nutes, not light... put the light back to where it was 'best', if that was the case before.
probably slightly overfed. too much S can do this. Other things can progress from this early symptom, though. If it has come on slowly, i'd give it a second to show its true colors and have an easier diagnosis. If it doesn't get worse, it's not too big of a deal. can look over your formula and how you fed and try something slightly different next time to avoid it.