Effect of Operating Frequency

Traditionally, fluorescent lamps have been operated at the same 50Hz or 60Hz frequency as the periodicity of the mains electricity supply. However when the world’s first installation of fluorescent lamps operating at high frequency was introduced, it was observed that lamp efficacy increased dramatically. Figure 14 reveals that it is possible to increase luminous efficacy by almost 10% when driving the lamp at frequencies in excess of 2000 Hz. This feature is capitalised on by the modern electronic ballast to achieve peak system efficacy from the lamp-ballast combination.

Incidentally, the world's first high frequency installation of fluorescent lamps was specially made to illuminate the train carraiges on the London Undeground. Formerly this company operated its own independent power station which generated a 400Hz mains frequency, and special low-loss and reduced size magnetic ballasts were specially made by Thorn Lighting to operate at the high frequency.