 So he does this, the light meter in the ancient lamp, and he has his numbers, but now he has to figure out a way to compare the price of light over thousands of years. So here's one measure he uses. If you take a day's wages, you work all day, you take all the money you earn in that day, and you spend it on light, how many minutes could you light up a small room at night with as much light as you get from today's modern light bulb? Here's the answer for ancient Babylon.