Dimmer switches suitable for LED lamps

A two wire dimmer switch for an LED lamp 8 provides a bridge rectifier 10 for connection to an AC supply and a semiconductor switch 20 that can be turned on at a zero crossing of a half cycle of the supply and switched off part way through that half cycle under a brightness control 12. The duty cycle of the semiconductor switch therefore sets the brightness of the lamp. A programmable chip 40 acts as a control circuit and uses power stored during the period when the semiconductor switch was off in a preceding half cycle.