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Question regarding colour Answered

Hi everyone!

So here is another confusion in my mind. 

I know that colours are a result of electromagnetic radiation in the visible spectrum interacting with our eyes.  The visible spectrum consists of 7 colours, abbreviated VIBGYOR.

Now my question is, what are primary colours and secondary colours? And how come mixing of two colours produce an entirely different  colour? I expected that all 7 of them would be primary. But that is not the case. 

Also, for illustrating the real world scenario from which this doubt crawled into my mind, consider that i have two pieces of translucent films, one blue, and other yellow. Now initially i place the blue film in-front of a white bulb, then it filters all other colours other than blue. Now place a yellow in-front of the blue, and there, you have green. What is the working principle behind this? How come the "blue" light turned "green" after passing through the yellow film?

3 Replies

kelseymh (author)2013-02-08

You want to read about color theory. First, your scenario is wrong. Color mixing of transmitted light (e.g., using filters in front of a white-light source) is not "red-blue-yellow mixing," but is based on red, green, and blue as primary colors. What you've described applies to subtractive mixing, e.g., combining paint pigments.

Put simply, metazoan eyes do not detect wavelengths of light directly. They have photoreceptors, some of which (in vertebrates and particularly in primates) have relatively narrow wavebands. The combination of receptors which fire for a given wavelength or combination of wavelengths determines what "color" is perceived.

Humans have photoreceptors which are approximately sensitive to "red", "green" and "blue" wavelengths. If both the red and green receptors at a given location are triggered together, the brain assigns that to the color "yellow."

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charmquark (author)kelseymh2013-02-09

Thanks for the amazing info Doc! I didn't know about these theories.
So, if i understand this correctly, then the wavelength corresponding to yellow in the EM spectrum actually triggers the photo-receptors corresponding to red and green and hence we see it as yellow, is that right?

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kelseymh (author)charmquark2013-02-12

Yup, that correct! And if you use both red and green lights at the same time, the combination of them will also look yellow.

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