The discovery that light is an electromagnetic wave is attributed to James Clerk Maxwell. In the 19th century, Maxwell formulated a set of equations known as Maxwell's equations, which mathematically described the behavior of electric and magnetic fields. Through his equations, Maxwell demonstrated that oscillating electric and magnetic fields can propagate through space as waves and that these waves travel at the speed of light.
Maxwell's groundbreaking work culminated in his publication of "A Dynamical Theory of the Electromagnetic Field" in 1865, where he presented his unified theory of electromagnetism. This theory showed that electric and magnetic fields are interconnected and that they can give rise to self-propagating waves, which he termed electromagnetic waves. Maxwell's equations not only provided a mathematical framework for understanding the behavior of electromagnetic waves but also predicted the existence of electromagnetic radiation beyond the visible spectrum.
Later experiments by Heinrich Hertz in the late 19th century provided direct experimental evidence of the existence and properties of electromagnetic waves. Hertz successfully generated and detected radio waves, which are a form of electromagnetic radiation, and his experiments confirmed Maxwell's theoretical predictions.
The work of Maxwell and subsequent experimental verification by Hertz laid the foundation for our understanding of light as an electromagnetic wave, revolutionizing the field of physics and paving the way for significant technological advancements in areas such as communication and electronics.