For a list of dimmers see the dimmers category.
A dimmer is a device which enables the intensity of a connected light to be adjusted via adjustment of the waveform. Commonly in the entertainment industry, dimmers are controlled via DMX and use SCRs or triacs to chop up the waveform, only allowing a portion of the full AC sinewave through. This gives the effect of dimming the light, but is infact turning it on and off very fast.
Using avalanche semiconductor devices (triacs, SCRs) in this way is known as Leading Edge dimming, since the power device is turned on at some point in the AC waveform, and off again as the waveform passes through the null. The slope at the turn-on point is known as the Rise Time, which is often quoted in dimmer specifications. A longer rise time gives reduced filament sing.
Wirewound transfomers (used in Pinspots and Neon lighting) offer an inductive load to the dimmer, and can be used with Leading Edge dimming. A good tip with low power inductive loads is to connect a 100W lamp in parallel with it, to give the dimmer a dummy load which helps solve glitching and flashing problems with some dimmers.
Electronic transformers (sometimes used in Birdies and other 12V lighting) vary in design. It is important to check that the particular transformer is specified for Leading Edge dimming. Some lower-cost electronic transfomers offer a capacitive load to the dimmer and are hence only suitable for Trailing Edge dimming. Trailing Edge dimmers are rare and expensive, since they use MOSFETs or IGBTs as the power switching device.
The latest technological advance in the world of dimming is Sinewave Dimming where instead of chopping the wave up to allow a portion of it through, the amplitude of the wave is varied. This produces almost silent dimmers and also reduces filament ring, often experienced when using Parcans with traditional dimmers.