So best I can tell is there are a few things going on. LED's if your food is out of whack can burn a plant in 24 hrs if the light is too close.
The reason I suggest keeping the light so high in veg normally is because if it is full spectrum, or bloom light it contains lots of reds and the PAR those put off at the early stages of life is a little harsh.
In this case however I am guessing the light has only been used in the veg state, so 12" to 16" is not unheard of and not that bad "If" the food is dialed in perfectly.
I am unsure of the nutrient level in the soil you use if any. I'm kind of taking a stab in the dark, but it looks like the plants were being starved, they lost the pigment at the top of the plant from that, and the light took care of the rest of the damage.
I'd put the light up at 2 to 3 feet and use some sort of mild food at seedling strength. It may be a little late, but worth the try if you have the time.