Reminds of a (daytime) flight years ago on SQ where the CC had slammed down the blinds while I was in the toilet. I raised them again when I got back to my seat. CC came over and told me to lower them as it was policy that the cabin was dark. I said 'no' and was then told that it was the 'law' that blinds must be kept closed in order to reduce the amount of radiation the crew was exposed to. Having had enough of this BS and spoke to the IFS in burgundy uniform who assured me (phew!) there was no such 'law' and that I could do with my window shade whatever I pleased.