BRIGHTNESS CONTROL OF FLUORESCENT LAMPS

A method of controlling the brightness of a fluorescent lamp from a low frequency alternating current mains supply is described in which the lamp has an associated ballast providing a higher frequency power supply. The ballast includes a microprocessor which controls the frequency of the power supplied to the lamp by the ballast. This frequency is varied in accordance with the desires of the operator by actuating a cycle of variation of the frequency supplied to the lamp and ending the cycle when the desired brightness is reached. The cycle of variation of the frequency may be initiated by operation of a control switch located in series with the mains supply such as an on/off switch; the cycle of variation of the frequency is initiated by momentary operation of the control switch. In an alternative embodiment the control switch is a dimmer switch which suppresses part of each cycle of the mains supply and the variation of the frequency is initiated by the control switch. In a further embodiment the cycle of variation of the frequency is initiated by an external radiated signal received by the microprocessor, such as an infrared signal directed to an IR sensor located in the ballast or a radio frequency signal directed to a radio-receiver incorporated in the ballast. The fluorescent tube may be detachably fitted to a ballast unit which forms part of the lamp base. There is also provided a fluorescent lamp ballast for use in the described method comprising a microprocessor which controls the frequency of the power supplied to the lamp by the ballast and which is varied in accordance with the desires of the operator by actuating a cycle of variation of the frequency supplied to the lamp and ending the cycle when the desired brightness is reached.