What is the difference between a leading edge and a trailing edge dimmer?

These two types of phase cutting dimmer inherit their names from the part of the AC wave that they cut off. Leading edge dimming cuts off the front edge of each waves’ half cycle. Conversely trailing edge dimming cuts out the second half of each waves’ half cycle.

Trailing edge dimmers are the most popular type of dimmer. They have several advantages over leading edge dimmers including smoother control, soft start and silent running when in operation.