Thomas Edison of the Edison patent to charge a more reasonable rate for the use of the Edison patent rights and lowering the price of the electric lamp. On October 8, 1883, the US patent office ruled that Edison's patent was based on the work of William E. Sawyer and was, therefore, invalid. Litigation continued for nearly six years, until October 6, 1889, when a judge ruled that Edison's electric light improvement claim for "a filament of carbon of high resistance" was valid. To avoid a possible court battle with Joseph Swan, whose British patent had been awarded a year before Edison's,
Automatic lamp changer with high precision. The device automatically detects when the currently active lamp has ceased to function and moves the next lamp into place. The automatic lampchanger was invented by Charles Wallace and patented in 1928. This original model held two headlight lamps from a Model T automobile. The United States Lighthouse Service had these in common use by the 1930s, as they moved to convert all navigational lights to electricity. Lamp changers in current use may have two, four, or six lamps and use either a spring-loaded mechanism or an electric motor to change lamps when required. They are used