How exactly does darkvision work?

[Setharious]

I know how it bumped dark light to dim and dim to bright, and removes colors, so on. But logically how does it work and why does it have a range? In real life humans don't have a range they can see until the curve of the earth prevents you from seeing around the planet. Animals can see at night and in a level of darkness but this is usually because of eyes that reflect moonlight or a difference sense such as echolocation or sensing vibrations but darkvision works without any light and with just their eyes. Without the answer of 'it is magic' what would you say is how darkvision works?

[Gurgeh]

It is magic - at least, within the (usually very) short range where you can see in total darkness. In every other respect it works exactly the same way as normal vision: a dimly lit space only has so many photons to bounce off objects and let you see them, and the inverse-square fashion in which radiation works guarantees a finite range to your perception.

[Unoriginal]

I know how it bumped dark light to dim and dim to bright, and removes colors, so on. But logically how does it work and why does it have a range? In real life humans don't have a range they can see until the curve of the earth prevents you from seeing around the planet. Animals can see at night and in a level of darkness but this is usually because of eyes that reflect moonlight or a difference sense such as echolocation or sensing vibrations but darkvision works without any light and with just their eyes. Without the answer of 'it is magic' what would you say is how darkvision works?

There is no answer except "it's magic". Specifically, the background magic of the universe.

D&D 5e Cats lack Darkvision, for example, only having the "developed senses" version of normal, natural abilities.

[PhantomSoul]

It is magic - at least, within the (usually very) short range where you can see in total darkness. In every other respect it works exactly the same way as normal vision: a dimly lit space only has so many photons to bounce off objects and let you see them, and the inverse-square fashion in which radiation works guarantees a finite range to your perception.

And even then, the oddity of seeing in absolute darkness is more a consequence of 5e ignoring absolute darkness existing than a success of in-world darkvision. After all, if "most moonlit nights" count as darkness (PHB 183), we're really just not modelling darkness with the 5e rules!

(Having a distance feels fine barring the above, though!)

[Pharaon]

Any attempt to bring real world physics in is going to fall short but the quickest explanation would be that creatures with darkvision emit some sort of energy that bounces off objects and back into their eyes to perceive the objects, much like infrared security cameras.

This falls short because any other creature with darkvision should be able to see these emissions, just as creatures with regular sight could see if one of them carried a torch. To use the emission theory, you have to go back to magic somehow discriminating which creature emitted the energy and only allow them to perceive on return.

[Silpharon]

In the real world, darkvision could work via infrared sight (just a bit further in the electromagnet spectrum) that can sense emission of object/creature temperatures. A range limit isn't surprising - infrared sensing is noisy (unless your eyes are cryo-cooled). Signals too far away don't have the signal-to-noise ratio to be distinguished. If there was a really hot object farther away, you'd think you'd be able to see that, but the darkvision range can be RP'd for most object/creature temperatures.

[Keravath]

The easy answer is magic and that is likely the appropriate one for 5e.

The longer answer is that vision has evolved as D&D has evolved.

Originally there were infravision and ultravision justified as seeing into the infrared and ultraviolet spectra. Infravision let you see in complete darkness while ultravision required UV and would work in lower light conditions.

These evolved in later versions of D&D into low-light vision and darkvision and the physics explanations were generally dropped since it is a magical fantasy game and they really weren't needed.

Finally, 5e combined low-light and the previous Darkvision into the new Darkvision which provides the ability to see much better in dim light along with the ability to see in black and white in complete darkness.

If you feel like having a physics explanation you could go back to the explanations from earlier editions and allow the creature to see different wavelengths of light and make their eyes more sensitive to photons in general. However, their eyes may not be as good at focusing these different frequencies and as a result, the range of clear vision is limited such that anything beyond 60' is just indistinguishable.

However, that is just making up some homebrewed lore that you could use in your game if you wanted a physical explanation, as I said initially, the easy answer is magic.

[Mastikator]

In the real world, darkvision could work via infrared sight (just a bit further in the electromagnet spectrum) that can sense emission of object/creature temperatures. A range limit isn't surprising - infrared sensing is noisy (unless your eyes are cryo-cooled). Signals too far away don't have the signal-to-noise ratio to be distinguished. If there was a really hot object farther away, you'd think you'd be able to see that, but the darkvision range can be RP'd for most object/creature temperatures.

Infrared vision would let you see where people have been by the heat glow, it would be much stronger than dark vision

[Athan Artilliam]

With your eyes, Bert

[Witty Username]

Back in Ad&d times there was Infra-vision (now correlates to darkvision) and Ultra-vision (now correlates to darkvision) for seeing Infrared and Ultraviolet light respectively. The idea being that the creature could see with normally invisible light.

How it works in 5e, "Repeat to yourself it is just a show, I should really just relax."

[PattThe]

Let's not forget the 5e feature is just a cope to try and ignore the fact that since OD&D there have been different kinds of 'dark vision' and 5e wants you to pretend they've always been just one throwaway explained feature to give to most all origins.

[Kane0]

With your eyes, Bert

However it isnt that simple beyond the surface. Natural philosophers believe the phenomenon to be closely linked to dead catgirls in a manner yet to be determined.

[Cicciograna]

The rod cells (but NOT the cone cells) in the eyes of creatures with darkvision are slightly more sensitive than those with just normal vision, and to regions of the spectrum in the near infrared. The amount of light necessary for them to perceive an area as normally lit is thus smaller, Beer's law still withstanding, so what would be "dim light" for other is "bright light" for them. Then, their sensitivity to the very near infrared, means that they are still able to discern shapes and movements, but without the visual acuity to actually see clearly.

[Burley]

In 3.5, darkvision was having eyes sensitive enough to see shapes and outlines in complete darkness, but you'd still need light to read or see fine detail, and you can't see color (because there's no light to be on a spectrum). Creatures with dark vision may have large pupils to let in more light or they're just a fantasy race with magic eyes whatever. I guess, technically, it's a supernatural ability rather than a magical ability.

As far as being able to only see a certain distance with darkvision, I imagine it has something to do with stereoscopy. Maybe darkvision eyes subtly vibrate to better discern the shapes in the dark but depth gets screwy with the astigmatism so shapes blend unreliably together after 30 feet or so.

[da newt]

It's a rule, so you follow it, but you have the freedom to make up any sort of 'justification' or flavor you want.

Maybe your PC has short range echo location.
Maybe they have super duper hearing and can hear breathing / heart beats / foot steps etc at close range.
Maybe they are electro-sensitive with ampullae of lorenzini or a lateral line that allows them to sense nerves firing. Maybe they can sense infrared / heat.
Maybe they have retinas like a cat - reflective and 10x as many rods as humans.
Maybe they have special smell-o-vision or can taste the air.
Maybe its mental - some sort of psyonics / telepathy.
Maybe its magic.

What ever flavor makes you happy - the rule does what it says it does, no more - no less.

[PhantomSoul]

It's a rule, so you follow it, but you have the freedom to make up any sort of 'justification' or flavor you want.

Maybe your PC has short range echo location.
Maybe they have super duper hearing and can hear breathing / heart beats / foot steps etc at close range.
Maybe they are electro-sensitive with ampullae of lorenzini or a lateral line that allows them to sense nerves firing. Maybe they can sense infrared / heat.
Maybe they have retinas like a cat - reflective and 10x as many rods as humans.
Maybe they have special smell-o-vision or can taste the air.
Maybe its mental - some sort of psyonics / telepathy.
Maybe its magic.

What ever flavor makes you happy - the rule does what it says it does, no more - no less.

Some of those are very much more mechanical than fluff (e.g. echolocation wouldn't be expected to be countered by Blindness but would be expected to be countered by Silence or Deafness).

[Draconi Redfir]

I've seen it described as being something of a thermal-vision myself. the viewer can see / sense the heat of nearby creatures and terrain, and that makes a limited "map" of the immediate area.


I just like to describe it as the characters having very good night-vision though. something like owls or cats mostly. Maybe a smidge of fantasy-logic for complete darkness situations like inside an unlit cave, that could also be explained as sort of an innate sense of your surroundings, like a vibrational energy signature thing, the thing that lets you know when someone is standing / walking behind you without you being able to actively see them. you're still blind and in total darkness, but you can "sense" movement and structures within a short area, so you're not AS blind as someone without that sense.

[MoiMagnus]

I know how it bumped dark light to dim and dim to bright, and removes colors, so on. But logically how does it work and why does it have a range? In real life humans don't have a range they can see until the curve of the earth prevents you from seeing around the planet. Animals can see at night and in a level of darkness but this is usually because of eyes that reflect moonlight or a difference sense such as echolocation or sensing vibrations but darkvision works without any light and with just their eyes. Without the answer of 'it is magic' what would you say is how darkvision works?

Some parts of D&D works much better if you try to use "physics as understood in ancient times". On major point of optical physics in the ancient time is that nobody really knew how the eyes were working, and one of the major theories was the reverse of reality:

Instead of light reflecting on surfaces, going to your eyes, and then to your brain, it was the other way around: your eyes were sending some kind of perception rays, who would directly feed to your spirit the colours and details of whatever they bounce of (assuming they were illumated enough).

With this understanding:

Darkvision gives you special vision rays that are better than usual, but with short range.
True sight gives you magical vision rays that bounce on spiritual stuff instead of material stuff.
Disbelieveing an illusion allows your perception rays to go through the illusion to see what's behind because your perceptions rays "know" that this is an illusion.

[Mellack]

The problem with the thermal idea is that they can still do things like read. An etched plaque or written parchment are read without any problem, even in total darkness. Thermal vision wouldn't have enough difference to make those possible. There is also nothing about glass windows no longer being transparent.

[Willie the Duck]

Without the answer of 'it is magic' what would you say is how darkvision works?
Personally, I like the notion that it's not one specific set of in-world mechanisms, so much as a in-game categorical of any creature that can deal with the problem of darkness (not just low light), regardless of how. This creature has a combination of near infrared and keen spatial awareness, this other one has weak echolocation, this one is really good at guessing, and this one can see u-ray emissions (what are U-rays? we don't have those here but trust me, they are ubiquitous in D&D worlds).


The longer answer is that vision has evolved as D&D has evolved.

Originally there were infravision and ultravision justified as seeing into the infrared and ultraviolet spectra. Infravision let you see in complete darkness while ultravision required UV and would work in lower light conditions.
Even before that, it was just infravision, and monsters all had permanent infravision "as long as they are not serving some character," highighting just how gamist this whole thing has been the whole time.


Let's not forget the 5e feature is just a cope to try and ignore the fact that since OD&D there have been different kinds of 'dark vision' and 5e wants you to pretend they've always been just one throwaway explained feature to give to most all origins.
What is 5e doing that each other edition (which posits a specific mechanism for the thing and doesn't go into detail about what previous editions did) did differently?

[Unoriginal]

Maybe Darkvision lets you see darklight, which is the light that let you see darkness.

[Kane0]

Maybe Darkvision lets you see darklight, which is the light that let you see darkness.

Oh I think we have a winner

[NotPrior]

Infrared vision would let you see where people have been by the heat glow, it would be much stronger than dark vision

I've always run darkvision as seeing heat, although I also say it's not good enough to help you track during the sun-heated day, only at night... when darkvision would already be necessary.

Does it not still work this way by lore? Mechanically things have varied but the novels used to be very explicit about the fact that darkvision sees heat.

Come to think of it I'm pretty sure Narbondel explicitly appears in Out of the Abyss, and without thermal vision that thing is just a big ugly rock squatting in the middle of the city.

[Athan Artilliam]

I always figured it was infrared, like a FLIR camera

[KorvinStarmast]

Maybe Darkvision lets you see darklight, which is the light that let you see darkness. A nice, soft reference to dark matter and dark energy, I like it. :smallsmile:

I always figured it was infrared, like a FLIR camera That's infravision, previous editions.

[Draconi Redfir]

The problem with the thermal idea is that they can still do things like read. An etched plaque or written parchment are read without any problem, even in total darkness.t.

can you? i thought you still needed light in order to make out fine detail like words on a book.

[Lalliman]

In the Monster Manual, badgers, frogs, lizards, octopuses, rats, spiders, and tigers all have darkvision. There are several more real and real-adjacent animals with darkvision in several sourcebooks. Clearly, darkvision is a natural ability, cats not having it is a mistake, and the designers simply ignored the difference between too-dark-for-humans and absolute darkness to keep the game simple.

[ftafp]

The Drizzt books outright state darkvision is seeing infrared radiation

[Willie the Duck]

The Drizzt books outright state darkvision is seeing infrared radiation

Yes, at the time it was.