Hey, I got that quite a few times on my plants and it was due to me having the lights unknowingly sitting on top of the leaves (touching leaves) or too close to them and the light is too hot for the plant/leaves which therefore dries out all the leaf that is in contact and a bit of the surrounding area and therefore you are unable to reverse that process but it will not spread; if you don't like the looks then pull the leaves of if your OK but not OK then just press down on the dried out bit and you will notice it is crispy and just let it fall off (the crispy bit).
I hope this detailed explanation helped and I hope I have correctly diagnosed your problem.