Effects of light scattering in optical coatings on energy losses in LED devices

The effect of light scattering in phosphor-containing optical coatings on energy losses in chip-on-board LED devices is considered. The energy losses have been evaluated by numerical simulation with the refractive index of the coating material ($n$ = 1.4–1.8) and the average radius of dispersed phosphor particles ($R$ = 5–50 $\mu$m) being the variable parameters. It is established that the energy losses most significantly depend on the level of total internal reflection at the coating/air interface. In the LED device configuration studied, the optimum refractive index of the coating material is $n$ = 1.4. It is also found that, in order to reduce the energy losses related to light scattering on phosphor particles, it is expedient to use phosphors with coarse particles ($R$ = 50 $\mu$m).