becomes vacant, and turn lighting off automatically after a preset time delay elapses. Users can manually turn lights on or off at any time by operating the ON/OFF button.

Time switches are suitable choices in spaces where vacancy or occupancy sensors are inappropriate. Users can select from simple push-button timers for uncomplicated applications to LCD display programmable timers in spaces where more flexibility is desired.

Timers

Clock switches or timers control lighting for a preset period of time. They come equipped with an internal mechanical or digital clock, which will automatically adjust for the time of year. The user determines when the lights should be turned on and when they should be turned off. Clock switches can be used in conjunction with photo sensors.

Daylight Harvesting

Daylight must be properly integrated with the electric lighting system for its energy-savings potential to be realized. A primary strategy, called daylight harvesting, is to use lighting controls that switch or dim the lights either manually or automatically in response to available daylight.

Daylight harvesting takes advantage of available daylight to augment electric lighting systems. Dimming ballasts and photoreceptors can reduce electric lighting loads proportional to the amount of daylight that enters the space. The more usable daylight entering the space, the more the electric lights can be dimmed, resulting in significant energy savings, as much as 60 percent of the connected lighting load to the space. [Illuminating Engineering Society (IES) of North America. Lighting Handbook, Reference & Application, 8th Edition. 1993.]

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