Is the "purple" in front of me?What is the purple you said?

Recently, Zhang Chaoyang mentioned a statement in his physics class:

"There is no purple in the solar spectrum, and people's eyes see purple to re -overlap the spectrum."

Is there a kind of? How does it seem to know every word?

In fact, in this sentence, the "purple" before and after is not the same "purple".

Just like the two three primitive colors we have studied in the textbook- "color light three original colors" and "color tri -primary color". Although they are all called "three primary colors", one is from the perspective of optics and the other is from the perspective of color.

The color of the color is red, green, and blue. The light of these three colors can get almost all colors of light through a certain proportion and superimposed together. Image source: wikipedia

The color of the colors refers to the red, yellow, and green. They can get almost all colors in painting through a certain proportion of mixing and overlapping, except for white. Image source: wikipedia

"Purple 'in the solar spectrum" and "‘ Purple ’” in the eyes are the same, one is an optical angle, and the other is the color angle.

Seeing this, did you have a new confusion:

If there is no "purple" in the solar spectrum, what is the "purple" of "red, orange, yellow, green, blue, 靛, purple" in the rainbow?

Let's take a closer look.

01

Is there really no "purple" in the sun?

This statement is actually inaccurate. There are still "purple" in the solar spectrum, but it is not the "purple" and "purple grapes" we understand the daily understanding of the "purple".

When the "purple" in the solar spectrum is represented by optical perspective, it has a proprietary term in English called "Violet", which represents the pure "purple" in optical — that is, the wavelength is 380 nanote-450 nanometer. One range of light.

In Chinese, this word is translated into "blue -purple" and is simply translated as "purple" by many people. But the "blue purple" or "purple" here is not a concept with the "purple" seen in life and mentioned.

Rainbow and visible light bands obtained by decomposing the sun with three prisms contain this pure purple (Violet). It is just that it is very small in the very edge, and it is too small to make it difficult to distinguish it.

If we decompose sunlight with a spectrometer, we can see some purple light. The small ribbon of the lower bottom in the figure below (different devices may be different in color):

The sun can be visible to the sun (the wavelength range is 400 nanometer-700 nanometer). Image source: NSO

If you feel that the picture above is not clear enough, you can look at the continuous spectrum map below. The area represented by "V" is the "purple" color of "violet".

You will find that the closer the wavelength is closer to 380 nanometers, the more "black", this is not because it is "black", but because the eyes cannot see the light (ultraviolet light) with a shorter wavelength than 400 nanometers, so our us is What you feel is black. In addition, the judgment of the eyes is actually affected by bright and dark.

Continuous spectral map. Image source: wikipedia

We can extract a few colors that can be distinguished from the "V" spectrum. The following is the "Violet" in the optical sense that the brain feels: the optical sense:

The picture comes from the author

Understand the purple (Violet), and then talk about what is going on with the "colorful" "purple" seen in life.

02

What is the "purple" in life?

How did it see?

From the perspective of art, the colors of mixed with red and blue pigments are also called "purple". This "purple" also has a proprietary word in English: Purple, which is the "purple" of many objects we usually see.

If you want to feel this "purple", the most intuitive way is to buy a box of watercolor pigments, mixing red and blue in a certain proportion:

One of purple, there are actually many kinds of purple, not a single one. It is very different from the "Violet) in the above optics. The picture comes from the author

Stacking red light and blue light together can also get "purple". But the difference between the "purple light" and the "violet" mentioned earlier is that- "violet" is monochrome, and the "purple light" we obtained by superimposed is mixed color light.

The mobile phone screen is the most intuitive application of this "mixed color".

If you amplify your mobile phone screen, you will find that there are only three colors of light -emitting units in the screen: red, green, and blue (that is, color light three primary colors). These three glowing units can make the phone screen present various colors by lightning and dark. For example, purple light is the color shown by the two glowing units of red and blue.

If you click on this picture and zoom in it, you will find that there are only three glowing units: "red, green, and blue". Gallery copyright picture, not authorized reprint

How do we perceive the "purple" in the mobile phone screen?

When the color appears on the screen, the three cone cells on the retina -sensitive cone cell L for yellow and green light, the most sensitive cone cell M and the most sensitive cone cell S for the green light will be It is stimulated, and at the same time send a signal to the brain, the brain will tell us what the color we see. If you see "purple", then the process of "seeing" is actually:

The red and blue light emitting units on the screen lit up, and the two light -emitting units stimulated the visual cone cell L and the cone cell S respectively. When these two cone cells were stimulated at the same time, the brain received the signal- "purple" Essence

Therefore, the color we "see" is actually the rearrack of the human eyes and the brain to the light.

Now look at Zhang Chaoyang's "there is no purple in the sun, and the human eye is not so difficult to understand when people see purple be superimposed to the spectrum"?

The second half of the sentence is undoubted. The "purple" we feel is indeed the redemption of the human eyes and the brain to the light. There is a problem in the first half of the sentence, that is, the solar spectrum is still "purple", but it is not "purple", but "violet" ...

Author ｜ Cui Yanhao

Review ｜ Liu Qian Beijing Astronomical Museum Researcher

The cover picture and text of this article are from the copyright gallery

The content of the picture is not authorized to reprint

Reprinted the original picture and text, please reply to "Reprinted" in the background

- END -