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Thread: Coating TIR Collimator

  1. #1

    Question Coating TIR Collimator

    Hi guys, I'm new to this area and with limited stuff to play with.
    I've seen some good reflector - lens combo out there, they seem great in term of efficiency because there is no light side spills, unlike transparent TIR optics. My question: What would happen if we reflective coat the entire side of a TIR optic to make use of those spills? Has anyone in this forum tried this before? It's better to throw the spill toward (whatever the projected beam would be) rather than waste it useless in a flashlight casing.

    Many thanks

  2. #2
    Flashaholic* AnAppleSnail's Avatar
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    Default Re: Coating TIR Collimator

    TIR spill doesn't come from light shining through the plastic. At the angles involved, the acrylic is 100% reflective. A similar effect is gained by wearing goggles just below the surface of a swimming pool - the water reflects the pool instead of the (much brighter) sky. Also, TIR optics tend to be encased in opaque tubes, so all light exiting comes out the front. Spill actually comes from the amount of light that goes through the TIR in a non-ideal way. This comes from having optics of a finite size, and a light source that is larger than a point.

    Generally, adding any coatings to a TIR will change its optical properties so that it doesn't work well. To get a light with no spill requires a pure aspheric, which can't capture much of an LED's output (Barring expensive optics)
    My biggest light-hog is my camera.

  3. #3

    Default Re: Coating TIR Collimator

    I understand about TIR phenomena. But some rays never 100% reflected (their incoming angle are too sharp), that's why we see "side spill" thru the TIR optics. Some cases are not truly opaque, sometimes glowing brightly. As long as the coating add up light to the existing "correct" beam pattern, then it's better than lost.

  4. #4
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    Default Re: Coating TIR Collimator

    As AAS said, the overall effect won't be good. While you'll get some of the rays going out the front, coating it will mean you don't have that same change in the refractive index from plastic to air. That will completely stuff up the TIR pattern. For a similar situation where someone tried coating the outside of a TIR, see here:

    http://www.candlepowerforums.com/vb/...int-and-powder

    Posts 24 and 32 for his results. While he was using glow powder and epoxy, it's the same situation, you're changing from the refractive index of air to something else.

    Now, putting a reflective coating around something surrounding the TIR but not in contact with it might squeeze a bit more light out the front. Getting any kind of cohesive beam out of it will be a challenge though.
    Last edited by Th232; 03-03-2012 at 04:39 PM.
    Finning does help dissipate heat. This is why the fins are removed before cooking fish. Otherwise it will throw off the heat and not reach the proper cooking temperature. --Duglite

  5. #5

    Default Re: Coating TIR Collimator

    lol, i,m pretty sure if it was effective manufacturers would do it long time ago.

  6. #6

    Default Re: Coating TIR Collimator

    Quote Originally Posted by Th232 View Post
    As AAS said, the overall effect won't be good. While you'll get some of the rays going out the front, coating it will mean you don't have that same change in the refractive index from plastic to air. That will completely stuff up the TIR pattern. For a similar situation where someone tried coating the outside of a TIR, see here:

    http://www.candlepowerforums.com/vb/...int-and-powder

    Posts 24 and 32 for his results. While he was using glow powder and epoxy, it's the same situation, you're changing from the refractive index of air to something else.

    Now, putting a reflective coating around something surrounding the TIR but not in contact with it might squeeze a bit more light out the front. Getting any kind of cohesive beam out of it will be a challenge though.
    Hey Ho! This is what I really looked for, a living experiment proof! Thank you Th232! So it's better to preserve the air gap. Now I'm thinking about painting opaque inside the whole casing with anything as reflective as possible. It's better than a glowing flashlight case anyway

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