The diagram below shows a normal 220VAC 50Hz cycle. If the dimmer delays the turn on of the cycle, it is a leading edge dimmer, but if the dimmer delays the turn off of the cycle, it is a trailing edge dimmer. Leading edge dimming hence produces a very quick or sharp inrush of voltage into the load during each 50Hz half cycle, which in turn causes a high inrush current into the lamp filaments or the electronic components of solid state lighting. Trailing edge dimming does not cause a high inrush voltage or current and is hence in general more “natural” for the load.
