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Thread: Any chance to focus a large LED area into a small area?

  1. #1

    Default Any chance to focus a large LED area into a small area?

    Hi,

    I just got a pair of 100 Watt LED bulbs. The area is quite large, so I can't get that narrow throw of light with a reasonable sized reflector.

    So I sat down and thinked for a while untill I got an idea from horn loaded speakers. A horns shape is exponential, and that shape I hope will solve my problem.

    I want to mold a solid acrylic lens that has the shape of an exponential horn. The LED light input is where the output surface normally are on a speaker horn, and the light output is where the speaker driver usually are.

    Attached there is a drawing of the idea. No calculations done, but the illustration shows what I am hoping this special lens will do. IF this work, I would put a reflective sphere or something that can spread the light into a reflector. This way the LED bulb can be efficiently cooled outside the actual reflector housing.

    Anyone here been thinking on the same thing? Or even experimented with it?



    Br.

    Vidar

  2. #2

    Default Re: Any chance to focus a large LED area into a small area?

    Interesting idea.

    I expect a considerable amount of light would be wasted though. From looking at your picture, much of the light coming from the left side of the emitter towards the right side of the lens would hit the lens face nearly head-on. Internal reflection wouldn't occur ... instead of entering at the correct angle for internal reflection, the light would transmit out of the side of the lens and be lost. The same would happen in reverse for the other side of the emitter. TIR reflectors work because the light hits the inside edge of the reflector at an angle sharp enough that almost all of the light reflects. If the angle isn't sharp enough the light is transmitted instead.

    I expect the idea might still work, but 50% of the output might be lost out the sides of the lens and fail to make it out the front. And if that's going to happen, why bother with a larger emitter and fancy lens. Might as well just go with a smaller, more efficient emitter.

    Perhaps this idea might work better as an aluminum reflector instead of a TIR lens? However, that would probably cause other problems because an aluminum reflector isn't as efficient and each time the light reflected off it, some would be lost.

    I'm not a technical person though, so perhaps someone with a more technical background could offer some insight.
    Last edited by Fireclaw18; 04-01-2014 at 10:13 AM.

  3. #3

    Default Re: Any chance to focus a large LED area into a small area?

    100w led has huge area, it will not be easy to focus it tight, you'll need lenses, and most likely more than 1. pbly frensel would be best bet cuz size of the lens needed would make it huge as well. and regular one would weigh alot, if you can even find one that big.

    read this thread, http://www.candlepowerforums.com/vb/...made-spotlight

  4. #4

    Default Re: Any chance to focus a large LED area into a small area?

    Thanks for your thoughts. Maybe the input of the lens should be angled differently - just enough to prevent light to transmit right throug the sides. The LED is placed at a given distance from the input surface, so the LED is not supposed to be visible when looking at the lens from the sides.
    I must think more, and figure out what I must do with the design - if it ever is possible to accomplish what I want :-)

    Br.

    Vidar

  5. #5

    Default Re: Any chance to focus a large LED area into a small area?

    If you used an aluminum reflector instead of a TIR, much of the light that hits the reflector head-on would be reflected back onto the face of the emitter. It might have the same effect as a Wavien Collar, further stimulating the phosphor and increasing luminance.

  6. #6

    Default Re: Any chance to focus a large LED area into a small area?

    Quote Originally Posted by Fireclaw18 View Post
    If you used an aluminum reflector instead of a TIR, much of the light that hits the reflector head-on would be reflected back onto the face of the emitter. It might have the same effect as a Wavien Collar, further stimulating the phosphor and increasing luminance.
    That might be an idea to test. However, the white light does not stimulate the phosphor that much. White LEDs are blue LEDs covered with phosphor, so if blue light could be focused on the phosphor, it would probably lit up more. Lasers are doing this in some of the hottest Mercedes and BMWs, but the "phosphor" is a transparent flourecent liquid that is fixed at the focal point inside the reflector. The blue lasers are pointed directly towards this liquid via mirrors. To prevent over heating the liquid is circulating (I think).

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