high efficiency and long life. However they are sensitive to power system voltagedisturbances, which result in visible light flicker and they produce harmonics. Furthermoretheir brightness can only be controlled over a narrow range (with active ballasts) and the lightspectrum produced is not ideal. The most efficient white LEDs now achieve light outputs inexcess of 100 lumens per watt of electrical input power, surpassing the efficiency offluorescent tubes. With suitable drive circuitry they can be made immune to electricaldisturbances, with dimming and controllable colour rendering readily achievable.A new multichip LED lamp with spectrum adjustment, mounted in a four foot fluorescentfitting, with ballast replaced by driver electronics is compared with a commercial white LEDfluorescent tube replacement and a white fluorescent tube, mounted in the same four footfitting, with conventional inductive ballast. Practical results for spatial distribution, intensityand spectrum of light output are compared for all three lamps, with the same power input.Sensitivity to mains disturbances and harmonic current draw are also compared.
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