Turning off projectors during breaks and lunchtimes...

[Pete10141748]

Ours here are generally left on all day, every day, which I'm happy with.

 

The exception is if classes have something like PE straight after lunch, in which case that's anywhere up to 2.5 hours when it would be on pointlessly - I try and encourage them to turn their projectors off for things like that but even then, I'm not going to stress over if they don't.

 

From a 'green' point of view they probably should only be turned on just before they want to use them and turned off as soon as they are done - but realistically that's never gonna happen in a school environment!

Edited March 20, 2012 by Pete10141748

[Marc-Engineer]

OK before I start this is in no way in reference to the above post mentioning GREEN its just so many people quoting GREEN from very old notes, eg. I was told “you must turn off TVs at night at the socket”,…..(oh boy) this is the worst thing you can do for “Green” as this will shorten its life “but” they say “it will use 45% of its electric when in standby” (lol) not even close to true, most 42” TVs now use less than 1w on standby so in a school year if you don’t unplug it, it will cost you about 30p, why will it cost more to unplug it? Because they are designed to come on from standby (electrically warm) not from cold (stressing the components) this is the same of may bits of modern kit. Starting it from cold every time will shorten its life, think about it when you last had a failure lamp or other wise when did it fail? I bet it was at turn on from cold. True even of house lights………

 

So be “Green” leave it on............

 

question:- Whats the biggest waste of power in a school?

answer:- laser printers left on overnight (they use a massive amount of power, only very new ones use "proper" power saving)

 

Marc

Projector Engineer

Edited March 21, 2012 by Marc-Engineer

[Rammie]

My vote goes to "turn it off when not in use, at lunch and end-of-day". I was always keen, but even keener after we found an HP projector melted after a half-term. The question of power-cycles shortening the life of the lamp? Okay, where's the evidence for this? The physics is clear with incandescent lamps (the filament is low-resistance when cold) and with flourescent lamps (startup surge strips the cathode material), but why would a power-cycle shorten the life of a high-pressure Xenon lamp? Granted, the globe can shatter, but they do that anyway apparently at random - ever wondered why they warranty them for 90 days? End-of-life failure occurs because the electrodes sputter and shorten, the arc gets hotter and the globe mists up with condensed metal vapour. All this happens only at full brightness, not at switch-on.

[SimpleSi]

Its just a judgement of statistical chance.

 

Their is an x% chance of the bulb blowing at a point in its projected lifetime which I believe increases with age.

 

Leaving it on for an hour extra at lunchtime just ever so slightly decreases the total expected number of days that the bulb will last.

 

You pretty much know what the downside is.

 

Turning it off and on again on the other hand - doubles the number of times the projector is power cycled. Nobody really knows what effect this will have on the lifetime of the bulb but us oldsters all "know" that leaving something on will almost always increases its lifetime over switching it off and on again (They don't like the surge up them captain! )

 

So - one one hand you can pretty much say that you'll reduce the number of days between needing new bulbs from 40*5*7 to 40*5*6 (e.g about 15% reduction by leaving it on all the time) but if you double the number of power cycles -?????

 

I'd rather take the known hit than the unknown one - but I'm predjudiced as I used to work with thermionic valves costing £10K and by golly - we treated them better than our own children

 

Si

PS who turns their servers off at night????

Edited March 22, 2012 by SimpleSi

[Marc-Engineer]

Rammie, the reason they fail at startup is because they need a high voltage and current to strike but not to maintain a already lit lamp so it is much more difficult for them to strike and it is two things that age a projector that you are saving if you switch it off, the lamp and the ballest unit as that ages too, the lamp does not have a "bulb" it has a small quartz tube this also contains meurcury too small to see which also deterioates at each switch on. So yes they do age more by switching on than when on, evidence ? i have seen numbers of projectors that are in "consent on" situations with projector lamp hrs of 6,000 to 9,000 (not recomended) difficult to get that on a projector you switch on every day, and still fairly bright too.

 

Marc

Projector Engineer