When properly designed and integrated with the lighting system, daylighting can offer significant energy savings by offsetting a portion of the electric lighting load.
Daylighting can help with the reduction in cooling capacity and use by lowering a significant component of internal gains. In addition to energy savings, daylighting generally improves occupant satisfaction and comfort. Recent studies imply improvements in productivity and health in daylighted schools and offices. Windows also provide visual relief, a closer contact with nature, time orientation, the possibility of ventilation and emergency egress.
A building designed for daylighting, but without an integrated electric lighting system will be a net energy loser because of the increased thermal loads. Only when the electric lighting load is reduced will there be more than offsetting savings in electrical and cooling loads. The benefits from daylighting are maximized when both occupancy and lighting sensors are used to control the electric lighting system.
Occupancy sensors detect when a space is occupied by using passive infrared, ultrasonic, or a combination of the two technologies. Once the heat or movement of the occupant is no longer detected, and after a preset delay time, the sensor will emit a signal to extinguish the lights. Occupancy sensors used alone are good for low or intermittent use areas such as storage rooms, restrooms, and even corridors.
Light Level Sensors
Light level sensors have a photoelectric "eye" that measures the illumination in a room. Threshold on and off values can be set to respond to specific lighting conditions. These sensors can operate on/off switching of various luminaires or lamps within luminaires, and they can also operate a continuous dimming system. Continuous dimming system will obviously cost more than switching systems, but they have greater user satisfaction, since the change in lighting levels is not as noticeable.