What Is Light
Early Theories | Modern Theory

The earliest speculations about light were hindered by the lack of knowledge about how the eye works. The Greek philosophers from as early as Pythagoras, who lived during the 5th century BC, believed light issued forth from visible things, but most also thought vision, as distinct from light, proceeded outward from the eye. Plato gave a version of this theory in his dialogue Timaeus, written in the 3rd century BC, which greatly influenced later thought.

Some early ideas of the Greeks, however, were correct. The philosopher and statesman Empedocles believed that light travels with finite speed, and the philosopher and scientist Aristotle accurately explained the rainbow as a kind of reflection from raindrops. The Greek mathematician Euclid understood the law of reflection and the properties of mirrors. Early thinkers also observed and recorded the phenomenon of refraction, but they did not know its mathematical law. The mathematician and astronomer Ptolemy was the first person on record to collect experimental data on optics, but he too believed vision issued from the eye. His work was further developed by the Egyptian scientist Ibn al Haythen, who worked in Iraq and Egypt and was known to Europeans as Alhazen. Through logic and experimentation, Alhazen finally discounted Plato's theory that vision issued forth from the eye. In Europe, Alhazen was the most well known among a group of Islamic scholars who preserved and built upon the classical Greek tradition. His work influenced all later investigations on light.

What Is Light
Early Theories | Modern Theory