1. 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

2. Outline
Introduction
Study & Discussion
Summary

3. 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

4. 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

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

6. 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.

7. 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.

8. 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

9. Outline
Introduction
Measurement
Design Consideration
Summary

10. 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 ↓

11. 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.

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

13. 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.

14. Conclusion

15. 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.

16. Thank You for Your Kind Attention!

18. Comparison of Conventional BL and Proposed BL Better color uniformity

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

20. Discussion of Yellowish Phenomenon

21. Chromaticity Difference

22. 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

23. Spectrum of Components Used

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

25. Why No Chromaticity Shift