What is the lifespan of a typical incandescent light bulb?
From 1924 to 1939 the lifetime of an incandescent lamp was not more than 1,000 hours. That's the duration of the Phoebus Cartel, in which the consolidated patent holders agreed on a strategy of planned obsolescence to boost revenues and fine any member that produced longer lasting bulbs. (It was a 30 year plan, the war shortened the 1959 end date.) Prior to that, longevity was a big marketing point. The Centennial Bulb is a famous bulb made by the Shelby Electric Company which has been burning in a California fire house since being installed in 1901.

Given that planned obsolescence is a profitable business model and the complete lack of any radical changes in incandescent lamps, it's a safe bet that 1,000 hours is in the ballpark right from the 60s through the 80s. I suspect most R&amp;D revolved around making them easier to manufacture or brighter.