About 300 years ago, Sir Isaac Newton saw a beam of sunlight through a glass prism. He discovered that light is made up of a spectrum of seven distinct visible colors. This spectrum of colors always appears in the same order. You can see this color spectrum (Red, Orange, Yellow, Green, Blue, Indigo, Violet and all the colors in between) when you look through your Rainbow Symphony Diffraction Grating Glasses. There are two color ranges that are not visible to our eyes in this spectrum: below red is infra-red and above violet is ultra-violet. In a rainbow after a rainstorm this same color spectrum appears in the same order. Rainbows are created when sunlight passes through rain drops that act as millions of tiny prisms.
The colors of the rainbow are the "basic spectrum" from which all the light we see is composed. Although these colors merge smoothly, they are sometimes divided into red, orange, yellow, green, blue, indigo and violet (and other names). Just as various musical sounds contain the tones of the basic scale (often combinations of tones, e.g. chords), so any colored light is made up of its "spectral components. "
Isaac Newton showed that not only can a triangular prism separate a beam of sunlight into rainbow colors (that had already been known), but also that, when a second prism brings the different colors together again, white light is once more obtained. Therefore white light is a combination of all the rainbow colors, and the prism separates its colors because the angle by which a beam of light is bent, when it enters glass, differs from one color to the next.
The principles of diffraction gratings were discovered by James Gregory, about a year after Newton's Prism experiments, initially with artifacts such as bird feathers. The first man-made diffraction grating was made around 1785 by Philadelphia inventor David Rittenhouse, who strung hairs between two finely threaded screws. This was similar to notable German physicist Joseph von Fraunhofer's wire diffraction grating in 1821.