Re: compact flourescents

Stan P.:
1. Can anyone tell me what amperage a "100 watt" incandescent bulb
would draw when 120 VAC is applied? My high school electrics tell me
100/120 = .833 amps, but not sure

(Right, as noted.)

Dave W.:
On the other hand, if it's a 100W 240V bulb, running it at 120V would
dissipate one quarter of 100W, i.e. 25W, 0.2A.

Wrong: it would be significantly more than that, although there's no
easy way to say how much more. The filament resistance of an incandescent
lamp depends greatly on the filament temperature. For example, I happen
to have here a multimeter and a 60 W, 120 V light bulb -- in operation
that bulb would draw 0.5 A and therefore must have a resistance of
240 ohms. With the bulb cold, though, the meter shows the resistance
of the filament as just 18.5 ohms. Which means it draws about 6.5 A
when first turned on -- but the filament temperature will rise in a
fraction of a second and raise the resistance to something like normal
before the fuse or circuit breaker can shut it down.

When a bulb is operated below its design voltage, the filament will run
less hot and the resistance will be less, compared to normal operation.
But, as I say, there's no easy way to say how much less.
--
Mark Brader "I can see the time when every city will have one."
Toronto -- An American mayor's reaction to the
msb@xxxxxxx news of the invention of the telephone

My text in this article is in the public domain.
.

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