Exploring the Physics of White Light

In summary, 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?It's a purely physiological effect.
  • #1
NanakiXIII
392
0
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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  • #2
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.
 
  • #3
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.
 
  • #4
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?
 
  • #5
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.
 
  • #6
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?
 
  • #7
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.
 
  • #8
I figured as much. Thanks for your replies.
 
  • #9
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.
 

1. What is white light?

White light is a form of electromagnetic radiation that is visible to the human eye. It is a combination of all the colors of the visible light spectrum, which range from red to violet. White light is produced by the sun, light bulbs, and other light sources.

2. How is white light formed?

White light is formed when all the colors of the visible light spectrum are combined together. This can be achieved by either passing light through a prism or by combining different colored lights using a color-mixing tool. When all the colors merge together, they create white light.

3. What are the properties of white light?

White light has several properties, including being able to travel in a straight line, having a constant speed in a vacuum, and being able to be reflected, absorbed, or transmitted by different materials. It also has different wavelengths, which correspond to different colors in the visible light spectrum.

4. How does white light behave when it passes through a prism?

When white light passes through a prism, it is refracted or bent into its component colors. This is because each color has a different wavelength, and as the light passes through the prism, it is slowed down at different rates, causing the colors to separate. This process is known as dispersion.

5. What are the practical applications of understanding white light?

Understanding the physics of white light has various practical applications, such as in photography, lighting design, and color printing. It also plays a crucial role in the development of optical instruments, such as microscopes, telescopes, and lasers. Additionally, understanding white light helps scientists better understand the behavior of light and its interactions with matter.

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