Visible Light and the Colors of a Rainbow

A very small portion of the electromagnetic spectrum is actually visible to the human eye. Red light has a wavelength of approximately 380 to 400 nanometers. As we move up the spectrum, the wavelength decreases. Violet has a wavelength of approximately 700 to 750 nanometers. The length of the wave determines how much it bends when it enters or exits a prism. The longest wavelength (red) bends the most. Orange bends a little less, followed by yellow and on down the line.

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That's why the order of color in the rainbow does not vary. Red (the longest wavelength) will always be on top with violet (the shortest) on the bottom.