A concept: LED bulbs for front projection systems

Discussion in 'After Hours Lounge (Off Topic)' started by Francois Caron, Oct 26, 2003.

  1. Francois Caron

    Francois Caron Cinematographer

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    As many of you may know by now, white LED lights are beginning to replace traditional incadescent and even halogen light bulbs in everyday products such as flashlights. For the same amount of light or more, LED lights consume less power, generate very little heat, and usually last longer than the lifespan of the entire flashlight. So I was thinking. Can this technology be used as a replacement for LCD and DLP projector bulbs?

    If you've ever changed a projector bulb before, you know it's basically nothing more than a high power light bulb mounted on a removeable cradle with two wires connected between the bulb and the connectors. For something costing hundreds of dollars, you'd expect a bit more for your money.

    Now imagine if in that same amount of space, you could add a two inch square panel mounted with hundreds or even thousands of tiny white LED lights attached to a power regulator designed specifically for the projector being used. You MIGHT end up with a satisfactory replacement bulb.

    I say MIGHT because I have no idea if such a concept is even possible. For now, the only white LED lights I seem to find on the Internet are the types that are already installed inside a clear plastic case. What I would need is practically the tiny LED element inside the casing, mounted on a board along with hundreds if not thousands of other identical tiny LED lights.

    Can a two inch square board packed with thousands of LED lights work as well as a regular projector bulb? Can it give off the same amount of light or more while at the same time give off nowhere near the same amount of heat as a regular bulb? Are there any companies out there that have tried this out yet? What is the smallest size white LED light currently available on the market?
     
  2. Mike Wladyka

    Mike Wladyka Supporting Actor

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    Hey Francois,

    LED's are awesome, and i think they could easily be used for FP's. However, they do generate lots of heat! I saw a demonstration of 6, 1 watt LED's with the casing off, and it was sooooooo bright that no one could even look directly at it, and about after 1 minute the circuit board was burning hot. I would tend to think that thousands of little LED's is not the way to go, but rather a couple big ones. There is 3, 5, and 10 watt LED's out there but they are expensive and can get very hot, and extremely bright. They do use very little power and will last a very, very long time. It is very cool technology that will eventually take over all lighting duty

    Mike
     
  3. Philip Hamm

    Philip Hamm Lead Actor

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    Mike,

    Incandescents and halogens, especially high intensity ones in FPs, also run extremely hot. [​IMG]

    It would be interesting to see numbers on the number of lumens per heat unit (calorie?) for both technologies.
     
  4. Todd Hochard

    Todd Hochard Cinematographer

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    LEDs are MUCH more efficient than comparable wattage incandescants/halogens. By an order of magnitude. And, I mean that from both an energy and heat perspective (with electronics, the two are inextricably linked).

    I think the problem with LED lights, in general, is that they just can't pack enough lumens into a given space. YET. The tech is improving, though.
     
  5. Mike Wladyka

    Mike Wladyka Supporting Actor

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  6. Brett_H

    Brett_H Second Unit

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    Francois,

    The cynic in me believes you may have answered your own question:

     
  7. Mike Wladyka

    Mike Wladyka Supporting Actor

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  8. Kevin P

    Kevin P Screenwriter

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    All the white LEDs I've seen are bluish-white in color, so color temperature would be an issue as well. I'm sure as the technology improves a high-efficiency 6500K white high-power LED (or array of LEDs) could act as a light source in a projector.

    But if you're going to use LEDs, how about just having a screen consisting of an array of miniature red, green, and blue LEDs like they have in scoreboards and the huge screens used in concerts?
     
  9. Mike Wladyka

    Mike Wladyka Supporting Actor

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  10. Mark Schermerhorn

    Mark Schermerhorn Second Unit

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  11. Mike Wladyka

    Mike Wladyka Supporting Actor

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    http://www.trainweb.org/girr/tips/ti..._led_tips.html


     
  12. DaveF

    DaveF Moderator
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    "White" LEDs typically are a blue LED with a phosphor covering. The phosphor absorbs part of the blue light and re-emits yellow light. The yellow plus blue appears white. This is a problem for viewing colored materials, since a lot of red is lacking and the appearance of colors will be different from what people are used to (compared to incandescennt bulbs or daylight). I don't know if this would be an issue for direct-view images (video).

    There are white LEDs in work which use a UV LED to excite multiple phosphors to emit blue and yellow light. There is also research to develop devices which emit a broader color spectrum, for improved color reproduction.

    And yes, LEDs are far more efficient than incandescent bulbs. But cooling is a problem because all the heat is generated at the backplane, rather than being emitted over a spherical area as with a lightbulb. They are also substantially more expansive than incandescent bulbs for now.

    (I know these few things because the October 23 2003 issue of "OE Magazine" had a few articles about LEDs. It's a publication of "SPIE The International Society of Optical Engineering" and is aimed at the general, educated audience, if you're interested.)
     
  13. Francois Caron

    Francois Caron Cinematographer

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    http://www.theledlight.com/led-specs.html#White_LEDs

    They advertise a 6500K white LED, but I have no idea if the information is accurate. At least someone is trying to make them.

    As for cooling the LED board's backplane, a standard heat sink should do the job nicely. Projectors are already designed with an efficient cooling system. As long as the fan blows or sucks fresh air through the heat sink fins, overheating should not be a problem.

    What I'll need are LEDs mounted inside SMT type casings. This way, I can pack them in tightly on the same two inch square board. But the question still remains. Will this design produce enough light for the projector?

    Another idea would be to use a conventional external light source which transmits the light inside the projector casing via a bundle of fiber optics cables. They don't even have to be data grade fiber optics.

    Another possibility. How hard can you push compact fluorescent technology before it explodes?

    I'm still thinking here! [​IMG]
     
  14. Dave Poehlman

    Dave Poehlman Producer

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    I'll have to look but there was a website (I think I found it someplace in the AVS forum) about a guy who had attempted to build a LED based projector.

    The light output wasn't enough to make a decent picture through a LCD panel. And he had used the super bright white LEDs.

    I'll see if I can still find the website.
     
  15. Mike Wladyka

    Mike Wladyka Supporting Actor

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  16. Dave Poehlman

    Dave Poehlman Producer

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    FOUND THE SITE!

    It's a very long thread (181 pages!!!) where this guy (vdi_nenna) assembles a LED array and, last I read, it didn't turn out bright enough.

    Apparently, there's some new information, however, since the thread is still going on. Perhaps I'll sit down and read it tonight.
     
  17. Francois Caron

    Francois Caron Cinematographer

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    Dave, great link! That guy did what he could to make it work, but the final result did come up short. My SMT LED based design MIGHT do a better job, but only if the device can output as much or more light than a standard projector bulb. If his initial design was already very dim on a small screen, producing enough light for a screen that could easily be ten times his screen's surface area will require ten times the number of LEDs. That means 480 LEDs at today's standards. Not good.

    I'm still studying the possibility of using compact fluorescent technology. Already the bulbs can output a lot of light at a very low wattage level. I have a 13 watt bulb in my desk lamp that outputs as much light as a 60 watt bulb. And it produces so little heat that I can actually TOUCH the bulb without burning myself. Inside a projector, that saving in heat will be of great benefit for the electronics. But how hard can you push a CF design?

    One poster mentioned that metal halide bulbs need a 400 to 600 spike to activate the spark in the element's gap. Do projector bulbs work on the same principle? Feeding off the projector's power supply for the bulb might fry the new bulb's electronics if the design is not quite right.
     
  18. Eric Kahn

    Eric Kahn Guest

    incandesent and flourescent bulbs produce the same heat per watt, 3.414 btu's per watt I think, but since flourescent bulbs produce more lumens per watt, they are more effecient and cooler

    I thought most of the newer front projectors used a metal halide bulb, not a halogen bulb, metal halide is an arc light, about 4 times the lumens per watt as a flourescent bulb, but lots of heat due to it being a plasma arc

    metal halide bulbs change color over time and small ones explode randomly when used beyond their usefull life which is why the projectors have time counters on them, the bulb exploding would do major damage to the projector
     
  19. Mark Shannon

    Mark Shannon Screenwriter

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    So I take it doing this with LED's is a difficult thing to do. What about Francois' suggestion a couple posts back. Could you use a bundle of Fibre Optic wires with powerful light coming from a seperate source?
     
  20. Philip_G

    Philip_G Producer

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