high efficiency and long life. However they are sensitive to power system voltage disturbances, which result in visible light flicker and they produce harmonics. Furthermore their brightness can only be controlled over a narrow range (with active ballasts) and the light spectrum produced is not ideal. The most efficient white LEDs now achieve light outputs in excess of 100 lumens per watt of electrical input power, surpassing the efficiency of fluorescent tubes. With suitable drive circuitry they can be made immune to electrical disturbances, with dimming and controllable colour rendering readily achievable. A new multichip LED lamp with spectrum adjustment, mounted in a four foot fluorescent fitting, with ballast replaced by driver electronics is compared with a commercial white LED fluorescent tube replacement and a white fluorescent tube, mounted in the same four foot fitting, with conventional inductive ballast. Practical results for spatial distribution, intensity and 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.