Red is the color on the visible electromagnetic spectrum that has the longest wavelength. The wavelength of red on the spectrum is 700 nanometers. Conversely, the color with the shortest wavelength is violet at 400 nanometers.
Although not visible to the naked eye, ultraviolet radiation falls directly below visible violet on the spectrum. Similarly, infrared radiation is found directly above visible red on the spectrum. Wavelengths below 400 nanometers are too short for human beings to see, and wavelengths above 700 nanometers are too long for human beings to see. In considering the spectrum as a whole, radio waves are the longest, while gamma rays are the shortest.