I don't much believe in the light leak theory either. They say that it can cause them to hermi, but I believe that in most cases plants hermi for other reasons. I have seen many examples of a veg station and a bloom station both operating in the same basement (different sides of course) without a tent or any kind of barrier between them.
Most of our lights direct their main beams downward, into the canopy. Light that is reflected into the area has several things going against it. First, it is reflected, at least once... and maybe it has bounced a few times. Each time the ray of light bounces, it loses a whole lot of energy, depending on the reflectivity of the surface it bounced off of. More important though, is the inverse square law, that looks at the distance between a light source and what it is affecting. Lets say your lights are 18 inches away from the canopy and produce a certain amount of light, X. Each time you double that distance, to get over to the other side of the basement, you lose 4x the original energy. If you have a garden at 21 feet away from the light source, you have doubled the distance that the plants are seeing the light from by 14 times, relative to the garden directly under the lights. If you are hitting the canopy with 40k LUX of light, the garden seeing that ambient light from 21 feet away can be seeing no more than .04 LUX, and less if it is reflected light. Moonlight is measured to be about .05 - .1 LUX. Plants grow just fine in moonlight, without hermying. I suspect that they can also handle a small light leak.
They say that lights on humidifiers and such in a tent can cause hermies. I have never seen someone prove that. I think more often it is bad genetics or stressing the plants in other ways that cause hermaphroditism. Light leaks are just a good excuse to use so that there is something to blame other than ourselves when things go wrong.
