500,000 years ago - Homo erectus generated light with open fires 40,000 years ago - fat-burning stone lamps appear 2000 BC - Babylonians use sesame oil lamps Middle Ages - tallow candles become widespread in Europe late 18th century - coal-gas lamps appear in homes and streets 1930s - fluorescent tubes and sodium vapor lamps 1980s and 1990s - compact fluorescent bulbs and halogen lamps > As we moved from open fires to tallow candles and then to compact fluorescent bulbs, the efficiency of light-making rose steadily. William Nordhaus, an economist at Yale, has studied this trend. The model of an enterprising academic, he couldn’t find published information on the lightproduced by open fires and sesame oil lamps, so he built his own fire, obtained his own Roman lamp (similar to a Babylonian lamp), and made his own light measurements with a Minolta illuminance meter. He concluded that the efficiency of light production—measured in terms of light output per unit of energy input—has improved by a factor of thirty thousand from the cave-dwellers’ open fire to today’s compact fluorescent light bulb. Since the time of the Babylonian sesame-oil lamp, efficiency has improved twelve-hundredfold. > His own experiments with fires and lamps “provide evidence that an hour’s work today will buy about 350 thousand times as much illumination as could be bought in early Babylonia.” He continues: “One modern one-hundred-watt incandescent bulb burning for three hours each night would produce 1.5 million lumen-hours of light per year. At the beginning of the [nineteenth] century, obtaining this amount of light would have required burning seventeen thousand candles, and the average worker would have had to toil almost one thousand hours to earn the dollars to buy the candles.” Source: [[Reference Notes/The Ingenuity Gap|The Ingenuity Gap]]