So according to my logic, it should lie between red and blue in the spectrum. But it doesn’t, its wavelength is less than wavelength of blue. How is this possible?
Why is wavelength of violet colour less than wavelength of blue colour?
The wavelength of light of specific colour increases as we go from left to right in the visible colour spectrum: “VIBGYOR”. Wavelength of green lies between wavelengths of blue and yellow. To me, this makes logical sense because when blue and yellow are mixed, it gives green. (By “mixed”, i mean the simultaneous presence of two colours at the same place give rise to a new colour). Wavelength of orange lies between wavelengths of red and yellow. To me, this also makes logical sense because when red and yellow are mixed, it gives orange. Now, when it comes to violet, its wavelength is the least in the visible spectrum. It is made by the mixture of red and blue. So according to my logic, it should lie between red and blue in the spectrum. But it doesn’t, its wavelength is less than wavelength of blue. How is this possible?
Cite
Follow
deezbugs
asked Jun 2, 2020 at 12:56
deezbugs deezbugs
357 2 2 silver badges 7 7 bronze badges
$endgroup$
$begingroup$ I think this could answer your question: physics.stackexchange.com/a/21777/247642 Also, you have it backwards: it is not the color that determines the wavelength, but the wavelength determines the color. In other words: wavelength is independent physical reality, whereas color is subjective human perception. $endgroup$
Jun 2, 2020 at 13:07
5 Answers 5
Sorted by: Reset to default
$begingroup$
Color is a double valued concept, different in physics and in perception.
In Physics there is a one to one correspondence between color seen in the visible spectrum and the frequency of light.
The whole electromagnetic spectrum covers many frequencies above and below the visible, which are the colors seen in rainbows.
The second value/definition of color comes from biology the way it is perceived by the brain as mixtures of frequencies.
So according to my logic, it should lie between red and blue in the spectrum. But it doesn’t, its wavelength is less than wavelength of blue.
How is this possible?
Because the mixture of frequencies to be perceived as a given color by the brain is seen in the chart. The brain sees the single frequency colors as shown in the first figure, but when frequencies are added new colors and hews are seen.
As the chart is not a simple function it happens that violet does no follow the simplified rule you expect. There is an article in Wikipedia on color vision.
Cite
Follow
answered Jun 2, 2020 at 13:26
anna v anna v
232k 20 20 gold badges 238 238 silver badges 637 637 bronze badges
$endgroup$
$begingroup$ Really nice answer. $endgroup$
Jun 7, 2020 at 16:10
$begingroup$ What are the axes on the second figure? $endgroup$
Sep 28, 2021 at 22:58
$begingroup$ @Rasputin the references are nested , I stopped here hyperphysics.phy-astr.gsu.edu/hbase/vision/ciecal.html#c1 “The calculation of the CIE chromaticity coordinates for a given colored object requires the multiplication of its spectral power at each wavelength times the weighting factor from each of the three color matching functions. Summing these contributions gives three values called the tristimulus values, from which the chromaticity coordinates are derived. ” there are four further links that you can pursue if you want $endgroup$
Sep 29, 2021 at 3:26
$begingroup$ Thanks @anna v! $endgroup$
Sep 30, 2021 at 17:34
$begingroup$
I’d like to challenge your idea that the fact that a mix of red and blue gives something resembling violet implies that violet must be between red and blue.
In practice, what you get from such mixture is a shade of purple. See the figure below. Here the black dashed line from blue to red covers the colors you can get by changing the amount of red and blue in the mixture. The purest violet is on the bottom-most part of the border of the colored shape (the visible gamut).
On the other hand, if you mix violet and sky blue, you can get the set of colors covered by the green dotted line in the diagram. See that blue is among the colors you can get from this mixture.
Do these two facts conflict? No. Most colors are not spectral: they are desaturated. Together they fill a two-dimensional shape, on which the internal points can be found as mixtures of pairs of spectral colors. And the pairs are not unique: e.g. you can get white by mixing orange and sky-blue, or by mixing yellow and royal-blue, etc.. So what you call violet is not a point in this gamut—rather it is an area, where you can pick any point and still call it violet.
Cite
Follow
answered Jun 2, 2020 at 14:36
Ruslan Ruslan
28.5k 8 8 gold badges 67 67 silver badges 142 142 bronze badges
$endgroup$
$begingroup$ What do the axes in the second figure represent? $endgroup$
Sep 28, 2021 at 22:58
$begingroup$ @Rasputin see CIE xy chromaticity diagram and the CIE xyY color space $endgroup$
Sep 28, 2021 at 23:00
$begingroup$ Thank you @Ruslan $endgroup$
Sep 28, 2021 at 23:15
$begingroup$
You are confused and I understand because even on this site, you can read phrases like “our eyes have cones for Red, Green and Blue light” and “Red light activates the Red cones”.
- It is a common misconception that the receptors in our eyes are so, that the different types of cones correspond specifically just to Red, Green and Blue light. In reality, the three types of cones are sensitive for a range of Short, Mid and Long (depending on where they are positioned in the visible scale) wavelengths. It is very important to understand that they cover a range of wavelengths, and that they overlap.
Even if you wanted to put a arbitrary conventional color coding for these, you would have to put Yellow, Green and Blue instead of RGB. But these cones have a range of sensitivity, and multiple types of cones could be sensitive for the same wavelength photons. All along the visible wavelength range, there isn’t a single position where only one type of cone would be sensitive, that is, every single wavelength photon would activate multiple types of cones.
- It is another misconception that whenever monochromatic light shines into our eyes, only one type of cone gets activated. In reality, whenever light shines on our eyes, may it be monochromatic or not, multiple types of cones get activated, it is just the level of activation that is different for different wavelength photons. Whenever monochromatic red light shines into our eyes, even if the photons would be all the same wavelength, they activate both the Long and Mid cones. The more the Long cone gets activated, the more reddish the shade is, the more the Mid range cone gets activated, the more Orange/Yellowish the shade is perceived by our brain.
Our brain is the one that perceives the colors as a combination of signals from the cones, and our brain is the one that perceives violet as a combination of signals from the Short and Long cones too. The more the Short cones get activated, the more violet the shade of the color is perceived by the brain, the more the Long cone gets activated, the more Bluish the shade is perceived by the brain. So this is the answer to your question, violet is the end of the spectrum, where the Short cone’s activity dominates. In fact, you need to add the Long cone’s activity to get away from the end of the spectrum, and move towards blue.
It is too correct, that a certain perceived color in the brain can be produced by multiple different combinations of signals from the three types of cones.
Contents
- 1 Approximations of spectrum violet
- 1.1 Color wheel violet
- 1.2 Electric violet
- 1.3 Vivid violet
- 2.1 Deep violet
- 2.2 Pigment violet (web color dark violet)
- 2.3 Web color “violet”
Violet (color wheel) — Color coordinates — Hex triplet #7F00FF RGB B (r, g, b) (127, 0, 255) HSV (h, s, v) (270°, 100%, 50%) Source Chromas/Achromas B: Normalized to [0–255] (byte) Color wheel violet
The color at right is called color wheel violet because, by its color formula, it is the color precisely halfway between magenta and blue on the HSV color wheel. It is also called near violet because this color, when plotted on the CIE chromaticity diagram is equivalent to a visual stimulus of approximately 422 nanometers on the spectrum, barely on the violet side of the transition between the violet and indigo parts of the spectrum, which occurs at approximately 420 nanometers if indigo is accepted as a spectrum color.
Electric Violet — Color coordinates — Hex triplet #8B00FF RGB B (r, g, b) (139, 0, 255) HSV (h, s, v) (271°, 100%, 50%) Source BF2S Color Guide B: Normalized to [0–255] (byte) Electric violet
The color at right is electric violet, the closest approximation to middle spectrum violet that can be made on a computer screen, given the limitations of the sRGB color gamut within the CIE chromaticity diagram. When plotted on the CIE chromaticity diagram, this color would have approximately the hue of a visual stimulus of about 400 nm on the spectrum, in the middle of the violet part of the spectrum. Thus another name for this color is middle violet. [citation needed]
Vivid violet — Color coordinates — Hex triplet #9900FF RGB B (r, g, b) (153, 0, 255) HSV (h, s, v) (273°, 100%, 50%) Source HTML Color Chart @273 B: Normalized to [0–255] (byte) Vivid violet
Displayed at right is the color vivid violet, a color approximately equivalent to the violet seen at the extreme edge of human visual perception. When plotted on the CIE chromaticity diagram, it can be seen that this is a hue corresponding to that of a visual stimulus of approximately 380 nm on the spectrum. Thus another name for this color is extreme violet. [citation needed]
Deep violet — Color coordinates — Hex triplet #9900CC RGB B (r, g, b) (153, 0, 204) HSV (h, s, v) (270°, 50%, 43%) Source Hexcode Color Chart B: Normalized to [0–255] (byte) Other variations of violet
Deep violet
Displayed at right is the color deep violet, a violet in brightness (value) between electric violet and pigment violet.
Dark Violet — Color coordinates — Hex triplet #9400D3 RGB B (r, g, b) (148, 0, 211) HSV (h, s, v) (282°, 40%, 40%) Source X11 B: Normalized to [0–255] (byte) Pigment violet (web color dark violet)
The color box at right displays the web color dark violet which is equivalent to pigment violet, i.e., the color violet as it would typically be reproduced by artist’s paints, colored pencils, or crayons as opposed to the brighter “electric” violet above that it is possible to reproduce on a computer screen.
Compare the subtractive colors to the additive colors in the two primary color charts in the article on primary colors to see the distinction between electric colors as reproducible from light on a computer screen (additive colors) and the pigment colors reproducible with pigments (subtractive colors); the additive colors are a lot brighter because they are produced from light instead of pigment.
Pigment violet (web color dark violet) represents the way the color violet was always reproduced in pigments, paints, or colored pencils in the 1950s. By the 1970s, because of the advent of psychedelic art, artists became used to brighter pigments, and pigments called “Violet” that are the pigment equivalent of the electric violet reproduced in the section above became available in artists pigments and colored pencils. (When approximating electric violet in artists pigments, a bit of white pigment is added to pigment violet.)
Violet (web color) — Color coordinates — Hex triplet #EE82EE RGB B (r, g, b) (238, 130, 238) HSV (h, s, v) (300°, 67%, 88%) Source X11 B: Normalized to [0–255] (byte) Web color “violet”
The so-called web color “violet” is actually a rather pale tint of magenta because it has equal amounts of red and blue, and some of the green primary mixed in, unlike most other variants that are closer to blue. This same color appears as “violet” in the X11 color names.
Another name for this color is lavender magenta.
Violet in human culture
- In Chinese painting, the color violet represents the harmony of the universe because it is a combination of red (yang) and blue (yin). [2]
- The variety of eggplant known as Chinese eggplant has pigment violet colored skin.
- Okinawan “yams” (actually a variety of sweet potato) are colored a deep lavender and in the Tagalog language of the Philippines are called “ube”. They are ground up and cooked with sugar, yielding a bright violet colored jam called halaya ube which is sold in Filipino grocery stores. (To see a picture of an Okinawan yam, go to: [1])
- In the United Kingdom in it is traditional to package chocolate in violet colored packaging because of the association of the color royal purple with luxury. [3]
- Amethysts are a shade of violet called amethyst.
Parapsychology
- Psychics who claim to be able to observe the aura with their third eye report that those who are practicing occultists (magickal thaumaturgists) often have a violet aura. [4] It is said that people with violet auras are forward looking visionaries who may be in occupations such as performance artist, photographer, venture capitalist, astronaut, futurist, or quantum physicist. [5]
- Violet is the liturgical color of Advent and Lent in many western churches.
- Violet is the color associated with the New Age deity Saint Germain. [6]
- The Invocation of the Violet Flame is a system of meditation practice used in the “I AM” Activity and by the Church Universal and Triumphant. It is believed to be invoked from Saint Germain and practicing it is part of these religions’ devotion to Saint Germain.
The truth behind true violet
B that produces the best match to the data. However, these matching functions are only accurate when the data falls within the sRGB gamut. If the data does not fall within the sRGB gamut, then the matching functions will produce colors that are off by one or more hues.As you can see on the CIE chromaticity diagram, violet falls within the ‘purple’ region and is not a spectrally pure color. This is why computer monitors can present a ‘violet’ that is different from the spectral violet that humans can see. The ‘Violet’ that a computer monitor can present cannot be the same as ‘spectral’ violet. If you search for links to
75 3
As you can see the red line fades out and stops at roughly 420nm.
Computer generate violet by mixing blue and red, so how do we see natural violet (405-420nm) if only blue cones react to it??
First I supposed that violet affects blue and red cones, but that seems not to be the case on the graph. The interesting fact is, that the increasing intensity of that violet light makes it look “whiter” aka affects the green cones too- staying in my hypothesis.
Please proof me wrong if it’s possible.- ‘Hot’ new form of microscopy examines materials using evanescent waves
- Widely accepted Weyl semimetal shown to be a magnetic semiconductor
- Model suggests that mammalian sperm cells have two modes of swimming
Drakkith
Mentor
2022 Award
22,720 6,937
Daniel Petka said:First I supposed that violet affects blue and red cones, but that seems not to be the case on the graph. The interesting fact is, that the increasing intensity of that violet light makes it look “whiter” aka affects the green cones too- staying in my hypothesis.
Please proof me wrong if it’s possible.According to wikipedia. the red cone actually responds to two different regions of the spectrum. The first is the yellow-red end and the 2nd is a small region overlapping the blue cone near the violet end of the spectrum. So violet light stimulates both blue and red cones, allowing it to be approximated by RGB color systems like those in your computer screen.
Likes pixel
sophiecentaur
Science Advisor
Gold Member
28,548 6,668
Daniel Petka said:
Computer generate violet by mixing blue and red,Basically, there are TWO Violets! But it’s nothing to lose sleep over.
The ‘Violet’ that a computer monitor can present cannot be the same as ‘spectral’ violet. If you search for links to the CIE chromaticity diagram you can see how the three analysis curves in your post can be condensed onto a two dimensional chromaticity chart. The three curves have very low values around violet and I think the errors are quite high in that region – the lines sort of peter out due to human response and the shortcomings of the tests which have to be used. No one can put a meter on the sensor outputs and get reliable Voltage values, as with a photoelectric sensor. This link is a bit long winded but has lots of info about colorimetry. In particular, it shows how the phosphors of a TV display can reproduce a range of colours – but only the colours within the Gamut ( the triangle) of the three phosphors when plotted on the CIE chart. Any colour within the gamut can be represented by an appropriate mix of the three phosphors. The term “violet” is just a name for a colour somewhere down in the bottom left hand area of the CIE chart.
The Curved border of the CIR chart represents the spectral colours and the tristimulus values that (average) people assign to those colours. There are very few instances where the actually see ‘saturated’ colours in real life (on the edges of the CIE chart). Rainbows are particularly useless as sources of saturated spectral colours because they are heavily desaturated by the grey / white / blue off the sky behind them. If you look at the spectrum from a ‘white’ light source, the luminance of the blues (including indigo and violet) is very low so it’s all a bit of a muddle down that end and it’s very hard not to mix up the two violets. Other areas of the CIE chart are much more useful; Greens and ‘skin tones’ are higher luminance colours (evolutionary advantage, of course)
That link I posted is pretty good – better than Wiki because it is fuller. It makes the point that the Red Green Blue description of our analysis is far over simplified.
There is also the point that a TV phosphors are not very saturated colours – the triangle is far away from the edges. Why? I think it’s because no one has found ‘spectral’ phosphors that are bright enough to produce a useful TV picture.
