Impact of the Geometrical and Optical Parameters on the Performance of a Cylindrical Remote Phosphor LED

Remote phosphor light-emitting diode (LED) modules could offer advantages over intimate white phosphor converted LEDs in terms of phosphor operation temperature, light extraction efficiency, and angular color uniformity. Existing commercial devices show a large variety with respect to the dimensions of the mixing cavity, which raises a question about the optimization of the topology. A simplified simulation model applying a two-wavelength approach and considering the remote phosphor as one virtual surface to which three bidirectional scattering distribution functions are attributed (respectively, describing the blue-blue, blue-yellow, and yellow-yellow interactions) is developed and validated. This model has been used to analyze the impact of the cylindrical mixing cavity parameters such as the absolute reflectance, the diffuse-to-specular reflectance ratio, and the height of the mixing cavity, as well as the pitch and angular full-width at half-maximum of the LEDs on the extraction efficiency, the yellow-to-blue ratio, and the irradiance uniformity. It can be concluded that in order to increase the efficacy substantially, the recuperation of the backward emission of the converted light can only be increased by avoiding further interaction with the phosphor plate. To this extent, topologies other than cylindrical mixing cavities must be considered.