You can use the poly like suggested above, but it costs about 5x more than the black plastic. With the black plastic, there is only like a couple inch strip that is not "reflective white". It shouldn't cause any issues. And if you want to get crazy, spray paint the black plastic white. Or just use the poly which will block light, plus will be reflective.
And as far as night stealth, what happens if you want to get laid one night?? Growing pot is great and all, but sometimes you just need little sumpin sumpin, if you know what I mean. Or what happens if someone unexpected comes over at night? You should have complete stealth no matter what the time of the day.