Organic emitters for solid state lighting

White organic light emitting diodes (WOLEDs) have gained considerable attention of academic and industrial research communities as promising alternative to incandescent lamps, fluorescent tubes and inorganic LEDs for low energy consumption lighting applications. WOLEDs are expected to become one of the next generation lighting sources because of their high color tunability and color quality, which can be easily achieved by proper chemical design of organic electroluminescent materials. Contrary to their inorganic counterparts, WOLEDs also bear the distinctive feature of being available as flexible and large area devices. Over the last decades, a lot of efforts have been spent on defining suitable strategies to highly efficient WOLEDs based on the use of properly tailored organic emitters. Here we survey the main chemical approaches to white electroluminescence from organic light emitting materials, highlighting strong and weak points of each strategy. Current research on new hybrid white light emitting devices based on the combination of inorganic LEDs and organic down color converters is also reviewed by some representative examples