How close it too close for the tops of plants 400 HPS

1st grow, I don't know how far a distance you have to keep your plants from the HPS light...If the tops are too close they can burn, Right? So if they get too close cut the top off?

I have one under 2 400w HPS. The lights are about 12-14 inches from the top of the plant. I have real good a/c and fans. I was told to hold your hand over the tops. If it's uncomfortable, it's too close. Are you growing in a cabinet/box/closet, or in a room?

I'm growing Avalanche from high grade seeds... Those trees suprised me and grew to 5 feet 2 inches. Its a closet grow with the closet dimensions of 8x4x2. The distance from the top cola to the hps light bulb is 12 inches with the light all the way on the top of the closet. The 5 gallon pot is about a foot the plant is 5 feet and the light ballast hangs down about a foot, so a foot gap. I even used the humbolts bush master once on the plant but it was stubborn and kept growing.

I dont know what the humbolt thing is, but I had the same problem. I didn't "top", and let it grow unchecked. I definately got a feel for how tall they'll get after switching to 12/12.
You might have to resort to this:




This girl was trying to go thru the reflector. You'd think that it would avoid the heat, but no. It'll grow right into your lights if you let 'em
For indoor growing, I believe I'll be topping, or "FIMMING" from now on.