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Re: Lights buzz on low dimmer setting


From: John370us@Yahoo.com
Category: Wallboard/Veneer Plaster
Email: John370us@Yahoo.com
Remote Name:
Date: 03 Jul 2007
Time: 05:50 PM


I have a new home (1999) which is sided with white - masonite color-loc. - This isding is now going bad.. the bottom of most is rotting away. Do I have any warranty??? The company that I purchased the siding from is now out of business (Home of your own, Inc in MN). Rhank you for any information that you might have. John370us@Yahoo.com (Cimarron, KS)

From: info@builderswebsource.com
Category: Electrical/Lighting
Date: 24 Nov 1999
Time: 10:54:57
Remote Name:


This is a great question and one that comes up frequently with homeowners. First the technical answer, then the practical solutions.

Inside a typical solid-state dimmer is a semiconductor called a Triac. It acts as a fast electronic switch that pulses the power on 120 times per second (twice the power line frequency rate of 60 cycles per second). If you've ever looked at A.C. electricity on an oscilloscope, you'll see a continuous sine wave (going both positve and negative relative to ground or neutral). A dimmer simply pulse-width modulates how much power is delivered to the lighting circuit. If the dimmer is on "high", then the Triac never switches off. If the dimmer is on "medium," then the Triac is on approximately 50% of the time. Similarly, if the dimmer is on low, the Triac is switched on only a small fraction of the time. This rapid modulation of the power creates sharp transitions in the voltage and inrush current, including additional harmonics that can cause the filament in the light bulb to resonate. Typically, buzzing is worst at mid-range settings, however this can vary depending on the combination of dimmer and light bulb.

Enough of the technical stuff. Here's how you fix the problem: First, since there are many variables, you may have to experiment to solve your problem completely. In order of simple to complex, our recommendations are:

1) By process of elimination, try to determine if the buzz is coming from a particular light bulb....or all light bulbs. Since different light bulbs have different filament types and resonant frequencies, sometimes changing the bulb will eliminate the problem. Try a heavy-duty bulb like a rough house bulb (sometimes called a garage bulb)...which has a much thicker filament and is less likely to resonate. Or, try a physically smaller bulb (which will have a shorter filament) or a lower wattage bulb.

2) If this doesn't solve your problem, you may need to upgrade your dimmer. If you're using an older or inexpensive rotary-type dimmer, this could be part of your problem. Some of the better dimmers from Lutron or Leviton have additional circuitry built in, such as noise and RFI suppression circuitry to help reduce harmonics. Together with the right bulbs, you can usually find a suitable combination that eliminates or signficantly reduces the audible hum.

3) Finally, as a last resort Lutron and others make a special noise-reducing coil that can be placed in series with the dimmer. This effectively "filters" the inrush of current to the lamp. However, the coil itself can emit noise so depending on where it's located, you may still hear a slight buzz -- this time coming from the coil, not the light.

4) Also, be aware that some lamps, such as Philips Masterline, may have internal diodes that interfere with proper dimming. So be sure to use bulbs which do not have diodes.


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