From my experience dark could only help you become more relaxed but when it comes to HI I think that doesn’t matter if it’s dark or not. If your body signals the brain that’s ready for HI part of the sleep then it will happen and then we again come to the part where you need to be relaxed and ready for the body to signal to the brain that’s ready. So if dark helps you then do it in dark but in my opinion dark isn’t crucial.