Less heat or more light?

So I just stepped up to a 400w HPS from 180w of CFL bulbs. I am growing in a 2x3.5x7 foot closet. I have a 6 inch duct coming in and another coming out for ventilation however it is still hot it my house due to my location. The ballast is dim able so if I run it at 300w my closet gets to 80-82. When I run it at 400 it gets to 88-90. My plant is only 18 inches tall in the second week of flower but it is 2x3 feet wide (Top and LST). My question is what is better more light or less heat for yield? I wont be able to spend more money on this grow.

I am using a DWC system. Fox Farm Hydro nutes.

have you got a oscillating fan that can blow the air above the canopy and and below the light as this will reduce the canopy temps a lot

and increase yeild as you can get the light closer to the canopy and it still reduces the canopy temps

temps are ok up to 33c before it affects your plants/yield

I have 3 fans, one is the exhaust out, one is the inline in and the other is blowing right between the canopy and bulb. Just wondering if 90 ambient in closet is too much or should I cut it to 82 and lose 100w.

Well dimming MHs suck kinda because you lose some blue spectrum light. But it may be your only solution as 90 is too hot to maintain as a normal day temp. If you can cool down your surrounding area(a/c-central air) that will help with temps in the grow room via the intake. A cool tube or air cooled hood is the other option but not one I like.
One could also do both. You could dim your 400 before the lights come on and then switch it to full 400 the second half of the day or vice versa.
Temps can be tough in smaller rooms.

That girl is a beauty, take care of her.

She is a beauty, and you should definitely find a way to run maximum light while keeping the heat down in the lower 80's. As mentioned, a fan blowing directly on your light source will help immensely and you should definitely consider a cool tube in the future.

Oh, BTW, clone that bitch !!!!!!!

I would run 300W with perfect temps anyday over 400W and 90ish ..

with lower temps you might also be able to move it a ince or two closer = more/same light as with 400W

a open hood with a 4" tube on top for some tubeings to your 4" outtake vents could also work great .. if you cant get a cool tube/hood ..
and yes .. get temps in the room of the passiv intake down or runn a tube to a open window/intake chanal or cool place ..

Ooh yea .. and just to make sure .. you do run it at night .. right ?

Thanks thehole and greenmonkey. If i bought a cool tube and reflector would i have to add anymore inline or exhaust or just stick to what i have?

Slipon- I'm researching cool tubes, and as much as i hate running at night in my room yes i am.

Slipon said:

I would run 300W with perfect temps anyday over 400W and 90ish ..

with lower temps you might also be able to move it a ince or two closer = more/same light as with 400W

a open hood with a 4" tube on top for some tubeings to your 4" outtake vents could also work great .. if you cant get a cool tube/hood ..
and yes .. get temps in the room of the passiv intake down or runn a tube to a open window/intake chanal or cool place ..

Ooh yea .. and just to make sure .. you do run it at night .. right ?

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I will also try to lower my light inch by inch while I figure out how to get 400w.

trux said:

I have 3 fans, one is the exhaust out, one is the inline in and the other is blowing right between the canopy and bulb. Just wondering if 90 ambient in closet is too much or should I cut it to 82 and lose 100w.

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Hi truk
90 is good for 2nd week in veg up to the 3 week in flower After that you
need to bring the temps down

Heads up. marijuana stops growing at 86 degrees F. Thats not an option in my grow room. 300w is plenty for that lil beauty! try to keep it close enough that you have to move it up every day, and dont be lazy with it. give plenty of water on those hot days. looks like your doing awesome. yes if you dim your ballast you lose some blue spectrum, but you want more red spectrum in flower anyway. turn that puppy down, save some energy (money) lower your light and increase your yeilds!

Ok
But my temps have been round 90 for last week and my plants look good

May be its down to the strain but
I thought you could go upto 34c
Without stressing you plant much

Sorry if got this wrong

78 is supposedly the ideal temperature. I have seen pot grown at higher temps and there were definitely issues. The grower thought everything was just fine. Of course, alot of people grow at higher temps and think it is "just fine". Well with the type of genetics we grow, yes its still going to be good. If you dont think your crop is taking a hit because of higher temps then you just dont know.

I disagree with "plants stop growing at 86°". They require more co2 at higher temps but I had a run where my temps were 84-88 a whole cycle and the results were still better then average. no co2 added. Its going to be dif for dif strains but id say 90 without co2 is pushing it. Id drop it to 300w. Your plants may look ok for now but I wouldnt risk heat stressing them over a extra 100w.

I stay between 75-79 lights on and 70-68 lights off now and my girls couldnt look happier

buy some dry ice or make a CO2 generator out of some yeast and sugar and 90's isn't a problem. well i should only say that as long as your closet it sealed you say that you have an intake and outake fan...is this passing through a hood? or just the room? if you're venting the room than c02 isn't an option.....but not only would co2 let you run higher temps but it would also increase yeilds.

yea Co2 is a option and can really increase yield .. atlest it look like it at the pics I have seen (no experiance here)

but be carefull .. dont run it in your bedroom Etc.

I have my grow room in my appartment .. so for me its a no go (just my oppinion) but I wouldnt bother .. Ill use the time/work/money on a cool tube or AC insted ..


BTW
Im working as a metel worker/welder and have for the last +20 years .. so I could have realy easy and cheap acces to Co2 tanks and all the ventils and stuff that follows ..

I think I am just going to play it safe on this one and run at 300w. I am really low on medicine and would hate to have to start over. After this grow temps should cool down enough in my area to use 400w and not be so hot.

mnmobbin said:

I disagree with "plants stop growing at 86°". They require more co2 at higher temps but I had a run where my temps were 84-88 a whole cycle and the results were still better then average. no co2 added. Its going to be dif for dif strains but id say 90 without co2 is pushing it. Id drop it to 300w. Your plants may look ok for now but I wouldnt risk heat stressing them over a extra 100w.

I stay between 75-79 lights on and 70-68 lights off now and my girls couldnt look happier

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Yep, this right here. They will grow below 90s and they will finish with good smoke at the end. But you run that same strain over again at the proper temps and you will see the difference. The plants will be much happier and happy plants is good.

watch your crop closely and you will find that if your temps are in the 90s F your plants wont put on much new growth when the lights are on but grow alot by the next morning. although they look healthy, they are mearly staying alive in the higher temps and then producing new plant matter with the cooler temps at night. it really shows up outdoors. proper temps=constant growth=higher yeilds

oh, also, a sativa dominant strain will put up with much higher temps than an indica dominant strain. can't remember what you're working with, but if it's sativa 90 degrees during veg really isn't going to mess with it.

300W will get her done, with fuller buds from the lower temps, imo. like Slip said, you may be able to get closer to canopy with lower temps, also