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Old 11th March 2016, 11:37 AM   #1
ernie Thread Starter
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Default Question about light

Something that has been bugging me for ages.


We all know different colours have different wavelengths.

eg. violet is a shorter wavelength, and higher frequency than red

Where I get stuck is if I shine a blue LED and a red LED at the same spot on a piece of white paper, it appears as a violet spot. So how is the shorter violet wavelength being created, is it really there, or some trick of the RGB receptors in our eyes?


- Ernie.

Last edited by ernie; 11th March 2016 at 11:46 AM.
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Old 11th March 2016, 3:40 PM   #2
evilasdeath
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http://physics.stackexchange.com/que...e-purple-light

Not sure the best way to explain it, but they are different.

But yes there is a difference between a colour received by monochromatic light and polychromatic light as it's perceived by the eyes/brain.


You can also ask, is the red i see the same as the red you see
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Old 12th March 2016, 6:35 PM   #3
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Very interesting, so the purple we see when red and blue are combined is an illusion made by our brains. I wonder what the biological benefit in that would be? Sure makes it hard for AI researchers trying to mimic human visual perception.


- Ernie.
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Old 13th March 2016, 8:19 AM   #4
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Quote:
Originally Posted by ernie View Post
Very interesting, so the purple we see when red and blue are combined is an illusion made by our brains. I wonder what the biological benefit in that would be? Sure makes it hard for AI researchers trying to mimic human visual perception.


- Ernie.

No problem at all for AI and it happens because it has to happen unless you want to build a vision system that measures actual wavelengths of light. That's beyond us and nature.

This video from the Royal Institute explains it very well.

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Old 13th March 2016, 5:48 PM   #5
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That is awesome! That's very 'clever' of the brain to create a colour instead of making it look green. That'd be a PITA!
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