The phrase “She would rather light a candle than curse the darkness” came from a Eulogy given by Adlai Stevenson for Elanor Roosevelt. This is of course a metaphor, as the bringing of light refers to bringing knowledge to an unknowing hence dark world. Aphorisms aside, let’s be literal. Let’s talk about lighting technology.
There is good evidence that one of our ancestors, Homo erectus learned to control fire close to a half a million years ago. Fire provided heat, protection from predators, and light to extend the day into night. The campfire of Homo erectus was wood and provided much more light than heat. Light was a byproduct.
Technology expanded light production with the creation of oil lamps about six thousand years ago. Made from clay, lamps were found at numerous sites, and depending on location these were fueled by animal fat, vegetable oil or even petroleum oil from natural seeps. The related technology of candles came later, possibly originating in China about three thousand years ago. The Chinese candles were made of whale fat. Other materials for candles include tallow, beeswax, and contemporaneously paraffin, a solid petroleum derivative.
Kerosene lanterns, still in use in much of the world were common by the nineteenth century. Gas lamps, using gas as opposed to liquid developed about the same time and were popular as stationery light sources, e.g, street lamps.
All these light sources share one property – combustion. Burning something, combustion, is an exothermic process. Burning gives off heat, and if you give off enough heat you get (visible) light. Thomas Edison recognized that if you get something hot enough, whether burning or not, you get light. His invention, the incandescent light bulb (ILB) employing electricity, revolutionized lighting and has illuminated the modern world since the start of the twentieth century.
The new revolution in lighting technology is the production of light sources much more efficient than incandescent bulbs. ILBs work by the heat, then light produced by resistance to the flow of electricity through the Tungsten filament. But it is an astoundingly inefficient process when illumination is the objective. Only about five percent of the energy consumed by an ILB produces light, the remainder is given off in the form of heat.
Luminous efficacy is measured by the product of the amount of light measured in lumens, divided by the energy to power it measured in watts. The luminous efficacy of an ILB is sixteen lumens per watt.
ILBs are cheap to produce but waste energy. More efficient are compact fluorescent bulbs (CFB). These have a luminous efficacies of about fifty to sixty. They are therefore cheaper to operate but have a few drawbacks; they take time to reach full illumination especially at low temperatures, they aren’t dimmable, and they contain small amounts of Mercury which complicates disposal.
The most promising entry to inexpensive lighting are Light Emitting Diode light sources. They are everywhere already in electronic technology in the form of various indicator lights. These LEDs have now been ganged in groups to produce illumination with efficiencies of over one hundred.
LEDs don’t suffer from the deficiencies of other bulbs; they are very efficient, “instant on”, dimmable, cool to the touch, non toxic, and will become even more efficient as they are developed. The future for LED lighting is bright indeed.