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By Denise Fong
October 2010 -
Lighting Article Use Policy
Daylight is a highly desirable light source and provides opportunities for energy savings. When sufficient daylight is present, control systems can turn off or reduce lighting in steps or through dimming in a slow, continuous manner. Studies reveal occupants who are stationary and perform critical tasks, such as open offices, prefer dimming to happen slowly so they do not notice it. Stepped switching can be jarring and break a person's concentration, but it can work well in public-transition spaces, such as lobbies.
Not every light source is dimmable, so managers need to coordinate the lamp type with dimming options. The appropriate ballast or driver can dim most fluorescent and light-emitting-diode (LED) sources. Some metal-halide lamps are also dimmable, but they usually have a smaller dimming range with more color shift, so they might be inappropriate for some spaces.
Technicians can install photocells on ceilings, walls, light fixtures or the building's exterior to control the flow of electricity based on the amount of daylight measured as reflected from task surfaces or entering the space at the daylight apertures, such as windows. Managers need to consider the location of photocells carefully to ensure they read the available daylight at a meaningful location.
Photocells also require calibration in the field to make sure they trigger lights at appropriate settings. Most products have factory presets, which technicians can adjust in the field or remotely, in the case of some digital control systems. Technicians also should test them periodically to see if adjustments are necessary.
When a space has multiple uses, it often is desirable to have multiple lighting scenarios. A preset dimming system allows a manager to program several common lighting scenes, then make modifications for special cases without changing standard settings. This technology provides the flexibility to use only the needed lights at the appropriate intensity at a given time. These systems can be stand-alone or a larger system that links similar spaces.
The Six Categories of Lighting Controls
Lighting Controls: Daylighting and Dimming Strategies
Lighting Controls: Design Impacts Efficiency, Occupant Comfort