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I have eight 50-watt lamps connected to a single dimmer switch. It makes a loud buzzing sound when the lights are dimmed. How can I fix this problem?
From time to time, we hear from folks who have noticed a buzzing sound coming from either their light bulbs or a newly installed light dimmer. They notice that something is not quite right because the buzzing was not occurring before the switch was installed. Is this normal and what can be done to minimize.
Sometimes when a triac-based dimmer controls a light, it can produce an audible hum from the light bulb or the dimmer itself. Our X10 wall switches use triacs, which are electrical semiconductors, like transistors, to control the flow of electricity through the dimmer. Like water flowing through a garden hose, sometimes less flow is desired so you turn the water valve to the desired output. To dim a light, the dimmer circuitry tells the triac to lessen the flow of electricity through the triac. The dimmer will reduce the flow of electricity by removing parts of the AC voltage when dimming is engaged.
In the diagram below are four oscilloscope displays of electricity from a normal mechanical switch, an inexpensive X10 dimmer at 100%, a SwitchLinc series dimmer at 100%, and a SwitchLinc at 50%.
 |  | | Output from a regular mechanical switch | X10 switch at full brightness | | |  |  | | SwitchLinc at full brightness | SwitchLinc at 50% Brightness |
So what's going on here?
When bulbs are at full brilliance, the triac turns on most of the cycle. At this point, there is not much loss of voltage, so the bulb doesn't buzz. When a lamp is dimmed, the triac is effectively switches the lamp on and off 120 times per second. If the filament in the bulb is not rigidly mounted, the magnetic field induced by the rapid rise in current can set it vibrating - resulting in an audible buzz. The noise is greatest at about the 50% dim level since the triac is going from 0 to 170 volts almost instantaneously (from zero to the peak of a sine wave). Even at full on, the dimmer's triac will "chop" out the first ~1.1ms of each half-sine wave.
What is real important is how do you fix it?
 If you are using typical incandescent bulbs, try using rough service bulbs. These are the type of bulbs commonly found in work lights, ovens, and refrigerators. These bulbs will have more supports for the filaments than traditional bulbs. More supports equals less movement equals less buzz. Although these bulbs tend to be more costly than regular bulbs, they have a reputation for lasting longer, (some have a life of 2000 hours). If they are hard to find in your town, check an auto parts store as they are commonly used with droplights. 130-volt bulbs are an alternative to rough service bulbs. These too will give quieter operation because the filaments are thicker than regular bulbs.
Better quality dimmers may help to reduce noise. All the dimmers we offer include an internal component called an LC filter. This filter helps smooth out the starts and stops of the triac. Think of it like a spring where it absorbs some of the jolts of voltage as electricity is turned on and off.
Sometimes, the noise can come from the dimmer itself. We have found that the noise is also more likely to occur when the total wattage controlled by the dimmer is near the dimmer's rated maximum. An entry-level 500-watt dimmer may produce more buzz on a 400-watt load than would a 600 or 1000-watt dimmer. If the existing dimmer cost less than $20, go try a dimmer that uses a toroidal filter or a densely wound bar choke. A filter with more copper turns will give better performance. In the photos on the right are two toroidal filters used in our two best selling wall dimmers. The one on the top is from a 2031 X10 Wall Switch and the one on the bottom is from a 2380 SwitchLinc 600-watt Dimmer Switch.
When the wattage controlled by the dimmer is near the rated maximum, there will also be more heat generated. Once again, a higher wattage-rated dimmer will help here too. To read more about this issue, please click on the link below:Here are some other comments we have heard from customers over the years. We have not verified this information, but do want to share it with everyone:
- Users of Sylvania Capsylite bulbs report that they don't produce any noticeable noise.
- Positive comments have been heard from customers who have tried some of the Phillips brand of light bulbs.
- The decorative bulbs and bathroom bulbs that have long filaments tended to have the problem.
- Good results have been found using halogen bulbs and 'heavy duty' bulbs. (Be sure to make sure you wall switch can work with halogen bulbs as some dimmers are only to be used with incandescent lights.)
- One customer reported that he was running the lights at 60 to 50 percent most of the time and the noise was too annoying. He changed the bulbs to ones rated at about half the wattage and ran the dimmer at full brightness and the noise disappeared.
 If all this experimenting with different light bulbs is too crazy for you, use non-dimming X10 wall switches. These units don't contain dimmer circuitry, but rather a hard-contact relay. Just like a mechanical switch, these units don't alter the electricity before it goes to the bulb. Smarthome has a few models for your consideration:
updated 6/28/02
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