for 400 watts i do 12-16 inches if the reflector is not air cooled. So probably a little closer id try 10-12 inches and watch those temps
Use the hand test.. Take your hand and put it right above your plant. Keep it there for a minute or two. If it to hot on your skin it will be to hot for the plants. Adjust accordingly. Everyones set-up is diff so were as some people with good ventilation can run 10 inches away others have to be at 16..Ya dig? You have to dial your set-up in for what you are doing.
You are going to want to try and stay below 80 degrees at the canopy level. I always hang a therm from a chain and adjust it as the plants grow taller. I like 75-77 but sometimes..esp in the summer keeping it under 80 can be a challenge. If you start getting into the mid to high 80s you are going to hurt quality..Do the best you can.
I have sorted my temps i have my light 16 inches from the top of my plants and my temps are staying between 75 and 77f. Thanks guys sorry about the double post didnt realise id,already posted.
My 400 watt is about 6 inches away and they arent burning but i have good ventilation and cant raise my light anymore. Otherwise i had mine about 13" away and it seemed just right.
Oh nice but take a note if u are still in veg they will shoot first few weeks when u turn the light 12/12.If it is sativa dominant they can keep grow during flowering