I was thinking about putting some items found in The Sword lyrics into D&D. One such item got me thinking about forms of vision. After a lot of reading (especially regarding infra) I came up with my own interpretation.
Infra works regardless of light conditions, though daytime above ground is usually too warm for visibility. Since most light sources in a quasi-medieval setting are heat sources aswell (torches especially), they tend to overload and blind infra (especially at close ranges).
Every normal creature is a heat source, but a much weaker one then a torch is a light (or even heat) source. So they won’t “light” their surroundings. Taking that into account, having infra ranges makes as much sense as having vision ranges. They’re probably a balancing attempt based on light-source ranges.
Visibly, when using infra, most normal creatures are double sized, because of the heat they radiate (Imagine it as a dark red flame surrounding them). Getting wet or standing at a place with strong winds or drafts negates this effect. Another difference (and a less positive one) is that see-through things like glass aren’t see-through in infra, and reflective materials don’t work either, you just see the appropriate heat of the object (probably room temperature). Creatures in water can not see or be seen with infra for the same reason.
Because of balancing issues and realism, I’m assuming a relatively mediocre quality infravision. That means footsteps cool too fast to be useful (<30 seconds) and faces can not be distinguished. I’d make and exception for powerful creatures or sentient creatures born with infra, but in that case, the eyes glow red. In the latter case faces and footprints still must be at arms reach to distinguish (climb on all fours to follow footprints).
Watching Predator and Predator 2 will educate you on the visuals of infravision.
Darkvision is a relatively new concept, developed to keep infravision but distance it from its real life counterpart. As such, it only works in complete darkness, but it’s user can not be blinded. In the presence of a light source, the user simply reverts back to normal vision. (The question remains about the effects on darkvision-only creatures.)
The quality and distance of vision is normal, but the user only sees shapes in black and white, not even grayscale. Colours and patterns can not be distinguished, making reading impossible. Naturally, reflective and see-through materials don’t work for such vision. If the Dungeon Master rules that the concept of darkvision is magical in nature, he or she can devise a material that mirrors such vision, or allows users to see through it. (Non-glossy iron could be an example for a mirror.)
As far as I can tell by googling, there’s only one picture in all of existence of what darkvision looks like. It’s in the 3.5 DMG. As a substitute, get a line-drawing of an underground locale, and invert the colours.
Low-light vision, or nightvision can be found in nature relatively frequently (cats are a well-known example). This is the same type of vision, it collects a larger amount of ambient light, allowing better sight in darker environments. As such, daylight (or similar strength light) blinds its user, if they don’t switch to a different method of vision.
With nightvision, starlight or the light from distant torches allow vision similar to darkvision: strong contrasts, minimal details, no reading or colours, though mirrors and glass work as normal. Moonlight or equivalent on the other hand allows for mostly normal vision, though mostly in a bluish tinted grayscale.
Ultra, a form of vision introduced into Labyrinth Lord with the Advanced Edition Companion, is a surprisingly difficult form of vision to reconcile. The reason is that ultraviolet vision in real life has none of the magnificent attributes given to it in the rulebook.
Basically, ultra gives its user a few additional colours to see (which is great for secret messages and seeing some otherwise well hidden plants and creatures). That would not be enough to make this form of vision useful in-game, so I added the ability to see radiation, magic and high-technology to its capabilities.
Ultra enhances the vision in twilight by the presence of background radiation form the Sun, giving the user perfect vision at dusk and dawn. As radiation is a strong form of UV, a strong enough source can blind its user. High-technology (more advanced than what we have) and magic spells are clearly visible (depending on strength) in ultra, but do not light their surroundings. Magic items and radiation on the other hand can be strong enough to act as a light source for the uv user.
If you don’t know what ultravision looks like, go watch CSI.
That’s the best I could do with these 4 forms of vision. As closing, an interesting tidbit I found regarding changes in lighting conditions:
“Pirates, for example, often wore eye-patches over one good eye – not because they were blind in that one eye, but because they often had to quickly go below decks into the dark. Changing the patch from one eye to the other allowed them to function without pause, but if one had to wait for their eyes to adjust to the darkness, that could take several minutes, which they could hardly afford during a pitch battle.” – James L.R. Beach