Prism Structure Recycles Stray Light in Thin Backlight Units

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Solution Overview

Problem

Existing backlight technologies face challenges in reducing the bezel width without increasing thickness, particularly due to stray light that is not coupled to the lightguide, leading to non-uniformity and efficiency losses, especially in smaller mobile and wearable devices.

Innovation Solution

Incorporating a prism structure on the frame underneath the lightguide, separate from the lightguide, which reflects stray light back towards the light sources, thereby reducing stray light extraction and maintaining efficiency without adding thickness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a barrier layer is positioned over the light source and lightguide to hide the LED area, then the non-uniformity and stray light are reduced, but the bezel width increases to at least 2-3 mm

Engineering Contradiction:

Improvelight uniformityVSAvoidbezel width

Core Design Contradiction:

Manufacturing precisionVSLength of stationary object

Solution Approach 1:

A prism structure is introduced as an intermediary element between the light source and the lightguide. This prism structure redirects stray light back into the lightguide, allowing the barrier layer to be positioned closer to the light source without compromising light uniformity, thus reducing bezel width while maintaining manufacturing precision

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The prism structure converts harmful stray light that would otherwise escape and cause non-uniformity into beneficial redirected light that re-enters the lightguide. This allows for a smaller barrier layer distance while maintaining light uniformity, resolving the contradiction between precision and bezel width

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Manufacturing precision

If the mixing area of the lightguide is increased to improve light uniformity near the LEDs, then the light distribution becomes more even, but the required bezel width increases

Engineering Contradiction:

Improvelight uniformityVSAvoidbezel width

Core Design Contradiction:

Manufacturing precisionVSLength of stationary object

Solution Approach 1:

The prism structure acts as an intermediary that enhances the light mixing process by redirecting stray light back into the lightguide. This allows for a reduced mixing area distance while maintaining light uniformity, thereby reducing the required bezel width without sacrificing manufacturing precision

Inventive Principle:

Principle #24Intermediary (Mediator)

3Manufacturing precision

If absorbing materials are used to reduce stray light extraction, then non-uniformity is reduced, but overall efficiency decreases by 5-10%

Engineering Contradiction:

Improvelight uniformityVSAvoidbacklight efficiency

Core Design Contradiction:

Manufacturing precisionVSLoss of energy

Solution Approach 1:

Instead of absorbing stray light (which wastes energy), the prism structure redirects it back into the lightguide, converting what would be lost energy into useful light. This maintains light uniformity while preserving overall backlight efficiency, resolving the contradiction between manufacturing precision and energy loss

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The prism structure recovers stray light that would otherwise be discarded or absorbed. By redirecting this stray light back into the lightguide, the system recovers energy that would be lost, maintaining efficiency while achieving the desired light uniformity

Inventive Principle:

Principle #34Discarding and recovering

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

Substantially reduces stray light contribution to non-uniformity by 80-90% while maintaining overall efficiency, allowing for a smaller bezel width without increasing the backlight's thickness.

Implementation Method 1

Incorporating a prism structure on the frame underneath the lightguide, separate from the lightguide, which reflects stray light back towards the light sources

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS9921357B2Thin backlight with recycling to reduce the bezel width

Publication Date: 2018.03.20 SHARP KK

AI summary

A backlight unit includes a lightguide, a light source that emits light to the lightguide, and a barrier layer positioned over the lightguide in a light emitting direction relative to the lightguide. The barrier layer defines a bezel area of the backlight unit, and an active area of the backlight unit from which light is emitted from the lightguide is an area adjacent to a boundary of the bezel area. A prism structure is positioned in the bezel area, wherein stray light emitted from the light source uncoupled to the lightguide is at least partially coupled into the lightguide by the prism structure or directed to a greater degree along the lightguide. The prism structure may be configured as a plurality of lenticular triangular prisms, and may be mounted to a mounting frame, back reflector, or flat panel connector of the backlight unit.