Lighting - Lighting Controls Lighting controls not only help conserve energy, but they also make a lighting system more flexible. The most common light control is the on/off switch. Other types of lighting control technologies include:
* Manual dimming
* Photosensors
* Occupancy sensors
* Clock switches or timers
* Centralized controls. Manual Dimming 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. Photosensors Photosensors automatically adjust the light output of a lighting system based on detected illuminance. The technology behind photosensors is the photocell. A photocell is a light-responding silicon chip that converts incident radiant energy into electrical current.
While some photosensors just turn lights off and on, others can also dim lights. Automatic dimming can help with lumen maintenance. Lumen maintenance involves dimming luminaires 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 photosensors 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. 
| Figure 115: Outdoor lights with photo sensors are controlled by the sun. |
Occupancy Sensors 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. Clock Switches Or 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 photosensors. Centralized Controls 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. Outdoor Photovoltaic Lighting What do a highway billboard, a campground parking lot, and your front walk have in common? Not a great deal at first glance, but they are all possible locations for outdoor solar photovoltaic (PV) lighting. Outdoor PV lighting is easy to install, virtually maintenance free, and in many applications very economical, as long as the system(s) will receive the manufacturer's recommended hours of sunlight.
Outdoor PV lighting systems use PV panels (or modules), which convert sunlight to electricity. The electricity is stored in batteries for use at night. They can be cost effective relative to installing power cables and/or step down transformers for relatively small lighting loads.
A few examples of outdoor PV lighting applications include:
* Billboards and Highway Guide Signs - In 1989 the Florida Department of Transportation used PV lighting to illuminate an important guide sign on an isolated section of interstate highway, several miles from the nearest utility service. Even in less isolated areas the cost of hooking into and installing traditional utility power for road signs and billboards can be two or three times the cost of a PV system.
* Campground and Recreation Area Entrance Signs and Restroom Lighting - The U.S. Bureau of Land Management, National Park Service, and State Parks Departments have installed numerous PV lighting systems on campground and visitor facilities around the country.
* Exterior Home Lighting - Several companies now market units for marking or decoratively highlighting driveways, walkways, and patios. Many of these designs are totally self-contained units that need only to be staked into the ground in a sunny location. Others have the lights separate from the PV panel(s) so it can be placed in a sunny location. Units vary in size from small eight-inch red glowing pathway markers to pole-mounted patio and high-beam security lights.
* Municipal Park Lighting - In Indiana, a PV lighting system installed to light restrooms and a parking lot in a county park saved thousands of dollars. It also avoided the trenching and disturbance to trees and shrubs required to run a mile-long utility cable to the park. In North Miami Beach, Florida, PV nighttime park lighting cost $900, instead of the $3,000 to bring in utility power.
* Streetlights - The Bent Tree Community Association, located in a west Miami, Florida suburb, installed 26 PV powered streetlights in the summer of 1991. Two 48-watt PV modules charge two batteries. The battery capacity enables the lights to operate from a full charge for 12 hours a night for four nights without recharging.
Home outdoor PV lighting systems are often available in hardware, lighting, and discount stores as well as through environmentally oriented mail order companies. Home outdoor PV lighting is practical for all parts of the country, though it is important to consider geographic and site specific variables when choosing a product. The key factor is that the PV panel or unit must be in a place where it will receive sunlight.
The "nightly run time" listings on most "off-the-shelf" products are based on specific sunlight conditions. Systems located in places that receive less sunlight than the system is designed for will operate for fewer hours per night than expected. Nightly run times may also vary depending on how clear the sky is on any given day. Operating times in the winter months may vary as much as 30% to 50%. Unless the PV system has been sized specifically for winter operation, the system will not operate for the specified number of hours per night in a given location. Shading of the PV panel by landscape features (vegetation, buildings, etc) will also have a large impact on battery charging and performance. Bird droppings on the PV panels can also negatively affect performance. Insufficient battery charging will significantly affect performance and may reduce the life of the battery.
Nickel cadmium, sealed lead acid, and lead acid batteries are most commonly used for outdoor PV applications. The bulb and the battery are the two components that are most likely to need servicing. Check with the manufacturer to be sure that replacement bulbs or batteries are available before you buy the unit. Also determine whether you will be able to recycle the batteries or how they can be disposed of properly. Some units do not provide the option of replacing batteries, so the entire unit may need replacing. Be sure that a safe recycling or disposal option is available.
Systems for large area lighting, such as for parking lots and billboards, may be available through outdoor lighting contractors or through PV system suppliers. |
