Optical Design of Phosphor Sheet Structure in LED Backlight System Yasushi Ito (Sony Corporation), SID’08 DIGEST, P.866 Speaker: Bo-Wen Xiao (蕭博文) Advisor: Prof. Yi-Pai Huang (黃乙白教授) Prof. Chung-Hao Tien(田仲豪教授) Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu, Taiwan July 29 2008

Outline Introduction Study & Discussion Summary

Structures of Direct-Emitting Type BL Conventional LED BL Proposed LED BL Blue LEDs + Phosphor White LEDs * Proposed by Sony Located on a diffuser. Doesn’t contact with LED chips. Phosphor Applied near LED chips. Blue light Quasi-white light

Study of Diffusion Layers in Phosphor Sheet Viewing angle Chromaticity depends on Incident angle Viewing angle Incident angle Total diffuse transmittance Phosphor Diffuser (c) Phosphor layer sandwiched between diffusers (a) Phosphor layer facing viewer side (b) Phosphor layer facing light source side

Viewing/Incident Angle v.s. Chromaticity Most desired structure. Very small shift Yellow shift Yellow shift

Total Diffuse Transmittance v.s. Chromaticity Diffuser Phosphor Sandwich-structure phosphor sheet Above 60% The total diffuse transmittance <60% can minimize chromaticity shift.  Chromaticity difference increase dramatically.

Summary The sandwich-structure phosphor sheet can reduce chromaticity shift at large viewing angle and large incident angle. The total diffuse transmittance of sandwich-structure phosphor sheet has to be less than 60% in order to minimize chromaticity shift.

A Backlight Based on Laser Diode and Its Design Considerations Yuta Inaba (Ritsumeikan University), SID’08 DIGEST, P.1564 Speaker: Bo-Wen Xiao (蕭博文) Advisor: Prof. Yi-Pai Huang (黃乙白教授) Prof. Chung-Hao Tien(田仲豪教授) Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu, Taiwan July 29 2008

Outline Introduction Measurement Design Consideration Summary

Structure of Side-Emitting Type BL Emission area of LD : 10um (408nm) Coupling efficiency ↑ Phosphor used here is developed for blue LED. phosphor plate CCFL or LEDs Emission characteristic for 408nm-LD is unknown. Thickness ↓ Coupling efficiency ↓

Measurement of Excited Light Close to lambertian.  The photon emission is isotropic. Intense peak :408nm Broad emission: 470nm~650nm Shape of this broad emission does not depend on the viewing angle.

Design Consideration for High Efficiency Phosphor particles dispersed & reflector surrounded. Power efficiency ↑ Losing photons emitting to opposite side.

Summary The side-emitting backlight based on laser diode has better coupling efficiency than conventional side-emitting backlight due to the small emission area of laser diode. The phosphor-dispersed fiber with reflector surrounded has higher power efficiency due to the recycling of back-scattered photons.

Conclusion

Conclusion The blue-light-excited YAG phosphor can be applied to direct-emitting type backlight and side-emitting type backlight. The chromaticity shift can be minimized by using sandwich-structure phosphor sheet with total diffuse transmittance less than 60%. The power efficiency can be improved by using reflector-surrounding fiber with phosphor particles dispersed.

Thank You for Your Kind Attention!

Comparison of Conventional BL and Proposed BL Better color uniformity

Viewing/Incident Angle v.s. Chromaticity Yellow shift Yellow shift Very small shift

Discussion of Yellowish Phenomenon

Chromaticity Difference

Optical Patterned Film (OPF) Ref: Atsushi NAGASAWA, Toshimasa EGUCHI, Yasuyuki SANAI, and Katsuya FUJISAWA, “Ultra Slim and Bendable Backlight System with a Unified Component for Liquid Crystal Display Applications,” Optical Review, Vol.15, pp. 38-40

Spectrum of Components Used

Prototype of LD-Based Side-Emitting BL Photograph of the LD-based backlight, emitting quasi-white light.

Why No Chromaticity Shift