XHP35: measured luminance and forward voltage

Yeah, I understand that they can easily go poof at or around 3A. I cringe a little every time I hit Turbo on this one. :wink:

:+1: Thank you.

Thanks! :+1:

I’m not really clear on the measuring technique and can’t help wondering if it’s creating more confusion than help? I say this because there’s no mention of any form of collimation to the light output and if that’s true you’re attempting to measure candela without focus. Seems it would be quite a skewed reading when compared to actual in-light performance. Measuring candela is largely a function of the reflector/lens/optic, as can be seen in the 703Kcd measurement of this same emitter in the large reflector of the TN42. Same emitter, pushed harder, in a MaxToch Shooter 2X makes some 332Kcd. So the candela (or lux) measurement is not a function of current/Vf, but rather a proper collimation of the output.

The formula applied confuses me. I truly don’t see how a meter reading taken at ~15 inches distance can be applied to surface illuminance. How did the figure of 38cm come into play? A mule (bare emitter with no reflector or optic) spreads light at 125 degrees as a component of the dome, wider if an HI variant, so there will be a great deal of the light dispersed beyond the meter at that range. Cree’s graphs don’t show a distance of apex of the transmission from the applied dome, nor from the dome-less HI (not that I have seen). Sounds pretty non-standard and as such the result, while looking good on paper, might be misleading. (at least, it is to me personally)

When I or TomE or Richard or a number of other forum members quote lumens from a light box it’s an out-the-front transmission of light. Mixing in candela on such graphs doesn’t really give a true picture to what the emitter is producing, as it’s not the normal standard we compare to.

Of course, there’s a lot I fail to understand.

I’m not saying any of this to be facetious or debunking, merely trying to understand such that I may use gained knowledge in the application of these emitters to my own lights. (as if I’d remember even if I understood)

I should also make note that I have learned to address a reply to the masses even when talking to an individual, so that others can see my thought process and if applicable, correct me where I’m wrong. I surely don’t intend to create my own confusion in others, but am relying on others to guide me into the light, as it were. :wink:

(I may have talked myself into a measure of understanding by constantly double checking what was said and charted in making my response. The question was one of throw, the large multi die emitter throws similarly to a de-domed XM-L2 while making considerably more lumens available, as such, the same intenstity at range is available in a broader hot spot. This was my finding when I converted the Shooter 2X, nearly twice the lumens, at 4 times the voltage, for similar Kcd)

Sorry for being so long winded in what seems to be a conversation with myself. :person_facepalming:

Makes sense to me. He measured surface luminance of the die itself. The throw numbers will still depend on focus of the reflector or optic, but this can be useful for comparing what is possible between different emitters.

Yes, Dale, I think your last paragraph kind of sums it up.

The measurement is non-standard, but I think it is useful so I will try to give a bit more background so it may be useful to more people.

This thread by DrJones is where I learned this stuff so please read it if you are not familiar with some of the terms or quantities.

A way of thinking about throw and how to predict it is summarized in this formula: I=LA. The luminous intensity I (in cd) is equal to the luminance of an object L (in cd/mm^2) multiplied by the apparent area A (in mm^2). For flashlights the apparent area is the frontal area of the reflector. When looking straight into the reflector it is filled with the yellow image of the LED die. When the flashlight is on the entire reflector has the luminance of the die. So with this framework one can predict what the throw will be for different hosts (different reflector areas) if one knows the luminance of the actual die.

This is what my above measurement attempted. I measured without any additional optical system in order to get information intrinsic to the die. The same formula, I=LA, applies here. I measured the luminous intensity (cd) at different currents by measuring the lux at a known distance. There’s nothing special about 38cm; it was just a convenient distance in my setup. Then I divided by the apparent area, which is the area of the actual die, to get the luminance of the die.

So the die luminance tells you directly what the throw should be in a given flashlight if you know the apparent area of the reflector. But this information also tells you something about the total output; the luminance multiplied by the die area should be approximately proportional to the total output of the die, since most LED dies are close to lambertian surfaces and their radiation patterns are similar. One can see this intuitively in your observation, Dale, that the XHP35 throws about the same as your dedomed XML2 but with a larger hotspot, so that means more lumens in the beam.

Great to see the XHP35 tested, thanks! I never came round to doing this one.

(Hmm, feel like picking up some ‘duty’ of testing emitters from me? I do not enjoy it as much as I did before, while modding lights is just as fun as it ever was :slight_smile: )

You cant get a better commendation than this EasyB. Its information like this that takes the guess work out of led and driver selection when building and customizing lights. :+1:

Well I’ll certainly do what I can when a new interesting emitter comes out. I agree testing like this is important; so much of my mod planning is based on djozz’s testing. And also all the modders who post their lux measurements helps to inform on what to expect in the real world. :slight_smile:

I guess Easyb's measurements can be anchored some by comparing or normalizing them to "luminous exitance" (total flux in all solid angles divided by emitter area) based on cree data sheets at relatively low power. I think lumens per emitter area is actually more the correct thing than illuminance, which is only measured at single angles, for throw, and is essentially what an integrating sphere is measuring.

To me, it's also pretty important to compare to total power though. A 12V light at 2.5A is using 30W of power. An XP-L can draw what, 24W max? pushing it darn hard? So even if max throw is about the same, the xp-l uses less power and wins. So it still sounds like the xhp35 is "pretty close" to being still not as good as the xp-l in throw per watts. Of course a big part of what throw measures in a generic sense is ability to get light down field with a small reflector, so if you need 30W worth of good throw, well I guess in xp-l you'll need two emitters, which means a bigger light head, so effectively worse throw. If you need 50W worth though :)... It all depends on specific design goals.

As far as the power consumption, it depends on what your priority is; if you just want throw, a dedomed XPE2 torch has a high luminance and lower power consumption, but not a lot of output. Lately I have been interested in how to get a whole lot of lumens down range, and for this purpose I think the XHP35 is the best choice. It has more output than the top binned XPL and apparently has close to the same throw. The XHP50 and XHP70 have more output, but they don’t throw nearly as well. The only problem with the XHP35 is the difficulty with driving it well, especially in single cell lights.

I edited the end of my post. Yeah, for 30W of good throw xhp35 is better, and since nothing else can get the same throw (in the sense of downfield light per lighthead size) in that class, you can't even compare on a per watt basis. It's just the only thing. But for 50W of throw, you need two emitters anyway, and xp-l might be better again. I'm not always impressed with "about the same throw but more output" That means about the same throw, but more night vision blinding from light up close. Again, it depends on the application. Actual ability to see downfield isn't just in the geometrical math. You have to calculate for how the observer works too. This is at least as true, probably much more, for cameras as it is for people (if you're not using a good zoom lens to match the throw), so another application.

I realized I can get a good estimate of the total output (lumens) from my measurements with a bit of math trickery. Because the radiation from the LED is distributed in angle in a known pattern (it is very close to a Lambertian surface), I can derive the total output if I know the luminous intensity directly above the LED. I did this calculation when I was trying to get an absolute value of the output from a ceiling bounce test.

I will outline it here:

Just multiply the luminous intensity (in cd) above the LED by pi to get the total output in lumens.

As a sanity check I will compare the output of the XPL V6 1A using this method with the XPL V6 2C that djozz measured, at 4.0A. LEDs with dome are also very close to Lambertian surfaces so this should be a good estimate. From here, the luminous intensity above the XPL V6 1A with dome at 4A was 522.7cd. Multiplied by pi we get 1642 lumens, which is close to the ~1575 lumens that djozz measured at 4A.

I added the plot with total output for the XHP35 to the OP.

2600 lumens from an XHP35 HI? That’s more than I was expecting. Very nice results. SO I could theoretically get 7000 lumens plus 300+kcd if I mod my SP03.

Nice algebra!

Right PD, the Thrunite TN42 makes 2643 lumens out the front in my lightbox. I have a modified L2 with XHP-35 making 2986 lumens at 3.17A. So, as long as the 3 in your SP-03 are still able to pull a current in the 2.6A range, you should see nice results. And amazing throw as well, probably in the 320-330Kcd range unless I miss my quess.

Nice work with that figuring EasyB, seems to correlate pretty well.
When you said to multiply by pi I figured I was in trouble, ate the last of the pumpkin pie just last night… :wink:

Didn’t know you had one hitting 2900 Dale. I thought 2300 was pushing it.

I’ve got one doing 2.8A in a MaxToch Shooter 2X, another in a MaxToch SN50 doing about 2.83A and the one in the L2 doing 3.13A. These are all using the LD-2 modified to work on 4 cells. The big MaxToch is using 4 18500’s, the Shooter 2X is using 4 18650’s. The L2 of course is using 4 of the 26350’s.

The TN42 is running on 2S2P Samsung 30Q’s. Been meaning to test it and see if it makes the same numbers on a lesser cell…

Edit: the one doing 2900 started out domed and I sliced it. The Shooter 2X is an HI variant and the SN50 is an HI as well.

Did the output fall after you sliced it?

I think i remember reading Dale had the XHP35 HD hitting over 2900 lumen. I think he also sliced the dome to test and lost about 600-700 lumen?