That's not likely to be light burn. It doesn't look right to me. The compost is too 'hot' for seedlings, so they're getting a little fert burn. I've seen plants survive much worse as seedlings, but you do have to flush. Lucky for you, they're little and easy to deal with.

The advice about ditching the HPS for now is sound. You definitely want a little more in the blue end for seedlings. CFLs, tube flouros, or MH is appropriate. Too much red light too erly can make plants express as males at a higher rate.