Back in the mid-1990s, an economist called William Nordhaus conducted a series of simple experiments with light. First, he used a prehistoric technology: he lit a wood fire. But Prof Nordhaus also had a piece of hi-tech equipment with him – a Minolta light meter.
He burned 20lb (9kg) of wood, kept track of how long it burned for and carefully recorded the dim, flickering firelight with his meter. Next, he bought a Roman oil lamp, fitted it with a wick, and filled it with cold-pressed sesame oil. He lit the lamp and watched the oil burn down, again using the light meter to measure its soft, even glow.
Bill Nordhaus’s open wood fire had burned for just three hours on 9kg of wood. But a mere eggcup of oil burned all day, and more brightly and controllably.
Why did he do this?
He wanted to understand the economic significance of the light bulb. But Prof Nordhaus also wanted to illuminate a difficult issue for economists: how to keep track of inflation, the changing cost of goods and services.
We’re all familiar with the technological impact of the light bulb, but Tim Harford dissects its economic significance – the labour which used to generate 54 minutes of quality light now produces 52 years. Not only are today’s lights more efficient, clean and safe, the price of light alone has fallen by a factor of 500,000.