Turn on the light

Today we just flick a switch, but it wasn't that easy to create light on demand in the past.

If you've ever been camping you know how nice it is to have a campfire at night. It keeps you warm, cooks your food, and gives light so you don't trip over anything. Fire was the earliest source of light for humans, and for centuries fire in different forms lighted the way.

While the cooking fire also lighted their dwellings, people soon learned to make a portable light source, a torch. The first torches were probably sticks tied together and lighted on one end. Later, people learned to soak rags in oil (vegetable oil or animal fat - petroleum wasn't widely used until the 1860s) and tie them to the end of the stick to make a longer-lasting light source. The oil soaked into the rag through a process called capillary action, where a liquid seeps into the tiny spaces in fiber or thread. This action proved very useful in the next big development in making light - the wick.

Around 70,000 BC, people began using lamps. The first lamps were probably hollow rocks or shells filled with moss or something else that soaked up animal fat. As people developed pottery, they created lamps with a bowl and a spout. The oil was held in the bowl while a wick placed in the spout drew - through capillary action - oil along the spout where it burned. While most of the flame came from the burning oil, the wick gradually burned as well. Lamps were often made of clay or bronze, but sometimes were made of gold, silver, glass, or stone. Handles were soon added to make them easier to carry. Lids were added to keep the oil clean.

The next great lighting improvement came with the development of the candle. Light on a string has long been used in Africa, where oily nuts were strung on twigs and burned to make light. Around 3000 BC the Phoenicians and Etruscans began using wax candles, coating the string with tallow (animal and vegetable fat) to form a cylinder. Capillary action works even uphill, so the string would pull melted wax upward from the top of the candle toward the flame.

Beeswax candles became an important source of light in the Middle Ages. Oil lamps tended to be smoky and could quickly make lighting a room unpleasant. Beeswax candles were expensive, though, so families often relied on the cooking fire to light their homes.

The early Chinese and Japanese got their candle wax from insects and seeds. In India, candles used in temples were made from wax skimmed from boiling cinnamon. The earliest "candles" in North America were used by native Americans during the first century. An oily fish was wedged into a forked stick and ignited. American colonists discovered that a sweet-smelling candle wax could be made by boiling the berries of bayberry bushes. It was a tedious process, however, as it takes 1-1/2 quarts of bayberries to make a candle.

During the 18th century, Swiss chemist François-Pierre Ami Argand made a number of improvements to the oil lamp. In 1783 he created a hollow wick that provided more air for the inside of the flame. Then he created a glass cylinder that worked as a chimney to improve the airflow outside the flame. The increased flow of oxygen made the flame burn more brightly. He also invented a way to raise and lower the wick to change the size of the flame. The Argand lamp holds a special place in the history of education. Can you guess why? It produced enough light for people to be able read at night. This brought many opportunities for those who had to work all day but still wanted to learn.

The next major step in lighting was gaslight, which burned manufactured natural gas instead of oil. Some of the first gaslights were installed in 1806 in a cotton mill in Manchester, England. By 1830, thousands of gas lamps were in use in London. Moving carriages, including those in the London Underground, carried a gas supply in bags on the roof. Gas produced a more even light than candles or oil lamps, but they had a tendency to explode when not handled carefully. Inventors kept looking for a better light source.

In 1809, English chemist Humphrey Davy created the first arc lamp. He used a powerful battery to "jump" a current across two charcoal strips held slightly apart. The current produced a bright light that eventually consumed the charcoal strips. Arc lamps are bright - too bright, in fact. Women hid behind their umbrellas to avoid them. Too bright for indoor use, they were a good source of street lighting well into the 20th century.

Most modern lighting evolved from the incandescent bulb, which finally did away with open flame, smoke, and burning gases. The problem that challenged most inventors during the 1800s was to find a practical material for the filament - the small thread that glows as electricity goes through it. Both Thomas Edison and Joseph Swan, a Briton, created bulbs with carbon filaments in 1879. They lasted only a few hours. Edison came up with bamboo filaments in 1880 that lasted up to 1,200 hours.

Other lamps were also being developed that used a glowing, not burning, gas to create light. In 1902, French engineer Georges Claude applied an electrical discharge to a tube filled with neon gas to produce light. In 1923, his company sold two neon lights reading "Packard" to a car dealership in Los Angeles. People called the early signs "liquid fire," and neon lights quickly became popular throughout the United States. Fluorescent lights, introduced at the New York World's Fair in 1938, were first called mercury vapor lamps. Many now use argon gas.

While many inventors worked to improve how we light up a room, others wanted to amplify or focus the light in specific directions.

Two Englishmen, Goldsworthy Gurney and Thomas Drummond, are jointly credited in the 1820s with discovering that burning quicklime produces a brilliant light. In 1826 this type of light, combined with a curved reflector, sent a signal that was seen 95 miles away. This focused "limelight" quickly became a popular lighting method in theaters, coining the phrase "in the limelight." Gurney also intensified the light from an oil lamp by introducing oxygen into the center of the flame. He used this "Bude light" (named for the seaside town where he lived) to light his entire castle by using prisms and mirrors to distribute the light into every room.

A more intense form of light was still to come, however. In 1960, American physicist Theodore Maiman built the first laser. (The name stands for Light Amplification by Stimulated Emission of Radiation.) Lasers use energy and reflectors to intensify light into an intense beam that can travel long distances without dispersing or scattering. Lasers can cut through diamonds and bounce off the moon and return to earth. They also "play" your DVD.

But for all the modern developments in light, nothing beats the reassurance of burning wood when you're spending the night at a campground.

Seeking the 'why?' of light

Scientists and inventors have long tried to understand the principles behind light and how it's produced. One theory that was popular for almost a century was the "phlogiston" theory.

In the early 1700s, German chemist and physician Georg Ernst Stahl proposed that all flammable objects contain phlogiston (floh JIHS tuhn). As objects burned, the phlogiston was given off. Air absorbed the phlogiston, which is why (according to the theory) fire needs air.

Plants remove phlogiston from the air, which is why they burn when dried. Eighteenth-century English chemist Joseph Priestley called oxygen "dephlogisticated air" because it "absorbed" great quantities of phlogiston. (Can you see how he might think that oxygen was "absorbing" lots of phlogiston? Pure oxygen makes a fire burn rapidly.)

In the late 1700s, French chemist Antoine Lavoisier began to study combustion. He carefully measured the weight of objects and air involved in the burning process. Based on his findings, he proposed a new theory of combustion and renamed dephlogisticated air "oxygen." Lavoisier helped explain the process of burning, but more study was needed to explain how light is made.

Modern theories explain light in terms of photons, which are emitted by atoms as they release extra energy. The extra energy is supplied by the heat or electricity applied to create the light.

Scientists admit they don't fully understand everything about light. So who knows? We may hear some different theories next.

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