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Fluorescent lights are not like incandescent lights; they need to have special ballasts in order to operate. Dimmable ballasts are an option with most efficient fluorescent lighting systems. They allow you to lower the lighting levels—and cut the energy consumption—when you don’t need the lights at their full brightness. Why pay for the light when you don’t need it? The lower the light levels, the lower the energy use.
Dimmable ballasts are often used where a skylight or some other kind of day lighting is in place. If your office space is subject to variable natural lighting levels, you can install dimmable ballasts to reduce—or even eliminate—the energy you use when more artificial lighting isn’t needed. The savings depend on the space they’re installed in. These ballasts are most cost effective during the installation of new light fixtures.

CASE IN POINT – Multnomah County (Portland, Oregon)
Daylight dimming controls were installed in the Multnomah Building. These control the ballasts in fixtures in the perimeter day lit zones for each floor. Photo sensors in the ceiling dim perimeter lighting fixtures in response to natural day lighting available. The estimated savings for this energy conservation measure is over $4,000 annually, and PGE provided a rebate of $21,000 for this measure.