how hot?

hello,
what is the rule of thumb for how close you can have your plants to the lights? is it if you can keep your hand under the light comfortably for 5 minutes, then its ok? or was it if you can keep your hand under the light for longer? thanks.

i keep my 400 about 18 inches in my flowering room,i assume your talkin about HID?but i know this plant very well have grown her and many of her offspring for 2 yrs now. imo 2 ft for 400 600 2.5 and 1000 3 but all depends on strain, ventlation,temp,etc hopes this helps GL

i remember reading about the rule of thumb on this site if you can put your hand under the light for x amount of minutes without it getting hot, then its ok. the reason i ask is because i am using a cooltube so i know you can go a lil lower with it than a non cooltube.

I'd like to know too as I can touch my cool tube and it's really warm but not unbearable.

I just found out that many people have different tolerances for heat around the hand area. It was suggested to place your balls on the cool tube and if that is uncomfortable...odds are the plants wont like it either.