streching plants

i have a 600wat metal halide.. how high above the plants should it be.

it looks like my plants are starting to stretch and stems are to long between the leaves.

About 60cm but check with your hand just above the plants,palm down for a minute and if it feels hot it`s too close.If they`re showing no signs of burning move your lamp closer.

hmm.. ok im about 14inches above the plants.. because i have good fan cooling the bulb down and venting out
but it still seems like they are so stretched