Interior of a domestic light dimmer switch. The black component with the perforated metal panel is the central element of the switching circuit of the dimmer. It is a small semiconductor device known as a triac ??a triode alternating current switch. This is a bidirectional triode thyristor which has a similar function as the variable resistors of earlier types of dimmers but is much more efficient and produces less heat, thus saving energy. The metal panel acts as a heat sink. The triac switches the light circuit on and off 100 times per second (in Europe) reducing the amount of energy used.