Optics in solid state lighting

Solid state lighting sources based on white light emitting diodes (LEDs) are considered as the third generation lighting sources. Generally, white light is generated by combination of the blue LEDs and yellow phosphor with the Stokes shift and wide-band emission (PC LEDs), which limits the maximum luminous efficacy with industrialization value. In addition, traditional packaged LEDs cannot be directly used in lighting with high efficiency, perfect lighting effect and low glare because of their Lambertian radiation distribution and super high luminance. The luminous efficacy limit of the solid state lighting is investigated based on the colorimetry theories. Results show that the luminous efficacy limits of the three-color mixing LEDs can be as high as 430 lm/W with R_a>80 at any white light chromaticities, and they are far higher than those of the PC LEDs. A series of achievements on LED optical system design finished by our group are summarized in this paper. To make the light distributions of the LED sources meet the lighting requirements, the non-imaging optics design theories based on the variable separation method and the feedback iteration method are proposed. For the application of the LEDs in the road lighting, a high energy efficient freeform optical system is obtained with the maximum luminance/illuminance ratio as well as satisfying the lighting requirements provided by Commission Internationale Del'Eclairage (CIE). For the application of the LEDs in the interior lighting, low glare, softly emitting and modularizing LED surface source is obtained by utilizing micro-ens diffusers designed with the non-imaging optics theories. Uniform collimating multi-surface optical systems are introduced for special lighting application.