Chrome on optics?

I have been playing about with making up and modding torches, using the optics that are mostly solid, with a tiny insert for the LED, and clear plastic. As far as I can see they actually use the inside interface of their back surface to reflect the light. I knopw they are supposed to be 85-90% efficient, but they do seem to spill quite a bit of light out the back, to the point that looking straIght at the back of them, not in a housing, gives quite a bright glow.

Having a couple spare and some "gold" spray paint lying about, I gave it a go, on the grounds that the paint would back onto the really smooth optic back and that would smooth it. It did not work. So a couple of minutges and a reflector or two...shrug....

BUT...would proper chrome paint work? Did my canned paint ruin the mirror finish, or is it just a matte finish whatever? Does even chrome paint not match the 90% perfect finish of the optics and just ruiin the play?

I would like to hear opinions and experiences.

I'm not sure what you're saying.

LED emit mostly forward....essentially a glowing plate. Of the ~ 180º emission direction from that plate, whatever misses the optic is spill, and can go somewhere else, including being bounced back into the flashlight.

I THINK you are saying you are using a plastic optic, and not a reflector bowl?

The optic may be somewhat reflective (No AR coating, etc), so some percentage of the light hitting it, bounces back instead of being sent downrange, etc.

If you have a lens over the optic, that too can reflect a percentage of the light back into the flashlight.

An AR coating, dedoming the LED, etc, may improve the issues you describe, if I understand what you are trying to do.

Changing the surface characteristics of an optic (Clear plastic bullet-shaped thing) will change the way it works. Even a clear oil coating, scratches, and so on reduce the efficiency. If you put the optic + LED on a table, shimmed so it shines horizontally, you can directly compare the OTF and OTB (Out the front and out the back) output. I expect you'll see 10-15% output lost, which is comparable to an aluminized reflector + window.

Don't do it! Put glow powder inside (Not on the optic) and you get a nice afterglow.

Some before and after figures, with a really good chrome spray paint would be nice. I suspect any difference would be detectable by the naked eye though, if any.

you'll see 10-15% output lost, which is comparable to an aluminized reflector + window.

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in my experience there is the same "efficiency" with good optics and good reflectors,
NO difference!
(when both focusing devices "work" at their best)


to that idea of applying whatever - in the beginning we used all kinds of sprays that give extremely shiny surfaces, like: aluminium / chrome / zink spray - does not work.
Seems to "dull" the reflective surface totally.

just try and give Your findings, but please dont do it with a part where a 100 % loss is a real pain

My understanding is that TIR optics work because of the interface between the sides of the optic and environment outside. Change that outside environment, by putting a coating on it, and it may no longer internally reflect properly. The result is you get less light out the front. It may look like a lot of light is being wasted out the back of your TIR optic, but it's still probably less than would be wasted in a conventional aluminum reflector. Spray shiny paint on the back and you might get extra reflection off the paint, but this would probably be more than countered by the loss of internal reflection off the sides of the TIR.

Not exactly what you are describing, but the Wavien collar does something similar ....

OK. Thanks guys. So the solid optis are as efficient as a reflector style anyway, and adding a shiny surface will probably just make things worse. That clears that up and has just saved mew $15 for a can of chrome.

Thank you all...even the ones that totally confused me

You're asking me? I am asking the question!

RobertMM said:

Some before and after figures, with a really good chrome spray paint would be nice. I suspect any difference would be detectable by the naked eye though, if any.

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yellow said:

just try and give Your findings, but please dont do it with a part where a 100 % loss is a real pain

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I have plenty of trial optics. It's the chrome paint I do not want to waste!

Some before and after figures, ... suspect any difference would be detectable by the naked eye though,

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to make it short, it will be like this:

when looking into the optic from the business end, there will no longer be a reflecting surface be seen, but a dull grey color "paint";
(a bit like those "temperature" paints used inside heating furnaces, or on bike exhaust pipes).
95 % (if not more) of the light emitted will be wasted there.

at least that was my personal experience with aluminium and zink spray - which gave really nice shiny mirror surfaces on other applications

OldNick said:

You're asking me? I am asking the question!

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nope, I was asking if anybody who had done an experiment and has measured data to chime in and enlighten us.

So, it seems it's no worth it, and just leave the optic alone as we can't really improve upon its reflective/refractive properties.

I'm not so sure if it is completely a bad idea, trying 'redirect' some of the light bouncing around behind the optic.

For example, if you look here, the optic used has the shiny film/paint on the back. I'm sure the optic was designed with this in mind from the beginning but it is somewhat of a hybrid of optic and reflector.

Would be be interested to see some before and after results.

OldNick said:

I have plenty of trial optics. It's the chrome paint I do not want to waste!

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Unless you can find a way to evenly distribute a fresh coat of the paint on a reflector, don't bother...from personal trial and error in the past, the best result I could attain was a semi rippled surface. It helps to use a lathe spinning at an angle, but the surface always ended up uneven. I've also tried chroming the backs of TIR lenses before with not so desirable results, it would chip off.

That isn't to say however that it can't be done...I'm just unable to do it. Best of luck, looking forward to your findings!

The visible finished surface will be against the optic and will be smooth as the finished surface of the optic I would think...though the application side may look rough unless finely sprayed.