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How did Isaac Newton use prisms to study white light and color?

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A horizontal gradient bar displays the visible light spectrum from violet to red, labeled with corresponding frequency in terahertz, wavelength in nanometers, and photon energy in electron volts. — light When white light is spread apart by a prism or a diffraction grating, the colours of the visible spectrum appear. The colours vary according to their wavelengths. Violet has the highest frequencies and shortest wavelengths, and red has the lowest frequencies and the longest wavelengths.

Isaac Newton revolutionized the study of optics by challenging the long-held belief that white light was simple and homogeneous. Through experiments conducted in 1665 and 1666, he demonstrated that white light is actually a heterogeneous mixture of colors.1

By projecting a narrow beam of light through a prism onto the wall of a darkened chamber, Newton observed that the light dispersed into a spectrum. He concluded that this phenomenon was not a modification of light, as previously theorized by thinkers like Aristotle and Descartes, but rather an analysis of light into its simple, immutable component parts.1

Newton discovered that individual rays of light refract at distinct angles, which causes the separation of colors. This process, known as chromatic dispersion, occurs because the speed of light in a medium like glass varies with its wavelength. Because he believed this dispersion—which leads to chromatic aberration—could not be eliminated in lenses, he invented the reflecting telescope to avoid the color distortion inherent in refracting systems.12