Molded light guide for optically coupling light from LEDs
A thin plastic light guide is formed to have cavities on one surface and TIR (total internal reflection) structures directly above the cavities. LEDs mounted on a printed circuit board are positioned in the cavities. The cavity walls are shaped to refract the LED light and direct the LED light toward the TIR structures to most efficiently make use of the TIR structures. The TIR structures may have a cusp or cone shape. The top ceiling of the cavities may be shaped to direct light at the TIR structure so as to leak through the TIR structure and blend the light with light leaking through surrounding portions of the light guide. The LEDs may be distributed only near the edges of the light guide or over the entire back surface of the light guide. A diffuser sheet may be laminated over the light guide to further mix the light.
1. A light emitting structure, comprising:
a light guide including a first surface and a second surface opposite the first surface, the first surface including cavities formed in the first surface, the second surface including total internal reflection structures that are aligned with the cavities, the total internal reflection structures being shaped to reflect at least some light into the light guide by total internal reflection; and
a plurality of light-emitting diodes positioned within the cavities,
the cavities being configured to refract light from the light-emitting diodes to impinge upon the total internal reflection structures,
each cavity shaped to have a convex central portion opposite a center of the corresponding total internal reflection structure,
the convex central portion being convex at its center,
the convex central portion adjoining a side wall of the cavity at a corner that encircles the convex central portion, and
the convex central portion facing a light-emitting diode of the plurality of light-emitting diodes that is located at least partially between a plane of the first surface and a plane of the second surface.
2. The structure of claim 1 , further comprising a diffusing sheet overlying the second surface of the light guide.
3. The structure of claim 1 , wherein a gap between the total internal reflection structures and their underlying cavities is equal to or less than 1 mm.
4. The structure of claim 1 , wherein the total internal reflection structures and cavities are only located proximate to one or more edges of the light guide.
5. The structure of claim 1 , wherein the light guide is a backlight for a display.
6. The structure of claim 1 , wherein each total internal reflection structure and its associated cavity are separated by a portion of the light guide.
7. The structure of claim 1 , wherein the light guide has light extraction features formed on the first surface.
8. The structure of claim 1 , wherein the light guide has light extraction features formed on the second surface.
9. The structure of claim 1 , wherein the cavities and the total internal reflection structures are formed into the light guide.
10. The structure of claim 1 , further comprising:
a diffusing sheet overlying the light guide; and
light extraction features formed in the light guide that cause the light guide to leak light out its second surface,
wherein light from the LEDs is directed by at least the cavities, the total internal reflection structures, total internal reflection off smooth light guide surfaces, the light extraction features, and the diffusing sheet.
11. The structure according to claim 1 , wherein the total internal reflection structure is essentially cone shaped.