If you matched the yellow light of one prism to that of the green light of another prism, say through a thin glass pane, what would be the resulting color?

  • 1
    $\begingroup$ Do you mean what colour do you get if you mix yellow and green light? If so yellow is (as far as our cone cells are concerned) a mixture of red and green light, so mixing yellow and green would be seen as yellowy-green. $\endgroup$ – John Rennie Apr 2 '14 at 15:24
  • $\begingroup$ I read there are two different forms of color making. One was RGB and another, I forget. One is based off pigment the other light. However, mixing colored lights, which is light made through a pigmented object, such as a red laser, is not the same in my eyes as light from prisms. $\endgroup$ – user42744 Apr 2 '14 at 15:27
  • 1
    $\begingroup$ The other one is probably CMY (or CMYK). RGB is additive mixing, like the screen on your phone, and CMY is subtractive, like your inkjet printer. $\endgroup$ – John Rennie Apr 2 '14 at 15:32
  • $\begingroup$ After additional reading, as I understand it, the RGB method, used by projecting on to black, and the CMY method, shades of RGB, used by projecting onto white. But in my question, the light is split by two prisms and projected onto a nearly transparent material which begs my question, would we see a variation. Just my puny mind at work. $\endgroup$ – user42744 Apr 2 '14 at 15:47

Irrespective of where the light comes from, your eye judges the colour of light by the way it stimulates the three types of cone cell. The cone cells have broad and overlapping spectral responses:

Cone cells

(picture from the Wikipedia article I've linked) but to a reasonable approximation you can think of the three types of cone cell as responding to red, green and blue light. This is why the LCD screen on your phone can reproduce a wide range of colours using just red, green and blue pixels.

In the experiment you describe the yellow light is not a mixture of red and green, it's light of a wavelength of around 580 nm. However it stimulates your cone cells in the same way as a mixture of red and green light does, so a mixture of red and green is seen by your eye as yellow.

So if you mix green and yellow light then as far as your eye is concerned you are mixing two parts green light with one part red light. The corresponding RGB value would be (128, 255, 0). If I use my graphics program to produce this colour I get:


So it's just yellowy-green.

  • $\begingroup$ How correct is the additive color explanation? Isn't RGB not capable to reproduce all colors, something like: en.wikipedia.org/wiki/File:Colorspace.png ? I never understood color spaces... $\endgroup$ – jinawee Apr 2 '14 at 16:32
  • $\begingroup$ @jinawee: If the cone cells just responded to pure red, green and blue light then RGB would be able to produce every colour the eye could see. However the cone cells respond to a broad range of wavelengths (as shown in the graph in my answer) and their ranges overlap. That means there will be some combinations of cone cell response that cannot be expressed as a sum of the individual responses to just red, just green and just blue light, and hence there are some colours that can't be reproduced using RGB. $\endgroup$ – John Rennie Apr 2 '14 at 16:36
  • $\begingroup$ However, your LCD screen and/or phone produce pretty convincing pictures using just RGB, so RGB reproduces enough colours to convince. $\endgroup$ – John Rennie Apr 2 '14 at 16:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy