beholder...
I was an Electronics Technician in the US Navy, and I'm also
a musician, which, you'll see, has some bearing here.
I believe you'll find that this article, 'Silence of the Lamps:
The New Wave in Dimming Apr 1, by Mats Karlsson, on the Live
Design website, answers your questions, as well as providing
a solution:
"the current goes from zero to full in a couple of microseconds,
causing a sharp current spike that results in a wide spectrum
of radio frequency interference. It also causes resonance in
the lamp filament, a phenomenon known as 'lamp sing.'"
Much more on the page:
http://livedesignonline.com/mag/lighting_silence_lamps_new/index.html
In addition to what can be learned from the rest of the article,
which discusses the problem in detail, as well as the solution,
let me elaborate...
Radio frequency interference (RFI) is the same as electromagnetic
interference (EMI), and what's occurring is that harmonics of the
varyious frequencies produced by the sharp current spike are
resonating with the resonant frequencies of the wire segments in
the filaments, causing them to oscillate.
Resonant frequencies are the base frequencies of a physical object,
at which it will begin to oscillate. If, for example, you determined
the resonant frequency for a bridge, you could cause it to begin to
oscillate and sway by having troops stomping on it at a harmonic of
that frequency (this has actually been done accidentally, and is the
reason troops are not allowed to march in lock step across bridges).
This also explains the oscillation of some bridges during earthquakes,
and the shattering of a glass when the resonant frequency for that
glass is hit and held by a talented singer.
This article on Ask A Scientist explains more:
http://www.newton.dep.anl.gov/askasci/eng99/eng99357.htm
A harmonic frequency simply means one that is a multiple of the
resonant frequency, which will still cause some resonance to
occur. If, for example, I have a guitar string tuned to a resonant
frequency of 440 cycles per second (cps), and I play a Viola string
tuned to a multiple of that - 880/1320/1760/etc cps - this will cause
the guitar string to vibrate due to resonance.
Because the sharp current spike in phase-controlled dimmers results
in a wide spectrum of radio frequency interference (or a wide spectrum
of interference frequencies), some of these frequencies are harmonics
for the resonant frequencies of the filaments, causing them to 'sing'.
Please do not rate this answer until you are satisfied that
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established through the "Request for Clarification" process.
A user's guide on this topic is on skermit-ga's site, here:
http://www.christopherwu.net/google_answers/answer_guide.html#how_clarify
sublime1-ga
Additional information may be found from an exploration of
the links resulting from the Google searches outlined below.
Searches done, via Google:
"lamp sing" cause OR explanation electromagnetic
://www.google.com/search?q=%22lamp+sing%22+cause+OR+explanation+electromagnetic |
