The XP-G3 and the mystery of the disappearing luminance

I agree some sort of TIR could utilize all the light from a XPG3 and properly mix the colors to solve the tint shift issue, but it won’t solve the low luminance issue.

Yes there are ways to collect all of the light from an LED including that from the sides.
A regular flashlight reflector also uses 100% of the flux, if you count the spill.

The point is that the light emitted at the sides is not useful for increasing the surface intensity, which is what contributes to throw.
Throw is pretty much what this entire topic is about.

Here’s the intensity graphs of the G3 ad G2 overlaid:

G3 definitely emits more light to the sides, even though the difference is very reduced due to the dome being on when the tests are done.
G3 is red, in case that wasn’t obvious enough already :stuck_out_tongue:

Great ‘detective work’ here :smiley: I would have never considered that there could be such a significant amount of light from the side of the die. If that could be captured and sent downstream, the lumen loss could be mitigated but the tint issues would remain.


fwiw, some people are reporting tint shift across the beam, on their new Zebralight SC5C MK II H CRI, with Cree XP-L2
your post helped me understand that it is not an isolated incident:

[QUOTE=jruser;5106891]I got mine today from the new batch. Beam pattern is terrible. yellow hole in the middle of the hotspot, surrounded by decent tint hotspot, surrounded by yellow ring, surrounded by decent tint spill.

What causes this? reflector? LED? centering is fine.[/QUOTE]

I’ve been puzzling over the cd/lm differences between the G3 and G2 in the Carclo performance data. Thanks for solving the mystery. Now I have to perform a root canal on my light bar and replace 45 XP-G3s with XP-G2s.

Oh no! Did you already install the g3s yourself?

Oh yes! I finished my build in May. Documented here: DIY Offroad LED Light Bar It will be more like 45 root canals.

I’m a noob and didn’t understand the factors that affect throw, so I was solely focused (no pun intended) on lumens per watt and the G3 looked best on paper. Now my beam pattern is broader than I wanted, so I’ve been searching for ways to improve it and found what a tremendous resource this board is.
I’ve ordered some XP-G2 S4 E3s to compare to the G3s I have.

I’m glad the measurements from me and others helped you.

At the same current, the XPG2 will have more throw than the XPG3, but only by a factor of 1.3x or so (in beam intensity). If you want a more significant increase you could dedome the XPG2 emitters. This would increase the beam intensity by a factor of ~1.9 over the stock XPG2. It would be more work to dedome them all, but it would be a significant bump in throw. The beam size should narrow by a factor of ~1.5 due to dedoming.

Yes, it’s fascinating! There is so much depth.

This Carclo data shows a bigger difference, do you think it is accurate?


Thanks for explaining what’s going on, EasyB :+1:
(hadn’t seen this topic yet)

Nice work! Thanks for the report EasyB.

That carclo data gives you the cd/lm, which is not exactly the relevant quantity here because the XPG3 and XPG2 output different lumens at the same current, although they aren’t that different. My estimate could be low; you might see a 1.5-1.6x increase in beam intensity at the same current.

A 1.5x increase in beam intensity won’t seem like a lot. It is a tough game we flashlight enthusiasts play: due to the ~logarithmic sensitivity of our eyes we have to go many times brighter to get the “wow factor”. :slight_smile:

To my eyes, on my iMac with “Retina Display”, the XP-G3 in the photo shows a greenish yellow tint. iow, like tint that is above the BBL.

That is an XP-G3 that was cherry picked for negative DUV… so, Im told it is not possible for it to be green tinted, and that the problem is with my eyes and or monitor.

could it be that the flip chip design puts green light out the side, but by the time the hotspot and spill get averaged together, that the XP-G3 measures below the BBL, while still looking greenish yellow to me?

Looks greenish yellow to me to. :+1:

Yep, that’s a main problem with XP-G3/XP-L2 based dies.

All of the light is collected in the dome.

That means even greener parts of the beam are collected at the center.

thanks for the reality check

I thought I was going into some kind of GreenSlider WromHole

[QUOTE=Hogokansatsukan;5274400]If you see green in these, see an optometrist. There is something seriously wrong with your eyes. If you think it’s green because of the photo, it’s time for a new computer monitor. After having those checked if it’s still green, one needs to get back on their medication.
Look at the sphere data. Check out where it falls on the black body radius.[/QUOTE]

so I guess there must be some kind of TemporalVisualDistortionField at play

The side phosphor and die emit different tints. Outside of a flashlight if they just measured the light above the LED that will take an average of the different tints. But in a reflector light different parts of the beam contains light from different parts of the LED. The beam center will contain just light from the die center while the outer parts of the beam will contain more light from the side phosphor. So a single averaged tint measurement won’t necessarily tell you what tint the beam will have. This is why you see tint measurements at different parts of the beam like maukka does.

Thank you
I had a hunch the flip chip design confounded the tint measurement…

Here is one of my green XP-G3, middle, in a stock Thorfire Tk05. The specs say its “neutral white”.

Mr. EasyB, this is very interesting study and I learn a lot from your explaination. Thank you very much!