From Fortune Magazine:

A Yale professor, William Nordhaus, compared the price of lumens (a standard unit of measurement for light) over time. In 1750 b.c., the average Babylonian, relying on lamps fueled by sesame oil, had to work 350,000 hours to buy as many lumens as the average American could buy with one hour’s work in 1992. The amount of light Thomas Jefferson could buy for $100 in 1800 cost just 3 cents (in constant dollars) in 1992.

Jim Fohwer, The Numbers Game, Fortune Magazine, Nov. 22, 1999.