The
Xenon Lamp is a single
element arc lamp that operates at over 30 atmospheres of pressure while operating and is under about +1 atmosphere of pressure cold. that means it will explode if broken cold, unless the
ceramic seal has failed.
the fill pinch on a lamp is designed to keep the
envelope closed and the internal fill inside up to a specific temperature. the forced air cooling keeps the lamp
envelope and housing below a specific temp. it is a misnomer to think that because a lamp is extinguished, that it then goes down right away. without forced air cooling the arc has been extinguished, but the fan is not cooling the arc, it is cooling the quartz
envelope, and once that fan turns off, there is a rise in temp on that
envelope. a safe presumption would be a rise of at least 10% for as long as 5 minutes, though that time might be a
bit long. i think all Xenon fixtures require a fan to operate while the lamp is off, while only some
HMI fixtures require that. that is based on the safe temp
rating of the fill pinch/
envelope.
as a matter of course, running the fan for 5 minutes after lamp off should be enough to cool the
envelope to a
point where the fan could be turned off (in a
house situation, not a touring/pack it up situation). i haven't read the
Lycian requirement for cooling but that should be the first step. my rule of thumb for followspots is if i can put my
hand on the top of the lamphouse and it is not hot to the touch (i can keep my
hand on it) then it is cool enough.
We all have done things for years without harm that in hind sight (or with further information) we found was incorrect, even if nothing untoward happened.
i'm reminded of a class in explosives i took back in college (WAAAYYYY BACK). we were out at a strip mine during the final
phase of a 1/4 mile shoot of a seam of coal. the lead shooter told us they had a 50 year experienced explosives expert on site. he was the go to guy for decades. they used
electric ignition for the cap and used a resistance
meter to make sure everything was good to the first cap. its quite an impressive site seeing 20' thick seam of coal and knowing that they've done the math on it to make sure that once the shoot is done all of the coal is broken to a
point that all the pieces are no bigger than your fist. anyway, one day a sales man came in to show them the newest resistance
meter available. everyone was around the sales man oooing and aahhing and when he said "and now even the battery compartment is easily accessed to you can change your batteryquicker than in your old model", the lead shooter said....
"what battery?"
he retired soon after. at least that was the story we were told. then they blew up about 4000 lbs of explosives. i guess you can see the moral of the story so i won't linger on it.
also, please note that
HMI/MSR/USR
etc lamps are not really under pressure cold, but they do contain, among other elements, Mercury. at room temp it is a liquid. it is a gas under operating temps. please don't dispose of in your normal garbage. (a 2500w lamp will have about a gram (? maybe a half gram, i've forgotten) of mercury in it. contact your sanitation company to find out about the local hazardous waste instructions.