Phosphor thickness effects on the optical performance of high power phosphor converted chip-on-board light-emitting diodes

The optical performance of high-power multichip Chip-on-Board (COB) white light-emitting diodes (WLEDs) with different phosphor layer thicknesses ranging from 1.5mm to 3.5mm were investigated in this paper. This investigation reports that the optical performance in terms of phosphor conversion efficiency, Correlated Color Temperature (CCT) and Color Rendering Index (CRI) readings of WLEDs are significantly dependent on the phosphor layer thickness (or phosphor-dispersed epoxy weight). WLED packages with thicker phosphor layer have lesser phosphor conversion efficiency, and functions with an excessive yellow-to-blue ratio that shifts white light output to a yellowish color, lowering both CCT and CRI values.