A compact high-directionality backlight module combined with a striped diffuser is proposed to achieve an adjustable viewing angle for ecodisplay. The micro-prisms on the compact light guide plate guide the emitting rays to the normal viewing angle, whereas a set of striped diffusers scatter the rays to a wide viewing angle. View cones of +/- 10 degrees/+/- 55 degrees were obtained for narrow/wide viewing modes with 88%/85% uniformity of spatial luminance, respectively. Compared with the conventional backlight, the optical efficiencies were increased by factors of 1.47 and 1.38 in narrow and wide viewing modes, respectively. In addition, only 5% of power consumption was needed when the backlight worked in private narrow viewing mode to maintain the same luminance as that of a conventional backlight.
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