I am creating an alien species with infrared vision, and am wondering if there are any hypothetical ways for infrared screens and/or touch screens to exist in their society, since infrared is put off by things with heat from what I could gather.
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$\begingroup$ Keep your displays cooled evenly? $\endgroup$– JoachimCommented Aug 6 at 21:41
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3$\begingroup$ Have you researched the various animals and insects that can see inside the infrared region to see how they're using that spectrum? Why creatures depend on infrared vision leads to how a display is developed and used. $\endgroup$– JBHCommented Aug 7 at 4:37
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$\begingroup$ The Predator has holographic displays IIRC; might want to look there for inspiration. As an alternative to touch screens, consider a bath of invisible radiation (read: non IR) emitted by the screen and stopped by whatever the local finger is. $\endgroup$– François JurainCommented Aug 9 at 13:00
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4 Answers
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Thermal infrared and near-infrared are different things. It is quite easy to take photographs in near-infrared, and some old school film camera lenses even had the ability to focus "beyond" infinity exactly for this purpose. All the sensors in ordinary digital cameras come with a built-in infrared filter specifically to avoid having near-infrared light affect the image. An animal can conceivably see near-infrared. On the other hand, having eyes able to see thermal infrared would be like placing your camera inside a floodlight lamp and wondering why all the pictures come out uniform white.
A body, any body, which is not at absolute zero temperature will emit electromagnetic radiation. The colder the body is, the longer the wavelengths are; the hotter the body is, the shorter the wavelengths are.
As you heat up a piece of metal, it will start glowing a dark red at about 450 °C to 500 °C, veering into orange at about 1000 °C, yellow around 1200 °C, and finally white at about 1300 °C. The filaments of old-fashioned incandescent light bulbs had a temperature of around 2,500 ºC (4,600 ºF).
The point is that just before the piece of metal starts glowing a dull dark red, it still emits a lot of light; but it is near-infrared light. (Even when glowing in the visible spectrum it continues to put out a lot of infrared.) Near-infrared behaves very much like visible light: it can be focused by lenses and can form an image on a suitable photosensor. (Photo film needed special treatment to make it sensitive to infrared light; digital photo sensors have the opposite problem: they are super-sensitive to infrared, and need cut-off filters to reject infrared.)
Yes, warm-ish things such as people and the walls of rooms emit infrared radiation, but this is thermal infrared (sometimes called long-wave infrared), with a wavelength of 8 to 15 μm. This is the infrared used by thermal imaging cameras. On the other hand, to produce near-infrared light with a wavelength of about 0.75 to 1.4 μm would correspond to much higher temperatures, starting at about 300 °C or 600 °F.
(Of course, you don't need to be that hot to emit near infrared light. There are other light emission mechanisms. For example, the monitor of my laptop is set to a color temperature of about 6500 K, but it is obviously nowhere near that temperature.)
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$\begingroup$ There are animals that can see in thermal infrared. The best-known are probably the pit vipers, which have an organ that's basically a pinhole camera for heat. $\endgroup$– MarkCommented Aug 8 at 2:18
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1$\begingroup$ @Mark: Pit vipers cannot see in thermal infrared, they can sense thermal infrared. The pit organs do not form an image. Humans can sense thermal infrared too via the thermoreceptors in our skin. The difference is that we can only sense really strong sources of infrared radiation, for example a stove. The pit organs of these vipers can sense feeble sources of infrared radiation, such as a mouse, and they can indicate the direction of the source. The snakes being cold-blooded helps. $\endgroup$– AlexPCommented Aug 8 at 4:16
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The technology would go through phases of sophistication:
A wet rag is colder than the room it's in.
First there would be a heatsink on the back of the screen with a wad or pad of cloth or fiber on it. This would need wetting (water and electricity, I know), then a little fan to cool by evaporation, the same way ceramic wine-coolers work without ice. Perhaps more suitable to cool desk-based devices. Incandescent heating elements would be used in an array like rows of miniature tungsten light-bulbs.
For a more handy and portable type, the development of thermo-electric cooling (Peltier effect) would need to be explored. The device battery would allow the screen temperature to be down-regulated a few tens of degrees at the touch of a button and the excess heat shunted into a heatsink (radiating heat and therefore acting as an infra-red torch!) or just dissipated by a fan without radiation. LEDs would come into their own here.
answered Aug 6 at 21:05
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It would actually depend on the ambient temperature of their environment and the actual band of infrared their eyes operate on.
What we call infrared spans a much wider part of the electromagnetic spectrum than our visible light. It's quite possible that your alien eyes would be tuned for a narrow strip of that wide band, just as our eyes are tuned to another narrow band where our sun has near-peak output and our atmosphere has very good transparency.
Then there's the fact as AlexP stated that every object emits EM radiation that corresponds to their temperature. It just happens that the temperatures that we humans live in happen to emit that in what we call the far-infrared (FIR) range. That's what we use for thermal imaging cameras.
The near-infrared we use for cheap security cameras is much like visible light, except that we as humans are unable to see it. Some animals like cats can.
The one thing you must decide on about your aliens is if the range of infrared they see is overlapping with the emission band of the environment they live in: If their visual band is higher frequency/shorter wavelength than the emissive band of their environment, then they do not interfere, and it is practically the same as what we already have, except that their screens always look black to us.
If there is overlap (ie. they see temperatures around them), then there are still ways of making screens. A high-tech way of doing that would be wave-guiding the natural thermal emissions of the screen into constructive/destructive interference with each other, so that you get controlled light/dark spots. (Very similar to what we do today with photolithography in semiconductor manufacturing.)
A lower-tech version would be cooling the screen to below their visual range so that it turns dark, and then using any available elements (incandasent filaments, LED's etc.) to selectively light up pixels.
For touch, I don't see any problems. The techniques we use today (resistive and capacitive) would apply. Only that the materials would have to be transparent in the range they see, therefore possibly different than ours.
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$\begingroup$ I don't see "wave-guiding thermal emissions into constructive/destructive interference" working. Controlled interference requires coherent light, i.e. a laser. Incoherent thermal emissions would just add up the classical way, without interference. But lighting pixels up as incandescent filaments, electrical resistors, or infrared leds should work fine. Even without cooling the screen, in that case it wouldn't turn fully dark, but the aliens could still see the displayed images. $\endgroup$– JanKanisCommented Aug 7 at 14:12
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$\begingroup$ @JanKanis: Interference only requires spatial coherence, it does not require time coherence. Lasers are not needed. In other words, antireflective coatings work just fine with ordinary sunlight and artificial light. $\endgroup$– AlexPCommented Aug 7 at 19:57
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$\begingroup$ @JanKanis, we wouldn't be able to see color without our wave-guiding cone cells in our retina. $\endgroup$ Commented Aug 10 at 12:41
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Touch
The touch part of the technology shouldn't present an immediate problem because in broad terms our technology to detect touch uses capacitance, resistive and/or pressure sensors wired in a grid to detect touch point positions rather than making use of light in the process. Aliens with slimy tentacles could be a problem though.
Camera
The technology used to capture IR images is also not particularly obscure to readers who are used to infrared imaging of everything from nocturnal animal behavior to nighttime warfare. Obviously the aliens are likely to have developed more nuanced IR technology than we have since their total sense of sight is restricted to the IR spectrum.
Display
A potential solution for the IR display used by alien devices would be for the aliens to have developed the equivalent of our current OLED displays - which have three separate LEDs to display color images suitable for viewing by the human eye, with the capability of the eyes perceiving the images in color.
Whether the aliens have color vision at all would need to decided on as it would be the result of the physiology of their eyes if the did.
Possibly you may have to have the aliens see in a particular part of the IR spectrum, say in what we call the "near infrared", for the OLED technology to make sense according to current human science.
Details
How much justification of the scientific plausibility of the aliens' sense of IR you wish to impart to readers, or what paths alien history took to develop their first TVs is entirely up to you as the author. Personally I would try to make readers comfortable that there are no physiological issues with aliens seeing in the infrared for them to worry about. It's common knowledge after all that if aliens go out in the noon day sun, they have to wear sunglasses that are completely opaque and look black to human eyes.
