Edison Perfects Light Bulb

October 21, 1879

Thomas Edison perfects the first commercially practical incandescent light bulb. Using a filament of carbonized cotton thread, his first attempt at this design results in a bulb that lasts about 13.5 hours before burning out. He later extends the life of the bulb to 40 hours. Edison’s successful design came only after he had tested over 6,000 different vegetable fibers during a span of over 18 months running 1,200 experiments and spending $40,000.