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Topic: Do you leave the Fan running?
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Douglas Meltzer
Moderator
Posts: 4554
From: New York, NY, USA
Registered: Jun 2003
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posted August 05, 2003 09:03 PM
Steven, If I only had 30 minutes before I had to pack the projector up and leave a location, I’d be using those fans. However, Any thermal shock to a lamp will shorten it's life. Eliminating the source of heat while keeping the cooling system on is a shock. I honestly don't know much about DLP technology, but when I'm on a set filming with HMI (daylight color temp) lights whose bulbs seem to cost one dollar per watt, the accepted practice is to let them cool naturally. Actually, these bulbs are very similar to the Xenons. One should avoid striking and re-striking as much as possible. When I fire up my 1200 xenon, that lamp stays on till the show's over! I'll have to check about that bulb test, but here's a similar one I found at http://www.capital.net/com/jaytp/EQUIP.HTM “About 15 years ago or so some one at the State University of New York (SUNY) was looking for a way to save money. They looked at how many projection bulbs SUNY went through in a year. So the did a study on how to make these bulbs last longer.
What they discovered was that bulbs that were allowed to cool down slowly last longer. If the cooling fan is allowed to run to cool off the projector, the uneven cooling of the bulb stresses the filament. Of course if the projector has to be moved right after the show it should be cooled one way or another because any mechanical shock to a hot filament causes greater stress than any about of uneven cooling.” Doug
-------------------- I think there's room for just one more film.....
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Steven Sigel
Jedi Master Film Handler
Posts: 701
From: Massachusetts
Registered: Jun 2003
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posted August 05, 2003 10:38 PM
It seems to me that there would be more of a shock to the lamp by not letting the fan run -- while the bulb is lit, the heat is carried away by the fan, which yeilds a fairly even temparature, but if you shut the fan off, the heat (for a time) is going to build up around the lamp. I would think that damage from excess heat would be greater than from cooling. Also the fan doesn't instantly cool the lamp - it still takes quite a bit of time to bring the temparature down -- all it's doing is carrying away the heat that is being generated.
That web page you quoted seems to be arguing that the fan would cause uneven cooling -- I think the oposite is true -- if you pass air over the lamp and draw away the heat, you will help it cool more evenly -- if there's no fan, then the parts of the lamp closer to the vent will cool faster than the other parts of the lamp.
The other thing to think about is what you are protecting -- even if you are correct about filaments, the glass still might be affected by the heat. And of course Xenon lamps don't have filaments, so any argument about filaments is irrelevant when talking about xenons (or any other ARC lamp)... I've got an Elmo 16-CL Xenon that I've been cooling with the fan since I got it (2 years ago), and I've easily run it for well over the lamps rated life with no problems, so I think I'll just keep on doing it that way until I see some scientific evidence that natural cooling is really better.
I absolutely agree with you that you should not strike a Xenon any more times than you have to -- I too always leave my GS fired up until I'm done with the show.
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