Discovery of Infrared Radiation

Background. Infrared radiation is electromagnetic radiation with wavelengths longer than those of visible light but shorter than microwaves. The infrared spectral band begins with waves just longer than those of red light, the longest waves in the visible spectrum, and is by definition invisible to the human eye.

The Discovery. In early 1800, Herschel was testing different filters to pass sunlight through and noticed that filters of different colours seemed to generate varying amounts of heat. In the course of these investigations, he discovered infrared radiation, establishing it as invisible radiation lower in energy than red light through its effect on a thermometer.

Publication and Attribution. Herschel published his results in 1800 before the Royal Society of London, and his original paper from that year announced the discovery of infrared light. The discovery of infrared radiation is ascribed to William Herschel, the astronomer, in the early 19th century.