Edison's improved Electric Light technological breakthrough (On This Date in History)

from Writer's Almanac (American Public Media: Garrison Keillor):
It was on October 21, 1879 that the inventor Thomas Edison finally struck upon the idea for a workable electric light. People had been trying to make electric lights since the 1820s to replace kerosene and gas lamps, but they had chosen the wrong material for the filament: platinum. And Edison tried carbonized cotton thread, carbon filament that worked much better. He later improved the design with a tungsten filament that lasted longer and glowed brighter.
One of the effects of the invention of the electric light is that people sleep less than they once did. Before 1910, people slept an average of nine hours a night; since then, it's about seven and a half. Sleep researchers have shown in the laboratory that if people are deprived of electric light, they will go back to the nine-hour-a-night schedule.