Experimental Setup

This paragraph showed the entire mechanism setup of the backlight module. As shown in Fig. 4.4, the VAS backlight unit included cylindrical Fresnel lens and seven LED light bars, and the locations of these light bards were coincident with Fig. 3.7.

Furthermore, Fig. 4.5 exhibited the combined Fresnel lens. The original length of this lens was 12 inch as mentioned in Table 4.2. Therefore, the Fresnel lens was divided into three parts in practical mechanism. Eventually, 7 inch VAS backlight module could be fabricated with twenty one LED light bars and the combined Fresnel lens.

Fig. 4.6 shows the upper Fresnel lens and the bottom LED light bars simultaneously, and Fig. 4.7 performs the actuated backlight module we’ve manufactured.

Fig. 4.4 The Schematic configuration of entire mechanism setup for the actual VAS backlight module

Fig. 4.5 The combined Fresnel lens

Fig. 4.6 The apparatus was demonstrated which included the upper Fresnel lens and the bottom LED light bars

Fig. 4.7 The entire VAS backlight module that we’ve manufactured was turned on

4.5 Measured Results : Normal and Oblique Viewing Modes

The results of cross-sectional luminance and angular distribution in one unit were exhibited for normal and oblique viewing modes in this section. As shown in Fig.

4.8 and Fig. 4.9, the green curves presented that the uniformity of normal and oblique

37 

modes could reach 80% and 75%, respectively. In addition, the FWHM of angular distribution of these two modes were +/- 20 and +/- 15 degree as shown in Fig.4.8 and Fig. 4.9. All above data could reach the design target as introduced in chapter 3.1.

Furthermore, the peak value of oblique mode in Fig. 4.9 (b) was located at 30 degree.

The FWHM and the peak value of oblique mode were different from the simulation results. This diverse result should be induced by the stray lights via the inner surface of this backlight module.

(a)

(b)

Fig. 4.8 (a)The luminance map and the cross-sectional luminance curve with the uniformity of normal viewing modes was 80%; (b) The angular distribution of normal viewing mode with the FWHM +/- 20° by integral sphere.

(a)

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(b)

Fig. 4.9 (a)The luminance map and the cross-sectional luminance curve with the uniformity of oblique viewing modes was 75%; (b) The angular distribution of oblique viewing mode with the FWHM +/- 20° by integral sphere.

Chapter 5

Conclusion and Future Work

5.1 Conclusion

In order to enhance the image quality and reduce power consumption in Eco-Display, the temporal, spatial, and angular modulation technologies of LED backlight shall play an important role in the future. Therefore, a prototype of the angular switchable backlight system with a 7-inch diagonal size had been accomplished and measured in this study. The developed module was shown in Fig.

4.7. Based on the novel opto-mechanical configuration shown in Fig. 3.17, the normal and oblique viewing mode can be switched by turning on the counterpart.

Table 5.1 exhibits the comparison of our VAS backlight module with the direct type backlight module. The targets of 70% uniformity and 0° to +/- 30° viewing angle control can be achieved. Besides, the most essential target, power consumption, would decrease to 30% and 50% in terms of normal and oblique modes, respectively.

The optical performance of normal mode is realized with over 80% uniformity and angular distribution within +/- 20°. In addition, the luminance peaked sharply at 30°

under oblique mode. Fig. 5.1 shows total performances of viewing-angle-switchable backlight. In the normal mode of BL, normal viewing has higher brightness than oblique viewing obviously. However, oblique viewing doesn’t have obvious brightness difference under the BL oblique mode. Therefore, improving the BL uniformity in normal and oblique mode should be put on the top priority, and viewing angle control should be in the second place.

[Table 5.1] The comparison between direct and tunable type backlight module.

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Fig. 5.1 The performances of VAS backlight in normal and oblique

5.2 Future Work

the Fresnel lens shall be replaced by a designed prism layer to impro

mode for normal and oblique viewing conditions.

In the future,

ve the performances in different operation states. According to Fig. 5.2, the

Fig. 5.2 The Fresnel lens shall be replaced by a designed prism layer

Fig. 5.3 The designed package for LED light bar can meliorate

t

prism angle α corresponding to ray incidence ω can be precisely calculated. In addition, additional package for the LED light bar shall be modified to meet in our backlight requirement to decrease the stray light. The light flux from LED can be redistributed to meet the needs of lighting in the target plane by the secondary optical lens. This freeform lens is constructed by solving refractive equation and energy conservation numerically, and these numerical results can improve the illumination of uniformity near to 90%. For example, a designed LED package can perform uniform illumination on the target plane as Fig. 5.3 shows [15].

to enable the ray (i.e. green line) redirected for normal mode

the uniformity and stray light issue of the VAS backligh

43 

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