Appl. Opt. 52, 2602–2609 (2013)

There is a strong worldwide drive to efficiently generate white light using light-emitting diodes (LEDs). In white LEDs, light is purposefully scattered many times to generate a 'random walk'; the light then becomes diffuse, which is crucial for even lighting. Photons are recycled to save on colourants and to improve cost and energy efficiency. Present challenges in understanding white LEDs arise from a limited knowledge of the light-scattering process, which hampers the development of efficient ones. Willem Vos and colleagues from Twente University and Philips have now performed an innovative study of this problem. The researchers collected and spectrally resolved all light that scatters inside LED diffusers. They used nanophotonic theory to derive the mean-free path for LEDs, that is, the average step-size of the random walk. A model without adjustable parameters was developed that successfully interpreted the results. The new insights are being used to design more energy-efficient LEDs that are more environmentally friendly.