Painted collar

Thanks. I have backupped all my flickr images at home too, but for them to re-appear I would have to fix all the hyperlinks in all my old threads which will not happen. But I may fix some of them, perhaps the ones that are linked to in my “djozz tests” thread.

But for the time being flickr did not remove the 2700 images of mine that are at threat, although they warned that from Feb6 on that could happen.

Argo, please excuse this slightly off Topic post, but your title caught my attention and I figured perhaps it was something related enough to be of some interest.

I experimented with this principle of corralling off-angle/side-angle light to a different situation - green tint-shift.

I observed that a fair amount of tint-shift results from stray light from the sides of prone emitters. In my experiments, I placed “Magenta Collars” around the perimeter of emitters in an effort to filter out green, with some success.

Some of my earlier experiments that were successful, ultimately failed but did put me on my current track.

Here is an example of what I earlier called a “Magenta Collar” attached around the cavity of a LED spacer -

It would be placed inside a light such as this -

Notice the tint affecting primarily the side off-angle which appears at center of the reflector -

And here are the results of original beam (on left) and beam after a Magenta Collar (on right)-

The same light, with the same emitter, taken at the same exposure and white balance, with the only difference being the Magenta Collar! The green is reduced without dramatically tinting the rest of the beam as a lens tint filter might.

I mentioned that my experiment with the Magenta Collar failed, that was primarily because the plastic melted from the high heat of the LED. I suppose a collar made of higher heat capable material could be done but I’ll leave that for others to pursue.

It was my latest approarch, similar to your post (and as it turns out djozz’s) of a directly painted/tinted collar where I’ve settled for now. Here for example is an XP-G3 (notorious for green tint-shift) where I magenta tinted directly on the base/bottom perimeter edge of the led itself. It was equally as effective in reducing green tint-shift in the beam. This approach was also less construction dependent. (Sorry no before/after photos for comparison as removing the tint from the emitter dome is more involved than simply removing a physical Magenta Collar from a spacer.)

This magenta collar approach could be something for fellow tint-snob to consider to help with (but unfortunately not entirely eliminating) green tint-shift. It has the added benfit of less light loss than lens filters.

In any event, I’m putting this out there for consideration. Perhaps someone can make Magenta Collars available commercially.

(3D printer anyone? Or BanL/BG interested?)

pc_light, I’m amazed by how far off the topic you managed to stray….and at the same not. :beer:

:blush: Yeah, I realize the only thing they have in common is “side emissions” and “collar” but you can imagine how your title caught my eye.

This was something I debated about writing up/sharing because it seems so silly but you know us tint-snobs, we’ll go to great lenths and spend a lot of green just to avoid the green.

Yes, I was just thinking out aloud. But there are optical adhesives that may also work as well as better match the refractive index of glass.

As to paint versus ZozzV6’s “slice and dice” method… I think that when you do the “dice” cut, the sides have a TIR effect as well, redirecting light either to the top surface, or back into the emitter itself. Maybe even putting a reflective coating on those vertical surfaces would enhance the effect.

I also thought of doing a ZozzV6 “slice and dice” and building up the outer perimeter with some kind of cement/epoxy mixture to make a giant version of a White Flat. Maybe not so useful, but it would protect and insulate the bond wires.

Yes, if you’re chasing the last percent, painted sides should work.
Actually it could allow you to avoid dicing at all. Just paint sides and you’ll eliminate side emissions. Maybe not the whole tint shift (because side phosphor may generate photons that go a bit upwards).

Collar tint (and CRI) issues aside, couldn't we also attain increased intensity/output by hitting the die off-angle with one or more blue lasers focused onto it? Without collar, of course. Plenty of available blue laser emitters with the same frequency as the emitter's blue die, there would be no tint shift and no CRI crapping (I hope).

Cheers ^:)

I forgot to say that before:
A very nice idea! Would really like to see it implemented with XHP70.2.
I wonder if painting the lower part of reflector would work?

I don’t expect any of this will be very successful. I expect The larger the difference in collar and die size the greater the return of side emissions directly back onto the phospohors.

A spherical reflector tries to reflect photons back onto the phospohors for recycling. The smaller the reflector the greater the change in incident angle across the die. Same reason a big lense is better then a small one. The smaller the dome the more likely the light hits off angle and ends up either getting lost due to being absorbed in the dome material, heading out the opening at an odd angle, or not hitting the phosphors at all.

It should but I was reluctant to mess with reflector in any way (I know better), the emitter on the other hand will withstand more handling.

Plus when I first did this, I figured if it was a disaster, I could simply de-dome. With a reflector I’d have no way of removing the tint without handling which would leave marks.

I posted a questing about the same thing. I too am very interested to see if the leds themselves can be laser pumped.

That said, if it was only the blue light from the led being bounced back and reexciting the phospohors then we wouldn’t see a doubling of intensity with a RLT collar, there just isn’t as much blue phospohors in the already converted white light.

I’m starting to believe the best way to think of the led surface as a mirror. If you can return all the stray light you get a much higher chance of it reflecting in the right direction. A laser just tries to get more light from the led, that doesn’t happen. If you can return the lost light it can have a chance of going the right direction the next time, it may take hundreds of tries, but it will eventually. Laser pumping still loses the stray light and doesn’t make the led make “more” light. You may get “reflections” of your laser, so you added that power, but it too goes random directions.
I expect the phosphors are like inductors, they can become saturated and not release more light, but maybe they can “reflect” the light coming back on them.

Once concern I have is how reflective is the paint going to be that you put on the dome. What color paint would you use? White? Silver? Mirror spray paint?

If you use white, the paint will reflect light in all directions… not just back to the source. If you try silver mirror spray paint… that stuff produces a mirror surface on glass, but isn’t designed for spraying on silicone. Not sure what result you’ll get.

And in any event, I doubt these paints are designed for high heat. Is your paint going to cook and catch on fire? Someone should try it and find out.

Engine block paint would work fine, heat wise. They may even have a metallic paint.

I don’t think a metallic paint would be any better than just using white paint. In both cases the light will scatter everywhere and a darker metallic color will probably absorb more than white.

What you really want is a mirror finish on the inside surface where the paint sits on the dome so that light coming out of the dome is reflected directly back to the emitter and nowhere else.

There is some special spray paint available that creates a mirror-like reflective surface when sprayed onto glass. Not so sure it would on Silicone and I doubt it could take the heat.

What about silver foil?

Howbow that new Nichia with the glass dome?

Well, there probably wouldn’t even be a need to paint, since even without the paint there is light reflecting off the surface of the dome from the TIR effect. But even if we could apply a reflective coating, I’m not sure how much reflected light would get back on the die. First, because the LES is not a small point in relation to the dome, the light may or may not reflect back to where it can leave the dome. Second, the perimeter of the LES is transcribed on a circle (the base of the dome) which accounts for at least a 57% larger surface area than the LES. So if the coating and silicone were 100% efficient and the light is randomly scattered, it would have a 64% chance of hitting the LES. On some emitters that area is coated with phosphor, but that area would be under paint. So selection of LED would be important - maybe a Nichia with its hexagonal LES may be a good candidate. Third, since the LES is at least as large if not larger than the unpainted aperture, the light may or may not leave that aperture with a defined angle the way it does with an RLT. But I could be wrong, and this would be fairly easy and inexpensive to test.

Djozz has seen 20% improvement with a silver mirror which he claims to be better than mirror paint which in turn would be much better than white paint. I trust that djozz is right so I think that his result is an upper bound for what can be gained. Or close to an upper bound.

That’s not exactly apples-to-apples because he didn’t dedome. I’m not sure if the expected improvement would be higher with or without dedoming.

Yes, I share the concern that a mirror paint wouldn’t work for some reason. But performane of white one would be way worse. F.e. with SST-20 die area is 2 mm² while under-the-dome area is 6.9 mm². Furthermore some light reflected off white collar would escape up through silicone - at wrong angle. So I see only marginal potential for improvement unless we can make a mirror.

ADDED: another small loss on a white dome: light reflected towards another part od the dome would risk being absorbed again.

It could be the opposite - it may work better with an SST-20, since the emitter is a lot smaller than the dome, the light reflected off the mirrored portion would reflect back a little more like you’d expect it to. But then, you would have to rely on the accuracy of the dome itself.

You can simulate this on a larger scale - get a cheap COB LED on eBay or Amazon then make a RLT collar that’s slightly bigger than the LES of the COB, then you can get an idea as to what the light does as it leaves the aperture. I have a hunch that the beam angle will not coincide with the aperture angle, but I could be wrong.

I’m not sure if I understand your comment correctly. Do you mean that white paint might work better with smaller LEDs?