 Hello, and welcome to Planet Money. I'm Jacob Goldstein. And I'm David Kestenbaum. Today on the show, the story of how we got from dim little candles made out of cow fat to as much light as we want at the flick of a switch. And I don't think I'm exaggerating here. This one little story, it explains why we are where we are today, why billions of people don't have to worry about starving today, why we aren't all subsistence farmers, why we can afford to have artists and massage therapists and plumbers, and yes, radio reporters doing stories about the history of light.