Edison’s bright idea
set quest for better bulb

In 1879, Thomas Edison heated a thin filament of carbon with electricity to capture nature's fire in a sealed glass jar and transform civilization as surely as the domestication of fire had done hundreds of thousands of years earlier.

Today's incandescent bulbs are not much different from Edison's original. They differ only in the material used for the filament and the contents of the bulb.

Edison's carbon filament was sealed inside a glass bulb from which the air had been evacuated to keep the hot carbon from bursting into flame. The filament in today's incandescent bulb is a coil of thin tungsten wire about three feet long that is wound into a spiral, wound again into a wider spiral, then sealed in an atmosphere of inert gases such as argon and nitrogen. Tungsten is used for the filament because it has a high melting temperature.

Even with the relative inertness of the tungsten, light bulbs "burn out," mostly from the surge of electrons in the wire when the light is turned on.

During the few microseconds that it takes for the filament to heat up to operating temperatures near 5,000 degrees Fahrenheit, it vibrates like a psychotic Slinky toy. After that, it continues to oscillate, but with less violence, under the continuously reversing surge of alternating current.

As much as they transformed us, incandescent lights are horribly inefficient, converting only about 10 percent of the electrical energy to visible light. The remaining 90 percent is radiated into the surroundings as heat in the form of infrared light.

A solution to the inefficiency problem began in 1857 when the French physicist Alexandre Becquerel began to investigate the phenomena of fluorescence and phosphorescence and conceived of the fluorescent light.

He would later discover radioactivity when he noticed a fluorescent material glowing in the presence of a uranium compound, but he never built the light.

Peter Cooper Hewitt, a U.S. scientist, patented the first mercury vapor lamp in 1901, which would prove to be the missing piece of the fluorescent tube, and also the prototype for the plasma lamp.

Mercury vapor street lamps dominated cities and freeways until the early 1980s. The light from the mercury vapor alone is strikingly bright, but unappealing in its blue-green color, so the mercury lamps were replaced by metal vapor lamps that produce a more pleasant but still harsh yellow-orange light.

To conquer the unpleasant color of the mercury vapor lights, several scientists worked to combine Becquerel's fluorescence and Hewitt's mercury vapor lamps. In 1927, the first fluorescent lamp was built in Germany by Edmund Germer and a race developed for first patent rights for a commercial version.

General Electric won the race, having bought Germer's original patent, and produced the first practical and viable fluorescent lamp. It debuted at the futuristic 1939 World's Fair and was a big hit. In 1941, the company obtained the "foundation" patent for what would be the prototype of today's commercial fluorescent light. In contrast to incandescent bulbs, fluorescent lights convert 60 to 75 percent of the energy to light, thereby "burning" cooler and saving energy.

Unfortunately, the color spectrum of fluorescent lighting is harsh and unpleasant to some. It emits a greenish hue that renders pigments in paint, print, clothing and cosmetics a slightly different color.

A modern fluorescent tube successfully combines a plasma core with a fluorescent coating to produce a cool and economical light.

The core is mercury vapor sealed in a glass tube at low pressure. High voltage electrical energy strips electrons away from the gaseous atoms to form a plasma. Eventually the energized electrons fall back to recombine with the atomic nuclei, emitting short wavelength light as they lose energy. Electrical energy is converted to light in an ongoing process of transforming gas to plasma and back again.

Each substance emits a unique color signature when in the plasma state, which is employed to colorful advantage in neon lights. Neon plasma by itself glows with a reddish-orange color, but varying the proportions of different mixtures of gases inside the tube produces a range of colors.

Glowing plasma is likewise the phenomenon behind the spectacular auroras that are produced when the low pressure gases in the thin ionosphere layer of Earth's atmosphere are energized by charged particles that have been ejected from the sun during a solar flare.

Miniature plasma tubes are now used in the design of flat-screen TVs and monitors, which illuminate microscopic colored pixels of glowing plasma to entertain us.

Fluorescence is named from the mineral fluorite, which is a naturally occurring calcium phosphate. When an atom within a fluorescent phosphate compound absorbs just the right amount of energy, it energizes, after which it trickles to lower energies.

A coating of fluorescent metallic phosphate on the inside of the fluorescent tube glows when a photon of light hits it, mimicking the emission of light by the excited plasma, by using light rather than electricity to excite the electrons, but not enough to strip them from their atoms.

A similar process lights the cathode ray tube (CRT) screens on a TV or a computer.

The propensity of phosphates to store and release energy is essential to the life processes as well. The compound ATP (adenosine triphosphate) is the primary chemical used to provide energy for heat, nerve electricity, light (as in fireflies), and muscle movement.

In the future, light emitting diodes (LED) will play a greater role in lighting as they become efficient enough to compete with compact fluorescent tubes.

We have come a long way in a little more than a century from using fire to produce light, and we are well on the way to producing virtually heat-free light. This we have done by using properties of energy and matter that span the spectrum of natural light-producing processes. All in the never-ending quest for a better light bulb.