Why does red and green in light make yellow, but in colors, like paint, it makes some other color?

Name: Yellow and cyan solution
Uploaded: 2014-01-21T02:24:15Z
Description: Each color you see comes from the pencil blocking one of the lights and the other two filling in the shadow.

A pigment (such as paint) works by reflecting a color and absorbing all others. Adding different pigments is like subtracting their colors while adding different lights is like adding their colors. If you have white pigment and add blue (one that doesn't reflect red and yellow) you will have blue. If you mix all colors in pigments you get black and if you mix all colors of lights, you get white. http://le-csss.asu.edu/sites/default/files/Mixing_Light_&_Mixing_Pigments.pdf

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Course: Exploratorium > Unit 2

Lesson 5: Colored Shadows

Yellow and cyan solution

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Each color you see comes from the pencil blocking one of the lights and the other two filling in the shadow. Created by Exploratorium.

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Jonathan Zhu
Posted 10 years ago. Direct link to Jonathan Zhu's post “Why does red and green in...”
Why does red and green in light make yellow, but in colors, like paint, it makes some other color?
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(20 votes)
Answer
- Flávio Júnior
  Posted 10 years ago. Direct link to Flávio Júnior's post “A pigment (such as paint)...”
  A pigment (such as paint) works by reflecting a color and absorbing all others. Adding different pigments is like subtracting their colors while adding different lights is like adding their colors.
  If you have white pigment and add blue (one that doesn't reflect red and yellow) you will have blue. If you mix all colors in pigments you get black and if you mix all colors of lights, you get white.
  http://le-csss.asu.edu/sites/default/files/Mixing_Light_&_Mixing_Pigments.pdf
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  (33 votes)
jeepers_peepers ✝
Posted 10 years ago. Direct link to jeepers_peepers ✝'s post “About the question under ...”
About the question under this one, is that why there is a yellow light underneath the red and over the green light in traffic lights?
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(3 votes)
Answer
- Paul Kang
  Posted 10 years ago. Direct link to Paul Kang's post “I don't think that the pl...”
  I don't think that the placement of traffic lights would have much to do with colored shadows, as there is constant interference from the sun, street lights and other sources. In addition, traffic lights would be too diffuse to produce the colored shadow effect.
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  (1 vote)
я̿€̿ρ̿Ł̿ɪ̿т̿Ǻ̿ƶ̿
Posted 9 years ago. Direct link to я̿€̿ρ̿Ł̿ɪ̿т̿Ǻ̿ƶ̿'s post “Why is one of the shadows...”
Why is one of the shadows off of his hand blue, when the pencil's shadow is not?
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(2 votes)
Answer
- zkossover
  Posted 9 years ago. Direct link to zkossover's post “His hand is blocking all ...”
  His hand is blocking all two of the lights (red and green) and so only blue light can get to that part. The pencil's shadows (because of the pencil's distance from the foam core and how narrow it is) only blocks one color per shadow.
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  (1 vote)

Video transcript

- [Voiceover] To understand the yellow and the cyan shadow, we have to remember that light travels in straight lines. So light from the red bulb travels in a straight line to the wall, but it's blocked by the pencil in this shadow over here. That's the straight line from the red to the board. In that shadow, light from the blue bulb can hit in that shadow, because the blue bulb is in a different position from the red bulb. And the same with the green. So in that shadow, we have blue and green light added together to make cyan. On the other side here, where we see a yellow shadow, once again, light traveling from the blue light in a straight line to the wall is blocked right there by the pencil. But the red and the green bulbs are in different positions, so they're light can fill in that shadow, and make yellow light.