Johann Wilhelm Ritter discovered ultraviolet light in 1801 during an experiment with silver chloride. His discovery came approximately 1 year after William Herschel discovered infrared light.
In 1801, Johann Ritter decided to expand on Herschel's light experiments in order to determine if invisible light existed beyond the violet end of the spectrum. He found that silver chloride turned black when exposed to sunlight, and he went on to investigate the reaction when the substance was exposed to different colors of light by using sunlight through a prism. He found that the silver chloride reacted more noticeably as he approached the violet end of the spectrum. He moved the substance beyond the violet end into a region with no visible light, and this generated an intense reaction. Ritter's Chemical Rays were later named ultraviolet light. The light has since been classified into three divisions: UV-A, UV-B and UV-C, with UV-C being the most dangerous.