5 ms·

This story makes me remember that I had heard a fun fact a long time ago that many people have never actually seen the colour "violet" which is a single wavelen

by tianqi 1y ago

This story makes me remember that I had heard a fun fact a long time ago that many people have never actually seen the colour "violet" which is a single wavelength of visible light. Because there are very few things that reflect only this wavelength in reality. The purple colour we see is formed from a mixture of red and blue, whether it's something in nature, screen displaying or printing. I was so intrigued that I bought a 405nm laser torch and invited some friends to a home party to ‘See the real violet’. That single wavelength of purple really made a different experience, and with good friends, we had a great day. The olo experiment was very interesting, and it told me that today we even have the technology to stimulate a single cone cell one by one in time. I know that we can't accurately display the olo on screen right now, which also prevents any of these articles from actually containing a picture of the olo. I think it's very close to #00FFEE, and I'm making it the colour of my Hacker News's top bar.

tines 1y ago
> Because there are very few things that reflect this wavelength in reality. You mean few things that reflect only this wavelength? Because I would think anything white would reflect this wavelength just like any other.
- tianqi 1y ago
  Yes, I meant reflecting only this wavelength. Thanks.
subb 1y ago
You did send a specific wavelength to your retina, but that wasn't violet. Because violet is a construct by your brain. Color is not a property of wavelength. There's nothing special about photons wiggling in the 380 to 750nm range. In general it's not necessary to be this pendatic, but given the topic here, I think it's important to realize this. It takes a while because we are so good at projecting our internal experience outward. Remember the blue / black dress?
- tianqi 1y ago
  In my personal conception, violet is the kind of colour at the lower edge of the rainbow, which is a single wavelength. And purple is what the brain constructs. However, of course, the names of the colours are themselves vague.
  - bdelmas 1y ago
    Hmm if you talk to a colorist violet and purple are 2 different colors one more on the red and the other more on the blue. That’s still the construct of 2 wavelength colors. So a made up color of our brain that doesn’t exist.
    - dleary 1y ago
      "Violet" is a spectral color, which means that it is a color formed by a single wavelength of light. And it is a member of the rainbow (the spectrum). "Purple" is a mixture of red and blue.
  - subb 1y ago
    Maybe that's a language issue, because purple and violet are color names around here. And as such, they are both a construct of the brain, as any other colors, like... white. What we label as "violet wavelength" is only a narrow projection of our experience outward. Case in point, we don't have such colorful (eh) names for other EM wavelength. I say narrow because you could take this pure laser and change th surrounding and you will inevitably perceive it differently, even though the power and wavelength are the same.
- eviks 1y ago
  > did send a specific wavelength to your retina, but that wasn't violet. It was, by definition > Color is not a property of wavelength. Sure, it's a label > There's nothing special about photons wiggling in the 380 to 750nm range. There is - they activate different receptors your brain relies on, hence leading to a distinct (from other wavelengths) sensation
  - 1y ago
scotty79 1y ago
How did you spread laser light over larger area? The idea I'm having right now is reflecting it off of the rough side of aluminum foil.
- tianqi 1y ago
  I remember we just simply shone at a white wall.
- deleted 1y ago
  [deleted]
perilunar 1y ago
> The purple colour we see is formed from a mixture of red and blue, whether it's something in nature, screen displaying or printing. Well if it’s on an RGB screen, or printed with CMYK inks then it’s not ‘real’ violet, but there must be plenty of natural and artificial pigments that are actually reflecting violet light and not blue + red light. I imagine any pure compound would be doing this. E.g cobalt phosphate (aka cobalt violet). You could tell by illuminating a sample with different light sources. See metameric failure: https://en.wikipedia.org/wiki/Metamerism_(color)#Metameric_failure https://en.wikipedia.org/wiki/Metamerism_(color)#Metameric_f...
erik 1y ago
> many people have never actually seen the colour "violet" which is a single wavelength of visible light The violet seen in a rainbow (in nature, not a photo) is legit single wavelength violet. Same with the rainbows created from shining white light through a prism. It's true that you don't really get to see it in isolation very often though. Maybe some flowers, birds, or butterflies? Or maybe the purple glow you get from UV lights?
- phkahler 1y ago
  Why is violet in the rainbow not a very blue color? I would think it only activates the blue cones. 405nm is a nifty color.
  - jfengel 1y ago
    Because the cone isn't really a "blue" cone, and neither is the "red" one. The curves overlap in complex ways. A pure violet photon also slightly stimulates the long wavelength cone. That's why red+blue=purple feels a bit like violet. It creates a similar double firing. (And why red plus green gives an even more accurate yellow. The long and medium cones have a lot of overlap.)
    - GrantMoyer 1y ago
      This is a common misconception, but the sensitivity of L cones ("red" cones) increases monotonically until about 570nm (monochromatic yellow), so violet light stimulates L cones the least out of all visible wavelengths of light. Magenta light, a mixture of red and blue wavelengths, stimulates L cones far more than violet light. See Wikipedia's LMS responsivity plot[1] or the cone fundamental tables from the Color & Vision Research Laboratory at [2]. I think the misconception comes from plots of XYZ color matching functions[3]. The X color matching function indeed has a local maximum in the short wavelengths, but X doesn't represent L cone stimulation; it's a mathematically derived curve used to define the XYZ color space, which is a linear transform of LMS color space selected for useful mathematical properties. [1]: https://en.wikipedia.org/wiki/LMS_color_space#/media/File:Cones_SMJ2_E.svg https://en.wikipedia.org/wiki/LMS_color_space#/media/File:Co... [2]: http://www.cvrl.org/ http://www.cvrl.org/ [3]: https://en.wikipedia.org/wiki/CIE_1931_color_space#/media/File:CIE_1931_XYZ_Color_Matching_Functions.svg https://en.wikipedia.org/wiki/CIE_1931_color_space#/media/Fi...
Nesco 1y ago
You can make the difference between a single wavelength color and a composite color which looks the same, by looking at objects nearby. If they are of one of the composite colors, they should appear in their natural hue Else they will just appear darker
bitwize 1y ago
Violet is a true wavelength, and does occur in nature. Magenta, formed by mixing red and blue, does not exist in nature. For that reason, "magic pink" (full-brightness magenta, #ff00ff) is often used as a transparency color when the image format does not support an alpha channel (e.g., sprite sheets, Winamp skins).
- jameshart 1y ago
  It's not true to say that mixtures of red and blue 'do not exist in nature'. Fuchsia petals really are that color. All you need is a substance that preferentially absorbs green wavelengths but reflects reds and blues. What 'does not exist in nature' is a single wavelength that produces the equivalent stimulation of your L, M and S cone cells as a mixture of red and blue light does. But most of what we see in nature is not single wavelength light - it's broad spectrum white light reflecting off things with absorption spectra. The reason stuff looks so weird under certain LED lights or pure sodium light is that the source light isn't broad spectrum - it's missing wavelengths already - so the way it interacts with absorption spectra is unintuitive. Something that looks blue under white light should still look blue under blue light - but a blue LED might just be emitting blue frequencies that the object absorbs, so it looks black instead.

by tianqi 1y ago

tines 1y ago

> Because there are very few things that reflect this wavelength in reality. You mean few things that reflect only this wavelength? Because I would think anything white would reflect this wavelength just like any other.

tianqi 1y ago
Yes, I meant reflecting only this wavelength. Thanks.

subb 1y ago

You did send a specific wavelength to your retina, but that wasn't violet. Because violet is a construct by your brain. Color is not a property of wavelength. There's nothing special about photons wiggling in the 380 to 750nm range. In general it's not necessary to be this pendatic, but given the topic here, I think it's important to realize this. It takes a while because we are so good at projecting our internal experience outward. Remember the blue / black dress?

tianqi 1y ago
In my personal conception, violet is the kind of colour at the lower edge of the rainbow, which is a single wavelength. And purple is what the brain constructs. However, of course, the names of the colours are themselves vague.
- bdelmas 1y ago
  Hmm if you talk to a colorist violet and purple are 2 different colors one more on the red and the other more on the blue. That’s still the construct of 2 wavelength colors. So a made up color of our brain that doesn’t exist.
  - dleary 1y ago
    "Violet" is a spectral color, which means that it is a color formed by a single wavelength of light. And it is a member of the rainbow (the spectrum). "Purple" is a mixture of red and blue.
- subb 1y ago
  Maybe that's a language issue, because purple and violet are color names around here. And as such, they are both a construct of the brain, as any other colors, like... white. What we label as "violet wavelength" is only a narrow projection of our experience outward. Case in point, we don't have such colorful (eh) names for other EM wavelength. I say narrow because you could take this pure laser and change th surrounding and you will inevitably perceive it differently, even though the power and wavelength are the same.
eviks 1y ago
> did send a specific wavelength to your retina, but that wasn't violet. It was, by definition > Color is not a property of wavelength. Sure, it's a label > There's nothing special about photons wiggling in the 380 to 750nm range. There is - they activate different receptors your brain relies on, hence leading to a distinct (from other wavelengths) sensation
- 1y ago

scotty79 1y ago

How did you spread laser light over larger area? The idea I'm having right now is reflecting it off of the rough side of aluminum foil.

tianqi 1y ago
I remember we just simply shone at a white wall.
deleted 1y ago
[deleted]

perilunar 1y ago

> The purple colour we see is formed from a mixture of red and blue, whether it's something in nature, screen displaying or printing. Well if it’s on an RGB screen, or printed with CMYK inks then it’s not ‘real’ violet, but there must be plenty of natural and artificial pigments that are actually reflecting violet light and not blue + red light. I imagine any pure compound would be doing this. E.g cobalt phosphate (aka cobalt violet). You could tell by illuminating a sample with different light sources. See metameric failure: https://en.wikipedia.org/wiki/Metamerism_(color)#Metameric_failure https://en.wikipedia.org/wiki/Metamerism_(color)#Metameric_f...

erik 1y ago

> many people have never actually seen the colour "violet" which is a single wavelength of visible light The violet seen in a rainbow (in nature, not a photo) is legit single wavelength violet. Same with the rainbows created from shining white light through a prism. It's true that you don't really get to see it in isolation very often though. Maybe some flowers, birds, or butterflies? Or maybe the purple glow you get from UV lights?

phkahler 1y ago
Why is violet in the rainbow not a very blue color? I would think it only activates the blue cones. 405nm is a nifty color.
- jfengel 1y ago
  Because the cone isn't really a "blue" cone, and neither is the "red" one. The curves overlap in complex ways. A pure violet photon also slightly stimulates the long wavelength cone. That's why red+blue=purple feels a bit like violet. It creates a similar double firing. (And why red plus green gives an even more accurate yellow. The long and medium cones have a lot of overlap.)
  - GrantMoyer 1y ago
    This is a common misconception, but the sensitivity of L cones ("red" cones) increases monotonically until about 570nm (monochromatic yellow), so violet light stimulates L cones the least out of all visible wavelengths of light. Magenta light, a mixture of red and blue wavelengths, stimulates L cones far more than violet light. See Wikipedia's LMS responsivity plot[1] or the cone fundamental tables from the Color & Vision Research Laboratory at [2]. I think the misconception comes from plots of XYZ color matching functions[3]. The X color matching function indeed has a local maximum in the short wavelengths, but X doesn't represent L cone stimulation; it's a mathematically derived curve used to define the XYZ color space, which is a linear transform of LMS color space selected for useful mathematical properties. [1]: https://en.wikipedia.org/wiki/LMS_color_space#/media/File:Cones_SMJ2_E.svg https://en.wikipedia.org/wiki/LMS_color_space#/media/File:Co... [2]: http://www.cvrl.org/ http://www.cvrl.org/ [3]: https://en.wikipedia.org/wiki/CIE_1931_color_space#/media/File:CIE_1931_XYZ_Color_Matching_Functions.svg https://en.wikipedia.org/wiki/CIE_1931_color_space#/media/Fi...

Nesco 1y ago

You can make the difference between a single wavelength color and a composite color which looks the same, by looking at objects nearby. If they are of one of the composite colors, they should appear in their natural hue Else they will just appear darker

bitwize 1y ago

Violet is a true wavelength, and does occur in nature. Magenta, formed by mixing red and blue, does not exist in nature. For that reason, "magic pink" (full-brightness magenta, #ff00ff) is often used as a transparency color when the image format does not support an alpha channel (e.g., sprite sheets, Winamp skins).

jameshart 1y ago
It's not true to say that mixtures of red and blue 'do not exist in nature'. Fuchsia petals really are that color. All you need is a substance that preferentially absorbs green wavelengths but reflects reds and blues. What 'does not exist in nature' is a single wavelength that produces the equivalent stimulation of your L, M and S cone cells as a mixture of red and blue light does. But most of what we see in nature is not single wavelength light - it's broad spectrum white light reflecting off things with absorption spectra. The reason stuff looks so weird under certain LED lights or pure sodium light is that the source light isn't broad spectrum - it's missing wavelengths already - so the way it interacts with absorption spectra is unintuitive. Something that looks blue under white light should still look blue under blue light - but a blue LED might just be emitting blue frequencies that the object absorbs, so it looks black instead.