Optimum distance on 250 MH

[canabaloid100]

ok so ive got a setup with a 250w MH... previously had a 125CFL but it didnt provide heat so i chnaged to MH

being a n00b (lol) i left at as same distance and it frazzled 3/5 of my plants... theyre not dead just have burnt leaves which i removed and now new growth is coming through on those 3... but the other started to grow quite fast! so i moved the lamp further back to avoid more cooking but now they seem to have slowed again... i have a fan in the room to cool it but now i feel like the light is to far away... does anyone know an optimum distance it should be? at the moment id say its about 2 1/4 feet... some leaves r curling up from heat stress and some have gone a dark green which i m not sure but i dont think they should be that dark until later on... they are about 2 inch high growing really slowly...

[cornish_dope]

I think about 10-12 inches, also i think it's leaf growth you should be looking at not hieght because if you have it too far away they will stretch and too close as you've found they will burn.

If you can't be assed to mesure then put your hand at the tops of the plants if it's too hot for your hand it's too hot for your girls.

[grey1223]

Certainly sounds like lightburn and heat stress. For a 2" plant they don't need a ton of light. They're stressed a little and will need a few days to recover. For now, leave light about 18" above garden, then lower a little at a time as plants start to recover. You can measure leaf temps. with one of those IR thermometers. The're cheap. A cheap light meter will be a big help also. I give cuttings about 3000 lumens(foot candles) from T-5's, 5000 for a few days after rooting, then build up to 10,000 for veg. When you change to HID lighting like your 250 MH it's much different than flouro's. More light and heat concentrated on a smaller area.

[canabaloid100]

well ive now got it at about a foot and a 1/2 away with a 9 inch fan constantly on them to lower the temp.. i left my hand there and it felt like it wasnt too hot. hopefully that will work! all i need to do now is work out how much air i should be moving in my grow tent but i guess thats another thread lol cheers for the info