I’ve got my first bunny recently and today I’ve noticed that one of LEDs (cree XPL HI NW) is dimmer:
It’s noticeable mostly on lower levels, especially if light is projected on white surface.
Did you have similar issues, what can be the reason, can it be fixed somehow?
I don’t know how it affects light on higher levels, probably as well, but I can’t check it - light is just to bright to observe smaller differences with naked eye and cameras are not able to show it as well.
Light was bought from Aliexpress LUMINTOP Official Store, I even got some discount (mentioned BLF). I didn’t discussed brightness problems with them yet.
Everything was quite ok. Tir lens came with small scratch and diffuser was a bit damaged (forced pushed onto the flashlight head) and dusty, so a bit below my expectations towards company like Lumintop, but generally I’m happy with the light and build quality, I really like this light. But brightness issue kinda hurts my OCD…
Does not look right. If it’s not an electronic problem, may possibly be a weak solder joint. Unless you have access to spare parts, your only choice may be to se t it back.
Parallel LEDs will rarely have exactly the same forward voltage, so especially at low levels (you see this mostly on COBs), one LED with a lower Vf will hog more current and look brighter, and one with a higher Vf will draw less current and look dimmer.
And simply, lights are in bins, a low bin-7 and high bin-6 (eg, 7.1 vs 6.9) might be very close in brightness, but a low bin-6 and high bin-6 (eg, 6.1 vs 6.9) might have a much larger difference in brightness.
Mmm, dunno. I think that would show up more at higher brightnesses than lower.
Flaky solder joint with more resistance would have more IR drop at (obviously) higher I, and a crappy thermal path would only cook the LED and reduce efficiency and thus brightness at higher current/wattage vs low.
I did little test to check solder joint/higher resistance on one LED - temperature measured on each one with the probe showed that indeed one LED is hotter.
Quick quiz - which one do you think was hotter? (photo of identical LED configuration from Lumeniac review)
One opposite to the switch -> with the less mass of metal close to it. Difference was few degrees measured on highest levels.
The darker one is on the left side of the bunny and had identical temp. as the right one.
(BTW, don’t know how accurate is my multimeter probe, but numbers during turbo on surface of LEDs easily reaches 150-180 C.)
If it’s indeed LED bin issue, then it’s kinda disappointing that Lumintop is not checking things like that.
I’m a novice flashlight freak and don’t have many lights yet, but nothing like this can be observe on IF25A (4xSST-20) nor TINI 2 or TIP SE (2xOsram P8). I’ve asked seller about ideas what do do next, but for now it’s really bit below my expectation for Lumintop…
Hm? If the LEDs are all in the same bin, ie, on the same reel, there’s nothing to check.
My point was that in my fictitious bining example, “bin 6” can be anything from 6.0 to 6.9999999, ie, just short of a full bin. No one’s gonna be matching brightness by eye or instrument when mass-producing lights.
That’s why one place where I worked used 1% resistors for brightness-matching (on instrument panels) vs cheaper 5% or 10% resistors.
Slapping LEDs in parallel, you have to contend with forward voltage and binning, and it’s luck of the draw.
Well, whatever the reason then, if verifying and correcting issue visible with naked eye is a problem for company quality control, then I’ll probably switch to other, for which that’s not that big deal.
And I don’t think switching to a different flashlight manufacturer will make any difference. I doubt ANY manufacturer actually tests their LEDs for brightness. They just order a reel of LEDs and install.
My recollection is that within each brightness bin there can be as much as a 20% brightness difference. It’s not exact.
I don’t think the problem is a bad solder joint under an LED. But if you think that may be the case, you could try removing the star and reflowing all the LEDs to see if anything improves.
Naah, don’t think it is as well, with higher resistance there should be temperature difference on this worse connection LED and nothing like this happens.
