Backlight unit with linearly reduced divergence having the width of an output aperture vary over the length of a light divergence reduction structure

1. A display apparatus comprising:

a) a light source;

b) a light guiding plate for transmitting light from the light source outward from a two-dimensional light-providing surface, one dimension of the light-providing surface defined in a width direction parallel to the path of incident light from the light source and the other dimension of the light-providing surface defined in a length direction, orthogonal to the width direction;

c) a linear divergence reduction surface for reducing the divergence of light from the light providing surface predominantly with respect to the width direction, to provide a linearly divergence-reduced illumination,

whereby divergence along the width direction at full-width half-maximum is less than about 50% of divergence at full-width half-maximum along the length direction;

d) a liquid crystal display component for modulating the linearly divergence-reduced light to form a modulated light according to image data, and,

e) a diffusing surface in the path of the modulated light;

wherein the linear divergence reduction surface comprises a film substrate featured with a plurality of light divergence reduction structures, wherein each light divergence reduction structure is longitudinally extended in the length direction along the light-providing surface, each light divergence reduction structure comprising:

(a) an input aperture optically coupled to the light-providing surface;

(b) an output aperture distal from said input aperture, wherein the output aperture has a surface area that is larger than the surface area of the input aperture and the width of the output aperture varies over the length of the light divergence reduction structure; and,

(c) a pair of curved side walls between the output aperture and the input aperture and extending along the length direction;

wherein, in a cross section taken orthogonally with respect to the width direction, the curved side walls approximate a parabolic curvature.

2. The apparatus according to claim 1 wherein the length direction is substantially parallel to the axis of a light bulb that provides source illumination.

3. The apparatus according to claim 1 wherein the light guiding plate and the linear divergence reduction surface are of the same material.

4. The apparatus according to claim 1 wherein the pitch between adjacent light divergence reduction structures is substantially equal.

5. The apparatus according to claim 1 wherein the liquid crystal display component employs in-plane switching.

6. The apparatus according to claim 1 wherein the liquid crystal display component is an optically compensated birefringence component.

7. The apparatus according to claim 1 wherein the linear divergence reduction surface is molded into the two-dimensional light-providing surface.

8. The apparatus according to claim 1 wherein the modulated light exhibits image contrast of better than about 150:1 without the use of a compensator article.

9. The apparatus according to claim 1 wherein the liquid crystal display component exhibits an asymmetric response to incident light, such that, for light at normal incidence, the luminance of modulated light from the liquid crystal display component with respect to the width direction of the linear divergence reduction surface differs from the luminance of modulated light of the liquid crystal display component with respect to the length direction of the linear divergence reduction surface by more than 10 degrees at full-width half maximum.