Backlight unit color compensation techniques

A method, comprising:

• receiving light from a light source at a first lateral edge of a light guide of a backlight unit, wherein the received light exhibits a non-uniform color characteristic across a distribution of viewing angles from an optical axis of the light source;
• propagating the received light through a propagation medium and towards a second lateral edge of the light guide, wherein the second lateral edge is opposite the first lateral edge, and wherein a first portion of the propagating light reaches the second lateral edge;
• using a reflective element disposed at the second lateral edge to cause substantially the entire first portion of the propagating light reaching the second lateral edge to retro-propagate towards the first lateral edge;
• using a plurality of light extracting features formed on a rear surface of the light guide to extract a second portion of the propagating light and to extract the retro-propagating first portion of the light;
• and
• mixing the extracted second portion of the propagating light and the extracted retro-propagating first portion of the light to improve color uniformity in light emitted from a front surface of the light guide, wherein the retro-propagating first portion of the light comprises more of the light emitted along the optical axis and less of the light emitted away from the optical axis, and the second portion of the light comprises less of the light emitted along the optical axis and more of the light emitted away from the optical axis.

A display device comprising:

• a liquid crystal display panel;
• and
• an edge-lit backlight unit comprising:
• a light source;
• a light guide comprising a first lateral edge, a second lateral edge opposite the first lateral edge, a front surface, and a rear surface, at least one of the front surface and the rear surface having a plurality of light-extracting elements, wherein the light guide is configured to receive light emitted from the light source along the first lateral edge and to propagate the received light towards the second lateral edge, and wherein the plurality of light-extracting elements is configured to allow a first portion of the propagating light to reach the second lateral edge and to extract a second portion of the propagating light, wherein the first portion comprises more of a first color and less of a second color, and the second portion comprising less of the first color and more of the second color;
• and
• a specular reflector disposed at the second lateral edge and configured to cause substantially the entire first portion of the propagating light to retro-propagate back towards the first lateral edge;
• wherein the light guide is configured such that the retro-propagating first portion of the light is extracted by the plurality of light-extracting elements, wherein the extracted retro-propagating first portion of the light and the extracted second portion of the propagating light is mixed and emitted from the light guide, and wherein the mixed light emitted from the light guide is substantially uniform in color.

A method of reducing color shift in an edge-lit backlight unit, the method comprising:

• receiving light emitted from a light source at a first lateral edge of a light guide;
• propagating the light towards a second lateral edge opposite the first lateral edge;
• extracting a second portion of the light during propagation towards the second lateral edge using one or more light-extracting elements;
• receiving, at the second lateral edge, a first portion of the light not extracted by the one or more light-extracting elements during propagation;
• retro-propagating the first portion of the light received at the second lateral edge towards the first lateral edge;
• extracting the retro-propagating the first portion of the light using the one or more light-extracting elements;
• and emitting the extracted second portion of the propagating light and the extracted retro-propagating first portion of the light from a front surface of the light guide, wherein the first portion comprises more of a first color and less of a second color, and the second portion comprising less of the first color and more of the second color.

An electronic device, comprising:

• one or more input structures;
• a storage structure encoding one or more executable routines;
• a processor capable of receiving inputs from the one or more input structures and of executing the one or more executable routines when loaded in a memory;
• and
• a display device configured to display an output of the processor, wherein the display device comprises:
• a liquid crystal display panel;
• and
• a backlight unit comprising:
• a light source configured to provide direct lighting to the backlight unit by emitting light that exhibits a non-uniform color characteristic;
• and
• a light guide configured to receive the light from the light source, wherein the light comprises a first portion comprising more of a first color and less of a second color, and a second portion comprising less of the first color and more of the second color, wherein the light guide is configured to cause the light to propagate from a first lateral edge towards a second opposite lateral edge of the light guide, to cause the first portion to reach the second lateral edge and to retro-propagate from the second lateral edge back towards the first lateral edge, to extract the second portion of the propagating light substantially prior to the second lateral edge, and to extract the retro-propagating first portion of the light;
• wherein the extracted second portion of the propagating light and the extracted retro-propagating first portion of the light are mixed to improve color uniformity in light emitted from the light guide towards the liquid crystal display panel.

A display backlight unit comprising:

• a light guide configured to receive light from a light source, wherein the light comprises chromaticity variations across a distribution of viewing angles from an optical axis of the light source, wherein the light guide is configured to cause the light to propagate from a first lateral edge towards a second opposite lateral edge of the light guide, and to cause a first portion of the propagating-light to reach the second lateral edge and to retro-propagate from the second lateral edge back towards the first lateral edge, wherein the retro-propagating first portion comprises more of the light emitted along the optical axis and less of the light emitted away from the optical axis;
• and
• a plurality of light-extracting elements configured to extract a second portion of the propagating light substantially prior to reaching the second lateral edge and to extract the retro-propagating first portion of the light, wherein the extracted second portion of the propagating light comprises less of the light emitted along the optical axis and more of the light emitted away from the optical axis, the plurality of light-extracting elements are arranged on a rear surface of the light guide and are configured to reduce the disruption of total internal reflection of the propagating light, wherein a size of the plurality of light extracting elements increases from the first lateral edge to the second lateral edge, and a spacing of the plurality of light extracting elements decreases from the first lateral edge to the second lateral edge;
• wherein the extracted first and second portions of the light are mixed and emitted from the plurality of light-extracting features as light output to provide substantially uniform color along an axis of the light guide, wherein the light output has a Δu′v′ of less than approximately 0.005 based upon the CIE 1976 color space.

A display backlight unit comprising:

• a light source comprising one or more light-emitting diodes (LEDs), wherein at least one of the one or more LEDs exhibits chromaticity variations across a distribution of viewing angles from optical axes of the respective LEDs, wherein the chromaticity variations comprise bluer light emitted substantially along the optical axes, and more yellow light emitted away from the optical axes;
• a light guide comprising a first lateral edge, a second opposite lateral edge, and a forward surface disposed between the first lateral edge and the second lateral edge, wherein the light guide is configured to receive light from the light source, to cause the light to propagate from the first lateral edge towards the second opposite lateral edge of the light guide, and to cause a first portion of the light to reach the second lateral edge and to retro-propagate from the second lateral edge back towards the first lateral edge, wherein the retro-propagating first portion comprises more of the bluer light and less of the more yellow light;
• and
• a plurality of light-extracting elements configured to extract a second portion of the light substantially prior to reaching the second lateral edge, to extract the retro-propagating first portion of the light, wherein the second portion of the light comprises more of the more yellow light and less of the bluer light, and to mix the first and second portions of the light as mixed light, wherein the plurality of light-extracting elements is configured to emit the mixed light through the forward surface of the light guide to provide a substantially uniform color light output from the forward surface.