# MH light height



## cleanbuds (Mar 11, 2015)

400w MH how high should it be? just started veg of 2 plants. it's currently about 12".


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## pcduck (Mar 11, 2015)

I use the back of my hand.
Place hand at canopy level.
Raise light until no heat is felt.


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## Kraven (Mar 11, 2015)

cleanbuds said:


> 400w MH how high should it be? just started veg of 2 plants. it's currently about 12".



At least 18" - 24"  I use the back of my hand method, if I can keep it there on top of the canopy for a whole minute without it getting hot the the light is at the right height. But that's on an open reflector hood. With a good fan blowing just under the hood and over the canopy i can keep it around 20". Younger plants cant take the intense light.


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## Kraven (Mar 11, 2015)

pcduck said:


> I use the back of my hand.
> Place hand at canopy level.
> Raise light until no heat is felt.



ditto the duck beat me lol http://www.marijuanapassion.com//www.pinterest.com/pin/create/extension/


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## The Hemp Goddess (Mar 11, 2015)

I've got mine about 6" away.  I have an air cooled hood and a 190 cfm exhaust fan running on low, a 32" x 32" tent in a room that is about 65F.


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## cleanbuds (Mar 11, 2015)

It stays surprisingly hot does MH run hotter than HPS? It's 80ish just about all the time. I'm considering adding a duct fan. THG are you blowing the cooler air through the hood into the tent? 

View attachment IMG_2383.jpg


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## The Hemp Goddess (Mar 12, 2015)

Do you have an exhaust fan?  You will not be able to run a 400 MH without one.  A duct booster fan will not cut it, though--do not waste your money.  Yes, I have a 4" centrifuge type fan in the space connected to the light with ducting and then it is ducted out of the tent.  But I am sucking the air through the light, not blowing it through the light--you want negative pressure in your space.  The intake is passive.  This morning, it is 64F in the room the tent is in and the tent is running at 71.5F.  Fan is running on low.  I can post up a pic later if you would like?


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## cleanbuds (Mar 12, 2015)

ok yeah that would be nice I have a 4" inline venting negative pressure out the tent. 

The thing is I just have an open window and passive air intake into the tent. I was trying to consider a way to bring in the fresh air with a duct fan and have the 4" inline continue cooling the light


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