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,
Henry Woodward (inventor) fully effective and sufficiently promising; they sold their to Thomas Edison. Thomas Edison obtained an exclusive license to the Canadian patent. Thomas Edison developed his own design of incandescent lamp with a high resistance thin filament of carbon in a high vacuum contained in a tightly sealed glass bulb which had a sufficiently long service life to be commercially practical. The relationship of the Woodward/Evans work on the incandescent bulb to that of others, including Edison, on electric light is explained in the following passage of an article in a 1900 issue of "Electrical World and Engineer" as follows: "The