Foglie bruciate.

heh, well, in your case not the cotyledons, but the lower leaves.. the moment thoe show a N-def, go ahead and start.

I don't think that's light burn. Never how it has progressed the 2 or 3 times i've seen it and once in last month and a half with new lights torching a younger rooted clone. That's likely nute burn than anything else. is the under side of the leaf soft like suede? or leathery? glossy? any of these coniciding points toward toxicity of some sort. It's early, so dial back slightly and it likely fixes itself in time, or give an extra water-only irrigation here and there. I see you just started feeding this week? You soil may be hot.. may not need it yet. Wait for cotyledons to fade and then start 1/4 str every third watering and slowly build up unless plant dictates otherwise.

Hi, it seems to be an initial light burn. However they look healthy and very dark green.