File:Tesla tube lights at Columbian Exposition 1893.jpg

English: Display of gas discharge tube lamps by Serbian American inventor Nikola Tesla at the Columbian Exposition in Chicago in 1893. Similar to modern neon lights, they consist of glass tubes filled with various gases at low pressure with a metal electrode sealed into each end. When a high voltage was applied between the electrodes, they lit up with different colors. Tesla did not invent these gas discharge lamps; called Geissler tubes, they were invented by German glassblower Heinrich Geissler in 1857. The point of the exhibit was that some of these were wireless lamps; when a nearby Tesla coil was turned on, the oscillating electric field would ionize the gas in the tube and it lit up without wires. Tesla was trying to develop a wireless lighting system, in which an electrode on the walls of a room would power lamps anywhere in the room, which did not have to be plugged in. Although Tesla had a demonstration system in his New York lab, he never produced a practical system.

Caption from Electrical Experimenter article: "This photograph represents a collection of Tesla's wireless lamps, such as he proposes to use in lighting isolated dwellings all over the world from central wireless plants. The two lamps at either corner of the bottom were illuminated, owing to the fact that a high frequency oscillator was in operation some distance away when this photograph was being taken. These tubes were filled with various gases for experimental research work in determining which was most efficient."