if its burnt it probably wont grow back but the rest can still grow fine if its not damaged
sounds like burn from light i also use 400watt hps and i need 1-2 feet or so depending on plants i have had some take the heat a lot better than others and i have burn to death many others, its just part of learning it took me a whole year to learn what to do when to do it and also my own unique tricks (i am sure others use the same ones i just dont hear about it) i have also designed my own hydro system (i bought a lot of good cheep parts from my local irrigation shop that went out of business) WOOHOO! 55% off everything! but i oly got 2 years under my belt so what do i know? NOTHING! FYI: my last grow was bouncing around 102-107F here in the summer and it went fine im smoking the wonderful erb now so some strains do better than others i pick the more heat tolerant ones due to my location