Red Blue

How does it happen that red+blue = violet?

Each of these colors has its own wavelength.
Red – 650nm.
Blue – 475-500nm.
Violet – 400nm.
No interference of red and blue waves is possible!

You’re right, Red+Blue=Violet. The light doesn’t have to interfere. You don’t have violet cones in your eye (you have 3 that are more or less maximally receptive at red, green, and blue)… your brain interprets equal amounts of blue and red neurons firing as the color violet. It also interprets equal amounts of red and green light as yellow.

Now you should wonder what happens when light of 400nm hits your eye. You don’t have violet cones, but this light is not in an energy eigenstate, so you can express it as a linear combination of red and blue wavelengths… the result is that 400nm light will excite red and blue cones in equal amounts so you view it as violet.

B DOUBLE E – Red and Blue KU (Official Music Video)