Originally Posted by AdvIvan
...Instead, to regulate the LED "strength", the DC voltage can be lowered or - which is more normal - the voltage can be cut using e.g. a turistor that cuts the DC into various length spikes depending on how much "strength" you want. In a way, you may call this AC but it really isn't. The frequency of the "spikes" can be up to a few thousand hertz. The eye cannot see this (about 25 hertz is usually enough for the eye), but a camera can.
Hope this helped someone :)
I'm very familiar with SCR motor speed controllers, considered old technology now for motor control, but for low power electronic uses like dimmers it makes sense.
Great bit of info, thanks!