Okay home grower, first of all, I don't see an intake and exhaust. I assume that's in the back of the cabinet or something.

To block the light from leaking out of your cabinet, and just as importantly, into your cabinet, use poly film.

You can buy sheets of poly film from online hydro retailers. You're going to end up spending maybe $20 and ending up with a lot more than you need. But that's okay because you may want to re-cut and re-shape it.

Here's what you need.
1. Velcro Tape
2. Poly Film.

Take one of the velcro adhesive strips and put it on the inside of your cabinet. Now cut a square (or rectangle or whatever) and line the outside edge of it with the velcro. Now obviously you place it behind your door, forming a light-proof seal.

Any questions?