Abstract

Secondary optics based on nonimaging optical theory has been widely used in street lighting to form a uniform rectangular illumination. When used in LCD backlight, the purpose of the secondary optics is to control LED emitting light to make them illuminate on the display area as much as possible, which can effectively increase the luminance. The paper first designs a double-freeform-surface lens to collimate light emitted from a LED. The lens is then cut to be rectangular. The simulation results show that the thickness has to be reduced to improve the uniformity. Four optimized lenses are then combined to form a 2 \$\times\$ 2 lens array. A dark strip along the minor axis appears and the detailed analysis is performed. A lens with the edge light slightly divergent can improve the uniformity. The backlight prototype with and without such lens array is measured. The practical measurement results show that with the same optical films, the luminance with the lens array increases by 96.4%, compared to the one without the lens array. The uniformity is almost same. However, the viewing angle with the lens array decreases to 23 \$^{\circ}\$ from 39 \$^{\circ}\$ of without the lens array.

© 2015 IEEE

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