Where to Consider Photocontrol for Inside Lighting
Consider photo controls for any space that has lighting from windows or skylights, provided that the space has fluorescent or incandescent lighting. Figuresf1throughf4 show favorable examples. Don’t overlook opportunities in spaces that are only partially day lighted. A common example is using photo control for the row of fixtures adjacent to the windows of a room, as in Figuref2. Figuref4 shows where photo controls should be installed in the area adjacent to a day lighted atrium. To find out whether there is enough daylight to make photo control worthwhile, survey candidate areas using a light meter. There should be a many hours during which the daylight level is about three times higher than the minimum lighting level required for the activities. The reason for this ratio is explained below.
If there is adequate daylight, consider whether the abrupt changes in lighting level that occur as fixtures turn on and off will be an annoyance. The worst problem is created by thick, localized clouds of the kind shown in Figuref5. However, don’t assume that clouds are an insurmountable obstacle. When light fixtures are turned on and off in a brightly day lighted space, the change is much less noticeable than turning lights on and off in a dark space.
Furthermore, if the photo controls are installed properly, the lights will not switch often. Interior photo control is most acceptable in transient areas, such as day lighted corridors (Figuref1), common areas in shopping malls that are illuminated by skylights, and day lighted atriums (Figuref3). Photo controls are less likely to be acceptable in offices and classrooms. However, a greater awareness of the need for energy conservation may make photo control acceptable even in such locations.
Security lighting is an especially fruitful application for photo control. Only low levels of light are needed for emergency egress, so day lighting may serve as emergency lighting for a much larger portion of the building than for conventional lighting. For example, photo control may eliminate the need for most emergency lighting on weekend days, when no people are present to require high lighting levels. Also, photo control of emergency lighting may not require the complexity of other applications. Check that local codes allow turning off electric emergency lighting when daylight is available. This is an unusual way of dealing with emergency lighting, so you may have to request a variance.