Inventing-around Edison’s incandescent lamp patent: evidence of patents’ role in stimulating downstream development

Ron D. Katznelson and John Howells ABSTRACT We provide an anatomy of the influence of Edison’s incandescent lamp patent U.S. 223,898 on downstream development and show how subsequent inventor activity adjusts to the improved certainty provided by court decisions as to the boundaries of a patent’s claims. First, we show that court decisions upholding Edison’s patent generated a surge of patent filings in the incandescent lamp classes at the U.S. Patent Office. Second, by inspection of the specifications of these later patents we are able to categorize certain design-around efforts by their evasion of specific elements of the claims of Edison’s ‘898 patent. Third, by analysis of forward citation to these patents we show that regardless of these inventions’ commercial viability in the incandescent lamp market, some became important prior art for new technological fields and some laid the groundwork for the later successful substitute for Edison’s carbon filament. Fourthly, we show that the recent view that Edison’s patent gave the patent holder General Electric (GE) a dominant position in the incandescent lamp market is incorrect: we show that besides commercially-successful invention around the claims of this patent, data for GE’s market share, number of manufacturers in the field and lamp price erosion through the period of the Edison patent’s enforcement reveal GE’s market position to have been stable, even weakening through the period of patent enforcement. Lastly, we derive from our account criteria against which any allegation of development block should be assessed and illustrate their utility by refuting allegations that Edison’s patent blocked downstream development.