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This topic comprises 7 pages: 1 2 3 4 5 6 7
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Topic: I get to see a carbon arc setup!
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Stephen Furley
Film God
Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
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posted 07-31-2006 01:02 PM
quote: Monte L Fullmer
Yes, automation was another main factor, but the oil embargo of 1974 also helped this with energy suddenly became costly in some areas...like it did with one theatre that suddenly changed out carbon for xenon when it's power bills took a drastic hike.
It seems hard to believe that the power savings from switching to xenon would be that great; certainly compared to the savings from buying xenon lamps rather than carbons, and savings in reduced maintenance required with xenons.
The luninous efficacy of xenon lamps is not that great, you still need several kilowatts of it to light a typical cinema screen. I don't have figures to hand for typical cinema lamps, but this one, intended for use on a tank, is very similar to the older three-electrode cinema lamps; it only manages 40 lm/W. I doubt if modern cinema ones are much better in this respect, though they are in other ways. Metal vapour lamps tend to have a much higher efficacy; the highest one I have in my collection is a low pressure sodium lamp which gets close to 200 lm/W. Now, the discharge in this lamp is almost three feet long, and it is almost monochromatic yellow, so it would be of no use for film projection, but it does show how relatively inefficient xenon lamps are. They are chosen for film projection because of the quality of their light, not their efficiency.
Where the quality of the light is not the highest priority even other projection light sources, mainly metal halide, can do better than xenon. The old GE Marc 300 lamp had a considerably higher light output than a 300W xenon. The somewhat similar Osram LTI lamps achieve about 75 lm/W. The main problem with metal halide lamps is the inconsistant colour, but they are often used in things like video projectors and certain types of stage lighting equipment. The ultra high pressure mercury lamps often used in the smaller video projectors manage about 60 lm/W, still about 50% better thin xenon. The colour rendering index is not as good, but the very compact light source, and small lightweight power supply is more important for things like data projection.
I can't find luminous efficacy figures for a typical high intensity projection carbon arc; does anyone else have them?
In terms of the total electrical power consumption of a theatre, including things like general lighting, cooking, HVAC etc., is the saving from switching to xenon that great?
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Stephen Furley
Film God
Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
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posted 07-31-2006 01:24 PM
The arc Voltage was higher, but the current was often lower, wasn't it? It's often difficult to compare; I can think of quite a few cinemas which were under-lit with carbons; when they converted to xenon they increased their light output, so comparing the meter readings before and after conversion may be misleading. How much of the increase was due to increased lamp power for higher light output, and how much due to the different characteristics of xenon lamps, I'm not sure.
If rectifiers of similiar efficiency were used, how much difference in power consumption would you expect to see, to put the same amount of light on the screen.
As a matter of interest, how does the efficiency of rectifiers compare to that or motor-generator sets?
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