Dark Vision (60 ft.)

[Anthony]

Originally Posted by Anaraxes

NOAA (for aviation purposes) puts the average for the northeastern US as between 2-3 miles (winter and summer).

Though that has nothing to do with the actual range of vision; that's the range at which atmospheric haze eliminates 95% of contrast (in GURPS terms, in addition to range penalties, there should be a penalty based on the opacity of the atmosphere, something like -1 per 10-20% of nominal visibility). If you're looking upwards, it's routinely possible to see much further (the Andromeda galaxy, at 2.5 million light-years, is naked eye visible under good conditions).

[Anaraxes]

Originally Posted by Anthony

that's the range at which atmospheric haze eliminates 95% of contrast

Which I'm sure you'd agree is as useful an operational definition of "vision" as anything else. If everything in your field of vision is a uniform mid gray thanks to lack of contrast, it's not usefully "seeing" regardless of how far the photons landing on your retina have travelling. Similarly, you can see Andromeda looking straight up -- but not during the day, because there's not the contrast as there is at night.

Taneli asked for something "typical", which I assumed to be a practical limit. So I gave him an example of one practical limit that's used in the real world.

We can see all the way the cosmic microwave background (if in the wrong wavelength for Mk I eyeballs), so the actual limit is nothing short of the size of the causally connected universe. But using that as a starting point for calculating typical ranges used for a human-centric viewer in an adventure game doesn't seem to me to be particularly useful, however appealing it may be from an abstract theoretical viewpoint.

As other threads have pointed out, resolving detail is another useful limit to consider. You can see Andromeda -- but a human can't resolve different star systems, or planets, much less two people standing three feet apart in order to target one and not the other, or identifying a lone person as someone specific rather than another. "Seeing" isn't really a simple monolithic act. The question inevitably entails some assumptions about "for what purpose" as well as "with what artifacts", whether night vision goggles, a spyglass, or a radio telescope.