Sir David Brewster KH PRSE FRS FSA Scot FSSA MICE was a British scientist, inventor, author, and academic administrator. In science he is principally remembered for his experimental work in physical optics, mostly concerned with the study of the polarization of light and including the discovery of Brewster's angle. He studied the birefringence of crystals under compression and discovered photoelasticity, thereby creating the field of optical mineralogy. For this work, William Whewell dubbed him the "father of modern experimental optics" and "the Johannes Kepler of optics."

In materials science, photoelasticity describes changes in the optical properties of a material under mechanical deformation. It is a property of all dielectric media and is often used to experimentally determine the stress distribution in a material.