Well since HPS isnt like CFL where you keep it 2" away from the plant, I read 3' is good for the HPS. Since seedlings are vulnerable to heat/dryness, and I have mylar everywhere, do I even need to worry about them being 3'? Stays at 80 degrees F at the pot.
Try to keep your light as close to your plants as possible without burning them. Light follows the inverse square law (link). If you can keep them 1 foot away without burning your plants, do it.
I concur with the above, as close as possible with out burning them. HOWEVER seedlings maybe add a few inches. I run the HPS roughly 12 inches from the tops of my babies now. The plants are roughly 10 days old today, take a look in my signature if you like.
Yours is also cooled via ducting. I dont have a hood like that and dont want to spend another $90~ for one. I have an air vent to the outside that I have a small fan in front of blowing on the light, maybe another blowing on the light and Ill be able to put the light close.
A fan blowing across the light is crucial, i still do it with an enclosed reflector. Use your hand with a little common sense be the judge of how close you can bring the light. You can see I hang this 9" Massey steel walmart fan from the light.
I'll be having 2 fans blowing on it constantly. Without any fans about 1.5' is good and not too hot yet. I'll be needing fans though
i have a 400w HPS, and i get them as close as possible w/o burning them..works out to about 9-12 inches. helps if you have a cooltube as well.
I was thinking 400w, if you can get it 1.5' that is great even 2' without an enclosed reflector sounds good to me. I would be absolutely certain your seedlings survive and back it off a bit for them. Give them a week to 10 days and bring it back.
Yeah, Cooltubes are a great investment. My plants can grow right up to the tube without much danger of getting burnt. Not that I let them ever touch it, but I don't raise my light until they get around 6" away. Then I only raise it a couple inches at a time. It keeps a 400W nice and cool
Hay guise, Not meaning to hijack the thread but this is related to the discussion. I have some plants vegging and they will be four weeks old this Thursday. I have a 400W HPS and it is roughly six feet hung in the air from the top of the plants. Is this way too far away? If so, how close should they be? Id say the plants are about 9 inches tall and it seems they are growing slowly, so I was just curious if the light height was the problem. Will heat be an issue if they are really close to the plants with a HPS?
Thats way too far. 3' is the furthest with a 400w. Get some chains to make a pulley system and get them as close as you can without burning them to the plants. Get fans to cool it so you can get it closer