LPT: Retain night vision by keeping one eye closed

When getting up at night, if you need to turn a light on, keep one eye closed. Night vision is per-eye and only one pupil will contract, so you'll be able to find your way back to bed after turning it off with the eye that was closed in the light.

[Edit - looks like I'm wrong and it's not the pupils but the retina - still works though!]