Infravision – Why and How

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The primary reason for using “Darkvision” in 3.0 and 3.5 is “because it’s much simpler mechanically”.

To quote Mr Sean K. Reynolds – one of the 3.0 game designers – “Infravision rules have a lot of holes in them, and cleaning up those holes isn’t worth the time and effort to do so. Darkvision is an elegant solution (it works just like normal vision and doesn’t rely on a science explanation that can be misinterpreted or exploited) and doesn’t require all of this extra work.”

To put that into the game, 3.0 and 3.5 system reference documents provide the following bit of rules:

DARKVISION: Darkvision is the extraordinary ability to see with no light source at all, out to a range specified for the creature. Darkvision is black and white only (colors cannot be discerned). It does not allow characters to see anything that they could not see otherwise—invisible objects are still invisible, and illusions are still visible as what they seem to be. Likewise, darkvision subjects a creature to gaze attacks normally. The presence of light does not spoil darkvision.

Uhm. Yes.

In fact, of course, darkvision is only “simpler mechanically” as long as no one asks questions. “It works like normal vision” has the advantage of drawing on a lot of real-world experience, but all of that experience is based on some pretty complicated physics – that “science explanation” Mr Reynolds wanted to avoid. A simple magnifying lens is a standard bit of d20 equipment, but it brings in refraction, the dual wave-particle nature of light, electromagnetism, the properties of materials, and more. In fact, it brings along thousands of pages worth of physics – all the stuff that underlies all those “common sense” notions about how the world works.

Sure, you can say that the physics of your world works some other way – but then you’re going to have to build and explain that physics as soon as someone starts experimenting (if you want to go that route, here’s an article on Elemental Physics to give you a start, and a followup on Dimensional Traits). You may get lucky and not have to deal with that, but if you run enough games, sooner or later you’ll get some players who keep wanting to know “why” and “how”. Those are the ones who want to try another route to problem solving; figuring out how things work in the setting and how they can take advantage of whatever you come up with – in other words, engineering.

I look through windows, wear glasses, and use binoculars, telescopes, and mirrors. What effect do those have on my darkvision? What is it that’s being refracted? If I’ve been cursed to need extremely powerful corrective lenses to see, how does that interact with darkvision? Can I make illusions or inks that are ONLY apparent to darkvision? Lamps and spells that extend its range? How does it work underwater? Do colored dyes that only block particular colors block darkvision? Are there dyes or gases that block darkvision but not normal vision? How about if I mix several of them? Are there materials which are opaque to normal light but transparent to darkvision? Can I use darkvision through a periscope? Can I see myself in a mirror in the dark with it? What’s reflecting? Are there darkvision mirrors that don’t reflect light? Why or why not?

Darkvision is “simple” because the rules don’t bother to give you any guidelines on how it works and don’t bother to answer any of those questions. Instead, you get chucked straight into house rules the instant some inquisitive character with darkvision picks up a magnifying glass or mirror and asks a few questions.

Another objection is that it complicates the rules – in part because infravision has a fixed range, which “doesn’t make sense”.

That’s true; it doesn’t.

The ONLY major difference between “infravision” and “normal vision” is that – to infravision – everything (including the air) glows a bit. That doesn’t show up on most infra-red images since those systems are only designed to detect thermal differences. Virtually every infra-red image you see on the net is actually the equivalent of a grayscale image, with phony “colors” assigned to represent brightness and make the images more interesting. In fact, two objects at exactly the same infra-brightness can – and usually will – have entirely different infra-colors. Infravision will tend to get swamped by the environmental background at long ranges, but it doesn’t have a hard range limit save by convenience.

In other words, discussions of “thermal signatures” with respect to full infravision are totally irrelevant. It doesn’t matter exactly how hot a creature is, just as it doesn’t matter exactly how brightly illuminated a yellow object is when it comes to normal sight; it’s still yellow. The colors will be different of course, and might have their own names – but the players will never care.

As a minor difference, Infravision provides a bit less detail and gets fuzzy more quickly thanks to the longer wavelength involved – but the actual difference is trivial as far as characters are concerned.

How will the differences work in the game? In exactly the same way that the rules cover how far away you can see a faintly glowing object, or can make out a lantern flame at night, or how much smoke cuts down that distance – by leaving it up to the game master, who has to describe what everyone sees anyway. Situations like that are subject to so many varying factors that it would take dozens of  pages worth of (rarely or never used) special-purpose rules to cover them. You don’t find those for sight, why should you find them for infravision?

Wanting to track by heat isn’t all that different from tracking by scuff marks on the floor, the slow ooze of mud back into footsteps, lingering traces of smoke, or by scent. That’s tracking – perhaps with a modest modifier for a method that suits the current situation better – whatever that method may be. Just a minute ago? Heat may work best. Climbed out of a stream? Sight works best. On a smooth floor? Scent works best.

Will spells have infravision-related side effects? Will Burning Hands flashblind people with infravision? Will Cone of Cold make it hard for them to see?

Probably not. Why not? For the same reason that bright spells like Lightning Bolt don’t flashblind people in the area and that flame spells aren’t listed as producing clouds of smoke (either inherently or from the stuff that’s been set on fire). If you wanted to worry about such effects, now you’d want to worry about who was looking that way at the time, and who was blinking at that instant, and so on – another mass of detail which will add little to play. That’s why it’s left to the GM to bring such things up if he or she feels that it’s important.

Does a person transformed into an elemental form or a cloud of gas have body heat? Why should they? What are various monsters thermal signatures like? Are undead inherently cold?

It doesn’t matter. Their infracolors will still distinguish them nicely.

Will infravision negate many illusion or visually-based spells? Why? The distinction between infra-red, visible light, and ultraviolet light is actually very small. They’re all just photons, and within a very narrow range of frequencies at that. There’s no reason to expect that tiny difference in frequency to mean anything to magic. In fact, humans can see ultraviolet light just fine if you replace the protein-based lens of the eye (which doesn’t transmit ultraviolet) with glass (which does) – an amusing fact discovered thanks to some old surgical treatments for cataracts.

Will infravision negate invisibility in particular? Again, why should it? If invisibility was a simple physical effect which let light pass through the user, or routed it around them, it would blind the user, since no light would reach their eyes. For that matter, it covers long flowing capes and mighty wings just as well as it covers mice. Is there any reason why covering up an “aura of heat” should be any harder than covering up condor’s wingspread?

Will a creatures own body heat interfere with its infravision? Pretty obviously not. If a creature has infravision, it necessarily has some method of dealing with this particular issue. It is, after all, quite possible even without magic; there are ambient-temperature thermal sensors in wide use now.

Both Darkvision and rules-based “Infravision” work the same way – and, in fact, are pretty much precisely equivalent – as long as characters are treated as playing pieces on a board. Once you take a role-playing view, and the players start asking questions, they’re equally complicated. The real difference is that Infravision offers a set of answers – however complex – while Darkvision (at least as written) simply tries to pretend that the questions don’t exist.

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3 Responses

  1. Interestingly, I think some of those questions should have been asked and answered anyway. I wouldn’t make a whole template, but being able to slap some labels on things such as “Chemical Metabolism” or “Arcane Energies” or “Divine Blood” would have been an interesting tool, allowed a lot more specialization, and been simple to use. It would usually have broken down along creature type, of course, and provided a very quick explanation of what the creature actually *was* beneath the skin.

    Secondly, it could have substituted for some of the grab-bag creature types. Some undead arguably should be vulnerable to poison. Some constructs should perhaps be vulnerable to dispelling or mental manipulation. And you can easily come up with other uses. The keywords won’t explain everything about the creature’s lifestyle and habits, but would give a big introduction with very few words on what they are, how they live, and what they do.

  2. […] have what you need to run the basic game smoothly. Unfortunately – as shown in the article on Infravision versus Darkvision – the Gamist approach runs into a problem as soon as someone starts experimenting and asking […]

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