Another idea to extract more light out of the TIR optics equipped lights

Perhaps we're all already know that even the best TIR optics always leaked (the light rays pass through to the side rather than collimated to the desired direction). And also the air gap between the LED primary optic (dome) also reduce the light by 8% (according to Avago's research). That's why some people put AR coating inside the TIR cup in front of the LED dome.
Source (find: AB I003 light guide techniques LED)
http://www.avagotech.com/cs/Satellite?blobcol=urldata&blobheader=application%2Fpdf&blobheadername1=Content-Disposition&blobheadername2=Content-Type&blobheadername3=MDT-Type&blobheadervalue1=attachment%3Bfilename%3DAB-I003-light-guide-techniques-LED.pdf&blobheadervalue2=application%2Fx-download&blobheadervalue3=abinary%253B%2Bcharset%253DUTF-8&blobkey=id&blobnocache=true&blobtable=MungoBlobs&blobwhere=1430858313879&ssbinary=true

I'm not an optic expert but I came up with several ideas that would yield better OTF lumens for our TIR equipped lights:
- Paint the LED holder or the internal surface surrounded the TIR optics with relfective white coating/paint. I think Ledil also doing this approach in their recent products, they make less black optics holder to improve optics efficiency. This way, at least, all the light spilled would comeback to the front (be it collimated or not).
- Get rid of the air gap by using optical grade silicone/epoxy to make the LED chip embedded to the TIR optics. I don't know could it be the answer of the problem with dedomed LED? Since the silicone primary optics are there to improve the light extraction, thus the dedomed LED with no/minimal silicone material always have reduced output. By "glueing" the LED to the TIR optics we could get the normal/improved light extraction.

Painting the optics surroundings (NOT the exterior of the optics, air gap must exist to achieve the TIR effect) with reflective coating/paint (I prefer white than shiny mirror finish to minimize the artifacts) is very easy. And we can also use super clear silicone to fill the air gap (it usually very small air gap, a drop is more than enough) after all the assembly is done. just put a drop of silicone in the optics where the LED would fit in, and then slowly press the optics down.

What do you guys think?

First you should ask yourself, with all the optics experts working on this, would they not have already thought of putting silicone or some other material in the gap between the LED and the optic?

SemiMan said:

First you should ask yourself, with all the optics experts working on this, would they not have already thought of putting silicone or some other material in the gap between the LED and the optic?

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Yes, I did ask myself. And I have answer for that: practicality! It's not practical to glue/clean the glue every time you need to assemble/disassemble. And it's too risky to ask customer for the glue-ing procedure. It's either successful or failure. AR coating the inside is also adds too much to the final price (let alone the impracticality during the manufacture). But I do remember clearly that one guy in this forum coated his home made TIR optic. I forget his name but he could make a big TIR optics.
FYI, later I knew that it's not my only idea but the tech guys at Avago also knew it too, they wrote it in the tech paper they published (I included the link in my #1 post). So, I'm not the only one who thought about it, and they have degrees and apparatus to prove that too! LOL

clemence said:

Yes, I did ask myself. And I have answer for that: practicality! It's not practical to glue/clean the glue every time you need to assemble/disassemble. And it's too risky to ask customer for the glue-ing procedure.

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If you are making 10's of thousands of units / day, and this cut your LED costs down by 6-8% (potential Fresnel losses), then gluing would not be risky and clean rooms for optical assembly are not unusual. You don't need that clean. As well, no one disassembles anything made in volume.

The paper you referenced was for a light guide, and even to that end, where they referenced the "100%" efficiency, this was not really true for the example they gave. In the example they gave, they said if you used epoxy to glue the LED into the light guide, then fresnel losses would disappear and you would essentially couple 100% of the light. While that is true, what they forgot to tell you (for their example) is that while 100% of the light would not couple into the fiber, a good portion of that light would be at wide angles ... and as opposed to bouncing off the edges (TIR), it would simply pass through and quickly exit the light guide.

Depending on the optic design and I am sure the serious optical experts will say for most TIR designs, the air-gap is a critical part of the design. Call it the first element in the optical system. It starts the refracting of light such that the rest of the optic can do its thing. Keep in mind that adding glue does not eliminate the Fresnel losses, unless the glue and the optic have the same index of refraction. You can get silicone that is close to polycarb and PMMA.

If you do couple without losses into a TIR lens ... then you have pretty much ended up with a reflector ... which is much cheaper

Semiman

SemiMan said:

If you are making 10's of thousands of units / day, and this cut your LED costs down by 6-8% (potential Fresnel losses), then gluing would not be risky and clean rooms for optical assembly are not unusual. You don't need that clean. As well, no one disassembles anything made in volume.

The paper you referenced was for a light guide, and even to that end, where they referenced the "100%" efficiency, this was not really true for the example they gave. In the example they gave, they said if you used epoxy to glue the LED into the light guide, then fresnel losses would disappear and you would essentially couple 100% of the light. While that is true, what they forgot to tell you (for their example) is that while 100% of the light would not couple into the fiber, a good portion of that light would be at wide angles ... and as opposed to bouncing off the edges (TIR), it would simply pass through and quickly exit the light guide.

Depending on the optic design and I am sure the serious optical experts will say for most TIR designs, the air-gap is a critical part of the design. Call it the first element in the optical system. It starts the refracting of light such that the rest of the optic can do its thing. Keep in mind that adding glue does not eliminate the Fresnel losses, unless the glue and the optic have the same index of refraction. You can get silicone that is close to polycarb and PMMA.

If you do couple without losses into a TIR lens ... then you have pretty much ended up with a reflector ... which is much cheaper

Semiman

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I am at the low end of tech savvy here but from a shooters perspective I have found that optics with lit reticles are much to bright on their higher settings..
They interfere with overall vision and obscure the target.

Think driving in your car at night with the dome light turned on and dialed all the way up.

So I would say is it even necessary to increase the brightness if it adds to cost of manufacture?

TOWFLYER said:

I am at the low end of tech savvy here but from a shooters perspective I have found that optics with lit reticles are much to bright on their higher settings..
They interfere with overall vision and obscure the target.

Think driving in your car at night with the dome light turned on and dialed all the way up.

So I would say is it even necessary to increase the brightness if it adds to cost of manufacture?

Click to expand...

I don't know about reticles at all, never use it before. But I was talking about increasing the OTF lumens out of anything with TIR optics (Fiber, collimator, light guide, panels, etc...). Is the modern reticles use it?
About the air gap in TIR, maybe that's why it's better to use AR coating rather than fill in the gap with any filler. Well, I'm not the expert, I'm just a practical hobbyist =).

clemence said:

I don't know about reticles at all, never use it before. But I was talking about increasing the OTF lumens out of anything with TIR optics (Fiber, collimator, light guide, panels, etc...). Is the modern reticles use it?
About the air gap in TIR, maybe that's why it's better to use AR coating rather than fill in the gap with any filler. Well, I'm not the expert, I'm just a practical hobbyist =).

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Apologies........... you said optics and my head went straight to rifle scopes.