Old dimmers used coils to stretch the sine wave. This was highly effective for superb full range dimming but unfortunately made them very large and very heavy.(The size of a bread box or a car tire)Todays dimmers chop up the sine wave to reduce light out put. The down side to chopping is occassionally at certain light levels, a slight flickering maybe noticed. Especially if you are using halogen lights. The cure for this is to burn the lamps at full output for 15 minutes every so often. The up side is of course you can dim alot of light from a small switch in the wall.