When cave dwellers hunkered around the fire pit, fire was a source of heat as well as light and there was nothing to read so the low luminous efficiency did not matter.
The visible light output of fire ranges from 0.004 percent to 0.3 percent of the energy consumed.
The incandescent bulb was a major improvement, but still radiated in the visible spectrum only about 3 percent of the energy it consumed. Although incandescent light has a pleasant “golden” spectrum, wasting 97 percent of the energy as heat is, well, wasteful.
Fluorescent tubes offer efficiencies upward of 9 percent, still wasting more than 90 percent of the energy. Due to the necessity of ballast to start the lights and the poor color rendering, the lights did not quite fill the bill.
Modern compact fluorescent lights (CFL) have mostly solved the ballast problem and the color-rendering problem, and are set to replace all incandescent bulbs in coming years, but still top out at 12 percent.
For decades, scientists looked for the secret to bioluminescence, the cold light given off by glowworms, fireflies and aquatic critters. They have made some breakthroughs.
In 1985, the cloning of the luciferin photoprotein (aequorin) and luciferase enzyme (firefly luciferase) heralded a major advance in biological research. The 2008 Nobel Prize in chemistry was awarded for the Green-Fluorescent Protein (GFP) that was cloned in 1992.
Today, many rapid and effective diagnostic tests as well as some fun applications flood the marketplace including luminous beer and light sticks for guiding aircraft, entertaining concertgoers, and aiding night fishing and camping.
Gene tags made from GFP can track proteins to study their localization and behavior within a cell. It can also make mice glow in the dark.
But with only weak output, even with the knowledge of many different luciferins and luciferases, the prospect for bioluminescent lighting is not good in the near future.
Developed in the 1990s, thin film luminescent lights (TFEL) use phosphors sandwiched between a conductor and dielectric and a transparent conductor that lets the light escape through one side. In this electronic sandwich, electrons flowing between the two conductors light the phosphors much in the same way that electrons in a fluorescent tube excite the phosphors on the inside of the tube.
TFELs are used for luminous watch faces and electronic control panels, but like bioluminescence are too dim for area lighting.
The latest addition to area and decorative lighting is the light-emitting diode (LED). A diode is a semiconductor that is treated like a transistor to create positive “holes” of electric charge within its crystal structure. Electrons from the power supply of certain energies fall into holes, gaining a quantum of energy in the process.
When they lose energy and come out of the holes, the electrons emit radiation that corresponds in wavelength to the energy of the holes. Different semiconductors and doping materials produce holes of different energy, which allows for LEDs of different colors.
Color rendering is less than satisfactory in the cold LED lights, but with efficiencies up to 40 percent, the prospects are bright for better lighting in the future.
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Richard Brill is a professor of science at Honolulu Community College. His column runs on the first and third Friday of the month. Email questions and comments to brill@hawaii.edu.
