]the light is at 6 inch .... for t5 and for hps around 12 inch and more ( cool tube )
12 inches with a 600 watt even in a cool tube is way too close! your getting light burn raise it to at least 18" I have a good hood with the glass below the light, and even at 18" I was getting light burn 22-26 inches see4m to work about the best
A good ball park if you don't want to break out the measuring tape is to put the back of your hand (not your palm) facing up towards the light at the top of your plant. If it's too hot for your hand, it's too hot for the plant. As an experiment, try testing with your hand like this, then raise the light up in increments of an inch or two. You'll soon feel a huge difference in temperature.