Wikipedia:Reference desk/Archives/Science/2022 October 15

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October 15

Seeing colors and animals questions.

1. Most birds typically see colors from the range orange to UV. So, they cannot see red. This is why red flowers don't typically appear in certain latitudes as fewer species of birds pollinate red flowers, but what does red look look like to birds under light, same as what infrared looks like to humans in light. So my question is, if there was a bucket of paint of the color "infrared" what color does it look like to humans under light? As well as paint of "ultraviolet" color?

Now the following are all animal questions so I doubt anyone here knows aside from Google searching, but I'll throw them in here just in case.

2. What animals can see IR - blue/indigo, so would not be able to see violet? Although I did a Google search for "what animals can see IR" it doesn't say if they can also see violet. Though it appears goldfish are the only animals that can see from IR to UV range. Certain animals can partially see some of the IR range.

3. I did Google searches for "can rabbits see color?" "can alligators see color?" "can frogs see colors?" and a whole bunch of those animals, they are missing the red rod. They have blue and green rod, but are missing red. To me, that is not red-green colorblindness, but simply red-colorblindness, because they can see blue and green the same way we see blue and green, but what does red look to them, seems to be a matter of debate. For rabbits, the ability to see blue seems to evolve from being attacked by predators from the blue sky. And maybe green for the ability to eat plants, and not seeing red, for fear of blood? But I'm wondering what animals have red and blue, or red and green rods instead of blue and green. It appears turtles have all 3. 67.165.185.178 (talk) 13:40, 15 October 2022 (UTC).

For 1 - if a paint absorbed visible light and reflected infrared you would see it as black. However near infrared can be detected by eyes if it is bright enopugh. So for example an 850nm remote control led can appear red. Graeme Bartlett (talk) 21:35, 15 October 2022 (UTC)

A remote control looked dim pale violet to me (2 photons ganging up on 1 photoreceptor molecule dozens of times a second looking like 425nm light?). I don't know if this can cause permanent eye damage. Sagittarian Milky Way (talk) 22:22, 15 October 2022 (UTC)

The remote control is quite safe to look at. I also have some IR camera filters. If I look through the 720 nm filter at a sunlit scene it is dim red. Through a 760 nm filter it is very dark red. And for 850, 950 and 1000 nm to me it looks black. Don't look at the sun through these though! Graeme Bartlett (talk) 01:28, 16 October 2022 (UTC)

If the 720 or 760 is between the eye and sunlit green plants what does it look like? Sagittarian Milky Way (talk) 02:25, 16 October 2022 (UTC)

IR photo comes out quite similar to what a human eye sees. The leaves on the tree are bright.

Trying out the 720nm with the eye, most plants are very bright; English box, rose, clover, elm, and moss are all about as bright as cream paint or clouds. However cypress is dimmer, and grass is quite dark. The sky is very dark. Graeme Bartlett (talk) 03:23, 16 October 2022 (UTC)

If a material (like on a wall) is of IR or UV material or a paint of that color, does that mean it will reflect say, UV light when light is shine on it, causing you to get a sunburn? Since people don't seem to get sunburns from a wall of a UV-color, I wonder if there is something in physics that prevents it to exist past certain wavelengths? Like a microwave color? 67.165.185.178 (talk) 03:01, 16 October 2022 (UTC).

You are talking about a reflectance spectrum here We probably have articles on this. But it depends on the material. Metals tend to reflect electromagnetic radiation from radiowaves through to ultraviolet light. But coloured metals like copper or gold don't reflect the short wavelength. (eg Webb space telescope cannot see blue or ultraviolet reflected from gold). Small particles with high refractive index, like titanium white reflect a lot at their surface, but if the wavelength is big compared to the particles, the radiation will penetrate. Most materials have some absorption cutoff where shorter wavelength radiation than some amount cannot penetrate, because it move an electron across a band gap. Some ridiculous materials like solid helium can let ultraviolet though deep into the vacuum ultraviolet. But air will stop your vacuum ultraviolet. Molecules in solids, or covalently bonded substaces also have absorption caused by vibrating atom to atom bonds, either bending or stretching. These kinds of materials may let some radiation in and reflect some back after going through the substance, so it will have the infrared bands subtracted from what it reflects. So this would include most common non-metallic solid things you see like rock, paper, skin, dirt, paint binder. Graeme Bartlett (talk) 03:23, 16 October 2022 (UTC)

If a wall is painted in UV, it will reflect UV whenever UV falls on it. It won't cause sunburn, unless daylight already causes sunburn. PiusImpavidus (talk) 11:42, 16 October 2022 (UTC)

Unshaded snowy environments, like ski slopes, can cause both a higher risk of sunburn and snow blindness, which is basically "eye sunburn", because the white snow reflects sunlight, including UV. You need ski goggles with sun protection, and yes, sunscreen on exposed skin. --47.147.118.55 (talk) 04:45, 17 October 2022 (UTC)

For 3, you are talking about subjective experience. See Qualia for an article on this. To get the experience yourself, see if you can get a cyan coloured filter that blocks red light and look through it. After a couple of days of this you brain will get used to it and it won't look tinted, and the experience could be similar to that of red-blind animals. Graeme Bartlett (talk) 01:28, 16 October 2022 (UTC)

Just don't get cyan-eyed. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:56, 16 October 2022 (UTC)

Ba-dum tish! {The poster formerly known as 87.81.230.195} 90.195.172.49 (talk) 08:25, 16 October 2022 (UTC)

1: Bird colour vision is somewhat different from human colour vision. Insect colour vision is way more different, as it's shifted quite a bit towards the UV. For that reason, blue flowers are typically pollinated by insects and red flowers by birds (except red flowers with a yellow heart, like roses, as this gives a very strong contrast in insect eyes). Pollinating birds would have great difficulty surviving winters, so these red flowers are a bit rare in places like Europe. A nice example of a plant with red flowers to attract pollinating hummingbirds is the schlumbergera from Brazil.

If we were to paint something in infrared, reflective only on longer wavelengths than the human eye can see, it would appear black to us. The same for ultraviolet.

2: Our article on colour vision states that "It is a myth that the common goldfish is the only animal that can see both infrared and ultraviolet light; their color vision extends into the ultraviolet but not the infrared." It would be quite useless anyway. Water is pretty much opaque to IR, so the IR part of sunlight is absorbed very close to the surface, so there isn't any IR to see. In air, the IR cut-off of sunlight isn't very sharp. Brightness of solar IR rapidly decreases with increasing wavelength and thermal noise increases, so it rapidly gets less useful. On the UV side, the hard limit is about 310 nm. Below that, the ozone layer absorbs all, so there's nothing to see. Apparently humans with normal vision can see the 365.4 nm mercury line, although sensitivity is quite low there. So different species and different individuals of a single species have different ranges of vision with fuzzy boundaries, but the differences aren't huge. And what exactly do you define as IR and UV?

3: It seems you missed the difference between being able to see a wavelength and being able to distinguish it from other wavelengths. All mammals can see blue, green and red, but most cannot distinguish green from red. A mouse cannot distinguish a red fox from green grass, making the fox well camouflaged (even though the fox is very obvious to humans). If the mouse hadn't been able to see red, the fox would have appeared black and not camouflaged. This is because the red and green cones are both sensitive over the entire visible spectrum, but the exact sensitivity and sensitivity ratio varies. So the human eye detects the signal ratio between the red and green cones – or rather, the difference between the logarithms of the signals. Many animals have better colour vision than mammals, not because they have larger range, but because they can distinguish more colours with more types of cones. The price they pay for this is less sensitivity in the dark, less temporal resolution, less spacial resolution or bigger eyes. PiusImpavidus (talk) 11:42, 16 October 2022 (UTC)

1. I would say blue flowers are pollinated by insects and birds, whereas for red flowers, just birds. Bumblebees cannot see red for example, however it is possible they cannot see orange either. But good post. 67.165.185.178 (talk) 14:20, 16 October 2022 (UTC).

3. Also I meant most animals completely lack the red cones, so green still looks absolutely green to them. So if red looks black to them, then their ability to distinguish red from green is the same as red from blue. So I think what you're talking about includes cats, which might have all 3 in various ratios. 67.165.185.178 (talk) 14:26, 16 October 2022 (UTC).

Most placental mammals except some species adapted to dark environments are dichromats, with S ("short" wavelength, blue) and L ("long", red-green) cones, equivalent to human red-green deuteranopia colorblindness. Humans and some other primates are trichromats with an additional M ("medium") cone. Mammals are of course just one lineage of animals. --47.147.118.55 (talk) 04:45, 17 October 2022 (UTC)

By the way I am curious, where does brown and pink fall in the EM-spectrum? As well as, a color that is half-red and half-purple, such as maroon. 67.165.185.178 (talk) 01:15, 17 October 2022 (UTC).

Pink and brown are not spectral colors, so do not appear in the spectrum. See the linked article which specifically describes both of those colors as examples of extra-spectral colors: Any color obtained by mixing a gray-scale color and another color (either spectral or not), such as pink (a mixture of a reddish color and white), or brown (a mixture of orange and black or gray). CodeTalker (talk) 01:21, 17 October 2022 (UTC)

Do they not have a wavelength then? So the EM-spectrum is incomplete? 67.165.185.178 (talk) 09:52, 18 October 2022 (UTC).

Functionally close to 100% of the colors you see (even simple things like yellow and green) are likely a mixture of wavelengths. Strictly speaking, your eyes don't see individual wavelengths. Your cone cells are each alone activated by a wide range of wavelengths; these ranges overlap, and all you detect is the intensity that each cone cell is activated; that intensity is affected both by the brightness (the amplitude of the light wave) and by the wavelength itself (wavelengths closer to the "peak" of the response curve cause a greater response in the cell). What you detect as colors is a complex melange of all of these signals that your brain processes and gives you the sensation of "color". For example, any yellow on your computer monitor is not yellow. Even though there is a wavelength of light that your eye will detect as yellow, a mix of red and green wavelengths in the proper proportion will also be sensed by you as the same shade of yellow, even though there is no wavelength corresponding to yellow reaching your eye. Non spectral colors are just mixtures of wavelengths that don't correspond to colors you find in the rainbow. --Jayron32 10:58, 18 October 2022 (UTC)

Rattle snakes have eyes to see in the visible range and can see infra red using pits in their skin and this is a better way than using rods in the eyes as the pits can be much cooler than the inside of the eyes. Same way as you can tell with your eyes closed using your forehead that someone has put their hand or something cold in front of your face, though of course we don't have anything like the ability or resolution of a rattle snake. NadVolum (talk) 12:37, 17 October 2022 (UTC)