Lighting – Default setting for dimmable light bulb on a non-dimmable lamp

Do not use a non-dimmable CFL with a dimmer. It shortens the CFL's life, and, in rare cases, a dimmer operating a CFL could result in fire. Change it out with a switch to be safe.

Dimmable CFLs aren't as good as incandescent for dimming. Their lowest settings are nowhere near that of incandescent, but they are good if you want the option to save on power and still be able to dim the lighting. Sometimes you will have to turn up the light to get it to kick on and then dim it. They can also be audible at their lowest setting. If you buy some, save the receipt as you may not like their drawbacks.

The two differences are

• Cost
• It can be dimmed with a standard dimmer

A standard dimmer reduces the RMS voltage going to a light to dim it; this may be done by a simple resistor or by chopping of the top of the waveform. So a dimmable LED lamp must be able to:

• Cope with a big range of input voltage including part formed sine waves, which isn't easy for the control logic.
• Detect from the input voltage the light level that the user wants, then give that light level.

It would be a lot better if a dimmer switch could send a digital signal (radio, or over the main wiring) to the lamp, so that the lamp could know what was required without reverse engineering the voltage back to the user's wishes. However this would need a new standard to be used by all switch and lamp vendors, so may take a little time-:)