Spectrum

The spectrum of colors contained in sunlight was discovered by Sir Isaac Newton in 1666. In fact, the word "spectrum" was coined by Newton to describe the phenomenon he observed. In a report of his discovery published in 1672, Newton described his experiment as follows:

"I procured me a triangular glass prism,... having darkened my chamber and made a small hole in my window shuts, to let in a convenient quantity of the sun's light, I placed my prism at this entrance, that it might be thereby refracted to the opposite wall. It was at first a pleasing divertissement to view the vivid and intense colours produced thereby." A diagram of Newton's experiment is illustrated here. Newton divided the spectrum of colors he observed into the familiar sequence of seven fundamental colors: red, orange, yellow, green, blue, indigo, violet (ROYGBIV). He chose to divide the spectrum into seven colors in analogy with the seven fundamental notes of the musical scale. However, both divisions are completely arbitrary as the sound and light spectrum each contain a continuous distribution (and therefore an infinite number) of "colors" and "notes."

Figure 1. A diagram of Newton's 1666 spectrum experiment. Illustration by Hans & Cassidy. Courtesy of Gale Group.

Figure 2. Black body emission spectra for sources at three different temperatures, corresponding to the Sun, a 500-watt incandescent light bulb and a candle. Illustration by Hans & Cassidy. Courtesy of Gale Group.