We’re all familiar with the otherworldly glow of the urban horizon and the lights that cause it: the office block fluorescents and the spot-lit monuments, neon signs, the orange motor lights and the traffic beneath them, the floodlit carparks of 24 hour supermarkets, the suburban streetlights that make us feel safe. We don’t like the dark, but light doesn’t come free. Excess light affects us, and the planet we live on, in some unexpected ways.