Light During daylight hours, people can see indoors by sunlight through the windows.

3.3.2 Light During daylight hours, people can see indoors by sunlight through the windows.

After the sun goes down on moonless nights, an alternative source of light is required for activities during the night, which is particularly long in northern winters. Fire was the oldest source of alternative illumination so that people could continue to do many useful things at night. Portable lights include torches, ceramic oil lamps, and wax candles. To shield the flame from the wind and rain, the lamp with enclosing glass housing was introduced. All such illuminations involved the risk of uncontrolled fire, especially when used in proximity to flammable substances such as curtains and Christmas trees. There have been many disastrous fires in his- tory, such as the Great Fire of London in 1666 and the Great Chicago Fire of 1871.

When a solid body is heated to elevated temperatures, it emits a broad range of electromagnetic radiations with wavelengths from the long infrared to the short ultraviolet. This radiation is barely bright enough to be visible at a temperature of 400

C. This “black body radiation” has a peak wavelength that becomes shorter or more energetic when the temperature is raised. For instance, the surface of the sun is at 5778K (or 5505

C) and the peak radiation of 502 nm is an orange color approx- imately at the center of the human visual spectrum. However, the much cooler wood

107 fire at 1200

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C would peak at 2000 nm, which is mostly in the invisible infrared heat range, thus giving more heat than light. Thus, if your desire a more efficient conver- sion of energy into light, you need a hotter body.

Much higher temperatures can be created by electricity, which is more effi- cient at producing illumination. Static electricity can be created by rubbing amber with silk, which was first observed by Thales of Miletus who suggested the word “electricity” from the Greek word for amber. Upon rubbing, the substances that become positively charged include skin, leather, glass, nylon, and wool; the sub- stances that become negatively charged include rubber, Teflon, and amber. Dynamic electricity can be created chemically by batteries or mechanically by moving magnets near electrical coils.

In 1791, Luigi Galvani published a report on “animal electricity” by using a frog’s leg connected to two different metals as electrodes. Based on this observa- tion, Alessandro Volta invented the Volta battery by replacing the moist frog tissues with a cardboard soaked in salt water. He also connected many voltaic cells in series and achieved a voltage of 50 V with a 32-cell pile.

Michael Faraday showed that electricity was created by chemical reactions of cations (positively charged) and anions (negatively charged) in a salt solution with metals. For instance, the familiar modern zinc–carbon battery has a central carbon rod as the positive terminal, surrounded by the electrolyte that is a paste of zinc chloride and manganese oxide dissolved in water, and the zinc casing as the nega- tive terminal. Electricity is generated when zinc is oxidized to become positively charged zinc ion and releases electrons, which can migrate by a copper wire to the carbon rod; the electron is then absorbed by ammonia and manganese oxide.

In 1802, Humphry Davy had a very powerful electrical battery, and he success- fully created an incandescent light by passing the electric current through a thin strip of platinum, which has an extremely high melting point of 2041K. However, this light was not very bright, and did not last long due to oxidation in the air. He also created an arc lamp in 1809, by passing electricity through two carbon charcoal elec- tric rods (melting point 4300K) connected to a 2000-cell pile. Many subsequent attempts were made to produce a partially evacuated enclosure for the electric rods, so as to reduce oxidation and increase longevity. Joseph Swan worked with carbon- ized paper filaments in an evacuated glass bulb and made a demonstration in 1860, but he had difficulty producing a good vacuum and an adequate supply of electricity.

The first practical incandescent light bulb was introduced by Thomas A. Edison (1847–1931) in 1878. He was the foremost American inventor and was called “The Wizard of Menlo Park,” which is the location of the first industrial research laboratory and held more than a thousand US patents in Edison’s name. He also built the first electric-power central station in New York City, as well as a distribution system to reach homes, business, and factories, which has been described in Chapter 2. Many other inventors preceded him in producing electric light bulbs, but they all had flaws such as an extremely short life, high cost, and requirement of high electric currents. None of the other inventors had the entrepre- neurial persistence and skill to overcome the flaws and to push their inventions into widespread use in society. Edison did not invent the first electric light bulb as is commonly thought, but he did invent the first commercially successful incandescent

108 CHAPTER 3 DOMESTIC LIFE: FOOD, CLOTHES, AND HOUSE

light that required the simultaneous distribution of electricity from power stations to homes.

When electricity flows through resistance, the rate of power consumption is of 10 W can be obtained by sending 100 V at 0.1 ampere or by sending 10 V at 1 A.

Edison decided to use the relatively low voltage of 100 V, which is safer but less energy efficient. His goal was to invent a lamp bulb to contain a filament, evacuated in very high vacuum to remove oxygen, which could burn for hundreds of hours.

From 1878 to 1880, Edison and his associates tested thousands of materials for their suitability as lamp filament. He declared, “I tested no fewer than 6,000 vegetable growths, and ransacked the world for the most suitable filament material.” He carbonized materials including bay wood, boxwood, hickory, cedar, flax, and bamboo. He contacted biologists and obtained plant fibers from the tropics. He even sparked a contest among his workers to contribute their beard whiskers for the experiment. After experimenting with platinum and other metal filaments, he returned to a carbon filament.

The first successful test was in 1879 for a carbonized cotton thread filament that lasted 13.5 h. His subsequent carbonized bamboo filament could last over 1200 h. This method of exhausting trial-and-error tests is called “Edisonian,” in contrast to having a theoretical understanding of and guidance for systematic plan- ning. Now that he had a practical incandescent light, the buyers of his electric lamps had to be ensured that there would be a convenient and inexpensive supply of elec- tricity. Edison concluded that he needed to solve a far more ambitious goal: to cre- ate a complete distribution system, from generating electricity in a central station to distributing it to numerous homes and businesses by cables.

The electric incandescent light bulb had a lot of advantages over other forms of illumination, and the most important competitors at that time were gaslight and the electric arc. Compared to gaslight, the enclosed incandescent electric light did not produce soot and smoke and greatly reduced the hazards of fire. The electric light was also much easier and quicker to turn on or off and involved no maintenance. But the biggest attraction was its much greater brightness over candles and lamps, espe- cially in public settings like theaters, sports stadiums, and major boulevards. The challenge was to persuade every home and business owner that it was worth the trou- ble to convert to this untried new technology, which Edison eventually won.

Throughout his career, Edison enjoyed a great deal of business success and founded many companies, including Consolidated Edison and Commonwealth Edison for electric power and the General Electric Company. He was named one of the most important people in the last thousand years. In 1983, the US Congress designated February 11, Edison’s birthday, as National Inventor’s Day. He died in 1931 at his home in West Orange, NJ.

Once people had electricity only for lighting, but other applications soon followed for numerous domestic uses, such as cooking, refrigeration, heating and air conditioning, cleaning, and entertainment. These labor-saving devices played a major role in the emancipation of women from long hours of daily chores in house- keeping, giving them precious time to combine domestic duties with participation in meaningful careers. Without a reliable electric supply, we could not have electric

109 motors for elevators; without elevators, skyscrapers and the dramatic skylines of the

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world’s major metropolises would not exist. In a modern office and factory, all the machinery operates by electricity.

Incandescent lights will eventually be phased out, as they are only 2% efficient in converting input electrical energy into output visible light, while the rest of the energy goes into heat and infrared radiation. Higher efficiency comes at a higher temperature. But even at the 7000K found at the surface of the sun (although there is no known material that remains solid at that temperature), the overall effi- ciency is no more than 14%. The way to produce light at higher energy efficiency is to avoid the method of black body radiation that generates a very broad wavelength distribution and to find ways to produce light only in the visible range. One current alternative is the compact fluorescent lamps (CFL), which have a rated lifespan

10 times higher and use only 20–33% of the power to produce the same brightness as incandescent lamps. In the CFL, electric current flows through the magnetic or electronic ballast into a tube filled with mercury vapor, causing it to emit ultraviolet light. The ultraviolet light then excites a phosphor coating on the inside of the tube, which emits visible light. Another alternative is the light emitting diode (LED) lamps, which are semiconductor diodes where electrons combine with holes to release energy in the form of light in an effect called electroluminescence. They are available in numerous colors and have found applications in electronic display pan- els for equipment, calculators, and watches. LEDs are very energy efficient, but the light output is low and the manufacturing cost is more than 10 times higher.