Fluorescent Dimmers

I don't have direct experience with dimmable fluorescents, but I do know a bit about them. You will never get the same level of dimming from a dimmable florescent bulb, because of how a florescent works. There is a minimum threshold on the tube to "fluoresce", or ionize the gas in the tube. Once you drop below that threshold, you get no light, not less light. I think those dimmable CFL's should state the % of dimming that's available, otherwise people will be taking them back to the store, thinking they are defective, because they don't work like the incandescent that they replaced. I do believe the "dimmable" tubes available in the stores today are intended to be used with the common dimmers available today, they are just not going to work like an incandescent.

I'm waiting on LED technology, dimmable LED lights will behave much more like incandescents, although it may mean new dimmers in the wall, we'll just have to wait an see.

Your typical store bought dimmer works by chopping up the incoming power into smaller and smaller pieces. Consequently, you can sometimes hear an audible noise they induce upon the load. An incandescent lamp doesn't mind this because the coil takes a relatively long amount of time to cool off between (pulses) bursts of power.

But a screw in fluorescent has to convert the incoming AC power into DC and then back into a higher frequency AC drive signal to operate the lamp. If you provide a chopped up (non sinusoidal) input to this device the high frequency components of the chopped signal will slip right past the filtering devices provided in the internal ballast. Opperating a two terminal "screw in fluorescent" will lead to destruction of the ballast circuit and probably a fire hazard. There is likely a label on the dimmer that tells you this.

A dimmable fluorescent ballast uses a DC control input that has a maximum of 5 VDC or 10 VDC depending on the manufacturer. An external DC power supply or variable resistance device is used to control the brightness. This needs to be on the order of 10Kohms. This special ballast provides a fixed amount of power to the coils inside the fluorescent lamp because a minimum electrode temperature must be maintained at any power level. If you rob the coil of this power, the plasma inside the lamp will evaporate all of the emitter coating and cause an abbreviated life to occur.

The only compact fluorescent lamps that operate on a dimmable ballast have four pins connecting to the two coils inside the lamp. Any other connection of less than four pins is not dimmable by design.