A light emitting device in accordance with an embodiment of the present invention includes a diffractive optical element, a first light emitting diode emitting first light having a first range of wavelengths, and a second light emitting diode emitting second light having a second range of wavelengths....http://www.google.de/patents/US6604839?utm_source=gb-gplus-sharePatent US6604839 - Multi-chip LED color mixing by diffraction
