Why do my new dimmable CFL bulbs hum?

Question

I just spent $100 upgrading our dining room lighting from regular incandescent bulbs with a dimmer switch to a CFL friendly dimmer switch with specifically marked dimming capable CFL bulbs.

At full power, they work fine. 5 x 60W equivalent bulbs put the room into "OH MY GOD I'M BLIND" mode quite nicely.

But slide the dimmer just a little bit and BUZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ an annoying hum comes from the bulbs.

On top of that - the fully dim setting only goes from totally blinding light to about full daylight mode.

Before I totally trash this setup and go back to my nice, warm, DIM incandescent bulbs, is it possible something is wrong with my setup? Maybe my hot and neutral are backwards? (Old old wiring, can't tell which is which w/o trial and error...)

Answer 1

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

Answer 2

Unfortunately that's the nature of flourescent lights.

The TL;DR version is that the ballast in a flourescent light (that's the ballast in the fixture itself for tubes, and built into the bulb for CFLs) works by creating voltage spikes that get the arcing in the bulb going, to produce the light. Dimmable CFLs do this with a HUGE jolt to provide an "instant-on" capability, which is necessary because the dimmer switch works by turning the power on and off for set intervals. This causes the ballast in the bulb to create a lot of very closely-spaced power spikes to start it up after each time the power's cut. Presto, you have buzz transmitted into the air by the transformer circuit and by the electrical arcing in the bulb's gases.

Things to try:

• Make sure you have a CFL-compatible dimmer; some CFLs may advertise they work with older TRIAC dimmers but usually the results are disappointing.
• Try a different brand of bulb or dimmer; certain combinations of bulb and dimmer are more "sympatico" and will produce less buzz than others.
• Most CFL-compatible dimmers have a sensitivity adjustment; different brands of CFL bulbs respond quicker or slower than others, so the timing of the on-off cycle can be adjusted to let the slide or dial go from bright to dim gradually along its full length. If moving the dimmer just one millimeter goes from blinding bright to off, the sensitivity is probably too high.
• Try LED bulbs if you can find a model suitable for your light fixture. LEDs dim using a different method (the on-off pulsing from the wall switch is translated by the bulb's "driver" circuit to much more rapid on-off pulsing on the other side of the rectifier stage), so they're practically buzz-less. Virtually all are dimmable with a CFL dimmer, and some are dimmable with a TRIAC.
  • However, LEDs are a new technology and are already pushing the envelope of what an LED can do. The bulbs usually require several LED elements to provide the required lumens, coupled with "driver" integrated circuits (yes, there are computers in your freaking light bulbs now) that provide the dimming capability, and rectifiers and capacitor banks to provide the necessary DC power. These generate heat, which electronics generally don't tolerate very well, and so various designs sacrifice light-generation surface area (and thus the dispersion pattern) for more casing to space and cool components, and vice-versa.
• If LED isn't an option for any reason, and this lighting is going to be dimmed most of the time it's on, then incandescents will actually save you more money than CFLs. Dimming a CFL, whether it's designed to be dimmed or not, shortens its lifespan (all those thousands of power spikes per minute) as opposed to lengthening it like with an incandescent. If you keep the dimmer at less than about 50% you'll pay more in bulbs than you'll save in electrical power.
• Remember that even incandescents will buzz when dimmed. The changes in the power waveform produced by a modern dimmer adds sharp "square" edges, and when you run that through something that can vibrate, you'll hear a buzz.

Answer 3

Did you compare the watts used including ballast and what the dimmer is rated? Lutron's C.L dimmer advertises it will dim 600W incandescent but the CFL & LED's cannot be over 150W. This also lowers if multi-ganged or if fins are removed. Some other CFL dimmers show that you are only allowed X number of lamps.

Your 5 x 60W sounds like you should be well below the level but maybe the ballast adds a lot more to it as you dim?

I would return the dimmer and either try a regular incandescent dimmer. A lot of makers of dimmable CFL's say you can use a regular dimmer.

I'll suggest the CFL dimmers to customers only because of the trim adjustment on the dimmers, to fine tune the dimming, but most people I know use regular dimmers. Where I work we stock them as a regular 3 way dimmer. Price and incandescent specs are the same as the incandescent dimmer, so no need to stock 2 different items.

Answer 4

I just had the exact same buzzing problem. I was using a Lutron incandescent/halogen dimmer from ace hardware and plain 60w bulbs. I replaced the bulbs with GE 40w bent tip bulbs and no more buzzing.

Answer 5

Check the SMS Transformer of the lamp. SOUND COMES BECAUSE OF LOOSE FITTING OF THE SMPS WHICH VIBRATE AS THE CURRENT INCREASES,