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Thread: Light and glass and heat..

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    420 Member ReactiveLlama's Avatar
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    Light and glass and heat..

    Greetings,

    Just a quick question. I'm going to build a small grow cab with a foot print of about 30x33 inches. I intend to put a 430 Watt HPS in there and grow a 3-4 plant scrog. Now I want to get my light down to give my screen the ideal amount of light. I was told for a 400 Watt that's about 18-24 inches. Now that's distance between light and screen the buds will be growing up into that space and I worry about the heat. I looked into a cooled hood but can't fit one in there comfortably. So I saw something else that might serve. I want to now put a plane of glass at about the 24 inch height (above screen) and lower the light right down almost on it. Then have a fan mounted slightly above that to blow on the light and glass. The fan I want to use is a 120mm PC fan on steroids. The thing is rated at 200 CFM.

    Think that'll keep the temps reasonable? The rest of the cab will be having its air exchanged by a 95 CFM fan with a carbon filter..

    Thanks!

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    Re: light and glass and heat..

    I would increase the cfm of the fans or install more of them.I have a set up with a foot print of 26wX34L.I have 2 105 cfm fans in the light box.In the grow box i have a 400cfm fan that exits into a carbon filter.I grow my plants 6 to 10 inch's from the glass and have never had a problem with heat.My light is a 400w hps.

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    420 Member Racefan's Avatar
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    Re: light and glass and heat..

    try and find tempered glass as it won't shatter from too much heat.

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    420 Member ReactiveLlama's Avatar
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    Re: light and glass and heat..

    Thanks Kush!

    So I can increase the 95CFM fan that I was going to use as the primary exhaust and replace that with something a little more macho. I can do that for only a few dollars more to an Active Air Exhaust Fan 265CFM w/ 4" Intake. If that won't do on a 50 CF grow cab what will? And for $30 I can use an Axial Fan 4" w/ Cord 105CFM for the light.

    Now an important thing to consider is that my light box and plants will NOT be sealed from each other. This is because I want to raise and lower my light for times when I want to grow something other than a Scrog, like when I want to grow out a pile of seeds to pick a good female, ect. The 265 (replacing my original 95) will be the fan pushing or pulling through a filter, and the small 4 incher will simply blow on the light/glass..

    Upping the CFM of my main exhaust fans toes in more with another thought I had which was to use a replacement vacuum cleaner filter (some even use Hepa filters) as a filter on my passive fresh air intakes. I know a filter at each end of the flow-line (is there such a term?) puts a lot more load on the exhaust fan which is why it's so much more powerful (and designed for such uses!).

    Thankfully for putting some air on the plants I have several spare 120mm and 80mm PC fans that can be wired in there.

    Racefan!

    Tempered glass? What thickness? Buying a plain pane of glass is something I've never done before, so I have to admit I'm not entirely sure what to get. My bong has 5mil glass and that seems plenty thick.. It feels thick enough to use as a weapon in a pinch.. NOT that I'd ever do something like that with my baby! I'd take a bullet instead!!

    Thanks!!

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    Re: light and glass and heat..

    I just had someone cut standard window glass for my hood. I use Ice Cap Fans(Temp. sensetive, around 20 bucks). I use one in the wall, one on the hood.

    Who told you 18 inches?

    I keep my 400w 3-4 inches MAX FROM the tops. No heat problem. I only adjust once a bud touches the glass. At 18 inches, they will be spindly, and take six months to grow.
    Last edited by Keith Lake; 02-14-2009 at 03:14 PM. Reason: Guidelines

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    420 Member Racefan's Avatar
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    Re: light and glass and heat..

    I'd go to a hydro store and buy a replacement lens for a air cooled light. About $15.00 and it's tempered. lol

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    420 Member ReactiveLlama's Avatar
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    Re: light and glass and heat..

    Quote Originally Posted by Theincubus View Post
    Who told you 18 inches? I keep my 400w 3-4 inches MAX FROM the tops. No heat problem. I only adjust once a bud touches the glass. At 18 inches, they will be spindly, and take six months to grow.
    The way it was explained to me is like this:

    Light as you know follows the inverse square law, ect ect.. So for a 400 Watt HPS the light's most effective range is from the bulb to between 18-24 inches. Any parts of the plant further away than that is getting less than ‘ideal’ amounts of light and it gets worse from there. Now this ‘ideal’ distance might just be for buds in terms of the light intensity, I’m not sure…

    I'm going to grow a scrog and as you know the plants then only grow 10 inches meet a screen and are trained. At that point the only parts of the plant you want to get light now are the bud sights and fan leaves and those should all be at the level of the screen by the time you're ready to flower. I plan on having a height adjustable light, so it became a matter of how close could I safely get to the buds unshielded and how close can I get with a simple shield rather than an actual proper ventilated hood. I don't know what kinds of height to expect from the buds once they start to flower.. Perhaps 3 inches, perhaps 20! But I want to give them all the light they can handle without burning or bleaching but at the same time don’t want to the bottom part of the bud to start lacking for the ‘ideal’ amount of light and that means the most above my screen I want to raise my light is 18 inches.

    That's what I was trying to get straight in my head in my usual backwards round about way... And now I have an idea, that with a glass shield and a fan I can almost have the buds touching the glass. Thanks!!
    Last edited by Keith Lake; 02-14-2009 at 03:14 PM.

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    Re: light and glass and heat..

    Just put your hand at the top of the plants. If it's hot to you, it is to them. With my icecap fans, I can hold my hand on the glass, it's warm, but not hot.

    That explains the fans. Even if you need to vent a small closet or box, these would work great. When the lights are off, they draw min. power, and run silent. As temp. increases, so does the fan speed.

    If you got a couple of these, attach the probe to your hood(or the hottest part you can find) you will be able to get the light closer.

    Those little fans are extremely impressive, and take very little power.

    You can buy them here: IceCap Variable Speed Fan 120mm - AquaCave
    Last edited by Keith Lake; 02-14-2009 at 03:44 PM. Reason: deleted dead link

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    420 Member Racefan's Avatar
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    Re: light and glass and heat..

    a 4inch fan runs $50.00. Pretty expensive considering you can buy a 4 inch fan from radio shack that runs on 120volt already for 25.00. One that runs 12 volt and requires a adapter like that icecap one uses runs about $10.00 or less. Yes the built in temp controller is alright but personally I don't want "any" power going to my fans unless my light is on and a running the power to the fan in conjunction with the on off switch for the light gives me that option already. With the cost of electricity I need to control what runs and when. Not the other way around. Plus with my enviromental controller my fans come on by temp "and" humidity already.
    Last edited by Racefan; 05-01-2008 at 08:30 PM.

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    Re: light and glass and heat..

    Those are 12 volt fans. They draw less than that when there is no heat. If your worried about the cost of electricity, these are even better. There is no adapter. That fan can only draw 12 v. MAX. They cost nothing to run, are silent, and move a shit load of air through the hood. I leave them on 24/7. as they pretty much shut off after the room is cooled. Lets not forget, the are silent running fans. You only hear the air moving threw the blades, you don't hear the fan itself.

    I suppose rather than pay more for a MH and HP lights, I could clime a light pole and steal one of those cheap street lights. I'm a firm believer, you get what you pay for. I would much rather run more light, than piss money down the drain on cheap fans.

    I put mine inside of the hood where the light socket is. Have run it for 3 years, never a problem.

    I want constant air circulation, and no humidity. I do just fine.

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    Cannabis Connoisseur Boss's Avatar
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    Re: light and glass and heat..

    I plan to run an intake from one side and exhaust out the other, so the fan will only need to be on when the light is on. But I really like the idea of an automatic fan.