Effects of Phosphor Application Geometry on White Light-Emitting Diodes

We fabricated white light-emitting diode lamps with three types of commercial yellow-emitting phosphors and studied the effects of phosphor application geometry. Two advantages were confirmed when low-concentration phosphor/silicone mixtures were employed: a 20% increase in output luminous flux and a reduced shift in the chromaticity coordinates upon change in diode current. We propose a simple model to describe these experimental results. According to the model, the results were attributed to reduced phosphor self-absorption (in the yellow spectral range) and reduced absorption saturation (in the blue spectral range), respectively, of the low-concentration mixture. The mathematical expression of the model will be effective for designing white light-emitting diodes based on the phosphor down-conversion technique.