Distance of light from plant tops

Hello Folks,
I have a quick question that I'm sure someone in this newsgroup will have the answer. I know the standard distance from the light to the plant tops has to be at least 30 inches depending upon the wattage of the lamp versus the air flow around the plant. My question is this, I have a 250 watt HPS that I run for 16 hours on 8 off and the distance that I have set up between the light and the plants is roughly about 20 inches and so far so good. Is there a formula to use in determining the distance of the light from the plant tops by using the wattage of the light as a guideline?

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Country Cowfreak

250 = 12-18in.
400 = 12-24in.(though I never keep mine closer than 18 )
600 = 18-24in.
1000 = 24in+

bro I gotta 600 watt hps in a small closet,,I keep the temps down to about 75-80,,,my light is about 12 -16 inches from the plants,,as long as they are doing fine,,,ie. no burning,,you can keep them as close as the plant will let you,,hope this helps

Keep on Growin

HoLE

golden rule i follow 1000w 1000mm, 600w 600mm, catch my drift chaps.

Thanks folks! I knew I could count on fellow gardners to help me find what I needed.

allright but I have a cool tube 1000w, so I can def keep it closer than 24 inches cuz it's on a light mover and it has cold air intake into it and then back out. So I'm going to keep mine almost on top of the plants. All you need to know is if your hand is to hot under it-your plants are to hot under it. Easy.

Here ya go

Father Jack, That is indeed the most in-depth chart I have ever seen! Thank you very much for posting it, it will come in handy!
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