High-power packages for phosphor-based white-light-emitting diode lamps

With the rapid development of high-power white light-emitting diodes (LEDs), advances in packaging are required to further improve the device performance. In this work, an optimized packaging configuration for high power LED lamps with enhanced phosphorescence efficiency is presented based on ray-tracing simulations and experimental results. Figure 1 shows two phosphor arrangements, namely a "proximate phosphor" and a "remote phosphor" arrangement. The surface of the reflector cup is assumed to be either specular or diffuse. Three different encapsulant geometries, i.e., a "flat" (no cap), "convex" (spherical cap with height h = r/2), and "hemispherical" (h = r) top surface, are used in the simulations. Figure 2 shows phosphorescence efficiency with different packaging configurations obtained by ray-tracing simulation. The packaging configuration with remote phosphor, diffuse reflector cup and hemispherical encapsulation shows a 50% enhancement of phosphorescence efficiency compared to conventional packaging configuration. This improvement is attributed to reduced absorption of the phosphorescence by the LED chip and the reduction of deterministic optical modes trapped inside the encapsulant of remote-phosphor and diffuse reflector cup configuration. The angular dependence of the reflectivity for a diffuse Ag reflector and a specular Ag reflector is measured and shown in Figure 3. The roughened Ag reflector has a more than two orders of magnitude higher diffusely reflected power compared with the specular Ag reflector, which leads to the extraction of the trapped optical modes occurring in packaging structures with specular reflector cups. Dichromatic LED lamps comprising an ultraviolet GaN LED (λ = 400 nm) with a blue phosphor and a blue GaInN LED (λ = 470 nm) with a yellow phosphor are fabricated with different phosphor arrangements and reflector cups. The emission spectra of the reference primary LED emitters and of the dichromatic lamps operating at 20 mA are measured in an integrating sphere, as shown in Figure 4. The phosphor power conversion efficiencies were calculated and shown in Table 1. A 27% improvement is obtained for the remote phosphor and diffuse cup configuration compared with proximate phosphor in specular cup configuration. The experimental results are fully consistent with the ray tracing simulation, confirming the enhancement of phosphor efficiency by employing diffuse reflector cups and a remote phosphor.