Infravision - seeing into infrared

[Yora]

Old editions of Dungeons & Dragons have an ability called infravision, which enables some creatures to see infrared radiation. A common argument why it wouldn't work is that the inside of a human-like creatures are warm and therefore emitting infrared radiation. So even if the sensory cells could sense infrared they would be permanently stimulated, effectively blinding you. Snakes can sense heat (which I assume really means infrared), but they have lower body temperatures particularly at night, and the sensory organs lie right on their skin and not inside the body.

But I think this problem could be overcome in a hypothetical human-like creature.
The eyes lie very close to the nose. If the blood vessels leading to the eyes pass through the nose first, the blood could be slightly cooled by air through breathing. No idea how effective that would be, but maybe it might bring the temperature down a degree or two, reducing the amount of infrared light emitted by the eyes.

Another effect is, that the intensity of light increases when it's focused. When you hold a magnifying glass into sunlight, the focus point whill be much brighter than the sunligh reaching the rest of the surface. Which is exactly what an eye does. Even if the IR sensing cells are not triggered by the amount emitted inside the body, the focused intensity of even lower energy waves could overcome the trigger threshold.
I don't know how large the image on the retina normally is, but the region sensing IR could be smaller than that for RGB, so the lense can focus the light even tighter in IR mode. The tradeoff would be a reduced image resolution. But when the alternative is complete blindness, just fuzzy blobs of higher warmth would be very useful.

I don't know of any vertebrate eyes that reach into IR, but I think in theory it should be possible. Any obvious holes in this?

[Jay R]

Light is reflected off my body too, but I can still see visible light.

The fact that my body is warm means that I would be able to see it with infravision, not that I couldn't see anything else.

A quick internet search shows that infrared goggles exist, allowing you to see heat images.

[Yora]

Yes, but the problem is that the insides of the eyes are warm enough to emit infrared radiation. You don't have visible light glowing from inside your eyes.

[factotum]

Yes, wearing goggles is not the same as trying to view IR radiation on a retina that's behind a lens which is at the same temperature as the rest of you, e.g. quite warm! Mind you, I think there are also issues with the lens itself in this scenario, because IR radiation is at a significantly longer wavelength than visible light and so the optics required would be quite a bit different. That would also make your solution not work, Yora, because the lens itself being warm would be the main issue and the lens has no blood supply of its own.

I think this is probably one of those things that we have to ascribe to magic, because I can't see any way this could ever work in a realistic creature...

[Telok]

You are assuming that the cells that detect the infrared light are on the back of the eyes, have omni-directional sensitivity, and are not insulated in any way. We are talking about a necessarily non-human eye structure here, the assumptions involved in human eye physiognomy do not apply here.

[SiuiS]

Would there be any way the eye lens could change the infrared to normal light? A secondary "fluid lens" that would keep the exterior cool enough to pick up shifts and would be of a composition to either A) shift incoming IR to visible spectrum or B) absorb IR and regurgitate similarly patterned visible spectrum light back into the eye? The eyes of elves would then be akin to film, and able to capture the last thing they saw. Literal windows to the soul.

[Jay R]

I have no idea what principle makes you think generating light makes it harder to perceive light.

I sometimes strap a small lamp to my head for hobby work.

I generate heat, and can feel heat.

I generate smells, and can smell things.

I have a taste, and can taste things.

How in the world does generating something keep you from feeling other generators of it? I can't think of any real-world example.

[SiuiS]

I have no idea what principle makes you think generating light makes it harder to perceive light.

I sometimes strap a small lamp to my head for hobby work.

I generate heat, and can feel heat.

I generate smells, and can smell things.

I have a taste, and can taste things.

How in the world does generating something keep you from feeling other generators of it? I can't think of any real-world example.

Real world example? Glare. Errant light from reflective surfaces will impede your vision, not only because of the splotch of color but also the acuity of yor 'clear' vision. In real life, you can manually block just the glare to see better. This happens often with flashlights and such; you focus your eyes better on an object with less light than one in full light that is glaring.

Heat passes through walls (eventually). The idea is that if the cells which would pick up IR are cost tangly stimulated by roughy 99° F all the time, they won't be able to see much past that 'glare'. Alternately, you'll get reverse vision where you see absences of things that are body temp and see actual space where things are cooler?

[The Grue]

Also, light pollution (http://en.wikipedia.org/wiki/Light_pollution).

[Ravens_cry]

Since thermal waves are longer, this makes restrictions on the level of detail possible at the 'redder' end of the spectrum I would think.

[factotum]

I have no idea what principle makes you think generating light makes it harder to perceive light.

I sometimes strap a small lamp to my head for hobby work.

I generate heat, and can feel heat.

I generate smells, and can smell things.

I have a taste, and can taste things.


Try inserting that lamp into your eye instead of the lens that's already in there and then come back and tell us it doesn't make it hard to see stuff. :smallwink: Generating heat and feeling heat is true, but you can only really detect something that's significantly warmer or colder than you are--stuff around the same temperature as you won't feel warm or cold. As for the other two, those are just ridiculous examples. (Oh, and you forgot your sense of hearing, possibly because you realise that making a loud noise yourself makes it harder to hear external noises and thus that completely disproves your theory?).

[Frozen_Feet]

You could copy the exact mechanism from a snake to a human and it would work just fine. The infrared sensor are located on the skin, not in the eyes, abd have more in common with how your skin can feel radiant heat. A snake's brain just has the necessary thingamajobs to translate the heat sensed by the sensory organs into a rough picture.

So. Separate patches of infrared sensors, either below or above your eyes.

It shoud be also noted that old D&D had two sorts of infravision. The first one was passive, and worked like above. The second was active, and would work by the creature's eyes or other organ actually emitting directed light, with another set of organs receiving the reflections. This is homologous to a human putting a flashlight on their forehead.

[Max™]

The tips of an elves ears are further from the head than say, ours are, and have an otherwise difficult to explain shape.

Perhaps that would be a viable location for infrared sensors?

[Ravens_cry]

The tips of an elves ears are further from the head than say, ours are, and have an otherwise difficult to explain shape.

Perhaps that would be a viable location for infrared sensors?
Depends on the elf. They could be pointed but otherwise close to the head and near the size of human ears (Tolkien by most reading), or practically at right angles to the side of the head and of a size that would make jackrabbits proud (a lot of anime).

[Max™]

Well, it is difficult to explain why pits or whatnot haven't been described for them before.

I wonder if a fibrous tissue bundle could work as a heat sensor for dwarves?

[Brother Oni]

I wonder if a fibrous tissue bundle could work as a heat sensor for dwarves?

It would certainly put rest to the question of whether female dwarves have these fibrous tissue bundles.

[shawnhcorey]

Pit vipers (https://en.wikipedia.org/wiki/Pit_viper) have separate organs for detecting heat. And they work more like your ears than your eyes. They can tell the direction of the hottest source but don't give high resolution.

[Fragenstein]

It shoud be also noted that old D&D had two sorts of infravision. The first one was passive, and worked like above. The second was active, and would work by the creature's eyes or other organ actually emitting directed light, with another set of organs receiving the reflections. This is homologous to a human putting a flashlight on their forehead.
Huh. I only remember the passive Infravision and then Ultravision. Which creatures had active Infravision, and which editions are we talking about? I have to admit I remember little of both Basic and Expert rules.

[Frozen_Feet]

1st Edition AD&D. Creatures with Infravision range of 60' or less have passive infravision. Creatures with infravision ranges of 120' or longer have active infravision. This is obvious if you read the descriptions of the visual modes: those with short range only get a vague picture, while those with long range are said to have almost full greyscale vision, with a special notion of how their eyes often gleam red.

[Fragenstein]

1st Edition AD&D. Creatures with Infravision range of 60' or less have passive infravision. Creatures with infravision ranges of 120' or longer have active infravision. This is obvious if you read the descriptions of the visual modes: those with short range only get a vague picture, while those with long range are said to have almost full greyscale vision, with a special notion of how their eyes often gleam red.

Right, I'd forgotten the 120' rule, thanks. We were always one of those groups that ignored lighting conditions, but I've read the books repeatedly enough that I should have known.

[Necroticplague]

1st Edition AD&D. Creatures with Infravision range of 60' or less have passive infravision. Creatures with infravision ranges of 120' or longer have active infravision. This is obvious if you read the descriptions of the visual modes: those with short range only get a vague picture, while those with long range are said to have almost full greyscale vision, with a special notion of how their eyes often gleam red.

I remember drow having an active version. Their eyes emitted heat, and in an act of cleverness, this meant they could talk in morse code by blinking in the dark (since their eyes showed up well on each others infravision when open).

[zabbarot]

I remember drow having an active version. Their eyes emitted heat, and in an act of cleverness, this meant they could talk in morse code by blinking in the dark (since their eyes showed up well on each others infravision when open).

And if they blink just right they could control the television. :smalltongue:

[tomandtish]

And if they blink just right they could control the television. :smalltongue:

Stupid Drow, always changing the station to their crappy reality TV.

Next on Lifetime "Real Drow Priestesses of the UnderDark. This episode, Verna and her sisters crash a party in Evermeet...".

[Jay R]

Real world example? Glare.

Nope. We're looking for an example in which the generated energy from the observer hurts the observations differently generated energy from somewhere else. Glare doesn't come from inside my eyes; it comes from outside.


Also, light pollution (http://en.wikipedia.org/wiki/Light_pollution).

Light pollution doesn't come from inside my eyes either.


Try inserting that lamp into your eye instead of the lens that's already in there and then come back and tell us it doesn't make it hard to see stuff. :smallwink:

I have no idea if it would or not. That's the point I'm trying to make. I have no experience with that - and neither do you.


Generating heat and feeling heat is true, but you can only really detect something that's significantly warmer or colder than you are--stuff around the same temperature as you won't feel warm or cold.

Huh? I can feel the body heat of somebody touching me who's the same temperature I am. Being the same temperature means they feel neutral; not that I can't feel them at all. That's how you check somebody for a fever by touching their forehead.

For something to be invisible to infravision, it would need to be the same temperature as the surrounding air, not the observer. In my game, I once assumed that undead could not be detected that way, because they don't generate heat, and are therefore room temperature.


As for the other two, those are just ridiculous examples.

That argument will work better if you explain what's wrong with them, rather than merely heaping scorn.


(Oh, and you forgot your sense of hearing, possibly because you realise that making a loud noise yourself makes it harder to hear external noises and thus that completely disproves your theory?).

Noises I generate are no more disruptive than noises generated elsewhere. But the reason I left it off it that sounds waves through the air are transverse waves. But heat is primarily carried by radiation. So sound is an irrelevant model. (Yes, heat can be carried by convection, but if infravision worked that way, it would be much slower, and would not work well in a wind.)

[factotum]

OK, explanation of why I considered the other two ridiculous: smell works by detecting chemicals in the air, and there are hundreds or even thousands of them that can be individually detected by even the rather weak olfactory system of a human being. As for taste, unless you're in the habit of eating yourself, then you DON'T have any discernible taste--you can't taste your own tongue, or saliva. In both cases the mechanism by which those senses work is so utterly different from the way vision works that you can't compare the two--in fact, pretty much the same reason you give for not including hearing in your list of examples.

As for the lamp example, you don't need to replace the lens in your eye with the lamp; just put it really close under your eye and shining into it, but not in such a way it directly blocks the view of what you can see. Believe me, that light will make it very difficult indeed to see anything beyond it, even if it isn't directly blocking your vision. The warm lens of the eye would have a similar effect if the retina could detect infra-red, and would, at the very least, make it impossible to see anything that's roughly the same temperature you are--which, unfortunately, are the very things you really want to be able to see with infravision!

[Tev]

it comes from outside.

Light pollution doesn't come from inside my eyes either.

I have no idea if it would or not. That's the point I'm trying to make. I have no experience with that - and neither do you.

....

Noises I generate are no more disruptive than noises generated elsewhere.

Oh well, nothing beats destroying your own argument.

Your voice is more disruptive than noises elsewhere precisely because they come from the inside (through the skull), and are therefore perfect example how infrared vision based on current human eye model would be so hard.

[Max™]

Put the sides of your hands on your head in front of your ears and talk, then slowly move them away from your head.

You're just used to the effect of sound coming through your skull.

[SiuiS]

Nope. We're looking for an example in which the generated energy from the observer hurts the observations differently generated energy from somewhere else. Glare doesn't come from inside my eyes; it comes from outside.

Light pollution doesn't come from inside my eyes either.


Irrelevant distinction; both are instances of ambient junk data triggering receptors before intentional data, which is the point.

Imagine the eye as a cutaway. Imagine stray light bouncing around and hitting the receivers. You can see how that would be a problem right?

Same deal here. You're constantly getting "light rays" bouncing around into the receivers and triggering them. The eye won't distinguish between external IR and internal IR.

[Xuc Xac]

Oh well, nothing beats destroying your own argument.

Your voice is more disruptive than noises elsewhere precisely because they come from the inside (through the skull), and are therefore perfect example how infrared vision based on current human eye model would be so hard.

By that logic, bats can't use echolocation because they're distracted by the sound of their own screeching and can't focus on the echoes.

[Tev]

By that logic, bats can't use echolocation because they're distracted by the sound of their own screeching and can't focus on the echoes.

You're exaggerating and missing the point.
Nobody said you can't hear anything when you talk. Also bats use AFAIK pretty special frequencies that are rare in their environment.
Point was that it's just not as trivial to hear something when signal is distorted by your own voice.
When you try to overcome same obstacle with infrared detectors you face similar problems just much worse, because there's so much IR noise from your own body (especially within the eye) and you can't really bypass that by emitting special IR frequency and detecting the echo as bats do; I also wonder how much different in frequency is echo from bat "shout".

[Jay R]

You're exaggerating and missing the point.
Nobody said you can't hear anything when you talk. Also bats use AFAIK pretty special frequencies that are rare in their environment.
Point was that it's just not as trivial to hear something when signal is distorted by your own voice.
When you try to overcome same obstacle with infrared detectors you face similar problems just much worse, because there's so much IR noise from your own body (especially within the eye) and you can't really bypass that by emitting special IR frequency and detecting the echo as bats do; I also wonder how much different in frequency is echo from bat "shout".

But that noise is going away from you. The eyes are receiving the infra-red rays that are coming into them. It's exactly like ordinary vision, except the photons are coming in at a lower wave-length. If I can see ordinary light even when light rays radiate away from my body, then infravision should let me see infra-red waves even when infra-red waves radiate away from my body.

The problems could only come from other light coming toward my eyes. The fact that my head is radiating heat shouldn't cause a problem. Those photons won't come into my eyes. But if I hold my hand up in front of somebody further down the hall, I won't be able to "see" their heat, because my warm hand is in the way - exactly like blocking my view with my visible hand.

[SiuiS]

But that noise is going away from you. The eyes are receiving the infra-red rays that are coming into them. It's exactly like ordinary vision, except the photons are coming in at a lower wave-length. If I can see ordinary light even when light rays radiate away from my body, then infravision should let me see infra-red waves even when infra-red waves radiate away from my body.

The problems could only come from other light coming toward my eyes. The fact that my head is radiating heat shouldn't cause a problem. Those photons won't come into my eyes. But if I hold my hand up in front of somebody further down the hall, I won't be able to "see" their heat, because my warm hand is in the way - exactly like blocking my view with my visible hand.

Well, no. The 'film' is being constantly exposed. You're making sense except there is a very real understandable issue with the heat sensitive film being hit by heat constantly and you've done nothing to discredit that except deny it.

I've seen home video where a loose case let light from an LED into the lens area to bounce around. It messed with the image. I have no reason to think this wouldn't be the same, and you haven't provided one either.

So... Why are the 'photons' coming through your skin, your bones, your muscles, your blood, not activating the eyes? Because these 'photons' are indeed reaching the optics. Constantly.

[Max™]

Dammit, starting me on wikiwalks, ended up at trap-jaw ants and the videos: http://www.berkeley.edu/news/media/releases/2006/08/21_ant_video.shtml made me think of a weird Ant Kerbal Space Program.

[Jay R]

I think I’ve worked backwards to our actual point of disagreement.

Many people in this thread seem to be assuming that any infra-red photon receptor must automatically be omni-directional. Therefore, you reasonably conclude that the receptors will be swamped by the infra-red waves coming from within.

But that is not consistent with the way our eyes perceive any other wavelength of light.

By contrast, I’ve been assuming that the eye’s photoreceptor cells would collect low-energy (infra-red) photons the same way they collect visible-light photons. It’s not merely feeling heat; it’s collecting photons that pass through the lens, which focuses them onto the infra-red equivalent of rods and cones on the retina. The photons hit the top of the photoreceptor cell, and chemically affect the shape of the rhodopsin (or photopsin) which triggers a visual phototransduction which will turn the chemical reaction into a nerve signal. The nerve impulse travels to the synaptic terminal and on to other nerve cells. The point is that the signal, like any nerve signal, has both an intensity and a direction. It therefore follows that any photon that does not come through the lens and hit the back of the eye from the front would not hit the top of the photoreceptor cells and thus would not trigger the impulse.

The earliest reference to infravision I can find in D&D rules comes from a spell description on page 26 of Men & Magic, the first pamphlet in the original D&D (1974). "This spell allows the recipient to see infra-red light waves, thus enabling him to see in total darkness."

I agree that if the process is merely feeling heat, then your own body heat might get in the way. But my first introduction to the idea came from that book. The description "allows the recipient to see infra-red light waves" seems to imply the usual process of seeing (which is phototransduction) just at lower wavelengths.

[SiuiS]

I think I’ve worked backwards to our actual point of disagreement.

Many people in this thread seem to be assuming that any infra-red photon receptor must automatically be omni-directional. Therefore, you reasonably conclude that the receptors will be swamped by the infra-red waves coming from within.

But that is not consistent with the way our eyes perceive any other wavelength of light.

By contrast, I’ve been assuming that the eye’s photoreceptor cells would collect low-energy (infra-red) photons the same way they collect visible-light photons. It’s not merely feeling heat; it’s collecting photons that pass through the lens, which focuses them onto the infra-red equivalent of rods and cones on the retina. The photons hit the top of the photoreceptor cell, and chemically affect the shape of the rhodopsin (or photopsin) which triggers a visual phototransduction which will turn the chemical reaction into a nerve signal. The nerve impulse travels to the synaptic terminal and on to other nerve cells. The point is that the signal, like any nerve signal, has both an intensity and a direction. It therefore follows that any photon that does not come through the lens and hit the back of the eye from the front would not hit the top of the photoreceptor cells and thus would not trigger the impulse.

The earliest reference to infravision I can find in D&D rules comes from a spell description on page 26 of Men & Magic, the first pamphlet in the original D&D (1974). "This spell allows the recipient to see infra-red light waves, thus enabling him to see in total darkness."

I agree that if the process is merely feeling heat, then your own body heat might get in the way. But my first introduction to the idea came from that book. The description "allows the recipient to see infra-red light waves" seems to imply the usual process of seeing (which is phototransduction) just at lower wavelengths.

That makes sense. I don't know how consistent it is with later information, such as the description of IRvision and ultra vision from one of the later books, where it goes on to describe what's functionally heat vision.

Electromagnetic spectrum always gets me with technicalities. Is there sufficient difference between heat radiating off of something and just low frequency photons to make this distinction? Ah well. Now that I think about it A) I'm not willing to work out the entire system of eye tissue and fluid and transfer rates, and B) you've satisfied the one real issue. Thanks.

[factotum]

Many people in this thread seem to be assuming that any infra-red photon receptor must automatically be omni-directional. Therefore, you reasonably conclude that the receptors will be swamped by the infra-red waves coming from within.

But that is not consistent with the way our eyes perceive any other wavelength of light.


But the point we're trying to make is this: the actual lens in your eye will itself be emitting infra-red radiation, because it's warm! It's nothing to do with IR radiation hitting the retina from the *back*, it's the stuff hitting it from the warm parts of the eye in front of it that's the problem. That's why I talked about replacing the lens in your eye with a lamp, because that's exactly what we would have in the case of an IR-sensitive retina.

[SiuiS]

But the point we're trying to make is this: the actual lens in your eye will itself be emitting infra-red radiation, because it's warm! It's nothing to do with IR radiation hitting the retina from the *back*, it's the stuff hitting it from the warm parts of the eye in front of it that's the problem. That's why I talked about replacing the lens in your eye with a lamp, because that's exactly what we would have in the case of an IR-sensitive retina.

Is it? And is it impossible for the eye to see depth? The lens may add a transparent layer and pick up objects through it? Jay R is making a distinction, however small, between radiant heat and low frequency photons. I don't recall all too well, but doesn't heat only radiate when it can't conduct? Conduction, convection and radiation were admittedly in my "boring, don't care" segment of science class, more's the pity.

[Brother Oni]

But the point we're trying to make is this: the actual lens in your eye will itself be emitting infra-red radiation, because it's warm! It's nothing to do with IR radiation hitting the retina from the *back*, it's the stuff hitting it from the warm parts of the eye in front of it that's the problem. That's why I talked about replacing the lens in your eye with a lamp, because that's exactly what we would have in the case of an IR-sensitive retina.

Wouldn't the brain be able to calibrate the information generated from the eye so that it can ignore any ambiently emitted IR by the lens?

[factotum]

I don't recall all too well, but doesn't heat only radiate when it can't conduct?

No--it will radiate, conduct and convect simultaneously depending on the ambient conditions.

@Brother Oni: The brain might well be able to edit out the stuff arriving at the particular temperature being emitted by the lens, but as I pointed out earlier, that's kind of the most important temperature--you wouldn't be able to see anything that was at around that temperature, including, say, the guy running toward you with a ruddy great sword?

[Frozen_Feet]

But the point we're trying to make is this: the actual lens in your eye will itself be emitting infra-red radiation, because it's warm! It's nothing to do with IR radiation hitting the retina from the *back*, it's the stuff hitting it from the warm parts of the eye in front of it that's the problem. That's why I talked about replacing the lens in your eye with a lamp, because that's exactly what we would have in the case of an IR-sensitive retina.

I don't think the lamp analogy is accurate. The muscles in the eyes are small and they're mostly water. Eyes do not themselves generate much heat.

If we wanted to test this, a closer analogue would be to see how passive infrared camera works in warm water. If the camera can distinquish an object that's around same temperature as the water around it, then we can conclude that infrared eyes are plausible.


I don't recall all too well, but doesn't heat only radiate when it can't conduct? Conduction, convection and radiation were admittedly in my "boring, don't care" segment of science class, more's the pity.

You got it the wrong way around. Heat always radiates. It only conducts or convects when there's a suitable medium to do so.

Basically, this means the only environment where heat only radiates is a complete vacuum.

[Jay R]

But the point we're trying to make is this: the actual lens in your eye will itself be emitting infra-red radiation, because it's warm! It's nothing to do with IR radiation hitting the retina from the *back*, it's the stuff hitting it from the warm parts of the eye in front of it that's the problem. That's why I talked about replacing the lens in your eye with a lamp, because that's exactly what we would have in the case of an IR-sensitive retina.

A lamp? I think you are grossly overestimating the level of heat emitted.

Yes, there will be a low level of photons hitting the back of the eye generally. By contrast, a warm object 10 feet away will emit photons that go through the lens and are defracted by it so that they are all focused onto a single point on the retina of the eye. No resemblance.

[Hexapuma]

Just a couple of notes on this topic -

All Infrared is not created equal. Just like there is a red end to the visible spectrum and a blue end, so there is a heat end and a light end to the Infrared band. Illuminators for nightvision systems (sometimes called Gen1) use higher frequency IR which is just out of human vision but within the visual range of cats. You can see it sometimes if you point a tv remote at a webcam and press a button. Heat IR, used for thermal imaging, is on the low frequency end of the band.

Now for high end IR to be what was used in Infravision, you'd have to have some sort of emitter... I suppose you could hypothesize some really common fungus or bacteria in the world that gives off IR at the right frequency. There are such Fungi that give off visible light so it's not such a stretch.

For thermal systems, all cameras designed to see heat used to be heavily insulated and cooled so that internal noise didn't screw up the picture. Over time, more advanced sensors have been developed that don't require the massive shield/cooling structure. There's no reason the eye couldn't replicate that. The problem with Infravision being based on heat is that the specification in the manuals describes it as being like normal sight but in black and white. That's not how thermal vision would present. In thermal vision, hot objects would appear as blobs with poorly defined outlines. You probably wouldn't be able to read the carving on a wall of uniform temperature. Invisibility would be ineffective against a being with thermal infravision as rather than light passing through, the invisible creature would be emitting its own heat. Infravision is never described as having the drawbacks you might associate with thermal vision.

To be honest, it sounds more like a natural form of Gen1 Nightvision... We just don't know where the IR source is. Oh, also, the further towards Heat vision you go, the lower the quality of your sight will go. The wavelength of light gets longer and longer down there and that affects the detail you can see. That's part of the reason figures in Thermal look blobby. The other is that living things have a corona of heat.

An additional, and possibly interesting note. Some people can see in UltraViolet. The cells at the back of some people's eyes are sensitive to UV but normally that doesn't matter as the lens of the eye filters out the radiation. However some people have their lens removed for medical reasons and then the UV can come in. This allows them to see things that the rest of us can't. It happened to Monet (http://www.downloadtheuniverse.com/dtu/2012/04/monets-ultraviolet-eye.html) so it could be that Infravision is misnamed and is actually Ultravision which would actually give the user the ability to see smaller details than normal. Downside, it would require that dungeons be lit with UV.... Which I suppose could explain all the hideous, mutated denizens.

[Maquise]

An additional, and possibly interesting note. Some people can see in UltraViolet. The cells at the back of some people's eyes are sensitive to UV but normally that doesn't matter as the lens of the eye filters out the radiation. However some people have their lens removed for medical reasons and then the UV can come in. This allows them to see things that the rest of us can't. It happened to Monet (http://www.downloadtheuniverse.com/dtu/2012/04/monets-ultraviolet-eye.html) so it could be that Infravision is misnamed and is actually Ultravision which would actually give the user the ability to see smaller details than normal. Downside, it would require that dungeons be lit with UV.... Which I suppose could explain all the hideous, mutated denizens.

Do note, however, that seeing in UV has major problems; mainly, that UV light tends to fry the retina. Any species that can see in it will likely go blind at a much earlier age.

Thinking about it, though, if the ambient UV was low, such as underground, it wouldn't be as much of an issue...

[factotum]

so it could be that Infravision is misnamed and is actually Ultravision which would actually give the user the ability to see smaller details than normal. Downside, it would require that dungeons be lit with UV.... Which I suppose could explain all the hideous, mutated denizens.

Wasn't there an actual thing called Ultravision in some earlier editions of D&D?

[aspi]

A lamp? I think you are grossly overestimating the level of heat emitted.

Yes, there will be a low level of photons hitting the back of the eye generally. By contrast, a warm object 10 feet away will emit photons that go through the lens and are defracted by it so that they are all focused onto a single point on the retina of the eye. No resemblance.
I think the comparison with a lamp was only made to give an example, and I find it to be quite fitting actually. To put this a bit more clearly, let's not use a lamp but an old fashioned light bulb. Now consider an experiment where the lens and eye fluid are replaced by said light bulb. The light bulb can either be on (transmitting the kind of light your receptors can detect) or off (transmitting a kind of light your receptors cannot detect).

If you're trying to see regular light, the theoretical light bulb is off - it does not emit the same kind of light you are trying to see and rays from outside can pass through to the receptors. If you're trying to see infrared however, the theoretical light bulb is on, and emits the same kind of light you're trying to see - in all directions. Now imagine trying to see something through an active light bulb.

As for the argument that the eye is not that warm, it's actually only slightly colder than body temperature, no more than 1 degree centigrade (see here (http://onlinelibrary.wiley.com/doi/10.1111/j.1755-3768.1952.tb00011.x/abstract) for example). The temperature of what you're trying to see is about the same as body temperature if you're trying to see other living things - volcanoes might be a different story entirely. While those object are slightly warmer and much larger, they're also much further away while the eye fluid and lense are directly in front of your receptor. The intensity of light drops with the square of the distance. So unless someone with high fever is hugging your eyeballs, the heat of your eye fluid will easily block his body heat.

I don't see infrared vision working unless the detector is directly on the skin, as others have mentioned before.

[Jay R]

I've explained my position and failed to convince you.

You've explained your position and failed to convince me.

Shall we call it a draw and move on?

[SiuiS]

Just a couple of notes on this topic -

All Infrared is not created equal. Just like there is a red end to the visible spectrum and a blue end, so there is a heat end and a light end to the Infrared band. Illuminators for nightvision systems (sometimes called Gen1) use higher frequency IR which is just out of human vision but within the visual range of cats. You can see it sometimes if you point a tv remote at a webcam and press a button. Heat IR, used for thermal imaging, is on the low frequency end of the band. Infravision is never described as having the drawbacks you might associate with thermal vision.

While this all makes sense, I know at least one book approaches the description of infra vision specifically as heat, detailing the blobs and how they work and how fire sources will thwart it and all. It wasn't always black and white.



An additional, and possibly interesting note. Some people can see in UltraViolet. The cells at the back of some people's eyes are sensitive to UV but normally that doesn't matter as the lens of the eye filters out the radiation. However some people have their lens removed for medical reasons and then the UV can come in. This allows them to see things that the rest of us can't. It happened to Monet (http://www.downloadtheuniverse.com/dtu/2012/04/monets-ultraviolet-eye.html) so it could be that Infravision is misnamed and is actually Ultravision which would actually give the user the ability to see smaller details than normal. Downside, it would require that dungeons be lit with UV.... Which I suppose could explain all the hideous, mutated denizens.

No, ultra vision was it's own thing. Some creatures had both, most had neither or just infra vision. Ultra vision is the one that went on to describe how the sky would look, I believe.


I think the comparison with a lamp was only made to give an example, and I find it to be quite fitting actually. To put this a bit more clearly, let's not use a lamp but an old fashioned light bulb. Now consider an experiment where the lens and eye fluid are replaced by said light bulb. The light bulb can either be on (transmitting the kind of light your receptors can detect) or off (transmitting a kind of light your receptors cannot detect).

If you're trying to see regular light, the theoretical light bulb is off - it does not emit the same kind of light you are trying to see and rays from outside can pass through to the receptors. If you're trying to see infrared however, the theoretical light bulb is on, and emits the same kind of light you're trying to see - in all directions. Now imagine trying to see something through an active light bulb.

As for the argument that the eye is not that warm, it's actually only slightly colder than body temperature, no more than 1 degree centigrade (see here (http://onlinelibrary.wiley.com/doi/10.1111/j.1755-3768.1952.tb00011.x/abstract) for example). The temperature of what you're trying to see is about the same as body temperature if you're trying to see other living things - volcanoes might be a different story entirely. While those object are slightly warmer and much larger, they're also much further away while the eye fluid and lense are directly in front of your receptor. The intensity of light drops with the square of the distance. So unless someone with high fever is hugging your eyeballs, the heat of your eye fluid will easily block his body heat.

I don't see infrared vision working unless the detector is directly on the skin, as others have mentioned before.

But we've established that Infravision != heat vision, and we've established that sophisticated heat vision anyway can be done without needing this complex insulation system. If actual heat cameras don't suffer this problem for reasons then it could easily be the eyes wouldn't either, if they were heat sensitive and not just picking up low frequency light.

[aspi]

But we've established that Infravision != heat vision, and we've established that sophisticated heat vision anyway can be done without needing this complex insulation system. If actual heat cameras don't suffer this problem for reasons then it could easily be the eyes wouldn't either, if they were heat sensitive and not just picking up low frequency light.
But I'm not talking about complex insulation systems. The difference between a heat camera and the eye is that the camera "looks through" a 2mm thick piece of room temperature glass, while the retina looks through 2cm of body temperature water. The problem is not that there is ambient heat in your body but that there is something in front of your "detection mechanism" that produces the exact same kind of low frequency radiation you want to see, in the direction you are looking, at a higher relative intensity than what you're looking at. It's not about insulation, it's about noise being generated directly in front of your sensor that's of the exact same kind as the radiation your're trying to detect.

To bring it back to the hearing example, if someone were to blow a trumpet in your ear, you won't hear an identical trumpet at the other side of the yard. But that's what you have to deal with if you want to detect any kind of light while the same kind is being generated directly infront of your detector.

And since I'm not sure if that was stated explicitly, I'll point out that any kind of heat sensor that operates at a distance where it can be called "vision" will detect low frequency photons. Convection and conduction play no role at these distances, as air is a rather good insulator and convection would be directed upwards only.

Edit: To put my problems with the "seeing" of heat through organs that function like eyes more clearly, a question to those who feel that it should be possible:

If it's as "simple" as adding a new kind of receptor to the eye and maybe adjusting the lens a bit, why are there no animals with heat vision? Most higher predatory species have eyes already and heat vision would be immensely useful to all those who live in temperate or cold environments and hunt mammals like owls, snakes or polar foxes. From an evolutionary point of view, it is a lot simpler to add a single receptor to the eye than develop an entirely new organ (as in the snake heat sensing example). Nature is incredibly good at optimizing bodies for a specific task. Why would she have missed this one across the board?

[Ravens_cry]

Do note, however, that seeing in UV has major problems; mainly, that UV light tends to fry the retina. Any species that can see in it will likely go blind at a much earlier age.

Thinking about it, though, if the ambient UV was low, such as underground, it wouldn't be as much of an issue...
There actually is many species that can see in ultraviolet, including dogs and cats (http://www.livescience.com/43461-cats-and-dogs-see-in-ultraviolet.html).

[Frozen_Feet]

You know, there's this old folklore belief that animals, especially cats, can see into the spirit world and see things invisible to the human eye. Now I know the latter, at least, is true. No wonder cats are wacko, they literally be seeing things, yo.

[Bulldog Psion]

An additional, and possibly interesting note. Some people can see in UltraViolet. The cells at the back of some people's eyes are sensitive to UV but normally that doesn't matter as the lens of the eye filters out the radiation. However some people have their lens removed for medical reasons and then the UV can come in. This allows them to see things that the rest of us can't. It happened to Monet (http://www.downloadtheuniverse.com/dtu/2012/04/monets-ultraviolet-eye.html)

Thank you for providing the most bizarre and interesting thing I've read all week.

[Maquise]

There actually is many species that can see in ultraviolet, including dogs and cats (http://www.livescience.com/43461-cats-and-dogs-see-in-ultraviolet.html).


One thing to note though, is that apparently animals with sight in the UV range can't make out as much detail as human eyes can.

[factotum]

One thing to note though, is that apparently animals with sight in the UV range can't make out as much detail as human eyes can.

That's actually not too surprising--all other things being equal, the shorter wavelength of UV will make the possible angular resolution lower. (See Rayleigh criterion for more information).

[Ravens_cry]

That's actually not too surprising--all other things being equal, the shorter wavelength of UV will make the possible angular resolution lower. (See Rayleigh criterion for more information).

I thought it was the other way around, since you can't see something smaller than the frequency. This is why electron microscopes are better than optical microscopes, for example.

[Xuc Xac]

I thought it was the other way around, since you can't see something smaller than the frequency. This is why electron microscopes are better than optical microscopes, for example.

Yes. Resolution is limited by wavelength. The wavelength is essentially your minimum pixel size. That's why you can't pick up small objects like people on radar and why things look fuzzier when you're in a room lit by a red light.

[SiuiS]

But I'm not talking about complex insulation systems. The difference between a heat camera and the eye is that the camera "looks through" a 2mm thick piece of room temperature glass, while the retina looks through 2cm of body temperature water. The problem is not that there is ambient heat in your body but that there is something in front of your "detection mechanism" that produces the exact same kind of low frequency radiation you want to see, in the direction you are looking, at a higher relative intensity than what you're looking at. It's not about insulation, it's about noise being generated directly in front of your sensor that's of the exact same kind as the radiation your're trying to detect.

Does this
A) account for the difference between heat and low frequency light, such that there is?
B) account for the races which emit IR light from their eyes as part of their Infravision?

It doesn't seem hard to have your eyes cool per than the rest of your body, even by a little, enough to see contrast between cool air and hot bodies, either. Just specialized vasculature.

[factotum]

I thought it was the other way around, since you can't see something smaller than the frequency. This is why electron microscopes are better than optical microscopes, for example.

My bad--I just realised I misinterpreted the Rayleigh criterion; I was thinking lower angular resolution was bad, but of course, it's actually better because it means you can pick out finer detail. Whoopsies. :smallredface:

[Murska]

No--it will radiate, conduct and convect simultaneously depending on the ambient conditions.

@Brother Oni: The brain might well be able to edit out the stuff arriving at the particular temperature being emitted by the lens, but as I pointed out earlier, that's kind of the most important temperature--you wouldn't be able to see anything that was at around that temperature, including, say, the guy running toward you with a ruddy great sword?

However, the brain doesn't need to edit out a specific temperature. The brain just sees 'okay, normally the eye receives this many photons of this energy which are generated by the warmth of the eye, so we'll translate that into seeing nothing much. But now when I look that way, the eye receives some more photons of that energy compared to the base level, which means some of the input isn't generated by the warmth of the eye, so we'll translate that into seeing a guy running towards me with a ruddy great sword.'

[Brother Oni]

Yes. Resolution is limited by wavelength. The wavelength is essentially your minimum pixel size. That's why you can't pick up small objects like people on radar and why things look fuzzier when you're in a room lit by a red light.

Apparently you can detect bird migrations on weather radar, so that's both rain and small avians on non-military radar. Admittedly, they're both wide large masses, but the granularity is apparently possible with higher powered radar.

As I understand it, paratroopers are not on the board for long enough (HALO jumps) or radar/Mk1 eyeball detection is not a concern (HAHO jumps).

[Hexapuma]

I wonder if you could eliminate the problem of your own body's thermal emission ruining your picture by making use of polarization...

If you could ensure that your body, or just in this case your eyeball's vitreous humor, emitted IR only in a certain polarization then the receptors in the eye could develop to screen out that polarization and that would leave you with only the randomised IR coming from the thing you were looking at. You'd lose a small proportion of the photons coming at you which would make small, indistinct objects harder to see but then the vision is only supposed to work over a 120 foot range.

This wikipedia article does actually allow that you can have polarized thermal IR emission. http://en.wikipedia.org/wiki/Thermal_radiation

Does this reconcile the two opposing views?

[Yora]

Apparently you can detect bird migrations on weather radar, so that's both rain and small avians on non-military radar. Admittedly, they're both wide large masses, but the granularity is apparently possible with higher powered radar.

As I understand it, paratroopers are not on the board for long enough (HALO jumps) or radar/Mk1 eyeball detection is not a concern (HAHO jumps).

Anything can reflect a radar beam. But the smaller an object is, the lower the chance of anything actually getting hit right on. A single parachute jumper would technically "detected", but the echo would be so faint that the detection device wouldn't notice it.
If you have a really big swarm of birds, or a massive cloud of water droplets, the sheer number of them will cause enough rays to be reflected back for a noticeable signal to be detected.

Infrared vision is not actually heat vision. You don't see heat, but you see photons emited by warm objects. Any warm object emits photons, but it needs to be really quite hot for the photons to be in the visible light spectrum. An extremely hot object first glows white, and as it cools down the glow is reduced to yellow, orange, and red. Even when it seems to have cooled down to a point where it no longer visible glows, it's still glowing infrared. Human eyes are just blind to these wavelengths and see nothing, but the glow is still there.

[aspi]

Does this
A) account for the difference between heat and low frequency light, such that there is?
I feel like there's been a miscommunication on a very basic level. So I'll go back to the workings of heat for a moment.

Simply put, heat is the movement of atoms and molecules on a very small scale. Unless matter is at absolute zero, it's atoms vibrate. The higher the temperature, the stronger the movement. Now if we take any object with a temperature, this temperature will try to diffuse in order to spread equally. If this diffusion takes place in an atmosphere, there are three main mechanisms:

Conduction: If there are solid object next to the heated object with a lower temperature, the moving atoms of the heated object will "hit" them and transfer part of their energy, thus heating the adjacent object. This kind of heat diffusion requires direct contact. Generally speaking, denser object tend to have a higher conductivity for heat. This is air is a good insulator and why bath water feels warm when you sit in the tub.
Convection: If there are gases or liquids around the heated object, they will be heated through conduction. However, since warmer liquids and gases are lighter than their cold equivalents, they will rise and be replaced by new gases or liquids that are then heated. This transports heat over a larger distance but is mostly directed upwards. This is how a radiator works.
Emission: This is completely independent of the surrounding of the object. Whenever an object is heated, this heat equals energy that is stored in the object. It will emit part of this energy as radiation - meaning photons. The frequency of this light depends on the temperature of the object but is generally not limited to a single frequency - it forms a spectrum. This is why stars can have different colors: they have different temperatures.

The important point that I would like to point out after this introduction is this: Conduction and convection are completely irrelevant to the task of seeing heat. Both sides have always been talking about those low frequency photons. So yes, while there will be conduction and possibly even convection inside the eyeball, there is also emission. The eyeball and the object we're trying to see with our heat vision do the exact same thing: emit low frequency photons. That they're also doing something else doesn't really metter to the problem if our receptors only detect photons.


B) account for the races which emit IR light from their eyes as part of their Infravision?
This is largely independent. We can split our system in two components for those species: an IR sender and an IR reciever. All the emitter does is send out low frequency photons that are reflected by the object we're trying to see. Kind of like an x-Box Kinect. This does not change our recieving problems though. The version that uses polarized light as suggested by Hexapuma might work with an active emission though. But I'm not sure I'd call that heat vision, as it would work with any kind of light.


It doesn't seem hard to have your eyes cool per than the rest of your body, even by a little, enough to see contrast between cool air and hot bodies, either. Just specialized vasculature.
This does not seem all that easy to me, actually. Getting rid of excess heat is no trivial matter, neither in nature nor in technology. An example where this is the case in nature are human male testicles for example, which have to be kept a little cooler than the rest of the body and are thus placed on the outside. However, the temperature difference is not large. It's not as simple as tuning the vascular system - you still have to bring nutrients to the eyes, and the eyes will generate small amounts of heat themelves, not just be heated by the blood. While it is possible to have organs that are not directly connected to the bloodstream and still recieve nurtients (such as the human spinal disc) this has problems of his own (if people sit too much, the disks are not massages by body movement and recieve less nutrients which is one cause for disk herniation).
There are organisms however, that work at much lower body temperatures, such as deep sea fish, so the idea of operating an eye at lower temperatures is doable. It might be possible to place eyes on stalks and keep them away fom the body for a cooling effect.


I wonder if you could eliminate the problem of your own body's thermal emission ruining your picture by making use of polarization...

If you could ensure that your body, or just in this case your eyeball's vitreous humor, emitted IR only in a certain polarization then the receptors in the eye could develop to screen out that polarization and that would leave you with only the randomised IR coming from the thing you were looking at. You'd lose a small proportion of the photons coming at you which would make small, indistinct objects harder to see but then the vision is only supposed to work over a 120 foot range.

This wikipedia article does actually allow that you can have polarized thermal IR emission. http://en.wikipedia.org/wiki/Thermal_radiation

Does this reconcile the two opposing views?
While using polarization is a pretty cool idea, I'm not sure if it's actually possible to have an entire transparent volume like the eyeball (as opposed to a surface) emit polarized IR light only. I might be wrong here but I think it is also much easier to filter out everything except a certain polarization than it is to do the opposite as we'd have to in this example.

But if we have the option of actually emitting light as well (as in the active infravision example) then using polarization might help. But then again if we can emit light, we could just chose a frequency that the eyeball does not generate itself and skip polarizing it.

In general I think the problem is that for most types of light outside of the visible spectrum that occurr naturally, that they are either not present in cases regular light is missing (like UV) or highly prone to noise because the recipient generates them as well as the target.

[Ravens_cry]

This (https://www.youtube.com/watch?v=kfS5Qn0wn2o) is rather humbling. Makes you realize how mind bogglingly vast an amount of the spectrum we are literally blind to.

[Kato]

Wow, I didn't expect this discussion to last that long but giving it some thought myself it actually is pretty intriguing...
If I may add my five cents to the matter...

As discussed, there's a large difference between heat vision and infrared vision.

Infrared is a pretty arbitrary term people came up with for light with wave lengths longer than what they can perceive. (Up to a point) Heat vision is... more difficult? The wave length of photons emitted by a body of a certain temperature are given by Planck's Law. "Cool" bodies have a pretty wide range of emitted photons with very undistinguished peaks when it comes to wave length/frequency depending on temperature (though you can still always calculate a particular particular wave length the majority of photons will have) This makes the task of telling the temperature of an object based on the emitted photons a bit tedious, when the body is not "hot" (as in, 1000K and above or so) But evolution can be pretty smart about these things.

Infrared, as in, "wave lengths longer than normal people can see" is no real problem, you just need biology to figure out a proper substance which reacts to the specific wave length(s). Which it probably can. However, this... doesn't serve much of a purpose. Okay, you can potentially see colors other people can not and thus you can use "invisible" ink or such but it won't help you see in the dark.

So, what we actually want is the ability to see the wave length of pretty long (roughly 10 micrometers, compared to the normal 0.5 micrometers or so) if we talk about body temperature and general temperature of our surroundings. In theory, not much of a problem, by the same logic as above (snakes do it) but the issue, as discussed, is if we will only see our body temperature, because... well, our eyes are at body temperature.
And the answer is... debatable? Something that should not be much of a problem is distinguishing considerably hotter (and colder) items but when it comes to things which are also about 310K it gets difficult. While I can't entirely rebuke it, the "let the brain sort it out" argument might work, but then if I constantly shine a bright light in your eye, would your brain be able to sort the more brighter from the less brighter spots (yes, bad English, I know). Would it be able to do so if it was optimized for it by millenia of evolution? Uh... maybe? The possibility exists, quite clearly, you can filter out a whole lot of stuff (and even if not, if you can not have lenses which perceive say 305-315K, you could still see a lot of stuff. Other living beings usually don't radiate at their body temperature all around, your receptors however would be only required to sort out these wave lengths. (Which kind of raises the question, if you get really hot/cold, would you see yourself all the time?)
This kind of brings me to another question... Does light at these frequencies penetrate living tissue substantially different from visible light? Visible light can't really go through your skull from the back, making the eye a good lens but if we just add some more cones, will they not only be affected by our body temperature but also from all kinds of other sources behind us etc? It would give you 360° vision but it seems hard to make out any shapes unless we really discuss entirely different organs which ideally would be just more eyes with possibly better insulation.

So, what is the best option to clarify this? Breed snake people with heat vision and test it out! :smallbiggrin:

[Jay R]

Your own body heat is diffuse and unfocused. It hits all parts of the retina equally, and is merely unchanging background noise. Infra-red photons that come through the lens from a specific outside heat source will be focused onto a specific point on the retina. Even with a constant background of heat, that additional focused beam will cause a specific change to the photoreceptor cell.

I assume that it would be easy to learn to ignore the unfocused overall heat and focus on specific focused signals, just as you can ignore any background noise and listen to a specific speaker. This could be similar to the photographic technique of using a low f-stop on your lens to keep the background out of focus so the viewer will concentrate on the foreground.

[A low f-stop is equivalent to using a wider lens, which is exactly what your eye does in low light.]

Who knows? Maybe everyone's eyes can pick up infra-red signals, and the races with infra-vision are merely the ones who have learned to suppress the generalized heat signal.

[Brother Oni]

Your own body heat is diffuse and unfocused. It hits all parts of the retina equally, and is merely unchanging background noise. Infra-red photons that come through the lens from a specific outside heat source will be focused onto a specific point on the retina. Even with a constant background of heat, that additional focused beam will cause a specific change to the photoreceptor cell.

I assume that it would be easy to learn to ignore the unfocused overall heat and focus on specific focused signals, just as you can ignore any background noise and listen to a specific speaker.

The unfocused overall heat affecting the resolution would explain why infravision is capped to 120' while normal vision can see ~2.5 million light years (http://en.wikipedia.org/wiki/Andromeda_Galaxy). :smalltongue:

[aspi]

I figured out another problem with the eye approach if we're using classic, liquid-filled eyes: water is incredibly efficient at absorbing infrared light. For light with a wavelength of over 1µ, even half an inch of water will reduce the intensity by half (source (http://oceansjsu.com/105d/exped_briny/13.html) Note that this is for solar radiation so absolute peak values are not directly applicable, but the interesting comparison is between the red and green line. And yes, I know it's ocean water but that's a pretty good approximation.) While visible light has little trouble penetrating short distances of water, IR is severely limited.

I think this is the reason why there are no IR eyes in nature. For our fantasy setting, we might be able to introduce gas-filled eyeballs...


Your own body heat is diffuse and unfocused. It hits all parts of the retina equally, and is merely unchanging background noise. Infra-red photons that come through the lens from a specific outside heat source will be focused onto a specific point on the retina. Even with a constant background of heat, that additional focused beam will cause a specific change to the photoreceptor cell.
While this is true, you are discounting the fact that the intensity of light diminishes with the square of the distance. Even if the object you are looking at is only 10 yards away, that's still 360 times farther than the less than one inch between your retina and the eye fluid. Now square that... The beam you are focussing is also limited to the width of the lense which is maybe 1/6 of a square inch.

[Max™]

The unfocused overall heat affecting the resolution would explain why infravision is capped to 120' while normal vision can see ~2.5 million light years (http://en.wikipedia.org/wiki/Andromeda_Galaxy). :smalltongue:

We can see quite a bit farther than that, there are a few galaxies visible around the 10 mly marker.

Regarding the comment earlier about emission not depending on the environment, the color at which the emissions peak isn't going to change, but the heat lost through emission has to, otherwise an object would have to magically produce or dispose of energy to maintain the particular level of emissions one expects from the SB law, which is only going to be achieved when a body is emitting into a vacuum with no sources nearby.

[Murska]

While this is true, you are discounting the fact that the intensity of light diminishes with the square of the distance. Even if the object you are looking at is only 10 yards away, that's still 360 times farther than the less than one inch between your retina and the eye fluid. Now square that... The beam you are focussing is also limited to the width of the lense which is maybe 1/6 of a square inch.

So the difference is small. No matter - machinery capable of measuring small differences is not uncommon in biology.

[Jay R]

While this is true, you are discounting the fact that the intensity of light diminishes with the square of the distance. Even if the object you are looking at is only 10 yards away, that's still 360 times farther than the less than one inch between your retina and the eye fluid. Now square that... The beam you are focussing is also limited to the width of the lense which is maybe 1/6 of a square inch.

Yes, you're right; I am discounting it completely. There's more than one possible solution. Either the threshold needed to activate the photo-receptor cells is just barely above the level it normally receives from body heat, or there is a baffling system to prevent a photon from reaching the top of the photorecepter cell unless it came through the lens. Or possibly it only registers changes to the signal. Or there is a neural solution, which removes the constant signal of your own heat, just as people are known to eventually learn to ignore smells and sounds that are constant.

I know a signal can be received through that lens, because I can see my screen right now. The only new issue is filtering out or ignoring a constant photon stream.

[Xuc Xac]

Apparently you can detect bird migrations on weather radar, so that's both rain and small avians on non-military radar. Admittedly, they're both wide large masses, but the granularity is apparently possible with higher powered radar.

Radar can see clouds and flocks of birds but with visible light you can see raindrops and individual feathers. Resolution is limited by wavelength: the wavelength is your minimum pixel size.

[factotum]

I know a signal can be received through that lens, because I can see my screen right now.

A *visible light* signal, yes. :smallsigh: The heat generated by the lens and the aqueous humour will make no difference to that. (And of course the lens actively blocks some wavelengths--the ultra-violet radiation mentioned earlier in the thread, for instance).

[Tev]

Yes, you're right; I am discounting it completely. There's more than one possible solution. Either the threshold needed to activate the photo-receptor cells is just barely above the level it normally receives from body heat, or there is a baffling system to prevent a photon from reaching the top of the photorecepter cell unless it came through the lens. Or possibly it only registers changes to the signal. Or there is a neural solution, which removes the constant signal of your own heat, just as people are known to eventually learn to ignore smells and sounds that are constant.

I know a signal can be received through that lens, because I can see my screen right now. The only new issue is filtering out or ignoring a constant photon stream.

Well we ALL know that it could be done, you could replace retinas with some IR sensors and modify the eye and stuff a bit and you could have infrared vision. No warpdrive physics behind it.
Problem remains - how practical will that vision be? Many people in this thread have shown real problems with such arrangement, so it's questionable how practical would that vision be. Especially compared to relatively easy methods like covering face with IR sensors, putting them eg on top of the ears, nose, chin?, whatever . . . or growing some ear-like cartilage antennas from top/side of your head with sensors at the end (that's actually logical evolutional progress from the first bruteforce solution).

so tl;dr version of the thread: Eye is quite well optimized for our current vision and constraints of our bodies. Making them IR is possible, but with too much hassle and too little real use.

[aspi]

So the difference is small. No matter - machinery capable of measuring small differences is not uncommon in biology.
I agree that biological sensors are completely amazing. But they're limited by physics and there is a hard limit to what you can filter out before the noise drowns out the signal. You're assuming that there is a completely flat baseline of incoming noise. This is hardly ever the case at such small scales. There's always fluctuation in the noise, and unless the actual signal is strong enough to be differentiated from naturally occurring spikes in the noise level, you cannot detect them with certainty. Especially since we're talking about light here, as there will be interference effects.


Yes, you're right; I am discounting it completely. There's more than one possible solution. Either the threshold needed to activate the photo-receptor cells is just barely above the level it normally receives from body heat, or there is a baffling system to prevent a photon from reaching the top of the photorecepter cell unless it came through the lens. Or possibly it only registers changes to the signal. Or there is a neural solution, which removes the constant signal of your own heat, just as people are known to eventually learn to ignore smells and sounds that are constant.
I've given evidence why the signal from the object that our theoretical IR-eye is watching is


less intense than internally produced light even before it hits the lense,
reduced by another 50% in intensity by the eye fluid for near infrared,
completely absorbed by the eye fluid for higher wavelength infrared,
and inquired why no such easy adaptations to the eye exist in nature if they are in fact possible.

I've never said that IR vision is impossible, I've stated why adapting the eye to IR vision is infeasable. If you're just going to discount the problems I find with your approach and suggest "baffling" systems to deal with them without any elaboration, that's your prerogative. In that case however, I don't think I have any further interest in spending my time to actually back up my statements.

[Murska]

I admit that there is much I do not know.

However, it seems to me that the problem does not feel like an unsolvable one.

My intuition, given what I know of infrared and of biology and of the genius of human intelligence, is that if we put this particular problem in front of the best engineers and the best scientists of the human species and gave them infinite resources to work on it, they'd be able to create an acceptable solution.

And if it's possible, that's all that was asked. It doesn't need to be feasible or useful.

[Jay R]

aspi has explained why physics proves that "adapting the eye to IR vision is infeasable." Nonetheless, cats obstinately continue to see into the infra-red spectrum, and make their way in the dark.


My intuition, given what I know of infrared and of biology and of the genius of human intelligence, is that if we put this particular problem in front of the best engineers and the best scientists of the human species and gave them infinite resources to work on it, they'd be able to create an acceptable solution.

As Randall Munroe said, "Any sufficiently advanced magic is indistinguishable from technology."

[factotum]

Nonetheless, cats obstinately continue to see into the infra-red spectrum, and make their way in the dark.


OK, we're into [citation needed] territory now--I have never heard anywhere that cats have IR vision. They have exceptionally good low-light vision, that much is true, but IR is not needed for that.

[hamishspence]

The Tapetum lucidum (http://en.wikipedia.org/wiki/Tapetum_lucidum) provides a boost to the night vision of many nocturnal animals - like cats. If they already have a high proportion of rod cells - they can have very good night vision. It doesn't provide IR-vision though.

[Bulldog Psion]

Well, I think the whole infravision thing was an attempt to give a pseudoscientific gloss to the concept "sees in the dark," basically -- and it was a lousy attempt.

[Frozen_Feet]

Nope. Whoever came up with the concept had pretty good then-current knowledge of passive and active infrared canning. It's one of those many seemingly out-of-place scifi concepts or sudden injections of realism that dot old versions of D&D. I say seemingly, because old D&D was as much inspired by scifi as it was by fantasy, and Gykax & co were affecionados of quite a lot of martial and scientific subjects. (This is also why so much detail was used on various polearms.)

[Lord Torath]

Is it? And is it impossible for the eye to see depth? The lens may add a transparent layer and pick up objects through it? Jay R is making a distinction, however small, between radiant heat and low frequency photons. I don't recall all too well, but doesn't heat only radiate when it can't conduct? Conduction, convection and radiation were admittedly in my "boring, don't care" segment of science class, more's the pity.Actually, it is impossible for an eye to see depth. You need the parallax from two offset eyes to be able to distinguish depth.

I've explained my position and failed to convince you.

You've explained your position and failed to convince me.

Shall we call it a draw and move on?What?!?!?! Don't be ridiculous. This is the INTERNET! :smalltongue:


Apparently you can detect bird migrations on weather radar, so that's both rain and small avians on non-military radar. Admittedly, they're both wide large masses, but the granularity is apparently possible with higher powered radar.

As I understand it, paratroopers are not on the board for long enough (HALO jumps) or radar/Mk1 eyeball detection is not a concern (HAHO jumps).
As far as radar (or should it be RADAR?) detecting small things like birds and insects, you're right, it needs to be high powered. Not because you need the extra radiation bouncing off the target (although that helps), but because you need the higher resolution provided by a shorter wavelength (which is naturally more powerful than a higher wavelength - and thus requires more power to generate). I believe battleships have millimeter-band RADAR for tracking shots from their "big guns" so they can more accurately line up the following shots (at least they did in Red Storm Rising by Tom Clancy).

AD&D did, indeed, have Ultravision. I don't think it was supposed to be seeing in the UV spectrum so much as it was just a different (non-heat sensitive) way of seeing in the dark that the Big Bads had (I recall specifically that Mezzodaemons had it) so they could be better than you. (Probably could see right through that Continual Darkness spell you had up that blocks infravision! Hey! Look! I made it back to the original topic! :smallbiggrin:)

[Murska]

Actually, it is impossible for an eye to see depth. You need the parallax from two offset eyes to be able to distinguish depth.

Interestingly, after a short test of closing one of my eyes and looking around, I can distinguish depth perfectly fine, especially with objects I already know the dimensions of.

[Max™]

Interestingly, after a short test of closing one of my eyes and looking around, I can distinguish depth perfectly fine, especially with objects I already know the dimensions of.

Your eye makes little micromovements all the time, saccade is the term for it btw, and your brain is a very complex bit of hardware for registering visual information. You can do a bit of depth estimation with one eye in part due to the saccade mechanism, as well as prior information, but the accuracy is not as good and it will probably give you a headache after a while until you get used to it.

It's easier to combine information from two inputs and use it to gauge depth.

A more accurate test there would be something like having an array of objects moving in front of you with something taking place in a certain order, and seeing how well you can answer questions about the placement and order of events with one eye covered versus using both eyes.

Similarly, with just one eye how are you going to distinguish between say, a basketball three feet away and a much larger basketball far enough away that it looks the same size as the first one? You would need to move side to side some to establish the same effect as you get from having two eyes.

[Murska]

Your eye makes little micromovements all the time, saccade is the term for it btw, and your brain is a very complex bit of hardware for registering visual information. You can do a bit of depth estimation with one eye in part due to the saccade mechanism, as well as prior information, but the accuracy is not as good and it will probably give you a headache after a while until you get used to it.

It's easier to combine information from two inputs and use it to gauge depth.

A more accurate test there would be something like having an array of objects moving in front of you with something taking place in a certain order, and seeing how well you can answer questions about the placement and order of events with one eye covered versus using both eyes.

Similarly, with just one eye how are you going to distinguish between say, a basketball three feet away and a much larger basketball far enough away that it looks the same size as the first one? You would need to move side to side some to establish the same effect as you get from having two eyes.

So, using two eyes is easier and better. But it's definitely not impossible for one eye to see depth.

[Max™]

Eh, I'd lean more towards you can "hack" your software to fake depth impressions with one eye, a big part of it is things like knowing your monitor fills x degrees of your visual field, the table behind it fills y degrees, and the actual dimensions of the two are similar, so if x >> y then the table is roughly ~z distance behind the monitor.

It isn't going to be very accurate, and it isn't going to be fast.

[Murska]

Same way we hack our software to fake depth impressions with two eyes. The picture drawn by our eyes is not actually three-dimensional, be it with two eyes or one.

[Excession]

You can also get depth information by sensing the focal depth of your eye(s). Depth perception is a combination of a lot of different and imperfect sources, filled in by your brain just making stuff up based on what you remember. Optical illusions often work by messing with these multiple sources plus expectation.

[Jay R]

OK, we're into [citation needed] territory now--I have never heard anywhere that cats have IR vision. They have exceptionally good low-light vision, that much is true, but IR is not needed for that.

You're right. I can't find it either. I withdraw the comment about cats seeing into lower registers than we can.

[Lord Torath]

You can also get depth information by sensing the focal depth of your eye(s). Depth perception is a combination of a lot of different and imperfect sources, filled in by your brain just making stuff up based on what you remember. Optical illusions often work by messing with these multiple sources plus expectation.You're right about the focal length. But that's only really useful at close range. Once you get out beyond 50 feet or so your focal length is no longer gives useful information. The tree 50 feet away is just as in focus as the moon 250,000 miles away.

For proof of the lack of depth perception from a single eye, watch OK Go's latest (http://www.youtube.com/watch?feature=player_embedded&v=m86ae_e_ptU). It's shot with a single camera, and there's no focal length adjustment. Makes it really hard to tell how close something is. Plus it's really cool! :smallwink: