Enhancing ACU of White LEDs by Phosphor Coating Based on Electrohydrodynamics

Abstract

High angular color uniformity (ACU) is strongly required in many illumination applications. In this letter, we propose a low-cost and facile phosphor coating method based on electrohydrodynamics to realize high ACU for phosphor-converted white light-emitting diodes (LEDs). By applying an electric field around a liquid phosphor-silicone encapsulant, a normal force is induced on the air-liquid interface, resulting in a phosphor layer with cone morphology. Consequently, the ACU of white LEDs with the cone phosphor layer is greatly improved compared with that of white LEDs with the traditional spherical cap phosphor layer. The angular correlated color temperature (CCT) deviations are as low as 393 and 40 K at the average CCTs of 6500 and 5000 K, respectively.