Hi, wondering if anyone has experienced this with any other LED: I was cleaning the lens of my Amutorch DM90 when I noticed small black marks on the LES. Its not dirt, it looks like burn marks below the tiny window protecting the led.
Its even clearly visible when the flashlight is turned on, it still seems to function as normal, no unusual marks in the beam and no visible loss in output.
Anyone know what to do about it, is it safe to use? The warranty has expired as I had the light for over 1 year. I also know these emitters are really expensive, around $40-50.
This problem is so unusual that I have nothing conclusive to say. But I will jot down some random thoughts in case they are helpful:
The mark has a very unusual shape that is not simply-connected, there’s a hole in the middle of the main blob. The shape looks less like a burn directly on the phosphor, but looks a lot like some sort of liquid splatter, like molten solder or flux.
Idk if it’s a camera artifact, but the second photo seems to suggest that the dark spots are partly transparent. It’s probably attached to the glass cover. Are you sure what side of the glass it’s on? I couldn’t think of a way for stuff to get in between the glass and phosphor, and would be inclined to guess it’s on top of the glass, in which case one could scrape it off. But if it’s under the glass, then the dark spot could absorb more heat and transfer the heat to the phosphor, damaging it and starting a positive-feedback loop.
Thanks for the suggestion. Its really unusual, never seen anything like it. Im certain it wasn’t always there. I dont think its solder or flux, or a splash. With my eyes i can clearly see its below the glass. Maybe poor thermal contact between mcpcb and heatsink caused it. It makes sense about what you said about the dark spot attracting heat and making it progressively worse.
Now my real question is this. How can i rectify it? Is there any sbt90.2 on large diameter mcpcb or is a sfh55/sfh43 swap a good option?
I am not aware of SBT90.2s on a large custom PCB that is easily available. But if you can get some thermal paste and solder, you can easily reflow a replacement bare emitter in on a stovetop.
I’ve never done this and would defer to an expert who has, but one of the SFH/SFN emitters could be an option for getting more output while maintaining reasonable throw. One needs to figure out which one is 3V and has a footprint around 11mm times 10mm. [EDIT: the SBT90.2 is often said to have a 9090 footprint but that’s not true, the actual footprint is larger and more rectangular.]
I believe I’ve read about a round-die SBT90.2 imitation with just slightly lower performance, but a fraction of the price. I couldn’t quite find where I read it (as r/flashlight has garbage search indexing even through google), but this video and the description might be informative.
Since you are replacing this LED anyways, you might as well take the glass lens off. If the dark spot is on the phosphor, the LED is toast anyways and you lose nothing, you might even try your luck and scrape it off. If the dark spot is on the glass, you’ve solved the problem!
Given that this is a review of a complete light, it’s unclear how much of the lower output is attributable to extrinsic factors such as a smaller LES, worse heatsinking, or low driver output. But it is reasonable to expect this LED to perform generally worse than the SBT90.2 given the price and lack of documentation.
