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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