basic light trap, one elbow or two?

I can't believe I'm asking this question...

Is one plastic elbow tubular thing attached to the outside of your box on an intake hole enough or do you need to attach another elbow to the end of the first one? With one of the these elbows on there, the back of the box is perpendicular to the end of the the elbow... so it's just one complete curve... I thought that was enough to trap the light but now I am wondering if you need 2 curves. Basic physics I know, I just don't remember. I noticed the light from inside my box was reflecting through the elbow a little bit (maybe I just answered my own question). It is black plastic... is that just as good as painting it black? Would it still reflect if I painted the inside of it with black paint? I don't even think I could add elbows to the elbows I already have jutting out the back of my box because the ends of them are not perfect circles, they are warped.

In my experience 2 doesnt cut it, had 2 elbows on my small clone box and 2 the elbows didnt block the light from a 23W cfl.

Depends a lot on how you position them. You can get away with just 2 elbows but not if you line them up in the typical "U" shape. Make more of an "S" out of them, like so:



Paint also helps massively. Your plastic elbows are black but that's not enough. Pick up a can of this:



Flat protective enamels like this Rust-Oleum do a much better job of absorbing light than normal paint. Coat the inside completely and let it dry well:



Slip the elbows back together like this and I think the difference will surprise you. Good luck!

I use single elbows painted black and they work fine.

When I got my C13 back in 03/04 my first initial passive intakes were four 2" I.D. PVC tubes about 12" long with 2" PVC elbows.....not a leak.

Since then I have purchased some 8" x 8" louvered darkroom vents from adorama.com.
I like the louvered darkroom vents much more as they take up no florrspace and end up pretty much flush with the cabinents back wall/side.

If you're trying to just use PVC elbows then you'll need atleast two to make a light trap if not using any PVC pipe.Do like LadyLargely posted making an "S" with the two PVC elbows.

Remember your intake area should have 3.14x the area as the exhuast fan....To find the area of your exhuast fan all we need is the measurement of the fan,we'll use a 4" fan for reference.

the formula is pi x r2 = area of exhuast fan or 3.14 x radius x radius = area of exhuast fan

we know that the radius of a fan is half the diameter so

3.14 x 2 x 2 = 12.56 square inches/are of exhuast fan

Formula for intake area is

3.14 x 12.56 = 39.438 square inches for minimum intake area.

Jnugg, using Pi to figure intake orifice is three times the intake. That is overkill in most any situation. And quite costly if considering louvers.
That is your formula, yes?

An HVAC system will normally be designed to allow for the intake to be about 10% larger than the exhaust.

A system that is not quite optimum could require a bit more intake than 10%, and quite often hobby grows will be less than optimum in the air flow category. So, a rule of thumb for grows is to have twice the intake port as you have exhaust port. The system will never need more than double the exhaust port size, but could well need more than 10% over.

Damn man, three times as much intake area as exaust? Definitely seems like overkill to me. I mean, maybe if you're stuck using some crummy PC fans for ventilation, but if you have a decent axial fan capable of generating a good head pressure then 3x seems like a lot.

I run a dope-ass S&P mixvent fan: not-quite-axial-not-quite-centrifugal. With the pressure it makes I didn't see any temp improvements when I went from 1 times intake vs exhaust to 2 times intake vs exhaust.

*srugs* but having lots of inlet area certainly won't hurt. More the merrier as long as you can fit it in your design.

LadyLargely said:

Damn man, three times as much intake area as exaust? Definitely seems like overkill to me. I mean, maybe if you're stuck using some crummy PC fans for ventilation, but if you have a decent axial fan capable of generating a good head pressure then 3x seems like a lot.

I run a dope-ass S&P mixvent fan: not-quite-axial-not-quite-centrifugal. With the pressure it makes I didn't see any temp improvements when I went from 1 times intake vs exhaust to 2 times intake vs exhaust.

*srugs* but having lots of inlet area certainly won't hurt. More the merrier as long as you can fit it in your design.

Click to expand...

You are right LadyLargely it is somewhat overkill but here is my school of thought.

Using a bigger intake hole allows the intake/incoming air to be at a lower velocity which helps minimize mixing up of the air in the grow space which in return allows the exhuast fan to work more efficiently.

Now you might be saying to yourself well don't we need the air to mix up...sure but isn't that one of the reasons we use oscillating fans in our grow rooms/cabs/boxes/tents?!I mean not only do the oscillating fans mix the air a little so we don't create heat pockets,they also help sturdy our plant stems so we don't end up with weak stems that can't support the weight of the buds.