Towards the ideal white LED light source Youri Meuret The Light & Lighting Laboratory Optical Lighting Design Measurement Facilities New light Appearance sources Towards the ideal white LED light source for general lighting applications The ideal white light source for lighting? Specification/properties Ideal - Ef ficacy - ≈ 400 lumen/watt - Sp ectrum - CRI = 100 - Li fetime, stability, robustness - 100 khours at this moment - Co st - low cost per lumen x hours - Fo rmfactor - Application depending - To tal light output - Application depending - Ra diation pattern - Application depending - Lu minance - Application depending Overview • LED fundamentals • LED efficiency • Three key issues of LED technology • Efficient white LED light + state-of-the-art • LED luminance • LED alternatives LED fundamentals From a very simple solid-state physics point of view Conduction in intrinsic semiconductors E Conduction band Bandgap E g Valence band The recombination of a free electron and a hole can lead to the emission of a photon E Band gap E g For an intrinsic semiconductor at room temperature, the amount of free electrons and holes is low → the chance that these meet is low → the amount of created photons is low. c E  Ephoton  h.f  h.  n-type p-type semiconductor semiconductor + - + - Bandgap → the smallest frequency F. Schubert “Light-Emitting Diodes” Cambridge University Press (2006)