LIGHT BULB

SINCE early man collected firewood to illuminate his cave, history has been a long search for better light sources. Thousands of years ago, candles were invented in Egypt and Crete, and oil lamps in Babylon. The light they provided was steadier and more controllable, but over the centuries they remained prohibitively expensive. Then something changed. That something was the light bulb. By 1900, for the money you’d earn in a week of hard labour, one of Thomas Edison’s carbon filament bulbs offered ten days of continuous illumination, 100 times as bright as a candle. By 1920, with the advent of tungsten filament bulbs, one week’s labour would pay for more than five months of continuous light; by 1992, thanks to compact fluorescent bulbs, one week’s labour would buy you enough of them to give you constant light for 52 years. And modern LED lights continue to get cheaper and cheaper. No wonder the lightbulb is still the visual cliche for ‘new idea’ — literally, the icon for invention.