Light leakage with grow box

I am preparing to build a grow box that is approximately 30in x 30in x 36in or perhaps a little larger in size depending on how many plants I decide to grow inside of the thing.

I am trying to figure out what kind of fan(s) I should use for this setup to reduce light leakage. Ideally I would like zero leakage if possible.

I do not want to spend money on an in-line ducting fan as this box will be small, so I don't see myself needing larger than a 150CFM fan for this application but time will tell if temps are too high. Any ideas how to reduce light leakage?

An example of the problem at hand is the following:

If I use a 120mm PC case fan like below, the leakage will be immense.
http://www.amazon.com/Cooler-Master-120mm-Case-R4-C2R-20AC-GP/dp/B0026ZPFDE/ref=sr_1_cc_1?s=aps&ie=UTF8&qid=1340733861&sr=1-1-catcorr&keywords=muffin+fans

You don't want light getting out, or light getting in?

hornedfrog2000 said:

You don't want light getting out, or light getting in?

Click to expand...

I do not want light getting out. I'll have approximately 5000 lumens (maybe more) within the aforementioned area. Lights will be on 24 hours per day until the 12/12 cycle, and this will also be in my bedroom so minimizing light leaking out would be quite desirable.

You could do a darkroom-style light trap with staggered panels (or panels with holes in them). I've made a rough "top down" diagram to give you an idea of what I'm talking about. The major parts are labeled. The pine-colored parts are solid wood or plywood with routed notches to fit the panels (which should be caulked - or at least glued - during assembly). Make a "U" of frame pieces, caulk the notches, and slide the panels in. Then caulk the notches of the top piece, fit it, and screw it together. If you want to run a charcoal filter, install a 4" flange sticking out of the box and move the fan inside the box. A speed control is also a good idea for the exhaust fan (but it must run at all times). Lamp cooling (if any) should be on a separate duct run.


A variation of the above light trap can hold standard 1" HVAC filters. I'm a proponent of the "clean room" school of indoor growing. Catching spores/pests before they get to your plants is a good idea. The corners, doors, and other openings must obviously be well sealed or this won't work as well. To "encourage" incoming air to "go in the right way", make the intake hole(s) larger than the exhaust (6" - or the equivalent in square inches - should do well with a 4" exhaust). So that's my two cents...

I should add that the diagram is nowhere near right as far as scale goes. You'll need to do some math there; the space between the panels and the frame (or the size of the holes in the panels if you choose that route) should be equal (in square inches) to the size of the intake or exhaust. This goes for the space between the panels, too. Don't forget to take the thickness of the panels into account (though an eighth of an inch here or there probably won't hurt anything). It's better to go a little larger than needed rather than smaller (as mentioned in #1 above).

If you decide to attach the fan directly to the light trap (as I mentioned earlier) don't forget vibration dampening. Neoprene is a miracle substance in this respect (and it also helps to seal the fan/trap junction). Some vibration (noise) will be transferred no matter what you do, but I doubt that you were expecting absolute silence. The acoustic foam will help capture some fan noise but allow 3/8"~1/2" of extra space between panels for 1" pyramid/eggcrate foam - that's roughly its thickness when you average out the peaks/valleys).

I can't think of anything else to add at the moment. If you have any other questions, feel free...