How to reduce spill?

[gcbryan]

What are the ways to reduce spill in a led light? Spill is caused by the portion of the light from the emitter that is thrown straight out and not captured by the reflector I believe.

I have one light where the led is reverse mounted on the lens and pointed back into the reflector. This has no spill so this is one way.

I put a piece of white printer paper over my light and you can see a dark circle in the middle with the bright light around the perimeter. This bright light gets focused by the reflector and becomes the center beam and the dark spot becomes the spill.

I thought maybe a circular "sticker" in the middle of my lens would eliminate spill. It does eliminate the middle part of the spill but you can't eliminate the edge spill that way.

I don't know a lot about aspherics but they focus the led pattern and aren't what I'm looking for (I don't think). I think they're for increased throw which is OK. I can't find enough specific detail on what's going on with aspherics to know if they're the answer.

Is there anything I'm missing in my quest to eliminate some of the spill?

 

[allburger]

Try a collimator optic lens

 

[DimeRazorback]

Aspherical lens

 

[Packhorse]

I don't know a lot about aspherics but they focus the led pattern and aren't what I'm looking for (I don't think). ......

They can indeed focus the LED die but you can also defocus it and get a wide very even beam.

 

[LukeA]

An aspheric closer to the LED than its focal length will produce a spill-free even circle of light, the angle at which the light diverges naturally depending on the distance from the lens to the LED. And the optical efficiency is probably better with such a setup than trying to block the spill with something opaque.

Total internal reflection optics as suggested above are probably an even better option for your application. They, the relatively narrow angle optics suitable for flashlights, tend to concentrate light into an excellent beam with little spill compared to a reflector of equal size, and they do it with efficiency unmatched by reflectors costing a few orders of magnitude more.

 

[Sub_Umbra]

What are the ways to reduce spill in a led light? Spill is caused by the portion of the light from the emitter that is thrown straight out and not captured by the reflector I believe.

I have one light where the led is reverse mounted on the lens and pointed back into the reflector. This has no spill so this is one way...

Aside fron the aspherics there are two more options that I find interesting. The first would just be a deeper reflector like the Heliotek light. I used to have a pic of a cutaway Heliotek reflector and it was something else.

You mentioned a light in which the LED points backwards -- Pelican calls it a recoil light. It is a brilliant idea but the way Pelican does it borders on idiotic. Their Recoil light is very much like a conventional satellite dish setup -- the LED sits directly in front of a parabolic reflector and shines into it. This setup is great in theory but it suffers from a major drawback. In a fashion similar to a conventional sat dish Pelican's LED is blocking part of the parabolic reflector i.e. the LED's placement reduces some of the reflector's output. That's why it's saddled with a Lamberton LED. Actually, the repercussions of this design are even much worse than they appear at first glance because any high powered LED must have a heat sink. So sitting right in the middle of the parabolic reflector Pelican has not only put an LED but whatever thermal management scheme they have must also block perfectly good light from the reflector trying desparately to get past all of that junk so it may light something up. The 'Recoil' light gets a 97 on inspiration but only a 13 on implementation. The design has been dead in the water since it's inception. It can't go anywhere. After all of these years it's never been upgraded from a 1 watt light. They can't -- the heat sink would block most of the output. There is a way though...

Build a recoil light based on newer, more efficient satellite dish design. The LED doesn't have to be directly in front of the parabolic reflector. It will work much more efficiently if it is placed slightly below the reflector -- like a DIRECT TV dish. For decades this design has been known as an undershot antenna.

It's easy to see that with an undershot design it would be possible to step up to not only a more powerful LED with a bigger heat sink but also any LED used could be driven much harder and more of the light sould still be able to escape into the real world to do some work. The recoil light could finally escape the Lambertion LED.

An undershot recoil flashlight might look something like these drawings I did years ago:

Undershot parabolic reflectors might be out of the realm of doability for the modder but they are old hat for engineers who have worked with these same shapes for decades. I wish someone would mass produce them. The recoil light is screaming to be brought into the 21st century. An overdriven 5 watt undershot recoil would positively blow away Pelican's whimpy 1 watt light for foggy, smokey, dusty rescue missions and I'd buy one myself for my own bright, tight uses.

 

[Linger]

So gcbyran, until you re-invent the reflector for us (+1 to Sub Umbra for contributing theory and graphics)

Try a surefire TIR, a frean polymer collaminator lens, any 3-6 degree spot lens.

If you really want to reduce spill of even a lens, extend a black faced tube outward beyond the optic.
But an optic is a good start ($1.5 to $5 depending)

 

[gcbryan]

Thanks for all the responses, ideas, solutions everyone!

Sub Umbra, isn't UK doing the same recoil design with a much more powerful led including a heatsink coming through the middle of the lens? It's advertised as 900 lumens.

I'm not interested in buying that particular light but am interested in your comments regarding the design. I haven't examined it too carefully so perhaps it's undershot as you describe?

 

[Sub_Umbra]

...If you really want to reduce spill of even a lens, extend a black faced tube outward beyond the optic.
But an optic is a good start ($1.5 to $5 depending)

I've played around with black tubes and the results were kind of surprising. Even a very flat black interior wasn't enough in my experiments.The beam bounced back and forth inside the tube and still fanned out after it exited. The spill was attenuated but a surprising amount of it was still there. A grooved black interior would help a bit maybe. Something saw-toothy going around the tube at 90 degrees to the beam. I really dunno -- I couldn't figure out how to build it.

My best result from a black tube was pretty weird and I've done it to four various models of EL Blasters. Make a black tube with a covered end. Then either drill or die cut a hole on the end that is, of course, smaller than the tube. You need two tricks to really make this method work. First, the end with the hole smaller than the tube should be fairly thin -- a better aperture will be possible with a thinner material. Secondly, The hole must be made very carefully with no burrs or rough spots. Die cutting makes a very clean hole in some materials. The light still bounces around the flat black inside of the tube but anything but the hot part of the beam will have a much harder time finding it's way out.

It is a kludge of a solution as it merely chops off the spill instead of a more elegant solution that would fold the spill back into the beam and make use of it but it is an improvement.

IMO an aspheric lens is probably the simplest answer but I think that a powerful Undershot Recoil would perhaps produce a more uniform, useful beam. (For me anyway)

 

[ifpo238]

what if you mirrored the inside of the ring around the aperture? wouldn't that redirect some of that light back to the parabolic?

 

[ma_sha1]

What are the ways to reduce spill in a led light? Spill is caused by the portion of the light from the emitter that is thrown straight out and not captured by the reflector I believe.

I have one light where the led is reverse mounted on the lens and pointed back into the reflector. This has no spill so this is one way.

I put a piece of white printer paper over my light and you can see a dark circle in the middle with the bright light around the perimeter. This bright light gets focused by the reflector and becomes the center beam and the dark spot becomes the spill.

I thought maybe a circular "sticker" in the middle of my lens would eliminate spill. It does eliminate the middle part of the spill but you can't eliminate the edge spill that way.

I don't know a lot about aspherics but they focus the led pattern and aren't what I'm looking for (I don't think). I think they're for increased throw which is OK. I can't find enough specific detail on what's going on with aspherics to know if they're the answer.

Is there anything I'm missing in my quest to eliminate some of the spill?

I have similar needs & this is one solution that I end up with:
By mounting a small aspherical to the center of flat lens, it takes the spill & convert to additional throw, yet still maintain the round hotspot.

http://www.candlepowerforums.com/vb/showthread.php?t=250379

 

[Sub_Umbra]

what if you mirrored the inside of the ring around the aperture? wouldn't that redirect some of that light back to the parabolic?

None of the Blasters had reflectors -- they all had optics.

 

[Linger]

Sub, you're correct, tube wasn't the right word. The rear and front faces have a whole bored out for the hotspot to pass through.

re:gathering light back - too many angles involved. Once the light disperses you can't capture it back. Once you understand the beauty of a rear-facing emitter, you'll understand why there are no ' can't we add one more reflector' solutions.

 

[Sub_Umbra]

...Sub Umbra, isn't UK doing the same recoil design with a much more powerful led including a heatsink coming through the middle of the lens? It's advertised as 900 lumens.

I'm not interested in buying that particular light but am interested in your comments regarding the design. I haven't examined it too carefully so perhaps it's undershot as you describe?

I'm sorry I somehow missed your post until now -- have you got a link on that light?

 

[gcbryan]

http://www.uwkinetics.com/product/121

I'm sorry I somehow missed your post until now -- have you got a link on that light?

 

[Sub_Umbra]

Thanks for the link. I had not heard of that light. It IS a more powerful centershot design but I'm sure it would fry in very short order if it was exposed to the air while on. Quite a few specialized work lights for diving must be immersed to function. Back in the 80s I saw one blow in less than a second and a half when it was accidentally exposed to air while on.

I think it's interesting that they have pushed Pelican's original idea as far as they have.

I'd still like to see a powerful undershot recoil light. It would work in the air. IMO if one was built with a UI similar to the Photon Freedom it would replace the Pelican Recoil currently in wide use by Fire and S & R teams. :sigh:

 

[gcbryan]

This one works above water as well, it just does so at half the power. It's temperature regulated I believe.

Hopefully things have improved since the 80's.:thinking:

Thanks for the link. I had not heard of that light. It IS a more powerful centershot design but I'm sure it would fry in very short order if it was exposed to the air while on. Quite a few specialized work lights for diving must be immersed to function. Back in the 80s I saw one blow in less than a second and a half when it was accidentally exposed to air while on.

I think it's interesting that they have pushed Pelican's original idea as far as they have.

I'd still like to see a powerful undershot recoil light. It would work in the air. IMO if one was built with a UI similar to the Photon Freedom it would replace the Pelican Recoil currently in wide use by Fire and S & R teams. :sigh: