“A tallow candle in 1800 would cost roughly forty cents per thousand lumen-hours. A fluorescent bulb in 1992, when Nordhaus originally compiled his research, cost a tenth of a cent for the same amount of light. That’s a four-hundred-fold increase in efficiency. But the story is even more dramatic when you compare those costs to the average wages from the period. If you worked for an hour at the average wage of 1800, you could buy yourself ten minutes of artificial light. With kerosene in 1880, the same hour of work would give you three hours of reading at night. Today, you can buy three hundred days of artificial light with an hour of wages” How We Got to Now Steven Johnson