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From: burgess@hpfcso.FC.HP.COM (Ken Burgess)
Newsgroups: sci.electronics
Subject: Re: light bulbs buzz when dimmed
Message-ID: <7480016@hpfcso.FC.HP.COM>
Date: 9 Apr 91 04:28:02 GMT
References: <1991Apr2.162037@maximo.enet.dec.com>
Organization: Hewlett-Packard, Fort Collins, CO, USA
Lines: 28


My daughter disliked the noise made by a dimmed reading light she uses
and decided to try different bulbs to solve the problem. Eventually she
did a science fair project (largely un-noticed) to determine what types of
bulbs made noise and what types did not. She tried bulbs from 8
different manufacturers, all 60 watt types, and found a great deal of
variation in the ammount of accoustic noise they generated on a dimmer.

I don't remember all of her results but I do know that she found one
manufacturers bulb that made no sound whatsoever. Coincidently they were
also the cheepest bulbs in the test. She obtained them at a local hardware
store; they are made by "EXTRALFE" (model number 60 AFR 2000)
in Poland for the Supreme Corp. Mullins, SC 29574. They are advertized as
a "generic" bulb but have a nominal voltage of 130 volts instead of the 
120 V. usually specified. They claim long life.

As a part of her experiment Melissa broke the envelopes to examine the
structure to see if she could correlate the fillament construction with
the ammount of buzz they generated. What she found was that the tightly
coiled fillaments buzzed the worst. The best (including the EXTRALIFE) were
multiply supported straight wires. A few of the bulbs used this techniqe
for filiment support, but the EXTRALIFE used five supports whereas the others
used only three.

I thought she did a good job and I was very proud of her, unfortunately
the judges liked airfoil experiments better and she didn't even get beyond
her school competion. At least I found it useful, our lights don't buzz
anymore!