Does red light or blue light have a longer wavelength? how do you know?

Red has a longer wavelength than blue, The visible colors from shortest to longest wavelength are, violet, blue, green, yellow, orange, and red. Ultraviolet radiation has a shorter wavelength than the visible violet light. Infrared radiation has a longer wavelength than visible red light. The white light is a mixture of the colors of the visible spectrum.

Blue light is earlier on the electro magnetic spectrum