Hey man, kinda breezed through this thread. but an item that will help (if not fixed already) is to paint the inside of the tubes flat black. Spray in what ya can.
I already have those for my passive vents into the grow area. This thread was looking for help with my 6" circular hole for the hood vent.
I can recommend the vents for you, they block the light 100%. The only down side is they do offer up a some air resistance and they aren't cheap. But they look very professional and they work.
Today I added another fan to my set-up, a 6" Sun Leaves Wind Tunnel to help pull air through the cab. I wanted more air circulation for heat reasons and I wanted to add some HEPA filters to the back of the those light louvers so I have nice clean air getting sucked into the grow area - this new fan is able to pull right through the HEPA's and it is exchanging air nice.