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In my world I have introduced two super powers, and both can be accidentally acquired by an otherwise normal human: one is to see infrared and the other is to see ultraviolet. I am aiming to have that observation describe the Earth of 2019 exactly scientifically correctly.

For infrared I am thinking mostly near IR through thermal IR. For ultraviolet I am thinking mostly UVA, UVB, and UVC.

What sights would stand out to someone who has suddenly developed the ability to perceive in infrared and/or ultraviolet?

1. What light sources would stand out as having more or less UV and IR radiation than others, or a dramatic mismatch between one of those and the visible spectrum?

e.g. sunlight vs. moonlight, fire, lightning, stars, planets. What other than fire and bodies emit IR? What about UV? That sort of thing.

2. What objects would reflect or block or let through UV and IR radiation noticeably more or less?

How do he shadows of leaves, look in IR or UV? Do mirrors reflect different parts of the spectrum differently? Do trees? Are some things opaque to UV or IR that are transparent to visible light or vice versa? Etc.

[edit note: I changed this from the hard-science tag to science-based after editing it earlier.]

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closed as too broad by StephenG, 011358 smell, Frostfyre, L.Dutch Feb 28 at 13:35

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ I think it would be better to chop down your question in smaller pieces. I might have some answers, but not a complete answer to your current version. $\endgroup$ – L.Dutch Feb 28 at 8:21
  • $\begingroup$ Thanks for the tip, I'll do exactly that. $\endgroup$ – Nathan Hinchey Feb 28 at 8:25
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    $\begingroup$ After your edit the question remains too broad. We cannot go for a complete list of all materials and tell you how they interact with UV and IR light. There are entire books for it. $\endgroup$ – L.Dutch Feb 28 at 8:59
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    $\begingroup$ Photography using mixed visible, IR and UV components has been in use for decades. There is nothing here that simply looking these things up will not tell you. Your questions are, I think, far too broad. Spectral transmission characteristics of materials is actually an entire specialty that simply cannot be summarized in a simple answer. And "how they would appear" depends on exactly how then brain receives and processes the data - far too broad a thing. $\endgroup$ – StephenG Feb 28 at 9:38
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    $\begingroup$ Just to give you an example of the consequences of a "too broad" question like this: you have got an answer only about flowers. But you asked about all object. So that good answer fails in covering your question. $\endgroup$ – L.Dutch Feb 28 at 11:45
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The world will look mostly the same, but there will be some small differences. For example, while you will technically now be able to see UV/IR light from the sun, it will not be noticeable because the sun emits such a broad spectrum of light that any particular additions won't matter.

  • The color of the sky will be slightly more UV-looking due to Raleigh scattering in the atmosphere.
  • All screens will be somewhat "off". Right now, color screens are calibrated to look most like the real world to a human eye. However, if we change what the human eye can see, then current screens will not be able to represent it accurately. If you take a picture of something UV/IR-colored, the camera could pick it up depending on the lens filters, but will register as a combination of red, green, and blue light, therefore looking different when viewed on a screen.
  • Security cameras, remotes, and phones will all flash lights at you. Security cameras have big IR flashlights on them, remotes communicate with IR light, and your iPhone X will flash an IR light in your face every time you unlock it.
  • Foliage will look different. "Green" plants reflect sunlight in green and infrared wavelengths, so lots of plants will change color. Two plants that were the same color might not be anymore.
  • Some things will look slightly more tinted, some things will look slightly more visible. Remember, you are not losing the ability to see anything, so a window that blocks UV light (aka all windows) will let the same amount of light as before, but the outside is slightly brighter due to the UV light, so it would appear slightly tinted. On the other hand, some plastics let UV light through but not normal light, so these would appear translucent and UV-colored where they were previously opaque.
  • Mirrors will appear the same as before. Lenses/glasses might give you some chromatic aberration in the UV/IR spectrums that would have gone unnoticed before, but I doubt this will be noticeable.
  • Unfortunately, stars, planets, and the rest of space will look the same. All the cool astrophotography you see is done with sensitive equipment over long periods of time, picking up way more light than a human could see. At best, it's a tiny bit brighter because of the extra photons you can pick up, but the extra brightness of your environment would cancel it out.

EDIT: My answer was actually based on the assumption of near-IR, which behaves pretty much like visible light, and not true infrared where you could “see” heat. With that in mind, I’d have to change a lot of my answers. Yes, you would be able to see people in the dark as they radiate heat. As for everything else, hot stuff would glow kind of like extremely hot metal, except at normal temperatures. Also, there are some metallic surfaces that act as mirrors to infrared/heat, so you’d possibly be able to use them to see things you ordinarily couldn’t. Unfortunately, almost any transparent object blocks heat, so you wouldn’t have any effects looking through glasses or windows.

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  • $\begingroup$ Additionnal question cause the premise interests me as well: would you be able to see better at night? Since hot bodies radiate ... UV/IR? you would probably have a better perception of your surrounding? $\endgroup$ – Nyakouai Feb 28 at 10:23
  • $\begingroup$ Good question! Will update my answer as I misunderstood your meaning of IR a bit. $\endgroup$ – Leo Adberg Feb 28 at 10:30
  • $\begingroup$ I'm not the Original Poster ^^ I'm just curious since I have a character in an other setting that see near IR and UV. You answer was really informative (and pleasant to read) so I figured I might ask you that little "plus", as you seems knowledgeable on the subject. $\endgroup$ – Nyakouai Feb 28 at 10:37
  • $\begingroup$ Oops sorry I was on my phone and just assumed you were OP >_<. Glad I could help! $\endgroup$ – Leo Adberg Feb 28 at 10:38
  • $\begingroup$ Also, a lot of flowers will now look vividly patterned where before they were block colour. Flowers use UV-reflective patterns to guide pollinating insects to them. $\endgroup$ – Ynneadwraith Feb 28 at 13:51
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The question as asked cannot receive a definitive answer, because how luminous a light source appears depends on the response curve ("luminosity function") of the receiver. Normal human eyes do not produce a visual sensation for infrared and ultraviolet, so what the response curve should be depends on the decision by the author.

Photopic and scotopic luminosity functions of the human eye

Graph of photopic luminosity function of the human eye (black) including CIE 1931 (solid), Judd-Vos modified (dashed), and Sharpe, Stockman, Jagla & Jägle 2005 (dotted); and scotopic luminosity function, CIE 1951 (green). Image by Dicklyon and Innesw, available on Wikimedia under the Creative Commons CC0 1.0 Universal Public Domain Dedication license.

Note: This is why we have special photometric units of measurement such as candela, lumen and lux and we don't measure light in radiometric units. For example, one candela is 1/683 watt per steradian at 555 nm, but at 690 nm (deep red, near infrared), one candela requires almost one watt per steradian.

Nevertheless, some general impressions can be provided based on the vast number of infrared (and, since digital photography, ultraviolet) photographs available since the beginning of photography. (It is actually hard to make a photographic sensor with the exact same response curve as the human eye...)

Backyard garden near Moscow

Backyard garden near Moscow. Infrared photograph by sovraskin, available on Flickr under the CC BY 2.0 license.

Look at the (pretty typical) infrared photograph of a backyard near Moscow. Note the major dissimilarities with a photograph in the visible spectrum:

  • Grass and foliage appears very light; this is because leaves reflect as much infrared light as plant physiology can achieve -- infrared light carries heat, and plants don't have a good way of cooling, so they try to avoid absorbing infrared.

  • The cloud in the sky have a dramatic contrast. Clouds reflect infrared light, so they appear light, whereas clear sky is mostly devoid of infrared, so it appears dark.

Bobcat at Night

Bobcat at night. Infrared photograph captured by a remote camera trap operated by the [American] National Park Service. Photograph in public domain, available on Flickr.

  • When taking infrared photographs at night, mammals and birds appear light (sometimes even as light sources), because they are warmer than the environment.

Flowers appear dramatically different in ultraviolet; bees and other pollinating insects see ultraviolet light, and flowers are optimized to be attracted to insects and not so much to humans. There is an excellent blog, Vis-UV-IR Flower Photos by Dave Kennard, with many photographs of flowers taken once in visible light, once in ultraviolet and once in infrared, with descriptions of the differences. You may also want to read "Ultraviolet Patterns in Flowers,or Flowers as Viewed by Insects.

Mimulus flower in visible light (left) and ultraviolet light (right)

Images of a Mimulus flower in visible light (left) and ultraviolet light (right) showing a dark nectar guide that is visible to bees but not to humans. Photograph by Plantsurfer, available on Wikimedia under the CC BY-SA 2.0 UK: England & Wales license.

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One thing I know about is flowers. Bees can perceive UV. The flower has the regular colors we see, but much more: The UV light shows many stripes on numerous species of flowers. Those stripes guide the bee to the source of pollen and nectar. The location is the optimal one for cross-pollination, limiting self-pollination as much as possible.

There are some Youtube videos as well.

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I do a lot of work with thermal imaging, and scenes through IR can be completely different to how they appear in the visible range.

All objects with temperature emit thermal radiation according to the Planck function. The IR range is generally broken up in to 3 wavelengths (as far as people using thermal imagers are concerned)-

  • Long wavelength IR (~8-13 microns)
  • Medium wavelength IR (3-5 microns)
  • Short wavelegnth IR (~1 micron)

You also have near and far infrared either side. You'll notice that there are gaps between medium and long, for example- this is because the transmission of IR through air varies substantially. How the person experiences the world through IR would massively depend on the wavelength range they are sensitive to.

Infrared transmission spectrum

If you use a thermal imager in a room without any particularly hot objects in it, the entire room will seem uniform- you're pretty much unable to see the outlines of objects when they are the same temperature as the room so you can be 'blind' in many cases.

Some interesting things that you can pick up in IR that you wouldn't be able to pick up otherwise is things like handprints on objects (just placing your hand on a table for a second or so causes enough of a temperture change that it is clearly visible for the next few seconds in IR). Looking at hot objects (~700 degrees for example) would likely be very painful for the person, and depending on the sensitivity of their eyes to IR could potentially blind them. Picking out certain objects would be very easy for the person, like a person in foliage.

In addition, just because a material is transparent in visible, doesn't mean it would be in IR- glass and water, for example, strongly absorb many of the useful IR bands. This means that wearing glasses (unless they are made of something like germanium or quartz) would invalidate their ability to see IR. The sky at night would appear to be pretty much completely uniform, like rooms. During the day even looking at the sun could potentially blind the person (though then again, that's the same for everyone). Potentially, they could see people who are unwell with IR (many illnesses present with fevers, increasing skin temperature).

One property materials that is of particular importance when you're talking about infrared is emissivity- essentially it's how well a material emits (or reflects) thermal radiation. An object with an emissivity of 1 emits the maximum amount of radiation possible according to the Planck function given its temperature, and reflects none- conversely, an object with an emissivity of 0 that is non-transparent will emit no thermal radiation, and will be a perfect mirror. (Side note- emissivity also depends on wavelength, temperature and direction). Polished metal and graphite, when at the same temperature, would be visibly different due to the amount of radiation it emits.

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One way we currently view infrared radiation is through the use Forward-looking infrared (FLIR) cameras.

Which use detection of infrared radiation, typically emitted from a heat source (thermal radiation), to create an image assembled for video output.

You should be able to find many images and videos that illustrate how different things in our world look in terms of their IR-radiation

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