Thomas Edison did not invent the incandescent light bulb. Twenty three different light bulbs were developed before Edison's. The principle was to pass an electric current through a filament powerful enough to cause it to glow without combusting. Among the pre-Edison pioneers of electric lighting, Sir Humphrey Davy created the first electric arc lamp in 1809. Warren De la Rue designed the first incandescent light in 1820. La Rue's design depended on a platinum filament, far too expensive for any practical application. Over half a century of experimentation focused primarily on finding an inexpensive filament that could produce electric light for any useful length of time.