Powering off discharge sources

[mac.calder]

Okay, this may run a bit of controversy - Dishcharge sources - power off the lamp and leave the fan running, or power off the whole thing and let it cool down slowly?

 

Part of an academic argument I am currently having with some LD friends. I say power everything off and alow it to cool slowly, unless I need to move them quickly, my friends say un/de/* strike the lamps and let the fans cool it down.

 

I know there was a study done on it by a few companies but I cannot find it.

 

Any views would be welcome.

[cutlunch]

I tend to turn the light off but leave the fan on. Thinking about it the bulbs are designed to work with the fans on so having the fan going when the light is off won't do any harm. Also the fans should blow fairly evenly over the bulb. This would cool it fairly evenly where if you turn the fan off the bulb will cool at different rates ie top last. This may or may not stress the bulb.

 

I have never heard of the fan being left on damaging a bulb. But turning it off early would expose it to more risk of failure. Just my five cents worth( NB Five cent pieces won't be usable in New Zealand soon :) )

[niclights]

My thinking is if there is an option to run fan without lamp then this can only be beneficial. The radiating heat from the bulb will remain considerable for some time after and, without the forced air assistance, temperature in the unit will rise quickly. I have read various manufacturers comments on this, but can't point to anything specific. I'm sure it's rare that this is essential in which case it would be automatic, but I can't see any disadvantage in doing so manually if there is the option.

[bruce]

Also related, many data projectors now have capacitors which will allow the fans to run on for a few minutes if the power is turned off.

[Mark Powell]

Best practice is to;-

 

Place the lamp head in a horizontal position (if head is pointing straight down then rising heat can cause cooling / ballast issues)

Make sure all glassware is out of beam path (CMY etc).

Douse lamp.

Leave fixture to cool, 10 minutes + ideally.

[thedj]

Just my four pennith worth, We switch off the lamp and give it the time it takes to get to the plug on the other end of the stage to cool via fans.

It just seems like a good idea

 

thats all

[Dmills]

With big xenon arc sources it is common practice to let the lamps blow down for 5 minutes or so, mostly because the electrodes have a lot of thermal mass inside the envelope and with the fans turned off, it is possible for the glass to metal seal to overheat from the stored energy as the ends of the lamp are no longer being cooled.

 

This is unlikely to be a problem with smaller metal arc sources used in movers, but I would tend to let then blow down anyway.

 

Regards, Dan.

[Mike the light]

On a tenuously related note. I used to work for a film lighting hire company. We used to get photographers who would dry hire 2.5/4Kw MSR pars Or fresnels. As with most film discharge lamps the sit on the lamp base with tyhe yoke over the top of the lantern when not in use or in transit. The amount of f***wits who used to rig them on stands by turning them upside down rather than swinging the yoke round the right way, resulting in extreme melt down of the switch housing... Of course they'd swear blind it wasn't them, that the lamp was faulty etc. Bless their little cottons.

[Tomo]

Always do a remote/local lamp douse, and leave the fixture powered for ten/fifteen minutes to cool the fixture.

 

Hard-powering off reduces lamp life and increases the risk of lamp explosion - not hugely, but enough to make the extra ten minutes worth it.

 

Given that most fixtures let you do it under DMX control - douse the lamps from the desk after the show, do your housekeeping, show notes etc, then power down the fixtures.

 

That way you've lost no time anyway.