stupid question time

Discussion in 'Growing Marijuana Indoors' started by riffriff, Nov 19, 2014.

  1. my tent is really easy to keep cool because of where is is located, so cool that i can get my light to about a foot away from the pots, and still only read 78-80 F with the thermometer directly under the light. My question is if the light, not the heat it produces, but the lumens, can be that close without damaging the plants. Is it better to have them as close as possible to the light as long as my temp stays low, or should they be a certain distance away? I can pretty much set the temp to about 75 in the tent, no matter where the light is, by opening flaps at the bottom to let in more cold air, or by closing the top stack some to trap in more heat. It is a 400 wattmh/hps. thanks. 

  2. #2 ProGMOII, Nov 19, 2014
    Last edited by a moderator: Nov 19, 2014
  3. I would take it back just a hair from your plants just so there's more spread. 78 degrees is perfect temp. as far as i know about lumens is sure it can be that close but there is a max it can absorb and any others will just be wasted. don't think it will hurt the plant though.
  4. thanks guys.
  5. I'm so jealous. I'll never have this problem in SoCal.
  6. I don't even have my cool tube hooked up; in fact, i need the heat from the light. I have a little space heater on a timer for the dark period, and it drops to about 70 F. And my ballast is is basically in a fridge right now. But it will be all hell up there in the summer. I will need a window unit to cool it down.
  7. I can't get my temps below 85 (usually it's high 80s). they only go down to 76 with the lights off :(
  8. I'll make it even easier than the lumen charts. To get accurate figures, anyhow.

    Light "falls off" as a function of the square of the distance from the source.
    If the bulb's rated for 92,000 true lumens (a typical decent quality 1000 watt MH), this is at the bulb (an inch from light source itself), direct light.

    At 18 inches, this falls off by a factor of 18 squared or 1/324th the tested intensity at bulb. 237 lumens.

    What MAY give you trouble is lux, not lumens.

    Lux is a measurement of lumens per square meter of direct light. Reflected light loses energy. PERIOD.

    So while you'll get around 638 lumens direct light at 12 inches from the bulb (do the math, or use a light meter...that's very close), that's only true of the DIRECT light.

    So whatever is getting light direct from the bulb, not from refection off the hood or walls is getting around 638 lux.

    Sunlight delivers 128,000 lux.

    Answer your question?

    Oh...reflected light STILL delivers some illumination, so, though it's lower energy, and more diffuse, it still helps. But regardless, the only way you'll ever burn a plant with the actual LIGHT is too much UV (same way we get sunburn), which HIDs don't carry much of, or by rigging a light system that would brownout Los Angeles and immediately vaporize your neighborhood...3,000 watts HID at the bulb would do it, but since you'd need to move farther due to the heat produced, 200,000 watts MH at 1 foot from plant, or .54 megawatts at 18 inches.

    Now try to figure it for delivering sunlight intensity at floor level from 6 feet. Large scale plasma production levels of energy.
  9. #9 Indie-Kah, Nov 20, 2014
    Last edited by a moderator: Nov 20, 2014
    Multiple ways to deal with this.

    First...are you using fans to blow air IN, or suck air OUT? With a ducted hood, mount the fan inside, so it takes air in from the top of the tent (top of the inside of the tent), blows it over the lamp, through the hood, and then outside. Underpressure will bring cooler air in from outside. Use a high CFM fan to do's away from the plants, being mounted up high, so it won't hurt them, and underpressure in such circumstances will bring the new air in from down low, where it's cooler than even the general outside air (though not by a whole lot).

    Second...screw an air conditioner...expensive, expensive to run, and, frankly, too much of a draw on power for most of us to have circuits to "waste" on it....try this:

    Take a quart milk jug per 2 plants. Clean it REALLY well. cut it off just above the handle. Fill it halfway with water, place between each two plants.
    Every 2-3 days, drop a piece of dry ice in (calculate dry ice to put in about 400 ppm by volume at sea level, not by actual measurement.... the figure is .04%, so if you have a 4 x 4 x 4 grow area, that's 64 cubic feet, you want a dry ice chunk totaling .025 cubic feet, or about 43 cubic inches. 4 inches by 5 inches by 2 inches, or similar. Try to break it up evenly to fit in however many jugs you're using, so you get uniform rates of cooling and release.

    The "fog" is pure CO2, and is cold. The fan will draw it upwards, and it will expand as it heats...heat "moves" from hot spots to cold spots, not vice versa. Cools the whole tent, and supplements CO2 without $300 in hardware and $80 a shot on CO2 charges for the tank. Water stays remarkably cold, even in such low volumes, when treated this still under 40 Fahrenheit 48 hours after it stopped fogging, just before dropping the next dose of dry ice in.
    And the cold is down it keeps the grow medium cooler than the air...a good thing, as that's how it is in nature.
  10. such thing as a stupid question...just ones someone shouldn't have to ask because the answer's pretty obvious. And this wasn't one of them.
  11. My biggest problem is that my tent is in a walk-in, under-the-stairs closet so I can't get enough fresh air in and I'm renting so I can't cut vent holes.

    My setup is Cool tube=> 240CFM Fan=>out the top of the tent and out of the closet. I also have a big household fan on the ground blowing air into the closet.

    you're saying I should be pushing the air through my cool tube? I always thought I was supposed to pull :huh:

    I've never heard about dry ice being used like this but I'm intrigued. where is it sold?
  12. You can get dry ice at most grocery stores. That's where I get mine...Fred Meyer's (Kroger stores). Just ask when checking out for a pound of dry ice...under $5. It'll store in your freezer (don't let it touch anything you want to eat) with minimal losses, and use oven mitts (dry ones) when handling.

    Suck hot air out. Every time. Overpressure is a negative, unless you're talking a clean room, in which case, the air being introduced at higher pressure has been filtered to being sterile, and the purpose of being higher pressure is to keep non-sterile air out.

    You ever built a serious gaming computer? How do you most effectively cool the proc? All the fans on the back suck air out, and blow it away...ONE fan, on the side panel, blows air directly onto the heat sink. The rest of the air is brought in by negative pressure, and cools the MB, graphics cards, etcetera.

    Same principle. Heat moves from hot to cold. If you introduce cold air, the heat transfers from the hot air to the cold air. Not as good for removing heat, since you're just redistributing it, right? On the other hand, take that hot air and forcibly move it OUT, it's not there TO heat the cold air being introduced.

    So what you SHOULD be doing, to most efficiently manage this, is...well, the best way, without an enclosed ducted hood...go get a band clamp and some appropriately sized flexible duct. Straight duct works a bit better, but not really enough to matter, unless you're going to be making your flex duct look like a play tube at a damn Chuck E Cheese's.

    So you band clamp the duct to the ring around the intake from the fan (the exhaust is where it blows out), and move the open end of the duct to where it's right next to, and facing, the lamp's bulb, oriented as close as possible with the lamp (if the lamp is horizontal left to right, you want the duct as close to horizontal, left to right...basically so it's already oriented so you could tuck the light right into it by moving one or the other towards each other).

    This will suck the air across the bulb and into the duct, through the fan, where you exhaust it OUT of the enclosure.

    Naturally, this means you're losing 240 cubic feet of air by volume every minute from inside your enclosure, right?

    This means now the closet has lower air pressure than the outside room. The outside room's air is going to push itself in, trying to balance pressure. It'll TRY to do it at the rate of 240cfm. As long as there are enough gaps that aren't airtight for it to do so, it'll succeed. And the resulting cool breeze of fresh outside air will be coming in more gently than it would through a fan, because the inlets are more disbursed (it's coming from more places).

    So no, I wasn't saying you should be pushing air IN with the CoolTube, I was saying you should be pushing it OUT with it, but specifically drawing it across the bulb while doing so.

    Also, a nice thing about negative pressure....even if the inflow from pressure imbalance can't keep up (and a mere 240 CFM, it should be able to--I ran a 4 by 4 by 6 tent with an 8" WindKing 745 CFM this way, and the tent managed to pressure balance OK--in a Gorilla tent, which has a reputation for being rather good about self-sealing)...if the air pressure's lower, it means there's less air in there...less air in there means less air to be heated up, which decreases the efficiency of transfer of heat from bulb to air to plants and walls. Plus depressurizing cools things...that's how a radiator works, why a compressed air can gets cold as you discharge it, etcetera. Compress something, it gets hotter, reduce pressure, it gets colder.
  13. #13 dukedogg76, Nov 20, 2014
    Last edited by a moderator: Nov 20, 2014
    My setup is as follows: Filter -> exhaust fan -> Air cooled hood -> out of the room. This way I'm sucking through the filter (creating a negative pressure in the room, but blowing the air through the hood. Why would you want to blow the air through the hood versus sucking it through? My air cooled hood leaks. So I was cleaning the air first with the scrubber, but then the fan was pulling smelly air through the leaks in my hood and kicking out smelly air. By setting it up the way I did, the clean air coming in now pushes (positive air pressure) through my hood, keeping the stinky air out.

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  14. #14 Indie-Kah, Nov 21, 2014
    Last edited by a moderator: Nov 21, 2014
    Because, as you just said, your hood leaks.
    You create MORE pressure blowing in. This means more heat, and more air to transfer heat more efficiently.
    Suck the air across the bulb, the air coming across the bulb picks up the heat. Being lower pressure to begin with because it's being sucked through (that's what suction is...your outside pressure's higher than your inside, so the air pressure tries to balance), it's cooler just because it's lower pressure. And it's moving ALL the air past the bulb and away, leaks or no leaks...because the pressure around the bulb is lower, the cooler air outside the hood is at a comparatively higher pressure, sweeps in through the leaks, then out through the duct, all at lower pressure than the tent, which SHOULD be, if you're doing this, lower than the air pressure outside the tent.

    Use physics to your advantage, EVERY time.

    BTW, ALL hoods leak...some just leak less than others.
  15. My setup is just how you described. except I have to leave the main flap on my tent open so I'm not sure how my air pressure is working..

    I think my temps are as low as they can get without a better fresh air source. I'll have to look into an AC unit or dry ice..

    Thanks for your input
  16. this claims a 12 degree drop, without all the electricity usage of a small a/c, for less than $90.
  17. Purdy.
    That 12 degree claim is for a room in a house, though...where it's trying to drop a room with a disbursed heat source, not a small enclosure with a concentrated I have to wonder if it would perform that well in a tent. Might actually do BETTER, for all I know, but I doubt you'll see the "rated effect", whether actual effect is better or worse.

    Going to have to try one, myself, and find out, come warmer months...thanks for the find!
  18. I am assuming that this would need you to add the water to it; I wonder if you could throw some dry ice in the tank as well? Think that would freeze it up?
  19. Hell if I know...but I definitely need to check that thing out a bit better in person, down at the local store.
  20. Dry is in CT is about .80 to a dollar a pound. I work at an icehouse so have access whenever. Be careful handling it as it will insta burn your skin off

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