Providing you have a fan and the plants are not baby seedlings you can go around 8 inches for a 250 watt and about 18 inches from a 400 watt. These are just estimates and closer or further may be needed.
a 250 watt HPS is most effective between 5 and 11 inches from the plant a 400 watt HPS is most effective between 6 and 15 inches from the plant (these are figures from funknugs light chart that i got a while back from OG) keep in mind those girls need 10,000 or more lumens optimally.... and heat becomes a serious problem if you cant controll it .. GOOD LUCK .... HAPPY GROWING
hi and thanks for reply, but my bolb have high heating at the moment and i install my bulb on 25 in because my babies just have few days so i think if i bring it more down my babies going to burn any more information would be usefull and i dont know when i have to put fan on them?. thanks mate.
point a fan at the light NOT ON YOUR PLANTS and see if its uncomfortable heat on your hand at the top of the plants ==== hot on the hand =hot on the plant