Way is Night Vision 2 the human max anyway?

[BraselC5048]

In both Tactical Shooting and Bio-Tech night vision 2 is listed as the maximum for a normal human. The thing is, I can't discover any reason why that is. Obviously there's a limit, but why is it set at 2 instead of, say, 3? Apparently there doesn't seem to be a lot online about excellent vs normal night vision, or even measuring it at all.

Anybody got anything?

[Say, it isn't that bad!]

Originally Posted by BraselC5048

In both Tactical Shooting and Bio-Tech night vision 2 is listed as the maximum for a normal human. The thing is, I can't discover any reason why that is. Obviously there's a limit, but why is it set at 2 instead of, say, 3? Apparently there doesn't seem to be a lot online about excellent vs normal night vision, or even measuring it at all.

Anybody got anything?

Because at +2, based on the Size/Range table in GURPS Lite, you can see twice as far at night as someone with normal vision.

Which fits with my experience; I would put "Night Vision 2" on my character sheet, were I to write myself up, and I seem to have very good night vision, by comparison with other people.

[Varyon]

Originally Posted by Say, it isn't that bad!

Because at +2, based on the Size/Range table in GURPS Lite, you can see twice as far at night as someone with normal vision.

Yeah, when it comes to vision, I think 2x normal is the rule-of-thumb limit, and as noted that corresponds to a +2. Wikipedia notes that an absolutely perfect human eye would have 20/8 vision, which is only slightly better than +2 (20/6.67 vision would be +3). Having a similar night vision limit doesn't seem too outlandish.

Note here that while the natural response would be to say that Vision rolls can't have a base higher than 12, Sense rolls involve both detecting and interpreting (in terms of figuring out if that's a guy in camouflage or a tree, not in terms of figuring out if camo-man is on your side, which would require a different roll), so a higher value than 12 simply indicates better ability to interpret.

[Anthony]

Originally Posted by BraselC5048

In both Tactical Shooting and Bio-Tech night vision 2 is listed as the maximum for a normal human. The thing is, I can't discover any reason why that is. Obviously there's a limit, but why is it set at 2 instead of, say, 3?

Some curve-fitting sets each level of darkness at about 1/5 the illumination of the previous level, which is in fact more than the variance of normal human vision (which seems to be about x3 in either direction), meaning the actual physiological limit is probably 1, with an additional level representing experience in compensating for low-light conditions.

[Say, it isn't that bad!]

Originally Posted by Anthony

Some curve-fitting sets each level of darkness at about 1/5 the illumination of the previous level, which is in fact more than the variance of normal human vision (which seems to be about x3 in either direction), meaning the actual physiological limit is probably 1, with an additional level representing experience in compensating for low-light conditions.

Edit: Are you using standard deviation to set maximum limits?

[PK]

Originally Posted by Say, it isn't that bad!

You can't use standard deviation to set absolute outer limits. It's mathematically impossible.

It's not an absolute outer limit. It's just a recommended level for representing the peak of what is probably realistic human night vision. There's no reason you couldn't take Night Vision 5 in a game labeled as "realistic and gritty" unless the GM said otherwise -- but the advice in Tactical Shooting, et al, lets you know that doing so is arguably pushing things.

[Say, it isn't that bad!]

Originally Posted by PK

It's not an absolute outer limit. It's just a recommended level for representing the peak of what is probably realistic human night vision. There's no reason you couldn't take Night Vision 5 in a game labeled as "realistic and gritty" unless the GM said otherwise -- but the advice in Tactical Shooting, et al, lets you know that doing so is arguably pushing things.

Ah. Well, I can distinguish noticeable, though slight, colours when others tell me it's very dark, so "only one level" is something I'm skeptical of. :)

[Anthony]

Originally Posted by Say, it isn't that bad!

Edit: Are you using standard deviation to set maximum limits?

No, I was actually hunting studies on the internet and found this; it's old but I don't see reason to think it's much different. I'm assuming 'log' is log10, not natural logarithm, meaning the range for young men (20-24) was -0.53-+0.57 relative to the mean.

Originally Posted by Say, it isn't that bad!

Ah. Well, I can distinguish noticeable, though slight, colours when others tell me it's very dark, so "only one level" is something I'm skeptical of. :)

Most people can; you aren't entirely colorblind (scotopic vision) until around 0.01 lm/m^2 (roughly 1/10,000,000 of full sunlight). If you live in an urban area you may have never actually encountered that level of darkness.

[BraselC5048]

Originally Posted by Varyon

Yeah, when it comes to vision, I think 2x normal is the rule-of-thumb limit, and as noted that corresponds to a +2. Wikipedia notes that an absolutely perfect human eye would have 20/8 vision, which is only slightly better than +2 (20/6.67 vision would be +3).

Are you sure about that? It seems that, looking at the speed/range table, that about 20/8.5 would round either way (halfway between 7 and 10, compared to 20).

[Varyon]

Originally Posted by BraselC5048

Are you sure about that? It seems that, looking at the speed/range table, that about 20/8.5 would round either way (halfway between 7 and 10, compared to 20).

First off, you always round up with the SSR table. Secondly, I was referring to the effective xn to vision - to have x3 vision (corresponding to +3 on the SSR table), you'd need to have 20/6.67 vision - although 20/7 would certainly be close enough!

Also, 20/8 vision is for a flawless human eye, which you probably aren't going to find without a combination of genetic engineering and growth in a synthetic womb. Natural-born eyes are going to have at least a slight imperfection.

That said, Anthony's idea seems more sensible (based as it is on relevant data, rather than on extrapolating from distance-based resolution) - +1 for having really good (for night sight purposes) vision, +1 for being used to dealing with low light.