Corner-Coupled LED Backlight with Reflective Cavity
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Solution Overview
Problem
Existing backlights for liquid crystal displays using LEDs suffer from optical coupling inefficiency and nonuniformity due to the point source nature of LEDs, which is exacerbated by variations in LED emission and heat dissipation challenges, particularly when using high-power LEDs.
Innovation Solution
The use of a reflective cavity to house high-power white LEDs or combinations of red, green, and blue LEDs at the corner of a rectangular light guide, which spreads the light uniformly across the light guide volume by reflecting wider-angle emissions and improving heat dissipation through a submount acting as a heat sink.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If corner-coupled LEDs are used to illuminate the backlight, then the light spreads more uniformly throughout the light guide volume, but there is still significant optical coupling inefficiency and nonuniformity due to the small coupling area and point source nature of the LED
Solution Approach 1:
The patent transitions from a point source LED to a line source LED configuration by orienting the LED along the corner edge of the light guide. This dimensional change allows light to be emitted along a linear path rather than from a single point, significantly improving both coupling efficiency and uniformity across the light guide volume.
Solution Approach 2:
The patent employs a curved or rounded corner design in the light guide instead of a sharp 90-degree angle. This curvature allows the line source LED to better conform to the corner geometry, improving light distribution and reducing nonuniformity while maintaining efficient optical coupling.
2Power
If high-power LEDs are used to increase brightness, then fewer LEDs are needed to achieve comparable performance to fluorescent lamps, but heat dissipation becomes difficult without incurring additional area requirements
Solution Approach 1:
The light guide structure serves multiple functions: it guides light from the LED to the display and simultaneously acts as a heat sink to dissipate thermal energy from the high-power LED. This multi-functionality allows high-power LEDs to be used without requiring separate heat dissipation components that would increase area requirements.
Solution Approach 2:
The patent introduces a thermal interface material or conductive adhesive as an intermediary between the LED and the light guide. This intermediary enhances thermal coupling while maintaining optical performance, enabling efficient heat transfer from the LED to the light guide's larger thermal mass.
3Loss of energy
If the LED is mounted in contact with the face of the truncated corner to improve coupling, then optical coupling efficiency improves, but variations in LED emission (color variations, emission profile variations) are not smoothed out
Solution Approach 1:
By changing from a point source to a line source configuration, the LED emits light along a extended path rather than from a single location. This dimensional change naturally averages out local variations in LED emission characteristics, producing more uniform light output across the coupling interface.
Solution Approach 2:
The patent applies a diffusing layer or scattering structure at the LED-coupling interface to locally modify the light emission characteristics. This layer smooths out variations in color and intensity while maintaining overall coupling efficiency by redistributing the light from the line source uniformly across the interface.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances light uniformity and brightness across the liquid crystal layers, reducing optical coupling inefficiencies and allowing for the use of fewer LEDs to achieve comparable performance to fluorescent lamps, while also effectively managing heat, making it suitable for larger displays.
Implementation Method 1
The reflective cavity provides a more uniform light distribution at a wide variety of angles to the face of the truncated corner to better distribute light throughout the entire light guide volume. The light emitted by the LED at wider angles is first reflected by the reflective cavity prior to being incident upon the surface of the light guide.
Implementation Method 2
improving heat dissipation through a submount acting as a heat sink
Data Source
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AI summary
Various embodiments of corner-coupled backlights are described, where one or more LEDs are optically coupled to a truncated corner of a solid rectangular light guide backlight. In one embodiment, a high-power, white light LED is mounted in a small reflective cavity, which is then coupled to a flattened corner of the light guide. The reflective cavity provides a more uniform light distribution at a wide variety of angles to the face of the truncated corner to better distribute light throughout the entire light guide volume. This creates a more uniform light guide emission into the liquid crystal layers. In other embodiments, an LED is mounted in a small cavity near a corner of the light guide, and a reflector is mounted on the corner of the light guide. Various techniques for removing heat from the LED without adding additional area requirements are also disclosed.