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A driving technique that can operate with electronic ballasts for fluorescent lamps to drive LEDs without requiring the replacing of any electronic ballast circuitry or modifying the existing infrastructure of a lighting network is presented. This technology provides an eco-friendly and immediate solution to turn a lighting system with fluorescent lamps into the one with LED lamps. The proposed technology is based on controlling the input impedance of an ac/dc converter, which is connected to the output of the ballast, and converting the high-frequency ac power from the ballast into dc power for the LEDs. With such adjustable input impedance, the active and reactive power drawn from the ballast can be controlled. The power supplying to the LED lamp, and thus its brightness, can be adjusted independently by an external means, such as wireless control. An experimental LED lamp prototype for retrofitting a 36-W T8 fluorescent lamp has been built. It is studied together with a fluorescent lamp and with both lamps ballasted by a commercial nondimmable electronic ballast for dual fluorescent lamps. The light output of the LED lamp can be varied from 100% to 51% of full brightness, while the light output of the fluorescent lamp remains unchanged. The input power to the ballast is reduced by 26% over the dimming operation of the LED lamp. A comprehensive study into the electrical performance of the ballast, operational characteristics of the two lamps, system efficiencies, and light outputs under different dimmed conditions is presented.