My grow room needs absolute darkness for 12 hours to be optimal. Even 1 tiny LED light on a device eventually illuminates the entire room to my eye after some minutes. So I put a super thin bit on my drill and break the light.
Why don't you just illuminate the room 24x7 with green overhead lights? And by green, I mean the color itself. I've found that you can operate in the room and with the complete absence of both red and blue all photosynthesis should be halted.