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Lightsource for DIY LCD Projector 34

Posted by Cliff
from the bright-light-or-light-brite dept.
xpndsprt asks: "I'm trying to develop my own projector (i've been reading DIYAudio forums for a while and finaly decided to put together my own), but it seems that people are having problems with light source. The Slashdot crowd seems to always have interesting answers to problems at hand, so to get to the point: Does anyone know of a powerful lightsource (200w+) which would produce a high temperature light (5000K+) and would not heat up too much (ppl seem to be using mag.Hylide bulbs, but those seem to heat up tempreture in the room by about 10F. Xenon lights are out of question, since too hot and not bright or white enough. If someone could help, it would be greatly appreciated."
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Lightsource for DIY LCD Projector

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  • by The_Guv'na (180187) on Sunday August 04, 2002 @04:36PM (#4009066) Homepage Journal

    White LED's? lots of them. Probly not so cheap though.

    Some old scanner bulbs? If you look in the right places you might be able to grab a few. AFAIK they are pretty cold.

    Theft. Find a suitable projector light source at work, disconnect it inside the case. Complain that it's broken, get a replacement, reconnect the wire, pocket the brand new bulb :) Repeat as necessary.

    Ali

    • I thought about making a LED powered projector, and priced it out, but never put it together, because my room isn't big enough for a projector. I don't know about the color, but would guess that LEDs would be in the 7000K+ range, since the're just a filter on blue ones. I think an array of about 60 would be close to 3000 lumens. But they should last alot longer than the other options, and you won't have to cool them as much.
    • In my old scanner...
      The 'bulb' was flourescent. Why not a flourescent bulb of some sort. RealGoods, and some of the efficent energy companies sell extremely powerfull flourescent bulbs, and they stay fairly cool. I am not sure if they are powerfull enough, but its worth a try.
  • A friend of mine used a transparent LCD panel that he got off eBay and an overhead projector together to create a projector for less than $200, you can pick up the LCD projectors at any used office supply store, but you may find that they go through bulbs faster than slower...

  • LCD + OHP (Score:4, Interesting)

    by brejc8 (223089) on Sunday August 04, 2002 @05:35PM (#4009274) Homepage Journal
    We got loads of these 640x480 lcd screens for £1 each ($1.50). They work really well when they're placed an OHP. Here [man.ac.uk] are some things we did with them. I am currently thinking of placing four of them in a circle and having a powerful light in the middle. Then a simple GAL or FPGA to control it. then have funky colours shining on your wall. Or the time/wather and so on.
    Fat boy Matt made a network controled version [man.ac.uk].
    • more importantly, where can I get a 640x480lcd screen for 1 pound (1.50 USD (60$ cdn))
    • where did you get the LCDs? I'm in needs of lots of them myself...

      cheers,
      kitsch
      • Off an old friend of a supervisor. They sold us something like 100 of them for a £1 each because they were upgrading and these were supposed to go in the bin. Problem was they threw away the power convertors. So we have no way of driving the tubes. They did give us three they found after the scrapping but as for the other 97 I need to find a good way of lighting them. We shared them around the office and we only have one or two left. sorry mate.
  • If you put a 200W light source in, the room will be heated by 200W. Unless it has lots of windows to let the light out, but that seems unlikely.
    • However, a 200W laser will light up the room a whole hell of a lot more than a regular 200W incandescent bulb. For a constant amount of light output, the wattage of the bulb will vary.
      • Yeah, but unless the beam is being directed outside of the room (or at some reasonable sort of 'sink') even if the lightsource is (an impossible) 100% efficient at converting 200W electricity->light, you will in short order see a near-100% efficient conversion of light->heat.

        Or am I wrong about this? IANAPOAE.

    • Sure, 200W in is 200W out ... but remember that you're outputting light as well as heat. An incandescent bulb outputs a lot of heat and a fair amount of light, whereas the flourescent bulbs output a lot more light than heat.
      200W input == 200W output == (x degrees heat + y Lumens light + z Watts other energy)
      The trick this project needs is to find a light source that outputs a given number of ANSI Lumens (as I believe they're called), but that doesn't give out heat (or any other form of energy, such as sound or motion!)
      • Most of the light output will be converted to heat after it is bounced around and adsorbed. What is really important indetermining how much heat will be produced by the light, is the lights energy requirement.

        You can find many bulbs that are very bright, but don't consume nearly as much juice as an incandesant bulb of the same brightness.
  • by Mononoke (88668) on Sunday August 04, 2002 @08:08PM (#4009683) Homepage Journal
    Please don't take this the wrong way, but: Don't you think the LCD projector manufacturers are using the best light source for the application?

    Having said that...

    The only high color temperature light source you'll find suitable for this type of work will be arc lamps. HMI, MRI, HID, etc. In terms of heat:light output ratios, arc lamps put out the most light per btu of heat of any other point source lamp. Point source is important. Light from a diffuse source (flourescent, multiple LED, etc) is nearly impossible to deliver through optics in an orderly fashion.

    As you've probably found, getting the lamp is easy. Matching it to a suitable power source is difficult.

    Additionally: No matter what lamp you use, your LCD panels and optics will also need some cooling

    Once again, I've been of no help.

    • Here's a CatEye's Stadium 3 light [cateye.com]. It's a mountain bike light, not exactly what you would want to get, but... good for the basics:

      Expensive. This thing is $400. But, it's 1/4 the power (and heat) as halogen

      Big. As the parent stated, the ballast for these things is important.

      Not too good on the color rendition. It's important to remember that you don't just want to look for color temperature, you also need to make sure that the light gives good color rendition; that it has good spikes not only on the blues, but also the reds and greens.

      Good luck...

  • Three suggestions: (Score:3, Interesting)

    by Russ Nelson (33911) <slashdot@russnelson.com> on Sunday August 04, 2002 @10:01PM (#4009961) Homepage
    • White LEDs. Lots of them.
    • The sun. It's really bright and it won't heat up your room any more than leaving a window open would.

      • White LEDs. Lots of them.
        Is there an echo in here?

      • The sun. It's really bright and it won't heat up your room any more than leaving a window open would. *Sigh* ok here goes an explanation, listen up...

      /me starts on a dinner of sausages, chips [fries to yanks], and baked beans.

      OK where was I? Oh yeah, explaining the sheer stup^H^H^H^Himpracticality of trying to use the sun as a light source for a projector.

      First off, you need to gather the light, the best option being a huge mirror: a bit unweildy. It would have to be reflecting the sun directly into the projector, through a screen to diffuse the light so theres no light/dark areas, then through the slide and onto a screen. A fair chunk of light would be lost that way, but it might suffice for a very dark room. the mirror would also have to move to track the sun.

      /me finishes his heart-attack-on-a-plate.

      And you're almost certinly gonna need line of sight to the sun, which could be screwed up by blinds [meaning excess light in the room], being in an internal room, furniture, wrong side of the building, other buildings, clouds, and night time! Oh and you'd need L.O.S. from the mirror to the projector.

      If your post was just the Sun suggestion, it might have been worth a +3 Funny.

      Ali

    • not only is the sun not a reasonable source for the light, but your subject is "Three suggestions:". i only see two. please enlighten us with the third.
  • hmm (Score:2, Informative)

    by itzdandy (183397)
    LED lights are too dim.
    its hard to get enough in a small enough space to do much good, and you would require at least 75-150$ worth to get enough light to use the projector in daylight.

    IF you had enough space, you could group 150-200 white LEDs in a tight slightly curved mount the same arc as a compressing lense , then focues that light onto a diffuser, spread the beam to a freznel the size of your LCD screen and hope for the best.

    this would get expensive as a set of high quality lenses would be in the 100$ price range and 200 LEDs would run about $300, plus time.

    though youre light source would be good for 150,000+ hours, and would just slowly degrade when the LEDs got old and failed.

    and powering 200LED lights would not be too difficult, with the use of a PC power supply you can have 3.3/5/8.3/10/12/15.3/17/20.3/24 volt outputs , enough to drive many arrays of LED lights without any problem.
    • Remember that if you have sufficient cooling, LEDs respond well to upping the supply voltage and current levels. There are also tricks you can use, for example, pulsing the LEDs faster than you can see, but giving them enough time to cool down. You can also find very high intensity white LEDs on the cheap if you shop around the surplus houses.

      Steve
  • Suggestions (Score:3, Interesting)

    by adolf (21054) <flodadolf@gmail.com> on Monday August 05, 2002 @02:25AM (#4010610) Journal
    Light bulbs are generally rated by the power they consume, not by the light they create. An incandescant bulb creates a lot of heat, and a little bit of light, in terms of energy and efficiency. To top it off, unless you've got a window or an open door for that small amount of light to escape through, -all- of it will be turned into heat after some amount of reflection inside the room.

    Which is to say: A 200W light bulb may produce various amounts of light at various levels of quality, but will always produce 200W of heat.

    Your best bet? I'd vote on hitting a DJ supply store (or a guitar shop, or audio rental place - wherever you find musicians, DJs, or both) either online or locally. Note, however, that if all they have is a collection of PAR cans (glorified coffee cans with common flood lights), you're in the wrong place.

    More complicated DJ lights have to deal with the same problems you have: efficiency (heat inside the fixture), color temperature, lifespan, cost, and durability. They need to be close to point-source, so that the gobo patterns they project will be easier to focus. And they need to be extremely bright.

    I, once upon a time, had a Martin Robozap mounted on the wall at home. This fan-cooled light weighs 20-25 pounds, IIRC, and has a servo-driven mirror with two 150W overhead projector bulbs aimed at it. Whenever I fired it up, I had to increase air circulation in the room else it would get terribly warm, fairly quickly. I imagine the same would happen with a 300W floor lamp...

    Locally, the bulbs were fairly expensive, but I was able to find the type online for ~$10 from some specialty lighting shop that primarily just sold light bulbs. They were a halogen bulb, with an integral reflector. IIRC, it's a pretty common type for overhead projectors.

    Speaking of overheads, why not use one? You've appearently got an LCD display - just lay it on top of an overhead projector. Should be cheap, if buying used. Just clean up the optics and re-arrange the innards so that it's concentrating as much light as possible on the LCD display, and things should be peachy.

    I hope it's obvious, but it appearently isn't because at least two posters have mentioned it: don't use white LEDs. You'll -never- achieve even satisfactory focus using an array of LEDs, let alone good focus. Now, if it were possible to make them bright enough that you'd only need one for the project, it'd be a different story...

  • Photographic enlargers sometimes us "cold" lights. They are very carefully colour balanced as well. Check at your local photo supply store.
  • by matt_wilts (249194) <matt_wiltsNO@SPAMhotmail.com> on Monday August 05, 2002 @08:11AM (#4011104)
    If the heat's a problem, how about this? Put the light source (lamp, LED, arc light, whatever) in a box which you can cool and place some distance from the LCD part of the projector - thus keeping noise/heat levels down (water cool it, I dunno?). Then feed the light to the LCD using fibre optics.

    I can't take credit for this - I seem to recall seeing a diagram years back suggesting this for a car, with a central light source feeding all the car lights. Google searches bring up these links:

    http://www.halfbakery.com/idea/Fibre_20optic-lit_2 0office

    http://www.ind-auto.com/news/sept2000.html

    Matt
  • by north.coaster (136450) on Monday August 05, 2002 @08:20AM (#4011123) Homepage

    The mount of light that is output by a light source is measured in lumens, not watts. Other posters have mentioned that all light eventually gets converted into heat, but some light sources are more efficient than others when it comes to how much actual light they produce for a given unit of energy consumed (think watts). You need to identify how much light you need (in lumens), and then find a light source with a low lumens/watts ratio that produces enough light at the right spectrum to satisfy your application.

    /Don

  • HID Lamps (Score:2, Interesting)

    by bootprom (585277)
    I used to use HID (High Intensity Discharge) lamps for growing, uh, tomatoes, in college. I can say that after doing LOTS of research, these lights have the lowest heat/lumens ratio you will find unless you get into some really exotic / expensive stuff.

    Advantages of HID lights are: You can mount the ballast remotely - this help because the ballast generates almost as much heat as the bulb. The bulbs are relatively small, though certainly not as small as a halogen. HID's make lots of light for the amount of power they draw - ie: a 400W HPS (High pressure sodium makes 50,000 lumens, while a 100W incandescent makes about 2,000 lumens - that's 125 watt/Watt for the HPS and 20 lumens / Watt for the incandescent).

    The three popular types of HID lamps are metal halide, high-pressure sodium, and mercury vapor.

    Only drawback here is that the color temp stinks. You will have trouble finding bulbs that do better than 2500k. You might want to look into something called Sun-Argo, which is a HPS / MH hybrid kind of thing. You also might want to look into something called compact fluorescents - these provide a better color temp, but unfortunately, they are florescent, so they are kinda big.

    Good Luck.
  • Take a look at the Source 4 HID [etcconnect.com]. Althought it has less power than you ask, the combination of reflector and optics should more than compensate. You could try a par style fixture [altmanltg.com] for a smaller size and less $$$.

    The theatrical discharge fixtures usually have a lower color temperature (3000-4000k), but you trade that for cheaper, longer lasting lamps and better lamp availability.

    SD

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