For a long time, infravision has been a confusing and inconsistently applied rule meant to provide non-human races, particularly those used for character creation, a means of seeing in the dark that humans do not possess. Coined from infrared, usually a misunderstood form of radiation that includes, but is not limited to, thermal radiation. Because of this relationship, and too many films depicting night vision and “heat-vision,” the clarity of infravision has suffered by this connection. I hope here to settle issues surrounding the ability and better define its use.
InconsistenciesThe first inconsistency is that explaining what infravision is requires the use of terms that would not exist in a fantasy or pre-scientific era culture. The words we’d use – radiation, wavelengths, photons, the visible spectrum, electromagnetism and electromagnetic fields, quanta, radiant energy, oscillations of fields, vibrational excitation and so on, all necessary to explain what infrared light is, are simply anachronistic in the game world and not particularly useful in defining game rules. Nor is it enough to say, “magic causes it,” since we are left with the problem of “what” is actually caused? What exactly is the radiation that is seen, how does it originate and how do we measure it for game purposes? Without a strong background in hardcore physics, the best option is probably to say that infravision operates like perfectly normal vision, with caveats, and forget trying to measure what infrared light is.
The rules describing infravision quitting at a given distance, say 60 feet, has long been a point of contention. We have examples where human visibility is reduced, by the amount of light, fog or smoke, but as these things diminish at varying rates depending on the amount of light, water vapor or smoke, we don’t have any vision limitations that end specifically at a precise distance. How much is infravision diminished at 20 feet, or 40 feet? We are left with the question, if there is more infrared radiation, how come this does not increase the visibility range of the ability? Since the maximum distance named is utterly arbitrary, I say get rid of this maximum and simply say that a creature has infravision or it does not.
Next, we have this rule where “normal light” spoils infravision. This does not make sense. Even without the physics, it is plain knowledge that the infrared spectrum IS a part of normal light; it is the same light, just photons moving in a longer wavelength. We might just as well say that seeing the color magenta spoils our ability to see the color blue. Infravision should mean that the creature’s visible window of light is expanded and wider than the human’s window. This may be hard for us to comprehend with our limitations, but rationally a creature with infravision should be able to see all the wavelengths of visible light within its given range with equal ability.
This means that a creature with infravision, inside a circle of human-normal light, should be fully capable of seeing outside that circle without any effect on the creatures ability to see the infrared spectrum. I can see where some would prefer to preclude this ability, but consistency demands that we recognize the way that light works in this case or we rid ourselves of infravision altogether. The benefit is not such an increase over the original power infravision grants that it overbalances the game; there are certainly benefits that humans have that continues to encourage players choosing human as a race option for their characters. And if they do not, so what? The game remains the same.
UseVery well, how does infravision actually work?
We might imagine something crossbred between these images, where the infravision-possessing creature’s brain translates the mix of thermal imaging and increased radiation detection into an image consistent with what a human sees … for no other reason than this ends any arguments about being able to “detect” emotional states or other details about the environment in a way the human does not. Except for a unique ability to see better in darkness, we don’t want to ascribe further knowledge collection to infravision.
I suggest that if any light source exists to a specified degree, whether it is a sliver of natural light through a door or an artificial source like a slightly glowing magic orb or a candle, infravision allows effectively normal vision equal to our ability when outside in broad daylight, including color. Just as a dim vampire light on a computer will eventually enable a human to see the whole room, the infravision-possessing creature will have this ability without a waiting period. I suggest the equivalent of 1 candlepower of external light within a distance of 60 feet. This measure of light is precise enough that as a DM, I can comfortably define whether or not it exists. Note that the sky, whatever the conditions, would always fit this designation. The only other limitation to vision would be line of sight.
Any outside source of light that is less than 1 candle, whatever the distance underground, would be sufficient to provide twilight illumination. Such conditions would only exist underground. Because thermal radiation is part of the range of sight, and since the creature itself exudes sufficient thermal radiation, regardless of the actual subterranean environment, for the infravision-possessing creature to see, there would always be sufficient light for twilight illumination. Again, the only other limitation would be line of sight.
This is all I can think of at the moment.