Rainbow

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Photograph by Gabrielle Hovinen.

Gabrielle_Rainbow_600.jpg

Rainbow, showing a primary and a secondary rainbow, plus a bevy of Hovinens. The primary rainbow is overexposed, but the photograph clearly shows how the sky is brighter inside the primary rainbow and outside the secondary rainbow. See Figure 6 here.

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I recently tried to sort out an issue of what are the actual colors in the rainbow and discovered that the issue came down to my not knowing the names of the colors.

To sort this out in my own mind, I programmed an HP Prime graphing calculator to plot the visible spectrum from the response curves of the RGB cones of the human eye.

Wavelengths of the peak response of the Red, Green, and Blue cones are, respectively, 645 nm, 532 nm, and 437 nm. The curve for the Red cones actually has another smaller peak at about 323 nm. It is likely that that the other cones would also respond to shorter (more energetic) wavelength photons also, but other factors limit the response of the eye at both shorter and longer wavelengths.

The colors of the of the liquid crystal display of the HP Prime don’t corrospond exactly to those peak wavelength responses of the human eye, so there are some slight differences in the color mixing that occur with the display. These are noticible but not different enough to obscure the major result; which is that Red, Orange, Yellow, Green, Blue, Indigo, Violet are actually Red, Orange, Yellow, Green, Cyan, Blue, Magenta.

I don’t know if this is an issue with male, as opposed to female, human vision, but I suspect that what I and many other males call Blue in the rainbow spectrum is really Cyan, Indigo is really Blue, and Violet is really Magenta. It is not a matter of what males(?) see but more a matter of what they call it.

My understanding is that females make finder distinctions in color, hue, and intensity and are often more consiously aware of a much more extensive palate of colors and their names.

Magenta is formed by combining Blue with Red; and the human eye can’t perceive Magenta (Violet) unless there is some Red cone response that has an additional peak at shorter wavelengths where the Blue cones peak.

By playing around with the response curves in my program - I used double-peaked Gaussian curves and adjusted the heights and widths - I was able to get a pretty good replica of the rainbow spectrum. I discovered in the process that I could learn not only to recognize more subtle differences in color, hue, and intensity, I could also look at a color and estimate how much of each of RGB it contained.

Even as my eyes get older and have more problems, I now am able to see colors with much finer distinction.

I could have learned these lessons much earlier. Is this a male thing to not be aware of fine distinctions in colors?

I once saw a complete triple in NE Colorado off I-25. The colors on the inner and outer ones were arranged normally and the colors on the middle one were reversed. I thought it was pretty cool until a friend of mine said he saw one with seven in Thailand after a typhoon.

Once I was describing to someone taking a photograph of a rainbow. She was surprised and said that she didn’t know that you could take photos of them. Apparently she thought that they were hallucinations, or something.

Here is an interesting question about the bending of light by a gravitional well, such as a black hole.

Does white light passing by a black hole get spread out into a spectrum? Why or why not?

(Note: If Jason Lisle’s “theory of relativity” tells us anything, it would be that Lisle hasn’t learned much about the physics of light and matter.)

Mike Elzinga said:

Here is an interesting question about the bending of light by a gravitional well, such as a black hole.

Does white light passing by a black hole get spread out into a spectrum? Why or why not?

(Note: If Jason Lisle’s “theory of relativity” tells us anything, it would be that Lisle hasn’t learned much about the physics of light and matter.)

IANA physicist, or scientist of any kind, but I would be very surprised (and interested!) if it did get separated into a spectrum. Here’s my reasoning: Yes, blue light is more energetic than red, so maybe it would ‘resist’ the pull of gravity more and be less attracted to the black hole… but all wavelengths travel at the speed of light and none should be diverted or ‘sucked into’ the black hole more than any other. The beam would appear bent to someone at a distance, as the light follows a ‘straight line’ through the warped space-time near the hole, but wouldn’t all wavelengths have have to follow that ‘straight line’? Wrong, maybe, but if so, why?

Just Bob said:

Mike Elzinga said:

Here is an interesting question about the bending of light by a gravitional well, such as a black hole.

Does white light passing by a black hole get spread out into a spectrum? Why or why not?

(Note: If Jason Lisle’s “theory of relativity” tells us anything, it would be that Lisle hasn’t learned much about the physics of light and matter.)

IANA physicist, or scientist of any kind, but I would be very surprised (and interested!) if it did get separated into a spectrum. Here’s my reasoning: Yes, blue light is more energetic than red, so maybe it would ‘resist’ the pull of gravity more and be less attracted to the black hole… but all wavelengths travel at the speed of light and none should be diverted or ‘sucked into’ the black hole more than any other. The beam would appear bent to someone at a distance, as the light follows a ‘straight line’ through the warped space-time near the hole, but wouldn’t all wavelengths have have to follow that ‘straight line’? Wrong, maybe, but if so, why?

Light is spread out into a spectrum when it passes through a prism because the refractive index of the material (water or glass, usually) is different from that of what light was traveling through immediately before (usually air, in familiar examples), causing the light to take an angular path. The wavelength of the light also has an impact on the exact angle, so each wavelength goes through at a slightly different angle.

My take would be - likely wrong - that light getting bent by gravity is still traveling through a vacuum, so there’s no change in refractive index and no reason for a spectral spread. But Jason Lisle isn’t here to explain it to me.

The brain’s perception of different colors is due to our particular photoreceptors, of course. The frequencies and wavelengths of photons are a continuous distribution, I would assume approximately uniform (i.e. one wavelength as common as another). However, we have photoreceptors that are excited only by photons that fall within a certain relatively narrow wavelength subset.

Some of us have hereditary color vision problems. Personally, I have no problem with yarn tests for color vision, but cannot see the patterns in the charts used by, for example, the US Air Force or the Oregon DMV when I first took a driver’s license test. Would this deficiency be caused by a shift in the frequencies we are most sensitive to? Or would it be that some of the color vision cones are for some reason less sensitive than normal?

According to Patricia Fara, writing here, Newton

bequeathed to the future a rainbow of seven colors not because he counted more accurately than his predecessors but because he believed that cosmic dimensions should follow the rules of musical harmony based on octaves.

See also ROYGBIV.

I also have a vague recollection – maybe someone else knows – that what Newton called blue we call blue-green, and what Newton called indigo we call blue. I, at least, do not see any color between blue and violet.

I think also that at first glance you see or think you see colors for which you have names, and in fact if you spread the spectrum out wide enough and studied it, you would distinguish more than 7 colors.

Birds have a fourth cone with peak sensitivity out in the UV. It would be interesting to be able to see what they see; but on second thought, maybe a bird brain would be a bit too limiting to be able to do any scientific comprehension of what is taking place in our sensory systems.

When one considers all the kinds of sensory input that evolution has produced, one has to wonder what appears within the neural networks of animals that gives them some kind of “comprehension” of the world around them.

I have often wondered if the size of a neural network is as important as how it is interconnected. Perhaps “wisdom” and “comprehension” are just as likely in a smaller network that has a more efficient topology. The only reason we miss it when looking at other animals is because we don’t comprehend what their behavior is conveying to other members of their species. My cats sometimes seem to be conveying a message that I am stupid and just don’t get it. But then, maybe I am just being paranoid or hypersensitive.

Photons are photons, color sensation is a product of the human brain.

I know what the set of wavelengths I can detect visually and have been trained to call “red” since early childhood “look like” to me. They probably “look like” that to you, too, but there is no way to be sure. We can be sure that most people can agree that that wavelength set is visibly differentiable from others and can agree to call it “red” and that’s good enough.

https://en.wikipedia.org/wiki/Color_vision

Mike Elzinga said -

Birds have a fourth cone with peak sensitivity out in the UV. It would be interesting to be able to see what they see

A photon is a photon, it’s all about the detector and the nervous system that interprets the input.

It would be reasonable to say that light did not exist until some sort of photoreceptor with some sort of attached nervous system existed to detect it. The photons were always there but they weren’t any more “light” than any other photons until that happened.

What we call “light” is an entirely arbitrary subset of the electromagnetic spectrum, except that it is the subset we can detect with our vision. We can, of course, detect infrared radiation with heat receptors.

Visual systems on Earth do seem to cluster in the same range as human, though. There is quite a bit of variability but mainly only extension to photons with energy levels that are close to what we call “light”, like UV. There is an obvious reason for this; it’s where most of the photons that reach the Earth from the Sun fall in terms of energy level. (Therefore something I said above should be fine-tuned - here on Earth the distribution of energy levels of photons we encounter is more like a normal curve than a uniform distribution overall, with what we perceive as “light” being the most frequent energy levels. This could be quite different elsewhere in the universe.)

Just Bob and harold have zeroed in on a key feature of constant velocity of all wavelengths of light in a vacuum. The path that minimizes the time of travel is a geodesic in the given space time. If the velocity of light remains constant across some specified “boundary” in space, the path is a straight line; or, in the case of a gravitational field, the geodesic - which will be seen as a straight line for an observer traveling along that geodesic.

When minimizing the time of travel for light passing from Point A in a medium (or a vacuum) with speed of propagaion v1 to Point B in another medium with a different speed of propagation v2, the geodesic is two straight lines that break at the boundary of the two media according to Snell’s Law. (This is a relatively easy exercise in first semester calculus on how to minimize a function.)

The key diffence is the interaction of light with matter in which the accelerations of bound charges with mass determine the velocity of light in the medium. In general, the restoring forces for bound charges within condensed matter are nonlinear with frequency, and this means that different wavelengths of light travel at different speeds within the medium. The result is that the break angles of those two straight-line geodesics are different for different wavelengths and thus the different wavelengths leave the boundary at different angles.

But the minimizing of an action integral applies to all these cases; and if it were not for the fact that these integrals minimize (or “extremize”) in the way that they do, the universe would not be stable enough to exist in a form that produces condensing matter and the subsequent evolution of all the complexity we see.

When people like Jason Lisle try to mess with the laws of physics in order to make them fit with sectarian dogma, they produce a capricious and arbitrary universe that makes no more sense than their sectarian beliefs. Using that kind of “science,” they can make up anything they want on the spur of the moment to justify their prior committments to their beliefs, but then they are no longer referring to any real universe.

In Jason Lisle’s universe, light travels away from every point in space at infinite speed and toward every point at c/2 - or more exactly, according to Lisle, with speed = c/(1 - cos(Θ)) There can be no rainbows in Lisle’s universe.

Mike Elzinga said:

Magenta is formed by combining Blue with Red; and the human eye can’t perceive Magenta (Violet) unless there is some Red cone response that has an additional peak at shorter wavelengths where the Blue cones peak.

Very interesting. It would not occur to me to associate magenta with violet. But then my neurology is a bit weird in spots.

Violet is not the same as magenta. In additive colorimetry, you get magenta by combining red and blue. You can see a nice illustration here. That just does not look like violet to me. I am looking at the violet line in the mercury spectrum right now, and it looks a little bit like this and not at all like the magenta color in the first link. This more or less exhausts my knowledge of additive colorimetry.

Does anyone know why the colors are inverted in the secondary rainbow? The primary rainbow is ROYGBIV from inside (concave) to outside (convex), but the second one is VIBGYOR.

Sorry. I inverted the order of the spectra relative to the two rainbows, but they are still inverted.

As every fool knows, Vibgyor was the (Soviet) Russian scientist who invented light.

Thanks for the clarification. I though he was Roy’s dyslexic brother.

Matt Young said:

Violet is not the same as magenta. In additive colorimetry, you get magenta by combining red and blue. You can see a nice illustration here. That just does not look like violet to me. I am looking at the violet line in the mercury spectrum right now, and it looks a little bit like this and not at all like the magenta color in the first link. This more or less exhausts my knowledge of additive colorimetry.

Yeah, I think I understand that; but as I mentioned, I have not been very good at naming colors.

My color repertoir has been been quite limited; even to the point that my sister and my daughter - who both seem to me to have some kind of super ability to distinguish colors - have teased me about not knowing the names of colors.

I have taken a number of color tests, and they don’t reveal any abnormalities. My daughter thinks I have just been sloppy in naming distinctions. For a long time I called magenta pink, sometimes violet, and at other times lilac. I called cyan light blue and thought indigo was dark blue.

So, other than the primary colors, and black, brown, and pink, most of the rest of my repertoir consisted of those colors modified by light or dark.

Shebardigan said:

Mike Elzinga said:

Magenta is formed by combining Blue with Red; and the human eye can’t perceive Magenta (Violet) unless there is some Red cone response that has an additional peak at shorter wavelengths where the Blue cones peak.

Very interesting. It would not occur to me to associate magenta with violet. But then my neurology is a bit weird in spots.

I suppose what I would call violet is really a dark magenta. I have tried to mix blue and red at various intensities for each and at equal intensities but at varying levels. My daughter has names for many of those colors. but I have no clue what to call them.

Joe Felsenstein said:

Once I was describing to someone taking a photograph of a rainbow. She was surprised and said that she didn’t know that you could take photos of them. Apparently she thought that they were hallucinations, or something.

In a curious way she was actually at least half right!

As Harold has noted, what we call colour is a consequence of our brains processing data received by frequency sensitive photon detectors. What we call a photograph is a poor analogue of the real world produced by photon detectors engineered to match the characteristics of the human eye. A projected photographic image of a rainbow would be indistiguishable from the real thing when equiped only with a Mark 1 Eyeball, but totally different if viewed with a spectrometer.

And of course there is really no monochromatic colour Magenta. The traditional colour wheel works because of the way out colour vision works. In reality it is not a wheel but a spectrum strip just like a rainbow. A monochromatic source with a wavelength between that of red and green will trigger two detectors and appear yellow. A monochromatic source with a wavelength between that of green and blue will trigger two detectors and appear cyan. But there is no single wavelength of light that will produce a reponse from both our red and blue detectors. Magenta is a colour invented by our brains if both red and blue light is present in the absence of green.

Mike Elzinga said:

Matt Young said:

Violet is not the same as magenta. In additive colorimetry, you get magenta by combining red and blue. You can see a nice illustration here. That just does not look like violet to me. I am looking at the violet line in the mercury spectrum right now, and it looks a little bit like this and not at all like the magenta color in the first link. This more or less exhausts my knowledge of additive colorimetry.

Yeah, I think I understand that; but as I mentioned, I have not been very good at naming colors.

My color repertoir has been been quite limited; even to the point that my sister and my daughter - who both seem to me to have some kind of super ability to distinguish colors - have teased me about not knowing the names of colors.

I have taken a number of color tests, and they don’t reveal any abnormalities. My daughter thinks I have just been sloppy in naming distinctions. For a long time I called magenta pink, sometimes violet, and at other times lilac. I called cyan light blue and thought indigo was dark blue.

So, other than the primary colors, and black, brown, and pink, most of the rest of my repertoir consisted of those colors modified by light or dark.

Mike, the names are completely arbitrary. I almost never use words like “magenta” or “cyan”. Those words came into common use because of computer monitors and printer toner, although may have been commonly used in the art world before that, I don’t know. https://en.wikipedia.org/wiki/Magenta https://en.wikipedia.org/wiki/Cyan I used to have a lot of interest in art as a kid, read books about painting, and I rarely encountered those words before I started buying printer toner. We can differentiate far more wavelength combinations than we can name.

A wavelength is a wavelength. Objects reflect or emit unique combinations of wavelengths. Names and emotional qualities of colors are created by brains.

The test for normalcy of vision is ability to make distinction between colors. A person is only “color blind” if there is some circumstance in which they have relevant inability to distinguish between colors in some type of circumstance.

Some very basic color names are culturally relevant. Cyan is essentially a variant of “blue”. If you can recognize it but insist on calling it “orange” you’re wrong. If you call it “blue” some young kid who grew up on computers is likely to say “no, it’s cyan”. If a better formula for printer toner based on some other pigment combination is developed and the industry starts using a different name for a mainly bluish tone, the word “cyan” will sink back into obscurity. It will still be more related to “blue” than to “red” in cultures that have those basic color names for certain wavelength sets.

If you and your daughter agree on what things are the same color and can make the same color distinctions, to a fairly high degree, and one of you has normal vision, the other also does.

Painting, cloth dying, and printing make use of pigments. Pigments are chemicals that interact with photons to create interesting visual sensations for humans. You can create pure wavelengths that maximally stimulate photoreceptors with lasers, but you can’t do it with pigments.

A vast amount of our color vocabulary comes from naming pigments.

In my line of work “eosinophilic” and “basophilic” describe color ranges that everyone can reproducibly recognize. If I wanted to be an ass I could probably use those words to describe every day concepts.

Dave Lovell said:

Joe Felsenstein said:

Once I was describing to someone taking a photograph of a rainbow. She was surprised and said that she didn’t know that you could take photos of them. Apparently she thought that they were hallucinations, or something.

In a curious way she was actually at least half right!

As Harold has noted, what we call colour is a consequence of our brains processing data received by frequency sensitive photon detectors. What we call a photograph is a poor analogue of the real world produced by photon detectors engineered to match the characteristics of the human eye. A projected photographic image of a rainbow would be indistiguishable from the real thing when equiped only with a Mark 1 Eyeball, but totally different if viewed with a spectrometer.

And of course there is really no monochromatic colour Magenta. The traditional colour wheel works because of the way out colour vision works. In reality it is not a wheel but a spectrum strip just like a rainbow. A monochromatic source with a wavelength between that of red and green will trigger two detectors and appear yellow. A monochromatic source with a wavelength between that of green and blue will trigger two detectors and appear cyan. But there is no single wavelength of light that will produce a reponse from both our red and blue detectors. Magenta is a colour invented by our brains if both red and blue light is present in the absence of green.

Actually, violet wavelengths can and do produce a response from both our red and blue cones. That’s because violet is getting to twice the frequency of red, so while violet is still firing off the blue cones at a good rate, the red cones are coming within range of being fired off significantly again at the first harmonic. Thus you can get the combination of red and blue from one wavelength, or, more likely, from a narrow set of wavelengths.

Glen Davidson

https://me.yahoo.com/a/JxVN0eQFqtmg[…]X_Zhn8#57cad said:

Dave Lovell said:

Joe Felsenstein said:

Once I was describing to someone taking a photograph of a rainbow. She was surprised and said that she didn’t know that you could take photos of them. Apparently she thought that they were hallucinations, or something.

In a curious way she was actually at least half right!

As Harold has noted, what we call colour is a consequence of our brains processing data received by frequency sensitive photon detectors. What we call a photograph is a poor analogue of the real world produced by photon detectors engineered to match the characteristics of the human eye. A projected photographic image of a rainbow would be indistiguishable from the real thing when equiped only with a Mark 1 Eyeball, but totally different if viewed with a spectrometer.

And of course there is really no monochromatic colour Magenta. The traditional colour wheel works because of the way out colour vision works. In reality it is not a wheel but a spectrum strip just like a rainbow. A monochromatic source with a wavelength between that of red and green will trigger two detectors and appear yellow. A monochromatic source with a wavelength between that of green and blue will trigger two detectors and appear cyan. But there is no single wavelength of light that will produce a reponse from both our red and blue detectors. Magenta is a colour invented by our brains if both red and blue light is present in the absence of green.

Actually, violet wavelengths can and do produce a response from both our red and blue cones. That’s because violet is getting to twice the frequency of red, so while violet is still firing off the blue cones at a good rate, the red cones are coming within range of being fired off significantly again at the first harmonic. Thus you can get the combination of red and blue from one wavelength, or, more likely, from a narrow set of wavelengths.

Glen Davidson

And, of course, the cones and rods themselves are not specific for “one wavelength”. Rather, they have peak sensitivity to a very narrow range, with sensitivity dropping off rapidly for photons outside that range.

https://en.wikipedia.org/wiki/Photoreceptor_cell#/media/File:1416_Color_Sensitivity.jpg

All the detectors have some overlap, but red and blue the least by far.

The sensation of color, and the human experience of vision, is 100% a product of the way the brain interprets signals from the photodetectors. https://en.wikipedia.org/wiki/Cortical_blindness

There is the difference between violet and purple. Some people say that they are synonyms. Some say that they are clearly different.

https://me.yahoo.com/a/JxVN0eQFqtmg[…]X_Zhn8#57cad said:

Dave Lovell said:

Joe Felsenstein said:

Once I was describing to someone taking a photograph of a rainbow. She was surprised and said that she didn’t know that you could take photos of them. Apparently she thought that they were hallucinations, or something.

In a curious way she was actually at least half right!

As Harold has noted, what we call colour is a consequence of our brains processing data received by frequency sensitive photon detectors. What we call a photograph is a poor analogue of the real world produced by photon detectors engineered to match the characteristics of the human eye. A projected photographic image of a rainbow would be indistiguishable from the real thing when equiped only with a Mark 1 Eyeball, but totally different if viewed with a spectrometer.

And of course there is really no monochromatic colour Magenta. The traditional colour wheel works because of the way out colour vision works. In reality it is not a wheel but a spectrum strip just like a rainbow. A monochromatic source with a wavelength between that of red and green will trigger two detectors and appear yellow. A monochromatic source with a wavelength between that of green and blue will trigger two detectors and appear cyan. But there is no single wavelength of light that will produce a reponse from both our red and blue detectors. Magenta is a colour invented by our brains if both red and blue light is present in the absence of green.

Actually, violet wavelengths can and do produce a response from both our red and blue cones. That’s because violet is getting to twice the frequency of red, so while violet is still firing off the blue cones at a good rate, the red cones are coming within range of being fired off significantly again at the first harmonic. Thus you can get the combination of red and blue from one wavelength, or, more likely, from a narrow set of wavelengths.

Glen Davidson

Are you sure about that? I don’t claim much expertise on biological photoreceptors, but have a lot of experience on image sensors and colour TV. I’ve never come across anything that suggests there is a need to compensate for harmonic breakthrough in the detectors, and that would be necessary to make a TV camera/TV screen combination reproduce colours as originally perceived by the cameraman. I know colour fidelity is not a strong point in analogue colour TV, but the effect would also have to be compensated for in film photography.

Harold, whilst the terms cyan/magenta(/yellow) may have entered common parlance through printer toner, they have long had quite precise meaning in engineering, and have been in use in the context of colour TV since the mid-sixties to my personal knowledge. Well before computer CRT monitors were a cost effective interface to a computer in monochrome, let alone in colour (Remember that “futuristic” array of flashing lights from the computer in “Voyage To The Bottom Of The Sea?). I would also bet on the terms being used in photography and high quality printing well before that.

Dave Lovell said:

https://me.yahoo.com/a/JxVN0eQFqtmg[…]X_Zhn8#57cad said:

Dave Lovell said:

Joe Felsenstein said:

Once I was describing to someone taking a photograph of a rainbow. She was surprised and said that she didn’t know that you could take photos of them. Apparently she thought that they were hallucinations, or something.

In a curious way she was actually at least half right!

As Harold has noted, what we call colour is a consequence of our brains processing data received by frequency sensitive photon detectors. What we call a photograph is a poor analogue of the real world produced by photon detectors engineered to match the characteristics of the human eye. A projected photographic image of a rainbow would be indistiguishable from the real thing when equiped only with a Mark 1 Eyeball, but totally different if viewed with a spectrometer.

And of course there is really no monochromatic colour Magenta. The traditional colour wheel works because of the way out colour vision works. In reality it is not a wheel but a spectrum strip just like a rainbow. A monochromatic source with a wavelength between that of red and green will trigger two detectors and appear yellow. A monochromatic source with a wavelength between that of green and blue will trigger two detectors and appear cyan. But there is no single wavelength of light that will produce a reponse from both our red and blue detectors. Magenta is a colour invented by our brains if both red and blue light is present in the absence of green.

Actually, violet wavelengths can and do produce a response from both our red and blue cones. That’s because violet is getting to twice the frequency of red, so while violet is still firing off the blue cones at a good rate, the red cones are coming within range of being fired off significantly again at the first harmonic. Thus you can get the combination of red and blue from one wavelength, or, more likely, from a narrow set of wavelengths.

Glen Davidson

Are you sure about that? I don’t claim much expertise on biological photoreceptors, but have a lot of experience on image sensors and colour TV. I’ve never come across anything that suggests there is a need to compensate for harmonic breakthrough in the detectors, and that would be necessary to make a TV camera/TV screen combination reproduce colours as originally perceived by the cameraman. I know colour fidelity is not a strong point in analogue colour TV, but the effect would also have to be compensated for in film photography.

Harold, whilst the terms cyan/magenta(/yellow) may have entered common parlance through printer toner, they have long had quite precise meaning in engineering, and have been in use in the context of colour TV since the mid-sixties to my personal knowledge. Well before computer CRT monitors were a cost effective interface to a computer in monochrome, let alone in colour (Remember that “futuristic” array of flashing lights from the computer in “Voyage To The Bottom Of The Sea?). I would also bet on the terms being used in photography and high quality printing well before that.

Well I don’t know, I haven’t done the science or anything like that, but it’s how “violet” is typically explained. It’s no true harmonic, I should note–violet still isn’t double the frequency of red–but that red cone sensitivity rises somewhat toward the violet is claimed to be a fact, and that it could be a harmonic effect seems likely. To be sure, increasing red sensitivity in the violet region might not be due to harmonic effects but to some chemical quirk or what-not.

Wikipedia’s cone-response diagram, apparently based on a good source (paper in Journal of Physiology)

Red sensitivity isn’t way up, according to that, but it’s rising again, while green is fairly flat, in the violet region. Notably, though, blue sensitivity is declining substantially into the violet, so with green fairly flat there, red rising slightly, and blue sensitivity declining, that combination would seem a good explanation for violet light appearing “purplish.”

I would add that violet and purple as normally understood are not the same, since violet is usually considered to be a more bluish purple than flat-out purple. Of course violet isn’t different from bluish purple, but the cone sensitivity–with blue being a good deal higher, though declining–would seem to explain why “violet” is generally considered to be more bluish than your average purple.

I haven’t a clue how photographic film was configured to reproduce violet.

Glen Davidson

Harold, whilst the terms cyan/magenta(/yellow) may have entered common parlance through printer toner, they have long had quite precise meaning in engineering, and have been in use in the context of colour TV since the mid-sixties to my personal knowledge. Well before computer CRT monitors were a cost effective interface to a computer in monochrome, let alone in colour (Remember that “futuristic” array of flashing lights from the computer in “Voyage To The Bottom Of The Sea?). I would also bet on the terms being used in photography and high quality printing well before that.

That does not surprise me; it is consistent with my points above. The difference is that before the widespread use of computer printers, color printing was a highly specialized industry.

I would add that violet and purple as normally understood are not the same, since violet is usually considered to be a more bluish purple than flat-out purple.

As far as I can tell the color is named after the flowers, which of course also come in many other different colors. The etymology of the name of the flowers is eluding my efforts. I’m also not sure why musical instruments have this name. The word “purple” comes from some version of “Phoenician” because the ancient Phoenicians made and marketed a dye based on a pigment from seashells.

It is extremely common for colors to be named after an object that is that color; in fact that may be where all color names come from. Our word red probably comes from a proto-Indo-European word meaning both “blood” and “red”. Spanish has no word for “brown” but I’ve been told that “color of a bear” is sometimes used express the concept. Which is interesting because the English word bear (the animal) comes from an ancient root that probably also means brown. At some point it’s impossible to know whether bear meant “brown one” or brown meant “like a bear in color”. Modern languages also often use terms like “coffee” where we would say “brown”.

https://en.wikipedia.org/wiki/Color_term

What modern engineers may try to do, of course, is to promote redefinition and refinement of color names, trying to corral a color name so that it “correctly” refers to a specific wavelength or other defined physical characteristic. A daunting task.

It may be very difficult to get any two people to put the same name on the color of each of a large number of colored objects.

What we can test is whether people recognize two things as having the same color, whatever word they may use for it. They do, if they have normal color vision.

harold said:

Harold, whilst the terms cyan/magenta(/yellow) may have entered common parlance through printer toner, they have long had quite precise meaning in engineering, and have been in use in the context of colour TV since the mid-sixties to my personal knowledge. Well before computer CRT monitors were a cost effective interface to a computer in monochrome, let alone in colour (Remember that “futuristic” array of flashing lights from the computer in “Voyage To The Bottom Of The Sea?). I would also bet on the terms being used in photography and high quality printing well before that.

That does not surprise me; it is consistent with my points above. The difference is that before the widespread use of computer printers, color printing was a highly specialized industry.

I would add that violet and purple as normally understood are not the same, since violet is usually considered to be a more bluish purple than flat-out purple.

As far as I can tell the color is named after the flowers, which of course also come in many other different colors. The etymology of the name of the flowers is eluding my efforts. I’m also not sure why musical instruments have this name. The word “purple” comes from some version of “Phoenician” because the ancient Phoenicians made and marketed a dye based on a pigment from seashells.

It is extremely common for colors to be named after an object that is that color; in fact that may be where all color names come from. Our word red probably comes from a proto-Indo-European word meaning both “blood” and “red”. Spanish has no word for “brown” but I’ve been told that “color of a bear” is sometimes used express the concept. Which is interesting because the English word bear (the animal) comes from an ancient root that probably also means brown. At some point it’s impossible to know whether bear meant “brown one” or brown meant “like a bear in color”. Modern languages also often use terms like “coffee” where we would say “brown”.

https://en.wikipedia.org/wiki/Color_term

What modern engineers may try to do, of course, is to promote redefinition and refinement of color names, trying to corral a color name so that it “correctly” refers to a specific wavelength or other defined physical characteristic. A daunting task.

It may be very difficult to get any two people to put the same name on the color of each of a large number of colored objects.

What we can test is whether people recognize two things as having the same color, whatever word they may use for it. They do, if they have normal color vision.

For example, pathologists may be native speakers of English, Japanese, Turkish, or Hungarian, but we all recognize the same things as “eosinophilic”.

harold said:

A wavelength is a wavelength. Objects reflect or emit unique combinations of wavelengths. Names and emotional qualities of colors are created by brains.

And that is exactly how I and my colleagues talked about the electromagnetic spectrum in our research. Using wavelength or frequency designations is the objective way to talk about any such spectrum because these numbers enter into the mathematical theory of light and its interaction with matter.

Much of my work in the areas of CCD imaging and with Schottky barrier infrared detecting CCD imaging devices was expressed in terms of quantum efficiencies as a function of wavelength; and both my laboratory and theoretical work were to derive and measure these characteristics from ab initio calculations. I have never thought in terms of color names in my research; and this may be the reason I made no significant effort to learn the names of colors other than those in the visible spectrum and a few others such a brown.

My daughter thinks I am a nerd; and she is exactly right, of course.

An acquaintance of mine, Joann Dennett, wrote a detective novel (possibly See How They Scurry) whose solution – spoiler alert! – depended on the contention that in Chinese green and blue had the same name and were therefore the same color.

I do not believe that there is nearly enough intensity for ordinary violet light to cause second harmonic generation in the receptors. As a commenter noted above, the red cones show measurable sensitivity in the violet region of the spectrum. I have, however, heard claims that some people can see radiation from an ultraviolet laser, but I do not know whether those claims are justified, and I worry for their corneas. People can certainly see sufficiently intense infrared radiation, but that is just the result of the tail of the responsivity curve.

The colors in the secondary rainbow are reversed because there are 2 reflections. See the diagrams here.

harold said:

It is extremely common for colors to be named after an object that is that color; in fact that may be where all color names come from. Our word red probably comes from a proto-Indo-European word meaning both “blood” and “red”. Spanish has no word for “brown” but I’ve been told that “color of a bear” is sometimes used express the concept. Which is interesting because the English word bear (the animal) comes from an ancient root that probably also means brown. At some point it’s impossible to know whether bear meant “brown one” or brown meant “like a bear in color”. Modern languages also often use terms like “coffee” where we would say “brown”.

https://en.wikipedia.org/wiki/Color_term

What modern engineers may try to do, of course, is to promote redefinition and refinement of color names, trying to corral a color name so that it “correctly” refers to a specific wavelength or other defined physical characteristic. A daunting task.

It may be very difficult to get any two people to put the same name on the color of each of a large number of colored objects.

What we can test is whether people recognize two things as having the same color, whatever word they may use for it. They do, if they have normal color vision.

Thanks for that link, harold. Now if my daughter tries to tease me about color names, I’ll refer her to this link.

I’m beginning to suspect my daughter’s teasing may be just pulling my leg.

Mike Elzinga said:

harold said:

It is extremely common for colors to be named after an object that is that color; in fact that may be where all color names come from. Our word red probably comes from a proto-Indo-European word meaning both “blood” and “red”. Spanish has no word for “brown” but I’ve been told that “color of a bear” is sometimes used express the concept. Which is interesting because the English word bear (the animal) comes from an ancient root that probably also means brown. At some point it’s impossible to know whether bear meant “brown one” or brown meant “like a bear in color”. Modern languages also often use terms like “coffee” where we would say “brown”.

https://en.wikipedia.org/wiki/Color_term

What modern engineers may try to do, of course, is to promote redefinition and refinement of color names, trying to corral a color name so that it “correctly” refers to a specific wavelength or other defined physical characteristic. A daunting task.

It may be very difficult to get any two people to put the same name on the color of each of a large number of colored objects.

What we can test is whether people recognize two things as having the same color, whatever word they may use for it. They do, if they have normal color vision.

Thanks for that link, harold. Now if my daughter tries to tease me about color names, I’ll refer her to this link.

I’m beginning to suspect my daughter’s teasing may be just pulling my leg.

My pleasure, but the thanks go, as so often, to Wikipedia.

Mike Elzinga said:

harold said:

It is extremely common for colors to be named after an object that is that color; in fact that may be where all color names come from. Our word red probably comes from a proto-Indo-European word meaning both “blood” and “red”. Spanish has no word for “brown” but I’ve been told that “color of a bear” is sometimes used express the concept. Which is interesting because the English word bear (the animal) comes from an ancient root that probably also means brown. At some point it’s impossible to know whether bear meant “brown one” or brown meant “like a bear in color”. Modern languages also often use terms like “coffee” where we would say “brown”.

https://en.wikipedia.org/wiki/Color_term

What modern engineers may try to do, of course, is to promote redefinition and refinement of color names, trying to corral a color name so that it “correctly” refers to a specific wavelength or other defined physical characteristic. A daunting task.

It may be very difficult to get any two people to put the same name on the color of each of a large number of colored objects.

What we can test is whether people recognize two things as having the same color, whatever word they may use for it. They do, if they have normal color vision.

Thanks for that link, harold. Now if my daughter tries to tease me about color names, I’ll refer her to this link.

I’m beginning to suspect my daughter’s teasing may be just pulling my leg.

My pleasure, but the thanks go, as so often, to Wikipedia.

If this comment is duplicated, it’s due to PT issues.

Yep.

https://me.yahoo.com/a/JxVN0eQFqtmg[…]X_Zhn8#57cad said:

Well I don’t know, I haven’t done the science or anything like that, but it’s how “violet” is typically explained. It’s no true harmonic, I should note–violet still isn’t double the frequency of red–but that red cone sensitivity rises somewhat toward the violet is claimed to be a fact, and that it could be a harmonic effect seems likely. To be sure, increasing red sensitivity in the violet region might not be due to harmonic effects but to some chemical quirk or what-not.

Wikipedia’s cone-response diagram, apparently based on a good source (paper in Journal of Physiology)

Red sensitivity isn’t way up, according to that, but it’s rising again, while green is fairly flat, in the violet region. Notably, though, blue sensitivity is declining substantially into the violet, so with green fairly flat there, red rising slightly, and blue sensitivity declining, that combination would seem a good explanation for violet light appearing “purplish.”

Glen Davidson

That cone response diagram surprised me so I investigated further. In isolation the diagram is actually quite misleading; the true situation is more complex. Read the article at:

http://www.handprint.com/HP/WCL/color1.html

and particularly this diagram:

http://www.handprint.com/HP/WCL/IMG/conesens3.gif

From that article I see no evidence of harmonic effects. Green and blue cones seem to be like red cones with colour filters in front of them, which thinking about it is an obvious way for colour vision to evolve. What it means from an image processing point of view is that an equal output from all cones is perceived as blue, moving to green and red as the output from the other cones increases with decreasing frequency. It also suggests that colour perception at the blue end will be much more affected by secondary effects as “colour” become equivalent to the differnce between three near identical numbers. The frequency of transition from blue to green in particular must be very sensitive to scattering in the eyeball and leakage through different colour irises, or slight variation in the relative sensitivity of the different cones.

It also suggests that very bright white light will appear blue because the red and green cones will be saturated before the blue ones. Maybe part of the reason why WWII night bomber crews regularly reported being initially illuminated by a blue “master” searchlight before other white ones coned them?

Dave Lovell said:

Read the article at:

http://www.handprint.com/HP/WCL/color1.html

and particularly this diagram:

http://www.handprint.com/HP/WCL/IMG/conesens3.gif

Excellent!

I once asked an astronomer if there were any green stars. This helps explain why we would see so few.

Mike Elzinga said:

Just Bob and harold have zeroed in on a key feature of constant velocity of all wavelengths of light in a vacuum. The path that minimizes the time of travel is a geodesic in the given space time. If the velocity of light remains constant across some specified “boundary” in space, the path is a straight line; or, in the case of a gravitational field, the geodesic - which will be seen as a straight line for an observer traveling along that geodesic.

When minimizing the time of travel for light passing from Point A in a medium (or a vacuum) with speed of propagaion v1 to Point B in another medium with a different speed of propagation v2, the geodesic is two straight lines that break at the boundary of the two media according to Snell’s Law. (This is a relatively easy exercise in first semester calculus on how to minimize a function.)

The key diffence is the interaction of light with matter in which the accelerations of bound charges with mass determine the velocity of light in the medium. In general, the restoring forces for bound charges within condensed matter are nonlinear with frequency, and this means that different wavelengths of light travel at different speeds within the medium. The result is that the break angles of those two straight-line geodesics are different for different wavelengths and thus the different wavelengths leave the boundary at different angles.

But the minimizing of an action integral applies to all these cases; and if it were not for the fact that these integrals minimize (or “extremize”) in the way that they do, the universe would not be stable enough to exist in a form that produces condensing matter and the subsequent evolution of all the complexity we see.

When people like Jason Lisle try to mess with the laws of physics in order to make them fit with sectarian dogma, they produce a capricious and arbitrary universe that makes no more sense than their sectarian beliefs. Using that kind of “science,” they can make up anything they want on the spur of the moment to justify their prior committments to their beliefs, but then they are no longer referring to any real universe.

In Jason Lisle’s universe, light travels away from every point in space at infinite speed and toward every point at c/2 - or more exactly, according to Lisle, with speed = c/(1 - cos(Θ)) There can be no rainbows in Lisle’s universe.

Gravitational lensing will not produce a rainbow or other prismatic effects. As far as the light is concerned, it is “traveling” in a straight line through a vacuum. I use quotes because time does not exist for light and it essentially exists simultaneously along its entire apparent path.

All that’s needed now is some waterfalls and some unicorns, and some sunshine.

Marilyn said:

All that’s needed now is some waterfalls and some unicorns, and some sunshine.

Umm, it’s sunshine that’s making that rainbow, and those deep shadows.

Just Bob said:

Umm, it’s sunshine that’s making that rainbow, and those deep shadows.

You’re right. I meant in a new scenario.

Marilyn said:

Just Bob said:

Umm, it’s sunshine that’s making that rainbow, and those deep shadows.

You’re right. I meant in a new scenario.

Oh, well, then don’t forget the pan flute music by Zamfir.

Just Bob said:

Marilyn said:

Just Bob said:

Umm, it’s sunshine that’s making that rainbow, and those deep shadows.

You’re right. I meant in a new scenario.

Oh, well, then don’t forget the pan flute music by Zamfir.

And bluebirds. Got to have bluebirds.

Yardbird said:

Just Bob said:

Marilyn said:

Just Bob said:

Umm, it’s sunshine that’s making that rainbow, and those deep shadows.

You’re right. I meant in a new scenario.

Oh, well, then don’t forget the pan flute music by Zamfir.

And bluebirds. Got to have bluebirds.

If they are friends of Dorothy, there will be hissy fits all Obergefell The Rainbow!

Yardbird said:

Just Bob said:

Marilyn said:

Just Bob said:

Umm, it’s sunshine that’s making that rainbow, and those deep shadows.

You’re right. I meant in a new scenario.

Oh, well, then don’t forget the pan flute music by Zamfir.

And bluebirds. Got to have bluebirds.

Fresh out of bluebirds, can I interest you in some indigo buntings?

There should also be some turtles and fish, and Zinnia’s.

Glitter here and there, like in the mane and tail of the unicorn.

Just Bob said:

Glitter here and there, like in the mane and tail of the unicorn.

As the sun catches the hair it will glisten all colours.

Marilyn said:

Just Bob said:

Glitter here and there, like in the mane and tail of the unicorn.

As the sun catches the hair it will glisten all colours.

All the colors that cheer us up, and those that make us forlorn.

I know little to nothing of color theory, however I do know if nudge two of my window ledge prisms so that their spectra begin to overlap, I get ROYGBIM(magenta)OYGBIV. The resultant magenta band being quite intense.

In other words, you are overlapping the blue portion of one spectrum with the red portion of the other? See the reference I cited above. As they show in Figure 6, in additive colorimetry, red + blue = magenta. Presumably, red + violet =~ magenta as well.

Matt Young said:

An acquaintance of mine, Joann Dennett, wrote a detective novel (possibly See How They Scurry) whose solution – spoiler alert! – depended on the contention that in Chinese green and blue had the same name and were therefore the same color.

I do not believe that there is nearly enough intensity for ordinary violet light to cause second harmonic generation in the receptors. As a commenter noted above, the red cones show measurable sensitivity in the violet region of the spectrum. I have, however, heard claims that some people can see radiation from an ultraviolet laser, but I do not know whether those claims are justified, and I worry for their corneas. People can certainly see sufficiently intense infrared radiation, but that is just the result of the tail of the responsivity curve.

The colors in the secondary rainbow are reversed because there are 2 reflections. See the diagrams here.

Excellent! Presumably the tertiary rainbow makes 3 reflections in the water droplet, thus being even fainter and with the colors reversed yet again.

Interesting. But light being what it is, every droplet is reflecting both a primary, secondary, and tertiary rainbow. It’s just that we only see one or the other from a different point in the sky, because that’s the one pointed at us at that time. Of course, just as the perceived rainbow moves with you, and as everyone perceives their own personal rainbow, slightly different from the one that each other person perceives.

When there is a double rainbow, where is the pot of gold found? Or maybe it’s a pot of gold at the end of the main rainbow, and a pot of silver at the end of the secondary rainbow? Or is it a pot of silver at the end of a moon-rainbow?

Not a pot of gold. It’s a crock ;-)

A crock of Au?

About this Entry

This page contains a single entry by Matt Young published on January 18, 2016 12:00 PM.

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