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Hardware

LED Replacement for LCD projector Bulbs 20

Posted by timothy from the pipedream-but-a-good-one dept.
radiojock asks: "OK, I've got a question -- has anyone ever seen a way to replace a LCD projector's bulb (they burn out way too easily) with the new superbright LEDs ? this should be very possible, take a group of the LEDs and mount them on a board. Would this be able to replace the bulbs? And would the LCD projector manufacturers allow this? Think of the energy savings, and the heat reduction ... Just a thought." I would pay a lot of money for such a replacement bulb, and I suspect a lot of others would too -- which leads me to suspect that such LED arrays really aren't ready yet, or they would be on the market. I hope someone can contradict this -- are LEDs up to the task? I bet the LCD manufacturers would be eager to supply them if so.
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LED Replacement for LCD projector Bulbs More

LED Replacement for LCD projector Bulbs

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  • 50 (Score:2, Interesting)

    by Karma 50 ( 538274 )
    I think you would need a minimum of 50 LEDs.

    LumiLeds Lighting Produces 17 Lumen White LED [lumileds.com]

    But projector bulbs seem to start at around 1000 lumens [projectorcentral.com] and some projectors go up to 5000 [newsearching.com]
    • 50 LEDs seem like a lot, and whether there would be more or less heat with that many LEDs would probably be an issue...

      But what if you made a "light box" of some type, that had the LEDs in the box, focused and/or collumnated via a lens arrangement, then fed the light to the projector via a light pipe or fiber optic bundle? Would such a contraption work?

      Seems impractical, too me (and I thought the thing up), but interesting, all the same!
      • Looks to my math addled mind that with the company specs "This device operates at 350mA and 3.2Vf" you're looking at 1,000 lumens for about 60 watts of input power.

        Even assuming that all it was putting out was 60 watts worth of heat (and no light), it seems pretty sweet compared to halogen solutions.

  • LEDs aren't ready yet... (Score:5, Interesting)

    by stienman ( 51024 ) <adavis&ubasics,com> on Sunday December 09, 2001 @01:16PM (#2678676) Homepage Journal
    There are a few reasons why you couldn't do this:

    1) Even superbright LEDs are not nearly bright enough. Find your favorite LED manufacturer, and check out the specs. The projecter bulbs are several hundred (if not thousand) of times brighter than even the brightest white LED. The array would be huge.

    2) Superbright LEDs are not true white. They are white one of two ways: either three LEDs in the package (RGB) or a blue LED with phospher to emit RGB. So what? Well, the colors emitted by an LED are /very/ specific wavelengths. The color filters on the LCD will likely NOT match the LED colors closely enough to produce a good rendition. Projecter bulbs produce a nice even and wide band of wavelengths from just below visible to just above visible.

    3) Lastly, the lenses in the projector are designed for a specific shape of light, whether it's point source, straight filament (and orientation), bent filament, etc. You'd have to add your own lens system to make an array of LEDs look like whatever bulb you're trying to emulate, and it likely won't fit into the space set aside for the regular bulb.

    In short, you'll end up trying to fit a round peg into a square hole. Not only will it not fit, but it won't work well if you can make it fit.

    You'd spend far less money and time buying a few bright 19" screens, setting them up in array, placing fresnel lenses in front of each of them, and lining everything up perfectly so their images overlay each other (for brightness). And the monitors are rated for a lot more usage... Of course, you couldn't call it portable, but you now know how much portable really costs.

    -Adam

    This comment rated excellent by 5 of 7 slashdot users. You can buy this comment for $13.50, or you can check our auctions [slashdotshops.com]. The seller accepts PayGal, Karma, and Swiss Cheese, but does NOT accept Trolls as payment.
    • LCD projectors are actually extremely picky about bulbs. Not only is all of the above true, but the spectrum of light is especially critical as projector manufacturers "tune" the LCD based on the light they expect to have coming through it.
      This is why a cheap (off-brand)replacement bulb will sometimes cause a slight tint in the picture no matter how much you play with the color controls.
      You could, in theory, redefine the light parameters used by the projector, but I've never heard of anyone even trying.
    • I agree totally with your LED comments. Their optical power density is simply too low to be practical.

      What you really want is some sort of gas discharge lamp (e.g., xenon). They're bright, have a predictable flattish color spectrum, and last a couple of thousand hours. You can buy projectors that have them built in these days. (I wouldn't try a retrofit though. Getting the electrical drive, cooling, and lenses right would be more trouble than it is worth.)

  • Make the bulbs last longer (Score:4, Informative)

    by whydna ( 9312 ) <whydnaNO@SPAMhotmail.com> on Sunday December 09, 2001 @02:52PM (#2678869)
    Two tips to make the bulbs last longer:

    - when installing a new bulb, go to extreme measures to avoid touching the bulb directly; use a piece of clothe, etc. The reason is that the oil on your skin will stick to the bulb, and when heated with cause a non-uniform distribution of heat which causes the bulbs to die more quickly

    - turn the projector off if it won't be needed for a while. It's easy to forget, but don't leave the projector running if it won't be in use for a while. This seems like a silly thing to say, but a lot of people forget about how fragile the bulbs in the projector are.
    • The turning off is a valid point, but just as with car engines and computers, the heating and cooling cycle does damage to a bulb as well. I don't know of a good rule of thumb (and I'm sure it varies from one type of bulb/projector to the next) but if I'm not using it for only ten minutes or so I probably wouldn't.
      Over a half-hour, then definitely.
      Twenty-minutes? That's a toss-up...
    • Instead of turning the bulb off, what if you turned the bulb "down" - via some sort of rheostat or more properly, a potentiometer in a variable voltage divider configuration.

      I am just thinking of this because the other replyer mentioned the cycling (heating/cooling of the bulb leading the failure of the element via metal fatigue)...?

      Would this solution be better or worse?
      • Instead of turning the bulb off, what if you turned the bulb "down" - via some sort of rheostat or more properly, a potentiometer in a variable voltage divider configuration.

        Well, that depends on what the power consumption of the bulb is. If it is a 120 VAC incandescent bulb, a heavy duty Triac light dimmer would be the fastest and cheapest way to dim the bulb, and would extend the life of the bulb even at full brightness by allowing you to gradually increase the current. In the case of filament breakage, the sudden inrush of current into an old weak filament is what does it in, that's why a bulb is more likely to fail when you flip the switch than during the middle of use. Most failures during operation are due to bulb breakage, usually caused by fingerprints on the bulb as was stated in a previous post.

        However if the bulb is DC incandescent, a Triac light dimmer couldn't be used as a Triac depends on AC to work properly. A power rheostat rated for the wattage of the bulb would be required, or an adjustable voltage power supply could somehow be used.

        Of course, if the bulb is an arc tube, like used in some video projectors, yer outta luck.
      • Halogen light bulbs (as used in most projectors) will actually not last as long if you run them at a lower voltage. There's a cutoff point at which the halogen scavenging doesn't work anymore, and the filament will plate out on the bulb...
  • I bet the LCD manufacturers would be eager to supply them if so.

    I doubt that. How many LEDs are bought on a day to day basis? How many do you have in your home, your work, the shop you use for supplies and so on and so forth. There's a lot of LEDs in the world - and more every day.

    The increased revenue from making a few million LED 'bulbs' is hardly worth the effort of developing it - especially since they won't burn out for a long time.

    Ian Woods

  • LED output power doesn't match arc lamps (Score:3, Interesting)

    by lotsolens ( 542570 ) on Sunday December 09, 2001 @09:02PM (#2680018)
    The highest power white LED announced so far has a 17 lumen output with one Watt input. This is a much lower efficiency that is achieved by arc lamps, so to get equal screen brightness the LED's would actually produce more heat. If you wanted to project onto a very small screen it might make some sense.
  • This [att.net] is probably the kind of thing you're talking about; this is definitely NOT the right size to put into a projector, but it could be adapted. The advantage of this one, being RGB as opposed to white, is that it's very easy to achieve the right color balance. The manufacturer would probably need to get a custom run of the LEDs to match the LCD wavelengths, but that wouldn't really be all that difficult... just a matter of changing the doping materials in very minor ways...

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