Henry Woodward and Mathew Evans filed a patent in Canada for their light bulb invention on July 24, 1874. The patent predates Thomas Edison's U.S. patent by about five years.

Some have claimed that the Edison light bulb was more advanced than the Woodward and Evans bulb but the reverse is actually the case. Woodward and Evans's bulb was filled with nitrogen, a relatively inert gas which won't react with the carbon filament in the bulb. In contrast, Edison's design called for the bulb to contain a near perfect vacuum. Today, light bulbs of more than about 40 watts contain a mixture of gases which are selected because they are relatively inert (argon and nitrogen being the most common).

Thomas Edison later purchased an interest in the Woodward and Evans patent - a pretty strong indication that Edison felt that the Woodward and Evans light bulb patent was a threat.

It should be noted that Sir Humphry Davy, an English chemist, produced light using electrically heated strips of platinum in 1802. The problem was that the strips quickly burned out although the race was on and inventors around the world joined in. Later, in about 1860, Sir Joseph Wilson Swan, an English physicist, used carbon filaments in an evacuated glass bulb to produce light. Unfortunately, the filaments quickly burned out due to air in the bulb and the bulb wasn't particularily efficient. Swan did produce an apparently successful light in 1878 put didn't patent it in time.

There's another twist to the story - although Edison filed his patent application in 1879, the U.S. Patent Office ruled on October 8, 1883 that Edison's patent was invalid on the basis of prior art by William Sawyer and Albon Man.

Ok. So Edison's patent was invalid. Right? Well, as it turns out, not quite . . . on October 6, 1889 a court ruled that one of Edison's claims relating to the use of "a filament of carbon of high resistance" was valid.

But we're still not done . . . in 1979, Robert Conot published a book called A Streak of Luck. In the book, Conot reveals that Edison and his attorneys withheld evidence. Specifically, they removed the October 7-12, 1879 part of a notebook before providing the rest of the notebook to the court. The missing pages showed that Edison really was just expanding on prior art by Sawyer and/or Swan!

The bottom line is that although one can debate who did invent the light bulb, there seems to be little doubt that Edison didn't!

Edison can be given credit for commercializing the light bulb.


  • a photocopy of the Woodward and Evans patent (obtained from CIPO - Canadian Intellectual Property Office (i.e. the Canadian Patent Office))
  • a photocopy of an undated article from EUREKA! magazine (reprinted from the Toronto Star)
  • a biography of Sir Joseph Swan at http://www.acmi.net.au/AIC/SWAN_BIO.html (last accessed 2002/09/27)
  • a fairly detailed discussion of Edison's light bulb and patent saga located at http://www.willitsell.com/edisnmth.htm (last accessed 2002/09/27)