The barriers to harvesting daylight for energy savings include limitations on photosensor technology, marketplace obstacles and the unknown effects on lamp life due to dimming.
Photosensors are difficult to install, commission and maintain
All commercialized photosensors use analog technology in the dimming algorithm used to maintain a constant light level on a work surface. Analog technologies require manual intervention to commission the photosensor. This is a tedious process that, at best, is trial and error. Complicating matters is that the same signal level from the photosensor to different manufacturers' ballasts produces different levels of dimming.
Photosensor sensitivity doesn't match human visual sensitivity
Photosensors react to optical radiation, including visible light, ultraviolet radiation and infrared radiation. Humans, however, do not see or react to ultraviolet or infrared radiation. Photosensors with a broad spectral response (i.e., sensitivity to optical radiation of different wavelengths) often respond as if more daylight is in a space than actually exists. This can lead to problems where precise switching or dimming levels need to occur.
Photosensor light readings don't match with occupant lighting needs
Most photosensors detect and respond to only a sampling of the ambient light levels in a space, as viewed from the ceiling, rather than detecting the workplane illuminance. The advantage of the sensor's ceiling location is that the photosensor is not interfered by, and does not interfere with, activities in the space. The disadvantage, however, is that the ceiling illuminance does not usually correspond to the workplane illuminance as the balance between daylight and electric light changes. Illuminance differences between the ceiling and the workplane can leave a work surface inadequately illuminated.
Lamp life at dimmed operating modes is not fully understood
The effects of dimming on lamp life are not well understood by lamp and ballast manufacturers. Stories of premature lamp failures and other problems such as flicker and brightness striations permeate the industry and create a perception of high risk for fluorescent lamp dimming systems.
Costs for dimming ballasts are too high
Presently, dimming ballasts cost at least three times more than static, on-off instant-start ballasts. Electric energy is inexpensive relative to the incremental cost of dimming ballasts.
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