Selenium was first identified in 1817 by John Jacob Berzelius, a chemistry teacher in Stockholm. Berzelius and his colleague J. G. Gahn were studying a method of producing sulfuric acid in lead cameras when they observed residues of a substance with a very intense scent in the bottom of the camera. At first, they thought it was tellurium. However, a more careful analysis revealed that there were no residues of this element, in spite of its identical properties. To this new substance was given the name selenium, term that derives from the Greek selene (Moon), for analogy with tellurium, deriving from tellus (Earth).
For many years, selenium was just a laboratory curiosity, with no practical application. In 1873, Willoughby Smith discovered that the selenium electrical resistance decreases with increase intensity of incident light. This discover allowed for the development of photoelectric cells and other light sensors.