Cheap and easy light trap!

  • Food storage container, with one being 50% taller and about 2" wider (diameter) or 1"x1" WxD larger if square. (i.e. 4" diameter, 3" tall for one, and 6" diameter, 4" tall for second)
  • Krylon Fusion Flat Black Spray Paint
  • Pastic cutter, Dremel, or utility knife
  • sharpie or other way to mark your work
  • adhesive to connect plastics
Figure 1

Figure 2

Figure 3

Figure 4


  1. Remove the tops from both containers. (Figures 1 and 2 give example sizes for demonstration purposes)
  2. mark a line the size of your intake exhaust line on the inside of your smaller containers lid, making it no bigger than 1" smaller on every side cut out marked in area (refer to figure 3)
  3. center the smaller lid on the larger one and transfer the cut mark to the larger lid and cut it out as well, and attach them together (figure 3)
  4. Using the picture as a guide, cut slots out of the larger containers sides that are half as tall as the smaller container, starting from the top of the container. (Figure 4, containers shown upside down.)
  5. Turn the smaller container upside down, and cut slots out of the bottom of the container (refer to figure 4)
  6. paint insides of lids and containers, as well as outsides optionally, and allow to dry (1 hour)
  7. Attach the lids to your vent/intake surface, then attach small container then large container. (Figure 5, below)

Figure 5 - Assembled

optional: if you cut slots rather than a hole in the larger containers lid you can pack carbon material inside pantyhose/cheesecloth inside the smaller container for even more assured light leak prevention as well as odor control.

tip: this can be scaled to any size you need, really. You can even use trash cans, if you need a super sized light trap.

tip 2: air can flow either way. The flow diagram above is just an example.

Edit: Added better quality images.
Seems like you're only getting a small area for air intake.
It really all depends on your choice of containers and how you cut your vents. You could use a drill and make lots of holes, but that would impede airflow more than this method. Like I mentioned in the tip, you can definitely scale this all the way up to garbage cans if you're really in need of a large amount of flow for something like a large room grow.

Dr. Who

Well-Known Member
Hmm...The MINIMUM intake/output must be the same square inch's as the diam. of your fans! Better to oversize them slightly to make up for the airflow loss of going around the impediment (barriers). Don't recall the formula, but should be in the 25%-33% increase range.

Oh yeah found it,,,,
Pi x fan diam x # of hole's or barriers (for hole's include entrance and exit hole) /(divided by) Pi = required airflow area

so like this

6" x 3.14159 = 18.84954
18.84954 x 4 = 75.39816
75.39814 / 3.14159 = 24"

So then 24" in airflow around all barriers is needed to not impede your airflow!


Well-Known Member
It doesn't need to be that complicated. Seen from above, you can just make a box like this:

light trap.jpg

Or if you want a more "linear" flow (much better for the performance of the fan):
light trap 2.jpg

Paint the inside black and I bet very very little light will come through. The design forces the light to bounce multiple times to get out, which with black paint will reduce the initial light A LOT.

Dr. Who

Well-Known Member
And you MUST use the formula for the above due to the "NON SMOOTH" airflow in the "corners".

BTW, that's the type of light traps I use.


Well-Known Member
I like the creativity

tho I find it much more easy to trap the light with just a pice of Ducting with a few bends, also nice to direct to a open window at this time a year


Well-Known Member
I like the creativity

tho I find it much more easy to trap the light with just a pice of Ducting with a few bends, also nice to direct to a open window at this time a year
Exactly! It doesn't take much - the light just needs to bounce a few times, then there's very little left.

Let's say a black surface reflects 30% light. If the light has to bounce 5 times before it exits the trap, then there will only be 0,2% light left.