what is purple and violet and what are the differences? In the visible light spectrum, why violet is commonly referred as a spectral color while purple is not even though they are almost similar?

Answer 1

When physicists talk about violet, they are talking about light with a wavelength between 380 and 450 nanometers. This is what a spectral color means -- it is a color you see when light of a single wavelength hits your eye.

When a physicist talks about purple, they are referring to the color interpreted by our brain when light with a red wavelength and blue wavelength hit our eyes together.

Purple and violet appear similar to us because of the way our brain combines blue and red together.