once again, you're trying to simplify that which is complex.
My wife is near-sighted and considered legally blind without her glasses.
she can't see jack taco in the dark, nor can she navigate the house in the dark
I am far sighted, yet can read without glasses, and can see in the dark fairly well and can navigate my house with my eyes closed.
I find it ironic that the legally blind person can't function as a blind person, yet the awesome vision person totally rocks as a blind person.
Factors to consider:
individuals ability to see well in the dark (per my example)
indiividuals ability to navigate environments in the dark (not the same as 'seeing')
level of lighting
speed of adjustment to sudden light changes (going from light to dark)
nature of that which needs to be seen (size, color, reflectiveness, contrast with surroundings)
My old white chow stuck out like a ghostly blob in the dark. My new dog is mostly black, and she's pretty hard to see.
if they're just lying on the floor, not so easy to see. If they are in front of the window or another big object, I see contrast and can deduce what they are.
In college, we used to play NerfWars in this old victorian mansion I lived in. At night. In the dark, so we'd move slower. It was a stealth game, moving silently and sniping. I can't say the distances involved, but I could see movement for the longest LOS I could get in the house.