The protagonist in my world has its eyes and subsequently its brain altered (genetic alterations from conception) in such a way as to allow it to see into the UV and IR range via the addition of new cones with proteins sensitive to these wavelengths, The IR cones are sensitive to long wavelength IR and it's sensitivity trails off toward medium/short-IR. I don't know the exact wavelengths most suitable for animals and objects in a room. Or say navigating a dark hallway. But you should be able to distinguish enough detail to function normaly with this setup? If IR is your only intake. And anatomical changes to the eyes, mainly placing the photoreceptors on the opposite side they lie in modern humans, removing the species blind spots as the nerves aren't routed through a gap in the photoreceptors and reducing the fluid(I assume) light has to travel through.

Now assuming the brain has been changed to allow it to process these new colors without greatly reducing general intelligence by some means--perhaps limiting visibility of some wavelengths, which may indeed be a separate post, there remains a substantial problem with 'thermal' medium and long wavelength IR vision in a warm blooded biological organism, their own bodies would glow and particularly their own eyes which would make seeing a great difficulty.

Now I've supposed some of solutions of my own. But I find myself unable to properly justify them.

  1. The humanoids body operates slightly below room temperature. How could I justify such a cold human like this if possible and what would the consequences be? a-1. Could it be achieved without greatly slowing the metabolism?

  2. The eyes are cooled more than the rest of the body, below 20°C. While the rest of the body is still cooler. Not sure if this would be possible to specifically target and cool the eyes with biology. I figure this could allow for the body to be warmer if below room temperature is too cold to operate at 24/7.

3 The humanoid has glands similar to the pit viper for detecting the thermal IR wavelengths. Although it would sacrifice resolution. Perhaps located in its faces. I'm still uncertain if the output of these organs would be translated as visual perception on top of its eye output or some separate vision, or something else? There is also a limited amount of space for the organs to be placed, and consequently limited detection.

I've also considered that the 'thermal' range of IR 1,000 nm to 14,000 nm doesn't pass through water very well. And the eyes are filled with it. But I've had a hard time finding a suitable replacement to fill the eye.

I'm not sure if moving the photoreceptors as before mentioned alleviates this problem either.

I know its possible for some humans such as the Australian Aborigines to survive much colder temperatures more comfortably than the average man see: aborigines sleeping at lower temperatures Clearly the body can operate in an 0°C environment with their mutations, but their internal temps the study doesn't say. But this is when sleeping so it might be different than what I'm positing.

If I'm missing any other problems with IR vision disadvantages or something else. I'll update my post accordingly.

TL:DR a biologically plausible explanation for a human that has a colder body temperature than normal. Cold enough to see objects at room temperature in Infrared. The body has to be colder than 20°C perhaps by a few degrees. How much lower I'm not completely sure.

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    $\begingroup$ (1) "The humanoids body operates at a colder temperature than room temperature": that is obviously impossible unless provided with some sort of advanced cooling system, requiring the use of electric power (if using the Peltier effect) or else a refrigerant fluid circulating in closed vessels under pressure. (2) There is a wide gap between thermal infrared and the light-like near-infrared. Why do you want to go all the way to thermal infrared? Extending vision into near-infrared is perfectly possible; we already have devices which do it. $\endgroup$
    – AlexP
    Nov 20, 2020 at 17:07
  • $\begingroup$ "placing the photoreceptors on the opposite side they lie in modern humans"... in other words, your protagonist's vision is execrable. The reason the photoreceptors are behind the nerves is because the alternative is that they either aren't swimming in blood, which they need to "recharge" after being exposed to light, or rather than look through sort-of transparent nerves (with biological fiber-optics that make this far less of an issue than you think!), they have to look through much less transparent blood. Mammalian eyes are the way they are for a reason. $\endgroup$
    – Matthew
    Nov 20, 2020 at 17:12
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    $\begingroup$ It's doubtful that the brain even requires any modifications to be able to "process the new colors". No intelligence reduction is necessary. You could surgically implant these eyeballs into baseline humans, and I suspect strongly that they'd be just fine after they got used to it and stopped tripping out. $\endgroup$
    – John O
    Nov 20, 2020 at 17:26
  • $\begingroup$ @Matthew: Mammalian eyes are the way they are for the simple reason that this is how they were set up in the ancestors of the mammals. It's an accident. Using a "right side forward" retina would improve both sensitivity and acuity. (Fun historical factoid: The first sensors in digital cameras were fabricated in the manner of mammalian eyes, with the photosensitive elements behind the layer of metallic interconnects. Today almost all sensors are of the "back-illuminated" type, with the metallic interconnects behind the photosensitive elements.) $\endgroup$
    – AlexP
    Nov 20, 2020 at 17:30
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    $\begingroup$ @AlexP. Him I see your point, I want to go into thermal infrared because the human is intended to be able to communicate with an alien race that uses temperature changes to communicate. What sort of things do you think would be visible in the near infrared spectrum? Would heat from bodies or say a metal warming up but before the 'orange glow' stage be visible? $\endgroup$ Nov 20, 2020 at 18:03

2 Answers 2


There is a lot going on in your question. Also, as pointed out in the comments, the wavelength you choose matters a lot. If you look up the absorption spectrum of water, you will see that there is a blue green window where our eyes are optimized (visible spectrum ~ 400-750 nm), once you start going much beyond the red the absorption increases dramatically especially if the water has salts in it. The vitreous humor is actually transparent out to about 1400 nm, so one could easily imagine extending the spectrum using a "normal" by just modifying the retina (400-1400). Going into the near UV is a little harder, although babies see farther into the blue, and people who have had cataracts removed can also see a little further into the UV. If you replace the vitreous humor with designed transparent fluid, then getting to 5 ums might be possible fairly easily, but it gets harder as you go to longer wavelengths. With solid materials, you could design something out to 10-12 um, but now you are starting to become much more like a cyborg.

For the hallway part of the question, there are two parts.

  1. Normally we see light scattered off of objects. This can also be true in the near infrared (NIR) for night vision devices. Many of those devices come with a NIR illuminator like an infrared light emitting diode. In that case, the device is much like the eye and senses the photons scattered off of the hallway etc.

  2. In your case, you are implying that you want to see with the Far Infrared light that is from the black body radiation that would depend on the temperature of the objects in the hallway. If all the walls are the same temperature then they are all emitting the same wavelengths (at around 295 K, around 22 C, 72 F) those wavelengths are around 10 um. So the problem is there isn't any contrast. For example if a normal human puts his hand on the wall, then removed the hand, you can see a nice thermal handprint until the wall cools down again. So most thermal cameras will have some kind of specification that they can sense some fraction of a degree. Usually there will be some kind of temperature gradient, or if there is a door or window some temperature difference between the outside and inside environments. Note that your glass windows will be opaque at 10 um, so you wouldn't see through them, but could see heat leaking by the weatherstripping.

You are correct that that surrounding head would limit the ability to sense, that is one of the reasons that infrared detectors are cooled. Ones made out of semiconductor, are typically cooled to cryogenic temperatures, partly to minimize the glow from the surrounding packaging, but really because the narrow band gap semiconductors used are more conductive when warm than when cold, and to see a small change in conductivity (when the IR photon is absorbed and produces an electron) you are limited by the temperature of the semiconductor. However, you can also have room temperature micro-bolometer pixels that are commonly used for IR imaging these days. You can buy a handheld IR detector at the hardware store for example. They don't have the sensitivity of the high performance IR detectors, but they can still sense a fraction of a degree. They can function pretty much like a normal camera with a lens and a field of view. The number of pixels is still relatively small for reasonable prices.

So with physiological modifications, you can probably come up with some kind of optical system where you could have some kind of thermal imaging and not have to your beings be cold, as long as they are sensing the temperature differences.

  • $\begingroup$ If the thermal imaging doesn't require cold beings it would at least reauirs cold eyeballs. The lens and vitreous fluid would need modification, to see into the 10μm range, but the photoreceptors themselves would emit heat and trigger themselves. A cooling system I think might be necessary. In the microbolometer the cam itself isn't giving off that much heat. $\endgroup$ Nov 24, 2020 at 5:37
  • $\begingroup$ Do you have any ideas where to start designing a cooling system? I've done a lot of research the past few days. And seen a lot of different cooling systems. But none that would help cool an eye. Coolant would have to flow through the eye or the blood would have to be cold. $\endgroup$ Nov 24, 2020 at 5:41
  • $\begingroup$ From a purely technical perspective to get large benefits from the cooling, the cooling needs to be fairly substantial. Part of the reason bolometers work is that each micro-platform is thermally isolated from the surroundings and you really you are sensing the change in temperature of the microplatform in comparison to the surrounding due to the amount of energy that is depositied onto that pixel. $\endgroup$
    – UVphoton
    Nov 24, 2020 at 14:19
  • $\begingroup$ To have an organic cooling system, theoretically you could come up with some sort of electrically conductive molecules, one set p-type and the other n-type like semiconductors and grow something that would be like a peltier cooler., the cold side would be towards your sensor elements in the eye, and the hot side would towards a network of blood vessels that could remove the heat on the hot side. There are all sort of real world technical problems of how efficient this would be and details on how to not thermally short across the device. $\endgroup$
    – UVphoton
    Nov 24, 2020 at 14:36

Non science answer coming, as I have zero knowledge in this area. Instead I will wave my wand and say 'a wizard did it!' by offering the following: maybe the humanoid can do something consciously to activate the extra eye ball features? Like say, if he holds his breath, and his blood pressure begins to rise beyond a certain point, it activates a cooling system around the eyeballs and (insert wizard's wand wave here) presto! he can see in UV or IR. Dunno. Like I said, very hand wave-ee. Side note - very impressive answers already given. Man we have some seriously smart people on this site.


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