Projector

[mhussain]

Hey people I am faced with a dilemma should staff switch off projectors at lunch times? As the argument against this is the bulb life is shorted by switching the projector on and off (IS THIS TRUE?)

[Jamman960]

I'd guess switching it on and off more often is going to have some effect, I've got no idea how much of a bulbs lifetime would be reduced by on each switch on though.

I've always argued that if we were to have a powercut during a lunchtime when the projectors should be off we could lose a bulb or two when we really don't need to

[Chris-W-]

I think its unlikely that it could cause the bulbs more damage than say leaving it switched on for an hour (and possibly overheat!). Most projectors power down slowly and avoid instantly cutting power to the bulb/lamp.

[Marc-Engineer]

If your lunch is less than 1.5 hrs leave it on.

Marc
Projector Engineer

[maniac]

I encourage projectors to be switched off when rooms aren't in use out of good practise rather than anything else. The affect it has on the bulbs overall life are minimal, we have some teachers who persistantly leave them on and others who religeously turn them off, and bulbs last the same length of time as they all reach the 2000 hours that our projectors recommend the lamp being changed at. Contory to popular practise, we change all our projector bulbs when they report needing it. Even thou they may still work, it can damage a projector if the bulb is used longer than it's design life as the bulbs burn much hotter and with less efficientcy when they get older. The excess heat can damage projector units and cause burns on the optical path amongst other problems.

Mike.

[mhussain]

cheers everyone thanks for the replys

[Marc-Engineer]

OK, the way lamps operate is often not understood you wont of course remember but during the WW2 we used search lights very large reflectors using 2 large rods between which jumped a spark, this was huge (bear with me)and this produced a huge amount of light to light up aircraft in the sky. Ok now our little projector lamps are very like these, the large search lights had motor driven rods so as they burnt down the where driven together to keep the gap constant (important bit).
Our little lamps cant do this so the gap gets bigger, so what the projector does is turn up the voltage in an attempt to maintain brightness over its life as the rods get eaten away (no one asleep yet?) So this has 3 downsides with larger gap the heat goes up as its a bigger spark and funnily enough it is not the heat that burns the LCD and polarising panels it is the UV light (just like sunburn) that increases exponentially the third thing is the current goes up from the power supply with the attempt to maintain the brightness (nearly there).
The power and ballast unit the control the lamp become stressed if they work too hard, by over running the lamp as the gap becomes to big so next lamp in will not be as bright due to the power supply /ballast being stressed the first time (cost to replace ballast depending on unit £250 plus) and the UV may have dimmed by burning the polarising filters (yellowing).

So moral of the story DONT DO IT, change your lamp at around 2500 hrs regardless of how bright YOU still think it is and DEFINATLY DONT wait till it doesn’t light anymore as this is way too late. And don’t turn of your projectors if your away for less that 90 mins, remember you can not see he wear in a lamp and neither can your projector.

A maintained projector should easily last 7 to 8 years.

Marc
Projector Engineer

[flyinghaggis]

So moral of the story DONT DO IT, change your lamp at around 2500 hrs regardless of how bright YOU still think it is and DEFINATLY DONT wait till it doesn’t light anymore as this is way too late.

Thanks for the explanation Marc. We had a projector where the lamp was run for about double the recommended duration and sure enough, as you've suggested, when it finally went and was replaced the new bulb didn't actually make that much diffrence to the image quality/brightness which meant we ended up having to throw it away and buy a new projector.

I'd never have thought that simply running a lamp for slightly longer than it's rated duration would physically damage the other components in the projector but from our experience and your explanation it sounds like thats exactly what's happened!

[bossman]

@flyinghaggis:

Its a bit like cars, the initial 5 secs at startup does the most damage rather than constant running as the oil flow is not up to optimum temperature and therefore creates problems.

Like electrical units take more charge in starting than in constant running so people who think turning things off and then on again at certain times of the day are in fact generating more power surge's and thus using more electricity which costs the school or factory more.

I just wanted to get in on telling a story cos I liked the searchlight one and have similar experiences with electrical equipment and also cos I'm old hehe!!

Have a good weekend everyone