I covered this in the
preheat debate with some experimental results which are here,
"
Default Re: Preheating Conventionals?
Please consider, a 1000
watt 240 volt T19 on a
dimmer{for 120v thinkers just halve all the figures} It has a cold resistance of 3.8 ohms and a hot resistance of 57.6 ohms. A typical
dimmer will feed 1.65v at "0" and drive .35A putting 2.24 W into the lamp of
preheat.
@ 13V you can see the barest glow in the
filament and are drawing .96A and 12.6W
@30V you can see a real glow and are drawing 1.5A and 45W
at 60V you begin to get some output but at 1/4
voltage you are drawing 2A or nearly half the "full"
current
@80V which is 1/3
voltage you are drawing 2.3A which is more than half the full load
current and is also the
point at which the
dimmer starts to interact with the other dimmers on other phases.
This is why running all your dimmers at 1/3 is the worst thing you can do to your neutrals.
Now there is a benefit in Pre-heating 2k and 5k in the previous
cue, in
effect you are moving them up the
dimmer curve, but I have experimented with lamps and the increased resistance only lasts for a few seconds with 1/2k and a couple of minutes with 2k"s.
The thermal mass of a
theatre lamp has to be as low as possible to
enable it to light up and dim quickly, and pre-heating is not logical, especially when all your dimmers are "leaking" a few watts of heat anyway, so by all means turn on your lights to check them but be aware you are not helping to increase their lives and are probably shortening them and wasting a hell of a lot of
power in the process.
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This gives you approx answer to your question but with minor variations with different curves and lamps.
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