how dark?

Bruce bugbee on youtube has a video showing just how dark it has to be. e.g. you don't have to worry about most power lights -- assuming it isn't incheas away from a leaf. Even so, i still put a flap of cardboard or fold over tap (so only the edge sticks) to cover that stuff up -- better safe than sorry. tiny pinholes in tent shouldn't cause a problem, light coming from ducts can be something that people don't realize is a problem. I used to have a shared duct between 2 tents and the Tee lead to a window exhaust. Light was coming in through that setup even with a fairly long tack and 2 90-degree bends. You cna turn your lights on in the tent and see majore issues -- if light is coming out, it can get in, but do consider how much stronger your grow lights are than any ambient light inside -- direct sun light would be stronger, of course. Or, at teh brightest point of day you have to worry about, step inside the tent and zip it up... wait about 5 minutes for your eyes to adjust. Do you see any light? Better safe than sorry. Your eyes can't tell the difference between 10umol/s and 1 umol/s ... (bugbee's video has a threshold value, i am pulling these small numbers out of a hat.) 10+ hours is what you learn in a biology class, but genetic variety does exists. 12/12 will ensure 100% flower. I've never had a problem with 13/11, either, if you need an extra 8% DLI over current DLI provided, it's a good option.