Lighting – Choosing correct dimmer for halogen bulbs

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-:)

It looks like CFL bulbs are difficult to dim.

A dimmer typically reduces the effective voltage, which decreases current to the bulb. The science behind fluorescents just isn't meant to work that way, explained Paul McLellan with eLightBulbs, a division of Service Lighting, a Maple Grove, Minn., lighting supply company.

It can cause dimmer switches, or the ballast, to buzz. It can even affect other electronic devices nearby, such as radios. The distortion can even go so far as to cause flickering in the light bulb itself. Occasionally, you may be able to dim by 30 to 40 percent without any adverse reactions.

"We have looked at around 20 different brands and although some of them get close, the science is not yet there," McLellan said. "We do hear of some success, however, usually with high-quality, brand-name bulbs and dimmer switches." Sometimes it's a matter of finding which brand of bulbs works with specific dimmer switches. You may need to change the dimmer.

Remember, not all compact fluorescents are designed to work with dimmers, but CFLs made for dimmers are available. You can use regular compact fluorescent bulbs with dimmer switches, but doing so can shorten bulb life and nullify the bulb's warranty."

Taken from CFL Dimming Article