CFL's and Dimmer switches?

Question

Why is it that you cannot use dimmer switches with compact fluorescent light bulbs (cfl's).

Answer 1

A cfl has an eletronic circuit (inverter) that generates a constant high (>110V) voltage to get the lamp to light.
Dimmer switches work by chopping out parts of the ac waveform (scroll down for details).
If you provide the inverter in the cfl with such a chopped up power supply it will at some point no longer be able to generate the constant voltage that it is designed for and the lamp will not light. Its an all or nothing case.

Dimmers use triacs (used to be thyristors, but triacs are easier)
a triac has 3 connections:
2 switching and 1 gate
a triac will conduct if the current trough it remains above a certain level
a triac will conduct if the gate voltage (compared to a particular switching connection) exceeds a certain level.
so, if you have an ac power supply and a triac that happens to be conducting, it will turn off when the ac voltage hits zero (the current through it hits zero) which happens 100 times a second in the UK (120 times a second in the USA)
any time a sufficient gate voltage is applied it will start to conduct and reamain conducting untill the next zero crossing of the power supply.
So, if you time a trigger pulse to the gate you can get a triac to conduct for a percentage of the power cycle, thus dimming.

Answer 2

Flourscent lights depend on full power. THe dimmer switch actually cuts the power not just the light. So the ballast in the light won't be able to work properly and the light would just go out.

Answer 3

But don't forget, there are now CFLs that you can use with dimmer switches. They are more expensive, but they work.