When you dim a light source, actually you just remove power from the circuit. If you want to do forward phase dimming, you will chopping off the forward part of the sine-wave on the “positive current” end, and the back part on the “negative current” end. It is very hard for an electronic led drivers to reach the dimming because there are surges current through the circuit. If the voltage rides slowly and then just shut off, the electronic circuit will become much easier, we called it reverse phase dimming. The difference is most obviously seen in failure of equipment with time passed by.

Forward phase dimming is still the most common dimming method in US., over 150 million controllers in operation currently, although it is replaced by reverse phase dimming in some ways, but still with many important benefits.

Every lights type and led drivers will have its own ideal dimmer type, some of them are compatible only with forward or reverse phase dimming. However, you can purchase modern dimmers that are compatible with these both dimming methods, can save you money if you change your led transformers.