Several simple measures can make going to the bathroom at night a safer, easier experience for someone with mild dementia:
Start by making sure the path to the toilet is clear. Remove small tables, rugs, and baskets along the path from bed to bath, including in the hallway.
Try using regularly spaced nightlights to guide the path.
Another option, if you lack sufficient outlets, is to run a string of lights (like Christmas-tree lights or party lights) to lead the way from bedroom to bathroom.
Install a lighting option that's not visible by day: reflector tape used with motion-activated nightlights that plug into a hall socket and light up only as you walk past (about $15 at hardware stores).
To make seeing the toilet easier: Older men hit their mark better when the commode is a contrasting color from the surrounding walls. So if yours are both, say, white, consider investing $10 in a can of paint in a deep, warm color for the wall behind the tank.