A lamp that runs off sunlight. Neil MacGregor, Director of the British Museum, looks at the final object in the series: a solar-powered lamp with a charger that can bring cheap light and power to people around the world with no access to the electric grid. Simple, cheap and clean - is this the revolutionary technology of our future? With contributions from Aloka Sarder, a mother and adult student in West Bengal, and Nick Stern, expert on the economics of climate change. (Duration: 14 mins)