A study on the yellow ring distribution of MR-16 WLED triplet lens module

The yellow-ring (YR) is a chromatism phenomenon which is caused by the inhomogeneous phosphor layer of the whitelight LED (WLED) and can be observed from the projected WLED lightspot. In general, the lights emitted from a WLED will focus on the specific range to form a circular lightspot; in the meanwhile, the YR will appear on the periphery of this lightspot. In our previous study, the evaluation of YR phenomenon was graded by the YR index (YRI), which is the product of the yellow light intensity (Y) and total light intensity (I). Therein, the maximum value of YRI is a crucial optical parameter for determining the YR degree and a YR evaluation model is as the criterion for quality control of WLED. In this article, the YR distribution of MR-16 triplet lens module related to the distance (pitch) between two of three WLEDs will be discussed. Experimental results show that the YRI of triple lens WLED module is lower than one of single lens WLED module due to the overlapped effect of WLED lightspots. In addition, the YR degree of triplet lens WLED module will be lower if the pitch is longer, but the unintended dark-corner effect will appear when the pitch is enough longer.