History of LightEdison's greatest contribution to the problem of electric light was in filament design. He tried more than 6,000 alternative filament materials over two years and spent $40,000 conducting more than 1,200 experiments.
After testing substances from around the world, Edison found platinum to be effective. However, it was expensive and provided only limited efficiency as a practical filament. Finally, Edison tried carbonized cotton sewing machine thread. On Sunday evening, Oct. 19, 1879, Edison and his assistants powered up his cotton filament and took turns watching it around the clock. More than 40 hours later, it was still glowing and Edison knew he had the problem solved.
The invention of the electric light bulb was announced in the New York Herald on Dec. 21, 1879. In following weeks, gas stocks dropped dramatically while stock in the Edison Electric Company soared, eventually hitting $3,500 a share.
Light bulbs went on sale in 1880, and while the first full-scale introduction of the Edison lighting system was made in London at Holburn Viaduct in early 1882, the era of general electric illumination via a centralized municipal power source began on Sept. 4, 1882 at the Pearl Street Station, New York City. In response to a reporter's question Edison said simply, "I have accomplished all I promised."
Learn more about the evolution of lighting.