The formal study of light began as an effort to explain vision, which early Greek thinkers associated with a ray emitted from the human eye. A surviving work with Euclid, the Greek geometrician, laid out basic concepts of perspective, using straight lines to show why objects at a distance appear shorter or slower than they actually are.
Eleventh- century Islamic scholar Abu Ali al Hasan ibn al-Haytham known also by the Latinized named Alhazen- revisited the work done by Euclid & Ptolemy and advanced the study of refraction, reflection, and color. He argued that light moves out in all directions from illuminated objects and that vision results when light enters the eye.
Thanks to better glass- grinding techniques in the late 16th and 17th centuries, researchers including Dutch mathematician Willebrord Snel noticed that light bends as it passes through a lens or fluid. Although his contemporaries believed that the speed of light to be infinite, Danish astronomer Ole Romer in 1676 used telescopic observations of Jupiter’s moons to estimate the speed of light as 140,000 miles per second. Around the same time, Sir Isaac Newton used prisms to demonstrate that white light could be separated into a spectrum of basic colors. He believed that light was made of particles, whereas Dutch mathematician Christiann Huygens described light as a wave.
The arrival of quantum physics in the late 19th and early 20th century prompted the next leap in understanding light. By studying the emission of electrons from a grid hit by a beam of light- known as photoelectric effect- Albert Einstein concluded that light came from what he called photons, emitted as electrons changed their orbit around an atomic nucleus and then jumped back to their original state. Though Einstein’s finding seemed to favor the particle theory of light.
Later an experiment of optics showed that light and matter itself behave both as waves and as particles.