A comprehensive discussion on colour conversion element design of phosphor converted LEDs

For a systematic approach to improve the white light quality of phosphor converted light-emitting diodes (LEDs) for general lighting applications it is imperative to get the individual sources of error for correlated colour temperature (CCT) reproducibility and maintenance under control. In this regard, it is of essential importance to understand how geometrical, optical and thermal properties of the colour conversion elements (CCEs), which typically consist of phosphor particles embedded in a transparent matrix material, affect the constancy of a desired CCT value. In this contribution we use an LED assembly consisting of an LED die mounted on a printed circuit board by chip-on-board technology and a CCE with a globe-top configuration on the top of it as a model system and discuss the impact of the CCE size, the substrate reflectivity as well as the thermal load of the CCEs on CCT maintenance and the respective radiant fluxes. It turns out that optimized solutions for CCT maintenance and high radiant fluxes in regard of one of the relevant influence factors do not need to be optimized solutions in regard of another one.