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Lets RIDE!
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Discussion Starter · #1 ·
I want to use some of the DX cree 8° optics without the optic holder. I was going to run a fat bead of silicone around the inside edge of the housing and just squash the optic down into it until it seats on the LED. Is that OK? Will the silicone on the back side of the optic's "cone" affect it's performance at all?

JZ
 

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Very big no to that one, even a finger print on on the back side of the optic has a bad effect.
That's why the optic holders don't make contact with the back of the optic as it would mess with the TIR of the optic.
 

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aka RossC
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The optics work off
. The refractive index for silicone will differ to that of air which is what the lens is designed to work with.

You would be better off to sand the optic holder down until it is paper thin and then seat the whole thing in silicon. You would be amazed how much material you can take off an optic holder and still have it work.
 

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Discussion Starter · #6 ·
I had a feeling it might be a problem...messing up the refractive boundry.

Modifying the holder was my original plan Salty, but the holder is too big for what I'm doing....squeezing the optic into a .75" square Al tube with a .625" i.d. (16mm). It might be possible to grind it down to a 16mm square, but all that would be left holding the optic would be a couple mm at each corner. I'll have to give that some more thought; maybe there's another way.

Without the holder, the cone of the optic fits just about perfectly in the 16mm square opening, with the flange at the front resting on top of the tube. Maybe a little epoxy to secure the flange to the end of the tube, and then seal the corners with a bit of silicone (but not letting it ooze in and get to the optic.

JZ
 

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Discussion Starter · #8 ·
I did a little experiment tonight to see what the effect of silicone on the back of the optic would be. Didn't want to foul it up with silicone, so I used aloe vera gel (a water-based herbal sunburn treatment) as a substitute. First try I put a heavy band of it on just the top 25% of the back of the optic...simulating my idea of setting it in a bead of silicone. I shined it (and an identical led/optic combo without the gel as a control) on the ceiling about 5' above the bench) It had virtually no effect on the beam that I could see. Then I tried completely covering the back of the optic with a thick layer. This time there was some dimming and unevenness of the beam, but not nearly as dramatic as I was expecting. And my optic smells great now!

So I'm thinking it would probably be OK to use a small bead of silicone to secure optics, just near the outer edge of the optic.

But Salty got me thinking again about modifying the holder. My original thought had been to grind the holder to a 16mm square so it slipped entirely inside the tubing. But I found I could just notch the cone-shaped part of the holder slightly on 4 sides, allowing it to drop into the tubing, with the front cylindrical part of the holder sitting flat on the end of the tubing. (a photo would explain this better, but my camera is broken) These holders are made of very soft plastic, so it took just a few quick cuts with a razor blade. Thanks Salty! Not as compact looking as with the optic alone, but maybe better alignment and beam. I might just try it both ways....I've got a bunch of cheap DX parts to play with. I just have to work out my switch choice and I can start building.

JZ
 

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Had a look at this today.
Two identical Q5s in series.
Using the nice tight Cree optics from DX. Have heaps of these as I got 10 for 10$
Silicone fishtank caulking which is my glue of choice for front windows on lights.

Left has the left side of the back covered in the glue.



See a lot of light is scattered out of the silicon, going places you don't want it going.


A couple of shots down the front.
Note looking into them with any decent drive current its hard to see this, this is with very low drive currents.




This is the best shot and gives the best indication of whats going on. Paper towel held a little way above the optics.
Unfortunately I only had my point and shoot so couldn't do individual beamshots but this is just like what I was seeing on the ceiling when looking at individual beams and high drive currents.
Yes, about half as bright which shows the silicon completely stuffs the optic.
 

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Spanish biker
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znomit said:
Had a look at this today.
Two identical Q5s in series.
Using the nice tight Cree optics from DX. Have heaps of these as I got 10 for 10$
Silicone fishtank caulking which is my glue of choice for front windows on lights.
Link, please :rolleyes:

Greetings - Saludos

msxtr
 

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Thanks for the info znomit.
Actually I was planning to use black RTV silicone to seal around the front of a Rocket optic, on the basis that black silicone wouldn't refract the light at all. Any thought on that?
 

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hootsmon said:
Thanks for the info znomit.
Actually I was planning to use black RTV silicone to seal around the front of a Rocket optic, on the basis that black silicone wouldn't refract the light at all. Any thought on that?
Just a guess...
I think the light would still go into the black silicon but get absorbed there, the colour won't change the refractive index hugely if at all. So it would be even worse.
 

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Discussion Starter · #17 ·
Regarding the black RTV silicone....Some of the "DIY Dinotte" builds have used a narrow ring of it at the edge of the front side of the optic, to hold it in place. I don't think this will be a problem, as long as it's kept very close to the edge.

JZ
 

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Nice work! Thanks for the visual lesson ...good info!

Black silicone is black because it reflect NO light ...as you may imagine, not what you want. I used it once for gluing a base, and was annoyed because the black could be seen in the lens w/o the light on. Looked strange ...clear is much better looking, and at least transmits some light. My 2 cents.
 
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