what is a good distance for 400 hps?

I was wondering what is a good distance from the canopy to the light with a 400 watt hps?
Heat is not an issue, temps are at 75 degrees when the light is 6 inches off the canopy, but I'm seeing signs of stress. Can I keep it like 12-15 inches and still have good light intensidity?

this should help

i had one 8" away for 5 weeks and she loved it, got her under a 600 now about 12" from the tips.might be the strain, master kush.

yeah from 8 to 12 inches is just right

thelightison said:

this should help

Click to expand...

Cools charts, thanks man. +rep.