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,
Opposition procedure before the European Patent Office (the decision instead maintaining the patent as granted or in an amended form) leaves the way open for revocation by the national court. The EPO decision does not create an estoppel precluding a subsequent challenge by an unsuccessful opponent at the national level (at least before the English courts). The validity of a European patent can be scrutinised both at the national level, before a national court, and at the international level, before the European Patent Office during opposition. The same is not true for infringement proceedings, upon which national courts exercise exclusive jurisdiction. Each party to the opposition proceedings