Flashlight Optics - Dome, Dedoming and Throw

Thanks for taking the time to do this excellent article, I’m about 1/2 way through, but determined to finish it.
tabs

whoa, i missed this before, thanks for the btt, tabetha, and for the science, Dr. Jones.

I’ll be studying this before I decide whether or not to de-dome a green sst-90 J)

I want to leave this god awful country I live in!!
Sorry rant over!!

DrJones,

Which high powered LED now has the highest luminance? Is it still XR-E, or is there anything that surpasses it? The XP-G2, XP-E2, XP-C or anything else?

Also, is there any breakdown anywhere that lists the luminance of all the different LEDs, like the Cree, Nichia, Luminus, etc, so that we could look at that data and decide which LEDs we want to play with and which ones we would not?

Thanks and thank you for the article,

Justin

this doesn’t have all the data you’re looking for, and you’ve probably seen it, but anyway, a good reference

http://flashlightwiki.com/Brightness_Bins

What he needs to find is the flux per mm2. I may go add that to my LED sheet.

I just did a bit of math and I think a XP-E2 would actually beat a XR-E.

XR-E=114 (max brightness at 350 ma)/.81 (area of EZ900 die)=140.7407

XP-E2=142 (max brightness at 350 ma)/1 (area of die)=142

So this means that a XP-E2 has a higher surface brightness than a XR-E.

Would it also beat an xre r2? If so does that mean it would out throw the xre r2?

Well, this shows that the XP-E2 produces more light per mm2. Of course the XP-E2 has a wider viewing angle at 110 degrees v. the 90 of the XR-E. Then you have to take into account the XP-E2's efficiency at higher currents.

You can beat the h*ll out of a XRE (heat&current-wise that is ) without destroying it, this remains to be seen with the XPE2. In other words: what does it do at 2 Amps instead of 350mA.

Excellent post, thank you very much Dr.Jones!

Thats an effective write up! Thanks, you made leds and even etendue much more clear to me.

Thanks much for this. Great write-up!

Very Good Info.

thanks for the article, very educational. i learned a lot.

i have a question. according to your explanation, d=sqrt(I/E0)=sqrt(L*A/E0)=sqrt(L*pi*0.9 / 4*E0)D = ~ 8200 D,

throw distance is directly proportional to reflector diameter. so what is the purpose of deep reflectors such as solarforce skyline, HS-801/802 ? what do deep reflectors do?

another question. is there a limit to the throw distance-reflector diameter relationship? i mean, having a reflector infinitely big doesn’t give u infinite throw, right? at which point would the reflector size has no effect on throw distance?

I’ll have a go at this. When it is deeper the spill diameter is reduced because the led is farther from the opening. That little bit of light that would have been in the outer spill that is blocked by the longer reflector is instead reflected out the front with the rest of the light, resulting in that fairly dim amount of light being added to the light in that smaller area. So while it does add a little to the hotspot, it’s not enough to make much of a difference.

Wow. You are one scary Dr Mr Jones. Thanks.

Prometheus:

Reflector depth has only a small influence on throw: It affects the size of the reflector's 'dead hole'. An XM-L emits light into the full hemisphere, so those parts of the parabola which would be behind the LED cannot contribute. The deeper the reflector, the smaller that area is. With 'typical' reflectors you get about 10% dead apparent area (that's the factor of 0.9 in the equation), deep reflectors have a few percent less.

A deeper reflector has about the same throw, a smaller spot core, but a wider corona.

However the "deep reflector for throw" rule comes from older times when the typical LED was the XR-E, and the XR-E's collar reduced the maximum emission angle to about 120° (instead of the ~180° hemisphere); that results in a bigger dead hole (about 30% dead area for a typical reflector) and then a deeper reflector gave a more substantial improvement. BTW the XP-E thus does have an advantage over the XR-E regarding throw in a reflector due to it's smaller dead hole.

There is no principal limit to the d to D relation, however the bigger the reflector gets, the better it's quality must be to still reflect the LED precisely into the center beam. Still much less quality than for a professional astronomy telescope of the same size for example, but the price for a D=2m reflector with sufficient quality would be astronomical none the less (16km NEMA-throw...).

If you have access to a, say, 25cm reflector telescope and can get a LED into it's focal plane... -> 2km NEMA-throw. More if you use an XR-E EZ900 R2 :)

1 Thank

thanks for the reply Tecmo and DrJones :slight_smile:

Damn impressive knowledge on this subject. Greatly appreciate you sharing it with us. :slight_smile: