Adding reflector to optic to catch wasted light

Hi all,

Since a reflector is so much more efficient than an optic due to all the wasted light that's cast backwards by the optic, is it possible to have both?

I mean, have an optic, AND a reflector? I figure you could coat the back of the optic with metalic paint, then you'd have a reflector and an optic. Would this work? Or does the optic require the area behind it to be air/optic material, for proper light reflection?

- Tony

Re: Adding reflector to optic to catch wasted ligh

why would you want to use the optic when you have the reflector in place anyway? /ubbthreads/images/graemlins/grin.gif
although some people are talkng about painting the inside of the head behind the optic with reflective paint or such to achieve the desired effect.
bernhard

Re: Adding reflector to optic to catch wasted ligh

The optic relies on total reflection to work, which in turn requires a clean plastic-to-air interface. if you paint the surface, you actually break that interface and will have a much worse result. If you do want to improve the light output, you should coat the front-end of the optic (like the anti-glare coating on camera lenses).

Re: Adding reflector to optic to catch wasted ligh

If you have a reflective cavity surrounding the air gap I believe many otherwise-wasted photons will make it back into the optic and out the front. The optic's "leakage" is due to incomplete total internal reflection. While we have found that anything touching the cone of an optic messes with the beam, I still can't help but wonder that if it was done right, forcing the internal reflection to become total might increase the photonic output. I have a couple of vacuum-metallized optics that I hope to try fairly soon. /ubbthreads/images/graemlins/icon3.gif

Larry

Re: Adding reflector to optic to catch wasted ligh

I don't think you'll get much gain, but I'm curious to hear the results.

BTW the effect within an optic is refraction, not reflection - the result is it bends the light, it does not reflect the light. At best I'd guess perhaps a fraction more spill with a reflector behind it, perhaps unperceivable?

Chris

I've experiemented with focusing optics and reflector combinations for use with LEDs. What I found was that the hot spot is typically not noticeably brighter, but you do get some increased sidespill. If you use a shiny conical reflector, the sidespill will probably be ringy. Nevertheless I'm inclined to think it's useful.

One combination that I found that works well with a 5mm type LED is one of the shiny LED holders with a small acrylic ball lens (maybe 1/4") nestled in the mouth. I hold it in with heat shrink tubing and typically will run a small bead of epoxy mixed with glow powder around the edge of the heat shrink tubing on the end holding the ball. The net result is a broad, perfectly defined and focused circle of light. I'm convinced that the total usable light output with the combination is brighter than would otherwise be the case (and the ring of glow epoxy glows long after the light has been turned off).

Mark

Optics are complex critters! They function through a combination of refraction and internal reflection. Try holding various I.D. size washers in front of one. /ubbthreads/images/graemlins/icon3.gif

Larry