It does look similar to sunburn. I would just leave it.

Yea, most of the leaf is still functional, so leave it. I wonder, though, why the lower leaf would burn and not the uppers. Was the source set off to the side so that that leaf was face-on?

Do you know what the spectrum of the LED is? Maybe a lot of ultraviolet?

And what is that you're growing in? Looks like some sort of petrified berry. Or maybe wasp galls.

It's in a bit of a growth spurt, so that leaf was more prominent on Monday when I moved the LED. I took the photo two days later. The others have grown since, and it has drooped.

The LEDs are 460 nm, +- 10 nm half power, three of which I mounted on a heatsink and hung above the peppers. There should be as good as no ultraviolet, but I don't have the tools to actually confirm this. Can give you the model number if you want, however.

I'm actually growing in generic potting soil and a bit of perlite. The balls are LECA, which I use as a top covering to prevent the soil from drying out too much, and prevent anything else from growing. I've since discovered these forums, so will try some other mixes with my next batch.

Looks like it's dealing with the burnt leaf without a problem.

Two plants in the photo below: the lower one below the blue light, the upper one next to it. Lower one gets less sunlight, but an extra 5 hours of blue a day. I think it was the smaller one when I started, but now it's got quite a few more shoots.

These white habaneros grow quite slowly.

OCD..........

Remember, a watched plant never grows.

So sing to them with your eyes closed.

I know, I know :P

I have limited space, however, so I'm looking for anything that'll make them grow more bushy.