Dimming ballasts

In both my lighting classes in my interior design program, I learned that dimming lights saves energy. For fluorescents, dimmable ballasts were billed as the next great thing for realizing energy savings in large commercial projects because they offered an opportunity to reduce wattage use in response to daylight. More available daylight meant lamps could be dimmed and energy would be saved. Apparently LEED credits are available for installation of programmable DALI systems that incorporate dimming ballasts (Indoor Environmental Quality Credit #6.1 and 6.2, “Controllability of Systems — Lighting”), presenting an additional incentive.

However, Stan Walerczyk, writing in the December 2006 issue of LD+A: Lighting Design + Application, the IESNA‘s magazine, says fluorescent dimming ballasts and their associated control systems are not always the solution. In Dimming Ballasts: Let the Buyer Beware, Walerczyk runs some scenarios comparing high performance dimming ballasts to high performance non-dimming options and concludes that the dimming systems do not always result in the highest cost savings. The amount saved depends on many factors, including natural daylight conditions, siting, light needs, cost of equipment and energy, and types of lamps and luminaires used. He contends that many of the same savings can be realized with simple and less expensive switching controls.

The wild card, however, is how people actually use the systems. Walerczyk’s informal poll of facility managers revealed that they don’t like the hassle of maintaining dimming systems and sometimes end up bypassing the systems altogether. In addition, dimming systems that work beautifully when first commissioned may not yield the same savings after a few years if instructions on how to use the system aren’t passed from one manager or owner to the next or if physical changes are made to the structure or the interior layout that alter how effectively daylight penetrates into the space.

Walerczyk suggests doing some homework before deciding whether to use a dimmable fluorescent system – running some realistic cost comparisons, comparing alternatives, and researching current literature. He has a good point. While it is important to incorporate as many energy-saving technologies into a building, it’s often too easy to go with the latest technology without taking the time to really assess if, over the long run, the technology delivers on its promise.

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