Wouldn’t the cslpm1 need over 2000lm to beat the cslnm1 in luminance?
Great testing and photos again…thank you!
For your CRI readings and chromacity graph, what drive current was used, and fair to assume it was bare without optics?
Maybe. With my measurement method (putting reflector on LED and measure the brightness in 1 m distance to calculate luminance with given LES) the values are reproducible. I assume that the LED chips Osram uses for these emitters have side LES and some light is leaking through the opaque layer around the LED chip. Maybe also the viewing angle could be also a reason for the values. In any case, the measured brightness at 1 m using a reflector like in a flashlight is indeed somewhat higher with the CSLPM1 than with the CSLNM1.
Current was 350 mA, I measured the bare LED without optics.
Ok…thank you!
Ahhh, now it makes a lot more sense! The beam isn't fully formed at this distance, with the cross-sectional area being roughly equal to the reflector opening rather than diverging proportionally to LES size. Any intensity measurements at this distance would thus greatly favor emitters with high total output rather than high luminance.
These tests are awesome!! I would really love to see you test the SFT40.
The thing is - what is the best measurement method for luminance?
Some years ago there was a discussion in the thread of my Q8WP test about this topic already. Several BLF members assumed that the currently chosen method of using a reflector and measure the brightness to calculate the luminance based on given LES is the best method instead of measuring the LES on the emitter itself and get the brightness from the bare LED...
Thanks for the tests, nice and comprehensive 
I prefer the reflector method for actual numbers, emitters such as the XP-G3 show that the calculated cd/mm2 theoretical luminance can be significantly affected by other factors.
But QReciprocity isn’t questioning the method, just the distance at which the luminance is measured.
They are suggesting that 1m is not enough distance for the beam to be properly focused, so there will be a dark hole in the middle of the hotspot which will result in an incorrect reduction in luminosity that would account for the CSLNM1 seemingly lacking luminosity compared to real world performance against the other LEDs you have tested.
I don’t know what reflector you use but it’s a possibility.
I use the reflector of the Convoy C8 (SMO).
In 1 m there is no visible dark hole in the spot, even with the CSLNM1.TG emitter.
Usually I want to avoid to measure in other distances as 1 m since all my values are calculated based on measurements in this distances and I don't want to get additional possible errors. At the weekend I will try a measurement in 2 or 4 m. I think it is necessary to measure the LES of the reflector also in this distance?
I understand the need to be consistant throughout your tests, and it certainly makes it much easier for someone like me to compare numbers.
In this case it would be worth testing at a further distance, just to see if it has any effect on the numbers.
I don’t know why it would be neccessary to measure the LES of the reflector, if you mean for calculating the relative luminance at 1m you just multiply by the distance squared.
I.E. at 2m you would multiply the luminance by 4 to give the luminance at 1m.
At 4m you would multiply by 16.
I have a CSLNM1 in a C8 waiting for me to sort out the focus, i just shone it against a wall and it looks like it’s still converging as i move more than a metre away from the wall.
I couldn't really say what's a good distance to test things at--what I do know is that the throwier the light, the farther this distance gets. I measured my C8 running CSLNM1 with 5A driver and swapped it later to SFT40 ramping driver; at 4m, the SFT40 is giving slightly higher intensity, which is definitely wrong. Measuring at 30m gave more reasonable numbers. For a Fresnel lens thrower I built (estimated 3km throw), it takes at least 100m for the correctly focused beam to converge.
I think it is reasonable to simply obtain intensity via dividing total output by emitter LES area, eliminating dependence on distance. One can then use this number to extrapolate throw from reflectors, lenses, TIRs, whatever, via dividing the LES of the optical element by the LES of the emitter, and multiplying a universal normalizing constant.
What are the objections to this method again--I seem to have missed a discussion? [EDIT: read Q8WP thread, the objection is what I expected] The only problem I could see is if the emitter has a non-uniform surface (e.g., E21A, MT-G2, XHP gen 2, or anything with sideways leakage like XPL-HI) or non-rectilinear shape or non-Lambertian emission profile (e.g., domed emitters), in which case the reflector method should be ok because all non-uniform emitters I know are not extreme throwers.
The luminance (cd/mm²) is especially also dependent on the light emitting area, which must be calculated or measured. Only with the brightness in x meters alone, this information is still missing.
The same necessity exists with the method of calculating the luminance directly, which is why this does not really work well for LEDs with lateral radiation. This was once the reason why I changed to the method with the reflector, since the Q8WP was one of my first non-uniform style emitters with sideways radiation. When using a reflector, it is easier to determine the exact LES than with an LED where parts of the substrate around the phosphor are illuminated as with the XP-G3.
But the big problem is, most of the recent released emitters are from this non-uniform type. Even the CSLNM1/PM1 have some minor issues with light radiated sideways, and the smaller the luminous surface, the greater the effect on the result of even minor side radiation.
There are only few emitters like XP-E2 and XP-G2 (old) where this method is working properly. Even at some dedoming methods (shaving) and LEDs with otherwise perfect lambertian LED chip this problem can occur due to shining around the LED chip, as seen as example in my XM-L2 new design thread.
That's an excellent point, thank you for pointing it out! Looks like any integrate-then-divide method ain't gonna work.
I have another idea: instead of using a reflector, what if we used a small aspheric lens to focus the beam before measuring intensity? It takes shorter distance for the beam to fully converge, and you could easily tell when it does (the projected image of the die looks sharp). This also gives localized intensity information on different parts of the die.
[EDIT]: another thought: I think just using a smaller reflector (like S2+ instead of C8) would yield more accurate comparisons at short distances. Though some emitters are a pain to focus even in these!
To be honest, I'm not sure how I will deal with the luminance measurements in the foreseeable future. The method with an aspheric lens requires a whole new setup which I should build first (like an adjustable base frame to hold everything precise in place) and for the smaller reflector I need also a new frame to keep the reflector on the LED.
I will do some luminance measurements in bigger distance on the weekend, hopefully this changes something in accuracy. Since I am not very interested in extreme throw from flashlights my focus is not really on the luminance of the emitters...
The new setup would be very time-consuming. I think longer distance with the existing setup would be great. For most throwy emitters (1mm^2 die or larger) in a C8 reflector, I'd guess that measuring at 10m should give very reasonable numbers.
Only with the problem I don't have 10 m space for measuring LEDs :D
4 m has to be enough, more is simply not possible, even if I want to go for more...
Facepalm, I keep forgetting how complex and precise your setup is! I measure with the ceilingbounce phone app and thus have access to arbitrarily long distances outdoors.
A distance of 4m would not give reasonable comparisons between extreme ends of the LED spectrum. My readings at 4m indicate an SFT40 out-throws a CSLNM fully driven in a C8 reflector; if the SFT40 were replaced with an SBT90.2 or XHP70.3 HI, I would have gotten even worse data.
However, for LEDs with similar die size (say, XP-P versus CSLNM, or XML2 dedomed versus SFT40), 4m is more than good enough to give reliable comparisons between them.
In theory, the minimum distance for a good measurement should be the distance where the image of the emitter fills up the entire reflector. In practice, however, this appears to not suffice: 4m is enough for a CSLNM to be fully magnified by the reflector. I suspect the issue is deviations of the LED angular distribution from the ideal Lambertian, causing the emitter to appear more intense from certain angles.
LEDs with wide viewing angles might be in advantage here, if it comes to the shortest distance for filling out the whole reflector. But most LEDs have viewing angles of about 110 to 120 degrees. Also the type and calculation of the inner reflector surface/geometry might be also a thing.
I just red in a scientific paper that luminance measurement is also possible with microscopy. Since the luminance is (in most cases) proportional to the light flux it is maybe enough to measure the brightness from magnified LED chip, so based on this values the luminance at maximum power could be calculated. For me the advantage is that it is easier to do, since complex base frames and something like this are not necessary, but it requires equipment with much higher precision, which I do not have at the moment.
To be honest, since the topic 'luminance' is not the most important thing for me I don't know if I would test this method further for my self.
Would you link the microscopy paper? I am interested.
Your data has more than enough accuracy for the average flashlight hobbyist--all the top thrower LEDs at the moment have intensity differences that IMO are not noticeable in practice. If anyone is hardcore enough to pursue the absolute best, I think the onus is on them to gather and provide more precise data.
In my opinion, I would not worry about adjusting the setup given how much effort it takes. As said before, your data is good enough 99% of the time. I think the community benefits more from testing a wide variety of LEDs (as you have done recently, which I appreciate very much!) than spending the same effort trying to pin down minute differences in intensity.
Thank you. :)
For me the most important part is color and light quality. Efficient are almost all emitters, even in High CRI (except for some horrible inefficient emitters like the pre-production Getian tested several months earlier), and also the trend for many flashlight enthusiasts goes to light quality since more or less precise light measurement devices like the "Opple" are cheap and easy to use. Only through such equipment do most people even perceive the topic of light quality and effects on the human body. Before, terms such as Ra and duv were only theory for most, and now this topic can even be applied in daily life, for example in lighting for living spaces.
And yes, it is important for me to test many different emitters, from highest luminance to best color rendition and even pure exotic things like SFP55 and other obscure emitters.
I will search for the microscope luminance paper. It was a while ago, I don't even remember in which journal it was published...
It is very interesting to hear what your priorities are regarding emitters, given how many of them you have tested and are intimately familiar with. It is true that emitters are becoming extremely efficient, even the high CRI ones. (I actually don't know if they're even truly less efficient than their low CRI counterparts, since lumen/W measures efficacy, not efficiency...but that's a whole other discussion that I am more than happy to go in more depth.) I think many efficiency problems in flashlights can be attributed to the driver and optical element, more than the emitter.
Nowadays I require all emitters I have to be top-performers in at least one department, and as a result, the only white emitters I use are the 519A, CSLNM1, and SFT40. (I don't use any big lights but would have liked the 50/70.3 HI.) Many common emitters (e.g., SST40, LH351D), for me, are strictly inferior to another emitter in every department and thus have no place in my collection. For my EDC I care most about color quality. After a few months, I actually got tired of how pink the dedomed 519As are, and ordered some domed ones to put back in. Facepalm.
My other main is a C8 running SFT40, which for me is the emitter that perfectly compromises between throw, output, and efficiency/runtime. The SFT40 is crazy efficient despite being a high intensity emitter and has excellent tint given the low CRI. An argument can be made for the CULPM, but the SFT40 is so much easier to center and more mechanically robust.