Ways for Monsters to See in the Dark

[whswhs]

Originally Posted by ericthered

Digging deeper into the recommended books, it looks like underground generally gives -2 to heat-vision... which isn't bad, all things considered. I could give night vision 2 to cancel that out if its really needed. I'm still curious why we don't see heat vision in nature if it works in the dark that well.... other than for snakes targeting warm-blooded creatures, which is a very different context.

The GURPS concept of "infravision" (and similar concepts in other games, going back I think to D&D) conflates two things that are actually distinct. Near infrared gives resolution little worse than that of visible light, and apparently there are some animals that have it (some fish, I believe), but it requires an active light source; objects emit in this range if they're at 2000 K or hotter, which is far above any animal's body temperature, and an environment with sources at this temperature would probably be quite dangerous. Thermal infrared IS emitted by homeothermic animals, but its wavelength is about 20x that of visible light, so it gives much poorer resolution—about like 20/400. And those photons aren't energetic enough to trigger chemical changes directly, so you need receptors that respond to getting warmer, which I think means that they need to be hit by multiple photons. There are also the issues that Anthony points to about needing the receptor to be cooler than the source.

[Anthony]

Originally Posted by whswhs

The GURPS concept of "infravision" (and similar concepts in other games, going back I think to D&D) conflates two things that are actually distinct.

Not really. The D&D concept of infravision is thermal IR, most games are oblivious to wavelengths between visible light and thermal unless it's a high tech game and they decide to make a plot point out of being able to see beams from infrared motion sensors.

[Varyon]

Originally Posted by ericthered

Undead have a strong place in the setting and I was leaning towards them having their original senses, but having them able to see souls as well makes a lot of sense. The corporeal ones need to navigate underground, but a ghost that not only goes through walls but doesn't even notice them is interesting. Though there is also something fascinating about a corporeal undead who is as dexterous and agile as when they were alive, but can't see anything except the living. It results in some arcane and tragic behavior that just feels right for some undead. Including needing someone to lead them to the places where they can be properly dangerous.

One idea I like for undead that need to prey on the living, but haven't quite figured out the appropriate way to build in GURPS, is a sort of tiered Life Sense. At extremely long ranges (that is, using the Long Range Modifiers table), it doesn't really tell you much more than which direction the strongest signals are in (you'd think this would be Vague, but no, that just tells you there's something alive somewhere near you, which is pretty much useless on any planet with life). At typical ranges (that is, using the standard Size and Speed/Range table), it's good enough to figure out where a target is within a yard or so (pretty much just standard Detect). At close range (-1 per yard of distance), it gives perfect resolution for combat purposes (away from books, so can't recall the modifier, but basically the one that lets Detect work as well as Sight; I'll just call it Discriminatory).

Build-wise, this would be something like Detect (Living Prey*; Long-Ranged (Lesser!Vague -??%) +??%; Discriminatory (Close-Range -??%) +??%). Note this makes use of Limited Advantages. Mechanically, you make a single Sense roll. If you detect the target while taking a -1 per yard, the sense is Discriminatory and you can engage normally. If you fail there, but detect the target while taking standard SSR penalties (-1 at 3 yards, -2 at 5 yards, etc), you know the target's location to within a yard. If you fail there, but detect the target(s) while taking the Long-Distance Table penalties, you roughly know what direction prey is located.

*Most undead only have specific living things they can prey upon for sustenance - such as only sapient life - so set how common the category is based on that.

[whswhs]

Originally Posted by Anthony

Not really. The D&D concept of infravision is thermal IR, most games are oblivious to wavelengths between visible light and thermal unless it's a high tech game and they decide to make a plot point out of being able to see beams from infrared motion sensors.

But they also call it "vision" and treat it as if it let you see in the dark the way humans can see in the light. That's not remotely possible for thermal IR; the best possible resolution would count as being legally blind by human standards.

[Anthony]

Originally Posted by whswhs

But they also call it "vision" and treat it as if it let you see in the dark the way humans can see in the light. That's not remotely possible for thermal IR; the best possible resolution would count as being legally blind by human standards.

If you're willing to have lenses a few inches across you can achieve the resolution of vision.

[whswhs]

Originally Posted by Anthony

If you're willing to have lenses a few inches across you can achieve the resolution of vision.

Do you know of any animal that has evolved such a thing? And are there materials that can refract thermal IR similarly to visible light?

[Michael Thayne]

In a previous thread I started on the Infravision issue, the conclusion was the GM should be pretty generous in adjudicating what fantasy infravision can do. Sure, it's totally unrealistic, but so are lots of things in fantasy.

[thrash]

Originally Posted by ericthered

I do want bioluminence of some kind, and I suppose that will help a lot of critters have sight of some kind at least, for the occasions when it comes up.

Bioluminescence works well with near IR vision (as with IR chemsticks and NODs). There is also some evidence for emitters in the UV range in deep-water organisms.

[Agemegos]

The interior of the eye of a warm-bodied animal is flooded with thermal IR from the warm-opaque walls of the eye itself. Seeing things by their thermal radiation at the same temperature as the eye is like trying to use a camera with a light inside it: it’s exceeding difficult to get noticeable contrast in the image.

My thoughts turn to creatures with IR eyes on stalks that could be kept significantly cooler than body temperature. Those would only work in rather cold dark environments.

[whswhs]

Originally Posted by Michael Thayne

In a previous thread I started on the Infravision issue, the conclusion was the GM should be pretty generous in adjudicating what fantasy infravision can do. Sure, it's totally unrealistic, but so are lots of things in fantasy.

I grant that "infravision" is well precedented in fantasy gaming. But if I were running a fantasy campaign, it's not something I'd include. If I were going for a premodern worldview with supernatural elements, I wouldn't include "infravision," because it's based on the concept of infrared light, which was only discovered in 1800. (I'd have no problem with it in a campaign in the genre of "Magic, Inc." and Operation Chaos and The Case of the Toxic Spell Dump, of course.) On the other hand, if I were going to have fantasy races based on biology and anthropology, well, I'd use real biology and real physics.