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Need Help 400 watt mh light adjustment.

Discussion in 'Grow Room Design & Setup' started by purplepride, Oct 14, 2013.


    purplepride Member

    I am on my first indoor grow. I started out with a 400 watt mh air cooled hood in my tent. I have a fan circulating over plants and another fan pulling air through my sealed hood to outside my tent. Temps have been from 72 morning - 80 degrees during hotest part of the day. I started out with the plants about 18 inches from the bulb when they broke through the soil. I lowered it down little by little through the last 4 days and today is day 5. They stretched out to about 2 inches around day 2-3. I have gotten the light down slowly to about 12 inches from bulb to the tops of the plants and they are working on there 2nd pair of leaves this morning. My question is. Is it normal for the light to be this far away. I know its 400 Watt MH but even 12 inches seems far away. How do I know where the sweet spot is? I dont want them to stretch anymore but I dont want to burn them either. Please any serious or knowledgable advice would be appreciated. Thanks


    spek9 Well-Known Member

    I keep my 400w cooltube about 6" above the plants that go from the cloner into the tent, and when they get larger (about 2 weeks), I keep the light 2" above the tallest plant.

    Note that I'm in a 2x4x5' tent (small space) with a 440CFM at full blast when lights are on to keep it cool. Rule of thumb is put your hand palm-down on top of your tallest plant, then lower the light until it feels to hot for your hand after 15 seconds, then raise the light 2" from there.


    purplepride Member

    Wow thats the closest i've ever heard of. I'm not moving quite that much air through my tent. I have a 6" 334 cfm and I got it dialed down so it only moves anough air to replace the air in my tent every 1 or 2 minutes. But it keeps my hood ice cool. I just got mine set good enough today to run at 70-75 degrees. Thanks for the advice

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