When William Shakespeare wrote Love’s Labour’s Lost he would have used light from tallow candles at a cost (today) of £12,000 per million-lumen hours. The same amount of light from electric lamps now costs only £2!  But today’s low-cost illumination still has a dark side. Globally, lighting consumes more electricity than is produced by either hydro or nuclear power and results in CO2 emissions equivalent to two thirds of the world’s cars. This book documents a broad range of policy measures to stimulate efficient lighting being implemented around the world and suggests new ways these could be strengthened to prevent light’s labour from being lost.