Basically there are two main dimming methods today. Each of these is suitable for different types of loads. Please also refer to the recommendations by the manufacturers of lamps and other controls.
Leading Edge Dimming - the early part of each sine half wave is chopped off
All resisitive loads (ordinary incandescent lamps, high voltage Halogen, etc.), marked with „R“
All inductive loads (Coils, low voltage halogen with conventional transformer, etc.), marked with „L“
So a marking "RL" indicates the suitability of a dimmer for resistive and inductive loads. Not allowed on these dimmers are capacitive loads (see below).
Trailing Edge Dimming - the latter part of each sine half wave is chopped off
All resistive loads
All capacitive loads such as Low-Voltage Halogen transformers or primary dimming electronic ballasts. Indicated by a "C").
Do not operate inductive loads on this kind of dimmers - this will usually destroy the dimmer. Resistive loads are suitable for both dimming methods. However, Trailing Edge Dimming offers a softer mode of operation for the lamps and will extend lamp life.
Please note that some of the cheaper trailing edge dimmers in the market are only suitable for resisitive loads.