Johann Ritter is best known for his discovery of ultraviolet light in 1801. A year earlier, in 1800, William Herschel discovered infrared light. This was the first time that a form of light beyond visible light had been detected. After hearing about Herschel's discovery of an invisible form of light beyond the red portion of the spectrum, Ritter decided to conduct experiments to determine if invisible light existed beyond the violet end of the spectrum as well.
In 1801, he was experimenting with silver chloride, a chemical which turned black when exposed to sunlight. He had heard that exposure to blue light caused a greater reaction in silver chloride than exposure to red light. Ritter decided to measure the rate at which silver chloride reacted when exposed to the different colors of light. To do this, he directed sunlight through a glass prism to create a spectrum. He then placed silver chloride in each color of the spectrum. Ritter noticed that the silver chloride showed little change in the red part of the spectrum, but increasingly darkened toward the violet end of the spectrum. This proved that exposure to blue light did cause silver chloride to turn black much more efficiently than exposure to red light.
Johann Ritter then decided to place silver chloride in the area just beyond the violet end of the spectrum, in a region where no sunlight was visible. To his amazement, he saw that the silver chloride displayed an intense reaction well beyond the violet end of the spectrum, where no visible light could be seen. This showed for the first time that an invisible form of light existed beyond the violet end of the spectrum. This new type of light, which Ritter called Chemical Rays, later became known as ultraviolet light or ultraviolet radiation (the word ultra means beyond). Ritter's experiment, along with Herschel's discovery, proved that invisible forms of light existed beyond both ends of the visible spectrum.
After his discovery of ultraviolet light, Ritter continued to do research and became increasingly interested in electrical experiments. He had discovered the process of electroplating earlier in 1800. In 1802, he invented the dry cell battery and later developed a storage battery in 1803. In 1804 he began work at the Bavarian Academy of Science in Munich where he remained until his death in 1810 at the age of 33.
We now use ultraviolet light in many ways. In medicine, ultraviolet light is used to help kill bacteria and viruses and to sterilize equipment. It is used to disinfect products and containers. In science, ultraviolet light is used to study atoms, and to learn about the warmer objects in space. Several animals, including birds, butterflies and other insects can see ultraviolet light.