Early Lighting

The various inventors of early electric lights knew essentially of two ways to produce illumination: by running currents through wires or fibers until they glowed, or discharging arcs between electrodes. Arcs have never been suitable for general lighting purposes, though they are intense sources. As to filaments, most materials don't behave well when heated near their melting points. They will oxidize, unless surrounded by vacuum or inert gas, and they destroy themselves through internal stress.

Discovering durable filaments, however, does not solve a deeper problem in the physics of incandescent bodies, which is to say they radiate a broad spectrum of energies, or frequencies. In the case of a common 60-watt bulb, no more than a few percent of the total radiated energy is in the light-frequency range; most of the remainder is lost as heat. It would be far more efficient to excite electrons (which are responsible for all the emissions) more selectively, instead of heating everything up until there's enough brightness to read by.

It had occurred to many early investigators of electricity, when its properties and nature were still quite puzzling, to run currents through or into substances just to see what happened. As improved vacuum pumps, better glass manufacture, and higher-frequency sources were invented, the search moved away from brute incandescent effects. Alexandre-Edmond Becquerel was perhaps first to collide a tiny stream of electrons (inside an evacuated tube) with a fluorescent coating, resulting in a relatively cold glow (1859). Fluorescent substances emit light immediately when excited by high voltage or ultraviolet energy.

Tesla's Inventions & Innovations

Credit for the first practical phosphorescent lamp belongs to Tesla—phosphorescent substances are slower to emit light than fluorescent ones, and they continue to glow for some time after the power is turned off.

Tesla's earliest lighting inventions had operated as conventional filament or arc devices, but with high-frequency currents supplying power. As he quickly discovered, such currents could be made to bring diffuse gases to incandescence, or cause light emission in various solid materials. His innovations in this field, though influential and disclosed in a series of celebrated lectures, were seldom patented.

Inasmuch as Tesla created for himself more powerful apparatus, to operate at higher frequency and voltage than was available to anyone else, he was capable by 1890 of generating fields that would light up, without any wires, phosphorescent tubes across his laboratory. (His assistants recall these lamps strewn casually around the lab and working by their eerie green glow.) The energy is just long wavelength radio—from Tesla's high-frequency generators—though in this case the signal is very strong, strong enough to be useful as power, rather than as a means of communication.

His first demonstrations of wireless power—presented always with superb showmanship—left the electrical profession agog. And the general public, exposed to these mysteries at Tesla's lighting exhibit in the Columbian Exposition of 1893, came away with the impression that an age of scientific miracles was dawning.

Further Lighting Developments

It's easy to understand the fascination pioneers such as Becquerel, Tesla, Wilhelm Roentgen, P.A. Lenard, and J.J. Thompson felt in their personal work with electromagnetism inside curiously shaped glass worlds. New lighting was only the first result. Thompson, in 1897, identified the streaming "cathode rays" responsible for so many diverse effects as electrons. At ever-higher energies, where electrons occasionally run into nuclei, Roentgen and Tesla found electrons were jettisoning very powerful photons indeed, called x-rays. And John Fleming discovered a useful way of controlling electric currents inside a vacuum tube (the first electronic diode; 1904), inaugurating modern electronics.