plants distance to light (no heat issues)

I have 5 seedlings (10 days old) under a 400w MH (cooltube) and a fan blowing between the light and the plants.
I try to dial in the set up and to get the temps right, at 75 (24 celsius), i have to get the light at 12 inches away
I run the lights at night, big window opened, kind of cold in the room, but in the tent, at leaves level, the thermometer shows 75. And I try to mentain it to this level by slightly adjusting the amount of cold air that comes through the window. So far, after a lot of experimenting trying to get the best set up dialing, this method turned up to be the best to keep the temps even, at the right level (and also, the easiest way)

now, i am a little afraid of light stress. people say that a 400w should be kept between 12 and 18 inches away.
Is it too close in general? and especially because they are still young and fragile? am I pushing the limit keeping it only at 12 inches away?

the leaves are a very light green, but not yellow. is the green supposed to be light because they are still seedlings? I suppose so... No sign of yellowing or milting or burning. The leaves feel fresh, just light green.

your thoughts on this and any advice will be much appreciated
Thanks a lot!!

peace

I should mention that the window is slightly opened now, at the minimum, and the light at 12 inches, in order to keep a good 75 temperature. If I get the light any more distance, I will have to close the window, so I will not get fresh air into the room, anymore. That's why I am kind of constrained to keep the light at 12 inches.

Maybe get a " heating mat" theyr pretty cheap and designed for plants,, that way you can keep your light at a safe distance and keep the pot bottoms warm , close the window ,, eyr too young for cool air ,,

If you are worried about light stress,watch your leaves..the edges will start to curl up.You want to avoid that,generally its irreversible and will reduce the effectivness of the leaves doing their job.Indica cultivars are very susceptible to this.Seedlings dont need all that light,raise it up,if you see stretch with no leaf growth you went to high.

plantsinpants said:

Maybe get a " heating mat" theyr pretty cheap and designed for plants,, that way you can keep your light at a safe distance and keep the pot bottoms warm , close the window ,, eyr too young for cool air ,,

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Resinhound said:

If you are worried about light stress,watch your leaves..the edges will start to curl up.You want to avoid that,generally its irreversible and will reduce the effectivness of the leaves doing their job.Indica cultivars are very susceptible to this.Seedlings dont need all that light,raise it up,if you see stretch with no leaf growth you went to high.

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THank you very much for the quick repies!!
SO, should I understand that 12 inches is too close, no matter that there is no heat and the right temps?

Ya for seedling I think so.Try 24 if you get stretch like I mentioned,go to 18.

Resinhound said:

Ya for seedling I think so.Try 24 if you get stretch like I mentioned,go to 18.

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Thanks a lot, RHound!
I just raised the light.. I am somewhat pissed off cause i had a lot of headaches this past week trying to dial in the set up and finally it was working smoothly and constant.. Now i had to turn the room heater on and star all over again with the dial up )) soon it will be too warm inside the room. too bad that i can't use the lights as a heater. it was so easy to adjust it, if it was getting too cold late in the night (lights on), get the light a little closer. if too warm, get it a little further away
I will see how i can dial it in with the help of the heater cause I wouldn't like to close the window

Ya sometimes its tough finding that happy medium between heat and intensity,specially with seedlings.Once they get bigger and are a little tougher,youll have more room to deal with stuff like that.I think a heating mat is a good idea.