How is there a violet in the visible spectrum?


I heard that the violet in rainbow is only created because the bottom blue coincides with another inner rainbow’s top red. I forgot where I heard it but it sounds logical.

Whenever I see the EM spectrum, it always goes from red to green to blue then to VIOLET which I don’t know how it got there. What bothers me more is how there’s an infraRED and then it goes ultraVIOLET.

I remember in preschool that red + blue = violet so where did the red from the violet part of the spectrum comes from?

In: Physics

Violet is at the edge of the spectrum, with a wavelength of 380-450 nm.

Infrared and ultraviolet are just past opposite edges of the visible spectrum. Infrared means “below red” while ultraviolet means “beyond violet”. It doesn’t go from infrared to ultraviolet.

Mixing red and blue results in a similar color because of the way our eyes work. We can’t actually “see” every color – our eyes have 3 types of “color detecting cells” (i.e. cone cells), each is most sensitive to a specific range of wavelengths, so whatever color we can see is a combination of how sensitive each of these cell types to the specific color. In the brain, a combination of red and blue creates a color which is similar to the one created when you see violet.

Mixing light and mixing pigments do not have the same effect. Mixing red, yellow, and blue paints will get you a dark muddy mess. Mixing red, green, and blue light will get you white light. So the mixing of blue light from one rainbow and red from another is completely incorrect.

Visible light is just a very small portion of the electromagnetic spectrum. The different colors are simply different wavelengths. Just as your ears can only hear certain sound wavelengths (can’t hear ultra low sounds or ultra high sounds), your eyes can only detect a portion of the EM Spectrum.

Our perception maps to how activated the cones attributed to three colors are, not directly to the wavelength of incoming light. You can see a full explanation [here]( This becomes quite complex for mixes of wavelengths, but for single wavelengths you can see that it does smoothly activate the red cone, then the green cone, then the blue cone – but at the very end, the red cone is slightly more activated. This is what causes the subjective similarity between violet and a mix of pure blue and pure red.