CONTROL OF ENVIRONMENTAL CONDITIONING DEVICES

A lighting installation comprises (a) a light, having a brightness, powered by an AC power supply, said AC power supply having a cycle of period t; and (b) a dimmer comprising a semiconductor switch operable to switch the light on and off. In normal operation the switch switches the light on and switches the light off, and the brightness of the light is altered by altering the switching on or the switching off so that the light is on for a longer or shorter portion x of the period t. A method of protecting the lighting installation comprises monitoring a load current passing through the switch to the light and, when the monitored current exceeds a threshold value, reducing the portion x of the period t for which the light is on, so that power dissipated in the switch is also reduced.