Light Radius=0 and mapping out dungeons.

[eulf]

When you have a light radius of 0, it's just inconvenient that unlit locations you walk across aren't revealed as floor tiles, and that walls you bump into remain unseen. It actually appears to be more of a bug. Given how the run command will temporarily reveal the tiles you walked across, and will stop you if you'll run into an unseen (But not undiscovered) trap

Edit: It appears that having infravision removes this inconvenience