The recent announcement of Tesla’s new power storage systems got me thinking about the relationship between light, productivity, sustainability and the economy.The story of artificial light is a story of economic development. Before oil lamps and candles, people used to go to bed at sundown and slept in ‘two phases’ – first and second sleep. However, with the advent of artificial light, productivity patterns changed along with sleep patterns, as people’s activities became independent of the availability of natural light.