Light, whether natural or artificial, is a powerful material. It is fundamental to our lives, and it can help create new and interesting spaces in many different ways. Even though this tends to be unrecognised in most discussions, lighting is currently gaining a new momentum. It was given official status when the UN designated 2015 as the “UN Year of Light”. And, fuelled by new technologies, it has now taken centre stage in all sorts of discussions: on the economic and environmental costs of climate change, on aesthetics and city branding, and on the quality of life in cities. Bright street lights left to shine on empty streets are an excessive and unnecessary waste of energy that is bad for the planet. Images taken from space show vividly how much light is generated in our cities, and there are many attendant problems: high carbon levels, and light pollution which can result in poor sleep for humans and changes in nocturnal animal behaviours, to name but a few. But light plays a huge role in creating social spaces, too. It is the backdrop for all social interaction, influencing what we can do after dusk, how safe we feel, and how well we can navigate through nocturnal environments.