History
A carbon filament lamp using chlorine to prevent darkening of the envelope was patented[1] in 1882, and chlorine-filled "NoVak" lamps were marketed in 1892.[2] The use of iodine was proposed in a 1933 patent,[3] which also described the cyclic redeposition of tungsten back onto the filament. In 1959, General Electric patented[3] a practical lamp using iodine.[4]