There are various type of vision. They are as follows:
- Dark Vision
- Low-Light Vision
- Mindsight (via a feat in "Lords of Madness")
This post will talk about vision, dark vision, and low-light vision. To understand it, understanding of what photons are, and how they are made is necessary, as normal vision is based entirely on them, and dark vision is based on 'unphotons'.
An Unphoton is a photon that has the possibility of existing. They function much like normal photons, except that when they pass through a normal photon, they have a chance to blink out. The chance of blinking out is equal to the percentage of the light's intensity. For instance, dusk would have a 50% chance, making it possible for those with normal and dark vision to see about equally. They also don't reflect off of surfaces. Once they hit a surface that would reflect a photon of equivalent wavelength, they also blink out.
How are they created? In a sense, they are not. They are neither the absence nor the antiparticle of a photon. Instead, they are the possibility of a photon. Technically, unphotons are without energy levels, and thus wavelengths are not there either. Anything that detects them detects them only through a duo-color field, none of them being the same as their normal field of vision. When one has dark vision, they can detect these unphotons. Depending on how one creature's dark vision is, they can either see a 'there are unphotons in my field of vision', blurry objects in darkness not allowing the ability to read small details, or great dark vision allowing one to see details just as well as in darkness. Does dark vision have a maximum distance? If you follow these rules, it only makes sense that it would have a range similar to that of normal vision, unless the sensory organ for unphotons was incredibly weak. Of course, if that is true, normal vision should also have a maximum range, and spot checks should be needed to see distances in it.
So, what about those with dark vision, but not normal vision? In full light, they are effectively blind. This is similar to the way those with normal vision only are effectively blind in full darkness. But then, what is low-light vision? Low-light vision is the ability for those who see well in only one type of light to see partially better in places with at least 50% of the other type of particle. With it, they have the ability to kind of see the other type of photon but only as an unphoton blinks out or regular photons causes an unphoton to blink out, depending on the type of vision has the longest maximum range. Usually, for player characters, it is normal vision, as dark vision is usually 0ft. It allows one to see twice as far as usual (because you can only see half as far is the light intensity is 50%) in the range it has. Thus, if I have dark vision 50ft for spot check of 10 (normal field of view), light intensity 80%, and low-light vision to 30ft. Because I can see only 20% of 50ft with dark vision normally, I can see 40% of the distance with low-light vision. Due to the fact you are detecting the loss of a particle, it is only black and white vision, and somewhat blurry. Low-light vision does not let one see further than their maximum normal or dark vision (whichever is higher).
Those with dark and light vision can see fully in the range of the lowest max distance), and normal dark or normal light vision for the longer range vision. With low-light vision here, the distance of the lesser max range vision increases so that it is the average of the two max range visions.
And now, for a discussion on two common spells: "Light" and "Darkness".
They work by creating a point at the center of the effect that swarms out photons or unphotons. This means that you can blind a creature with dark vision by placing a darkness spell close to their eye, and a light vision creature by placing a light spell close to their eyes. They mirror each other. But what about a different way of getting these spells to work? Removing the blinding effect, these spells could work by merely changing all unphotons to normal photons, with the corresponding wavelengths they would have or by turning normal photons into unphotons. In either case, once the (un)photons leave the maximum range of the spell, they blink out.