Lighting is one of the largest users of energy in buildings, being responsible for around 20% of electricity use. Good lighting is essential to health, well-being and productivity, but the efficiency of light sources varies widely. To reduce carbon emissions, designers, owners and occupiers are looking at the energy efficiency of lighting. Light-emitting diodes (LEDs) are a proven technology that offers enormous possibilities for providing highly energy-efficient and good-quality interior lighting. This BRE Trust Report summarises the current LED market and various advantages of LEDs, and outlines the challenges and barriers to adoption of the technology.