LCD Projector Bulb life - when to turn it off

January 31, 2007 7:36 AM

To maximise bulb life, what's the minimum length of time an LCD projector should be turned off for?

Bulbs for my projector are awfully expensive (it's used off and on for about 12 hours per day) and contain mercury, so I want to replace them as rarely as possible.

So how long does a gap between uses need to be before it's worth turning a projector off? If I'm not using it for ten minutes? Thirty minutes? Ninety minutes? (For fluorescents, it's supposed to be 15 minutes, but projector bulbs are super-hot, so I assume undergo much more stress when turned on/off.)

I do try to replace the bulb when the warning message appears, but sometimes bulbs fail before that and sometimes someone else is using it and ignores the message.

posted by Busy Old Fool to technology (14 comments total)

Most of the projectors we use won't let you turn them back on until they are completely cooled off which takes 10-15 minutes so 15 minutes is the floor idle time we use. Execpt for operational reasons you don't _have_ to replace the bulbs until they actually fail. We keep using ours until they get too dim.
posted by Mitheral at 8:28 AM on January 31, 2007

Call me silly, but I can't figure out why you'd need a MINIMUM off time.

If thermal stress is the problem, it would seem that the hotter the 'off' bulb is, the lower the stress when turned back on?

I confess unfamiliarity with the system that these bulbs are in, and realize that there may be SYSTEM reasons involved, but I sure would like a good explanation of this if anyone has one.

Also, why the hell are these bulbs so expensive? In my experience, it's usually because of low volume, exotic materials, low yields, or high labor content. Not to hijack the question, but if anyone has a CONVINCING explanation for the high cost of these bulbs, I'd love to hear that, too!
posted by FauxScot at 8:58 AM on January 31, 2007

OK, never mind. ( I used google. Wow! )

Expensive Lamps, Why?

Some more lamp info

So the upshot... cycling the lamps has an apparent bulb start up cost in electrode wear if it's a discharge type. That still doesn't answer the question of whether there's an optimum anticipated use interval that speaks against turning off the projector, sadly.

My question seems to be answered by actual material cost plus NRE (non-recurring effort) amortization, plus a little oligopoly action, at least as far a Philips is concerned.
posted by FauxScot at 10:07 AM on January 31, 2007

Wait until the fan turns off before turning the projector back on. This is the power cycle time designed by the manufacturer.
posted by Roger Dodger at 10:21 AM on January 31, 2007

Can I piggyback on this? My projector bulb went out recently and I have searched online for a replacement cheaper than $300 - do they exists? Are there clearinghouses for sheaper bulbs? I have a Sharp projector and I'm in Seattle, and I checked Bulbman and Kelsun and they are pricy.
posted by vito90 at 11:41 AM on January 31, 2007

For optimum bulb life, wait until the unit is stone cold, absolutely room temperature, before restriking. How long that is varies based on the projector. I use an hour for mine.

The reason it's important not to strike a hot bulb is because the projectors have a pre-programmed voltage ramp that assumes room temperature. I'm not sure if the voltage ramps down or up, but it's designed to take a cold bulb up to operating temperature as safely as possible. If the bulb is already hot, it's hit with the wrong voltages at the wrong time, and that dramatically shortens its life.

I've seen arguments that the cooling fans after powerdown are actually bad for bulb life; it's apparently better to let it cool slowly. But because it's just so, SO bad to restrike while hot, they err on the side of caution and cool the unit as fast as reasonably possible. This stresses the bulb and shortens its life, but it's better than an uneducated user restarting the projector too soon.

vito: I don't have any good suggestions, unfortunately. The bulbs are made in small runs and have very expensive materials, so they are exceedingly expensive. It's important to remember that your projector has a run life, and to budget for your next bulb in your monthly expenses.

Cost per hour is an important consideration when buying a projector. And, sadly, you have to hope they're telling you the truth about bulb longevity. According to the specs on my projector, the claimed cost per hour is ten cents. I haven't had to replace the bulb, so I have yet to find out if they were truthful.
posted by Malor at 1:45 PM on January 31, 2007 [1 favorite]

We use mercury lamps in our fluorescent microscopes. The rule of thumb is to run them for at least 30 minutes before shutting them off, and once off, wait at least 30 minutes before starting it up again.

Throughout the day, I hear "Scope?" "Scope?" as people finish whatever they're doing and ask if anyone else needs/wants to use before turning the lamps off.
posted by porpoise at 3:59 PM on January 31, 2007

On some older mercury vapor sunlamps, you had to wait for the mercury to condense enough to bridge a pair of contacts in the igniter filament circuit before it would turn on again.
posted by jamjam at 8:03 PM on January 31, 2007

Mitheral: I heard that allowing the bulb to fail while in use could cause damage to the projector. A manufacturer-spread myth? Regardless, for operational reasons I don't want bulbs to fail mid-use.

FauxScot: If thermal stress is the problem, it would seem that the hotter the 'off' bulb is, the lower the stress when turned back on?
Even if that were the issue (and Malor's comment suggests it isn't), the bulbs seem to lose most of their heat in the first ten minutes after being switched off, so I imagine thermal stress is similar whether the bulb has been off for fifteen minutes or a day.

And thanks for the links. Have you seen this?

Malor: Do you have a source for the room-temperature-centric voltage ramp? (I'm not doubting you, it would just be useful to send something official-looking to colleagues in the same situation.)

Porpoise: It'd be nice to have a source for those numbers, but if I'm going to adopt an arbitrary rule, let it be one propagated by people with microscopes.
posted by Busy Old Fool at 6:18 AM on February 1, 2007

Busy Old Fool - trial and error. Sorry, we're biologists, not material scientists. Like Malor was saying, someone originally ran the lamp for a "good long time" (a few hours), then timed how long it took before it fell back to room temp. We have multiple 'scopes with different lamps and all of them cool down (sufficiently) by 30 minutes. Turning on a hot bulb can sometimes push them over the edge and burn them out right away (some of these are very powerful lamps).

As for why we run them for at least 30 minutes before turning them off again, I'm hazier on the physics. I'm told that it extends the longevity of the bulbs. If I was to speculate I'd suspect that the switches might not make an absolutely clean cutoff of the current (ie., there's a current/voltage spike when the switch is flipped) and that the bulbs might be more susceptible to damage until they get to their optimal and stable operating temperature.

Also, the more practical reason is that when we're doing quantitative imaging we'll let the bulb warm up for 30 minutes first so it gets to its optimal (and stable) brightness before taking any pictures so we can compare pictures across different days - which you won't have to worry about.

It also wouldn't be a bad idea to keep a log of how many hours the bulb is in operation - we keep logs on all of the 'scopes. For the interest of, heh, science! maybe keep a log using your current practices with a new bulb and when you have to change bulbs, implement the 30/30 rule...?
posted by porpoise at 10:15 AM on February 1, 2007

I suppose it could be possible. We've had a few newer bulbs explode on us so you'd think they could handle that.
posted by Mitheral at 12:15 PM on February 1, 2007

I'll try to find a source on the bulb info, but it's been at least a year since I last read up on the subject.
posted by Malor at 11:05 PM on February 1, 2007

Thanks for the follow-up, all.

porpoise, I hope my comment didn't come across as snarky; the best answer I gave you was genuine.
posted by Busy Old Fool at 7:52 AM on February 2, 2007

Not at all, just trying to be complete =)
posted by porpoise at 2:59 PM on February 3, 2007