What Is the Physics Behind White Light and Color Mixing?

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Discussion Overview

The discussion revolves around the physics of white light and color mixing, focusing on the mechanisms behind how different colors of light combine to produce the perception of white. Participants explore both physiological and physical aspects of color perception, as well as the implications of mixing various colors of light.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether the appearance of white light from overlapping colors is due to the properties of specific wavelengths or simply the way our eyes perceive those wavelengths.
  • Another participant asserts that the effect is purely physiological, stating that the light does not actually combine but rather that equal numbers of red, green, and blue photons stimulate the eye.
  • A participant explains that the human eye has three types of color receptors, and when they are excited equally, the brain interprets this as white light.
  • There is a discussion about the classification of primary and secondary colors, with one participant asking if the distinction is merely conventional.
  • Another participant describes how cyan, yellow, and magenta absorb red, green, and blue light, respectively, and reflects white light back, suggesting that the primary/secondary color classification is conventional.
  • A hypothetical scenario is posed regarding the dispersion of light from a mixture of red, blue, and green lights through a prism, questioning whether the dispersed light would show the original colors or a full spectrum.
  • One participant responds that the dispersed light would show only the original red, green, and blue colors, emphasizing that mixing beams of light does not affect individual photons.
  • Another participant discusses how the light from hot objects contains a range of colors and how the temperature influences the perceived color, noting that objects at certain temperatures can appear white due to the balance of emitted colors.
  • There is a reiteration of the idea that light can appear white by emitting a range of colors or by using controlled amounts of red, green, and blue light, as seen in technologies like LEDs and fluorescent tubes.

Areas of Agreement / Disagreement

Participants express differing views on the nature of color mixing and the classification of primary and secondary colors. While some points are clarified, there is no consensus on the underlying physics or the implications of color perception.

Contextual Notes

Some claims depend on the definitions of primary and secondary colors, and the discussion includes unresolved aspects of how light mixing and perception interact.

NanakiXIII
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I've been wondering about this lately. We've most likely all seen the basic example at school of projecting three colours of light at a screen and noticing that the area where the colours overlap turns out to be white. But what I'm wondering is whether there is actually any physics to that. Does the fact that it looks white to us actually have anything to do with properties of those specific wavelengths of light, or is it merely that our eyes have receptors for those three colours?
From what I understand, true white light is made up of all the different colours of the visible spectrum, so how could three single wavelengths produce the same effect physically?
 
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It's a purely physiological effect.
The light doesn't actually combine,simply an equal number of red, green and blue photons hits your eye at the same rate.
 
We possesses three different types of colour receptors (cones), one sensitive in the red, one in the green and the other in the blue. When all three are excited roughly the same amount, our brain interprets this as white.

Claude.
 
If we mix cyan, yellow and majenta, our brain interprets it as white. But why is it that red-blue-green is known as primary colors, and yellow-cyan-majenta known as secondary colors? just conventional?
 
cyan yellow and magenta work by each absorbing reg,green and blue - so if you reflect white light from them you get white light back.
The primary/secondary is just convention.
 
Let's say, I put 3 equal amount of red-blue-green colored lights to make a beam of white light. I pass this white light to a prism to cause dispersion. What will be the colors in the dispersed light? red-blue-green, or all visible colors in the spectra?
 
Just the red-green-blue of the original lights - if you mix beams of light the individual photons don't affect each other.

The light from a hot object like the sun or a light bulb contans a range of colours, each photon has a sllightly different colour and the temperature of the object controls how many of each colour is emitted and so the overall colour the object appears.
For objects that are a few 1000 deg C the amount of red and blue light emitted makes them look white to us because we have evolved under a sun at that temperature.

You can make a light appear white by emitting a whole range of colours at the correct temperature - like a lightbulb or you can 'trick' the eye into making it think it is seeing white by using controlled amounts of red, green , blue - this is what a white LED or a flourescent tube does.
 
I figured as much. Thanks for your replies.
 
mgb_phys said:
You can make a light appear white by emitting a whole range of colours at the correct temperature - like a lightbulb or you can 'trick' the eye into making it think it is seeing white by using controlled amounts of red, green , blue - this is what a white LED or a flourescent tube does.
A more complex example would be a TV screen, which is a whole bunch of green, red and blue dots.

Claude.
 

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