I got two xml2 t5 from IS today and I wondered what the point on the back would be….
So I freed one and it looks like a thermal coloring….
I had half a dozens XML2 before but no looked like this…any suggestions or tips
Edit: I just tried to power the emmitter up and it lights up…but I am doubting if it is reliable as I wanted to use it for modding a floodlight…
They may have been baked while still in the reel. Baking is a normal practice to eliminate moisture from a packaged product that may have been exposed to high humidity before being used. The dark spot seems to line up with the hole in the reel. Just a guess though. I’m not sure what could cause this. baking is usually at a relatively low temperature (below boiling), so discolouring like this should not occur.
I’ve seen a much milder version of this on my MT-G2 emitters from I-O. It was not as dark as this, and I think it was just part of the manufacturing process. The emitters worked fine.
The tin (or whatever it is) coating on the back is really easy to discolor with even small amounts of heat. It could even be from just exposure to air. Nothing unusual at all, I think every bare LED I've used has had some discoloration on the underside like that.