Seedlings under HID???

400-watt should be at least 12" - 14" above the plant top on plants older than seedlings as a start. In my experience. You say seedlings - how old/tall?
 
Go more like 3-4' above new seedlings, wait for 2nd set of leaves before you move closer(open bulb, i never bothered to air cool 400w as a fan faced at the bulb has always been plenty). Its pretty easy to cook seedlings under hids, humidity dome helps to keep them from getting too dry, and 1st week above soil they thrive in high humidity. They take off fast starting under the mh once they get a few leaves.
 
Yea I would put it about a meter above. Its a waste of of power but if thats your thing then just keep it up high. They dont need much light at this stage.
 
Not a problem at all to have young plants under a HID

Most modern ballasts are dimmable so you can turn it down to 50-75% if it's really an issue
 
Imo If your pots are roasting the perlite will begin to scortch. I start seedlings under 250w mh. The hand test is what I usually employ lol.
 
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Heh no need to troll on people. People are here to learn.
I usually share that attitude but the a one was begging it, it's all in fun though, didn't mean to offend.
Are you wondering why I'm asking about putting under an MH when I have the 400watt CFL beast?
Big ass cfls are great for seedlings but [this year] I started putting under 400w MH at 2ft around when 3rd node shows real good and it was a growth explosion I've never experienced. Could also be the switch to DWC but probably both.
 
I have 4 100watt equivalent CFLs that I'm using now here check it...the coil is aluminum for reflection and to raise humidity
 

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