XHP35 output and death test + PWM efficiency test by Texas_Ace

zoomies vary a lot in my experience with what you see OTF. At full flood ~70% is reasonable. At full zoom it can be at little at 25%.

Zoomies are fun though, I have an xhp35 1405 that is a blast, like a laser pointer. Not the most useful but super fun to play with.

For real world use I prefer the L2 xhp35 HI or my XP-L HI D01. Well Giggles is the best thrower I have but thats not really a fair comparison lol.

Hey TA, any update on where to purchase the BLF GT emitters? I believe their XHP35A H0 0000 0D0BD440E, I looked at a bunch of different sites, but the minimum order is 1000 and I don’t see myself needing more then 8-9. Do you think Lumintop would be willing to sell a few emitters on the side? I have no problem with paying a slight premium over the normal cost of some XHP35 Hi emitters if Lumintop would be willing to sell some.


I have wanted to do this same thing but have not found a source for them yet. I have been trying to talk Lumintop into selling the LED’s separately but that led us down the rabit hole of trying to find an even better LED.

We did find a 4500k that could be real nice but the samples they sent me were lost in transit and I have not heard anything since. Once things quite down with the GT group buy I will see about the LED’s again.

Thanks TA, I look forward to getting my hands on the GT’s 4000k emitters.

It seems like some of your highest outputs were between 2600 and 2700 lumen. This is a raw led, correct?

In a flashlight where you have losses in the reflector and lens, what do you think the “Out the Front” output would be?

DB Custom was saying the MF04 output might actually be 2700 lumen out the front. I’m pretty skeptical of that. You would need the raw led to put out at least 3000 lumen and I havent seen any measured that high.

Plus, I doubt the MF04 will be using a top bin led anyway.

Do you have any thoughts on this?

The OTF lumens on the XHP35 always seem to be lower then expected and I have no idea why. It just does not take to being overdriven as well as modern LED’s.

LED’s like the XP-L2 / XHP70.2 always surprise me with more lumens then I expected OTF.

Far as actual numbers, I would not even try to guess, too many variables. Better to just see what happens.

I would like to reflow a XHP35 but I’m not sure about the polarity. Can someone please tell me if the pad with the arrow (marked as anode in the datasheet) is the positive pole or the other pad?

simply google 2 word

That should be the positive pad. "Anode" essentially means "positive terminal"

If you're ever worried, and own a multimeter with a diode test function (on some multimeters, the diode-test and continuity function are the same), you can test that way. Although, come to think of it, I'm not sure if that would light a 12v emitter... I haven't tried that. Works great for testing all my 3v emitters though lol

99.5% of the Multimeters wont light a 12V LED
only a few are known like the EEVBlog

Thank you, Lexel and Scallywag! They could just add a + in brackets to anode for the idiots around :wink: The multimeter test function is also my favourite for 3V leds so I was worrying about the 50% chance of killing my led. :person_facepalming:

there is no 50% chance of killing an LED with DMM diode test
the DMM limits the current to a very low level and the LED blocks reverse polarity and has a protection device

The 50% chance of a dead led was intended if you just solder the led without looking at the polarity.
The XHP35 led is up and running in its flashlight now. :sunglasses: Thank you again! :beer:

Another way to test flashlight leds is if you don’t have a DMM is to use a 9v alkaline battery. The internal resistance is to high to give enough current to blow the led.

if you solder a XHP35 in reverse on a driver it simply is as if you would run the driver without an LED
No light, drivers usually run into high voltage protection and nothing happens

Good to know for next time, thanks! :student:

TA, I need a clarification on the PWM efficiency test…

Many FET drivers use resistors to slow down the FET. When a light is PWMed this reduces current, improving efficiency.
In another thread I see you stating that efficiency improvements are caused by lower temperature.
Some of there surely are but I would be interested in knowing whether temperature is really the sole reason why you got not-so-bad efficiency here or is it a combination of temperature and lower current.

So did you use a resistor to slow down the FET?

The resistor was very small on the FET (4.7ohm IIRC) , it would have negligible effect for the purposes of this test. It is there to prevent ringing and improve consistency at very low modes.

You are correct that adding a larger resistor is a way of transferring the heat from the LED to the FET. Although overall efficiency does not seem to be effected much in my testing except that the driver gets hotter now but the same voltage is burned off either way.

Yes, just the plain fact it is lower current also effects the final output along with the lower temperatures (they are related naturally).

I wish I had a good function generator so I could do a more scientific test but I stand by my results based on my anecdotal experience as well. Not to mention that most professional lighting uses PWM, that would not make sense if they would be loosing ~50–70 efficiency that some say. It makes perfect sense based on my results though where they would only be loosing 10–20 efficiency to maintain the same tint.

Overall while FET PWM is not perfect by any means, particularly on LED’s that tint shift I will have no issues at all using PWM to adjust the output vs a constant current. The minor difference in efficiency will not effect most people / use cases.

At a given current draw the battery will last exactly the same FET vs constant current. The only change will be the lumen output and in most cases the human eye will not even be able to see the difference without having them side by side.

With commercial lightning it’s different - they don’t overdrive their LEDs like we do but run them within very efficient region all the time.

Someone (L4P?) has tested the effect of temperature on efficiency. I can’t find it now. :frowning:
I wonder if it would be consistent with your result…

Can someone recommend a driver to use for my BLF A6 mod? Is it this one?

I know I need a 3v one? I'm doing the mod with this led.