Improvement in optical performance and color uniformity by optimizing the remote phosphor caps geometry for chip-on-board light emitting diodes

- Light extraction mechanism of COB LEDs with RPCs was studied by ray-tracing method.
- RPCs geometries were optimized to gain high light quality for COB LEDs.
- Optimized COB LEDs simultaneously achieve high luminous flux and color uniformity.

The remote phosphor caps (RPCs) have been studied theoretically and experimentally based on chip-on-board (COB) devices. We have investigated the effect of RPCs on the blue light and the yellow light emission distributions by ray-tracing. Moreover, the geometry of RPCs have been optimized to simultaneously achieve an excellent optical performance and color uniformity. Corresponding to simulation results, both the optimized (conical shape without straight side) and the reference (semi-spherical shape with straight side) RPCs have been manufactured by the compression molding method. These RPCs were assembled to the same blue COB source and then the COB devices have been measured. Compared with the reference RPC, the optimized RPC is able to significantly increase the radiant power and the luminous flux by 15.9% and 17.0% at a driving current of 350 mA, respectively, and it can also decrease the standard deviation of the correlated color temperature (CCT) by 48.9% for a total CCT about 4800 K. Hence, the proposed RPCs can provide a superior improvement in optical performance and color uniformity to COB devices.