HELP! 1 plant is being burnt by my 600w light even though other plants are closer?

I dont understand why but 1 plant is being burnt by my 600w light even though other plants are closer to the bulb, i even saw it starting to burn (yellowing top leaves/some crisp/curling) and moved it right away, so far that it is probabily not gettin the light efficiently now. I come up today and it has burnt even more! this time its becoming worrying as they have been in flower for almost 3 weeks now and it has slightly burnt the top bud side. im so blagged because as i said other plant are closer and theres nothing wrong with them, the plant that is burnt was like 1m away from light almost?