OLED Display Substrate Edge Light Extraction
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Solution Overview
Problem
Conventional OLED displays suffer from low optical efficiency due to total internal reflection, with a significant portion of emitted light being trapped within the substrate and layers, limiting the ability to illuminate secondary objects effectively, especially in watch applications where a passive display is needed.
Innovation Solution
The display assembly incorporates a transparent or semi-transparent substrate with a side face that extracts trapped light at an angle between 90° and 135° relative to the front face, using a higher refractive index substrate to confine light and a frosted side face for diffused illumination, allowing light to be redirected to illuminate secondary objects like a date disc or other passive displays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional OLED display is used with a transparent substrate, then light is emitted forwards to illuminate the primary display, but a significant portion of light (up to 80%) is trapped inside the substrate due to total internal reflection and cannot be utilized
Solution Approach 1:
The patent extracts trapped light from the substrate by utilizing the side faces (edges) of the substrate rather than only the front face. By changing the extraction dimension from 2D (front surface) to include 1D edges, the patent recovers light that would otherwise be trapped, converting harmful total internal reflection into useful illumination for secondary objects.
Solution Approach 2:
The patent converts the harmful effect of total internal reflection (which traps light inside the substrate) into a beneficial effect by using optical elements on the side faces to extract and redirect this trapped light. The previously wasted trapped light becomes useful illumination for secondary objects such as date windows or other display elements.
2Illumination intensity
If the substrate front face is optimized for light extraction, then forward light emission is improved, but light emission at angles higher than the critical angle undergoes total reflection and remains trapped
Solution Approach 1:
The patent addresses angular light trapping by extracting light from the side faces of the substrate. Light that reflects at angles higher than the critical angle at the front surface can still be extracted through the edges, converting angular-dependent trapped light into usable illumination.
3Adaptability or versatility
If a passive display device is added to the watch, then functionality is enhanced, but the device requires additional illumination which increases power consumption
Solution Approach 1:
The patent makes the trapped light within the substrate serve a dual purpose: it continues to illuminate the primary OLED display while simultaneously illuminating secondary passive display elements such as date windows or other informational displays. This self-service approach allows multiple display functions without requiring additional power for separate illumination sources.
Solution Approach 2:
The patent creates a multi-functional illumination system where the same light extraction mechanism serves both the primary OLED display and secondary passive display elements. The optical elements on the side faces provide universal illumination for multiple display functions, eliminating the need for separate lighting systems.
4Illumination intensity
If phosphorescent coatings are applied to illuminate passive displays in low light, then readability is improved, but the coating thickness increases and surface area is limited
Solution Approach 1:
The patent replaces the mechanical/phosphorescent coating system with an optical system based on light extraction from substrate edges. Instead of relying on phosphorescent materials that require thickness and surface area, the patent uses optical elements to redirect trapped light, achieving illumination without the limitations of coating-based solutions.
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 approach enhances light extraction and utilization, effectively illuminating secondary objects without increasing power consumption, improving readability in low-light conditions and reducing glare by redirecting trapped light from the OLED display.
Implementation Method 1
the efficiency of light emitting diode (LED) devices, including those with organic active layers (OLED in English or DELo in French) generally used for lighting these displays, is greatly limited by optical efficiency, due to the difficulty in extracting light from a highly refractive medium to a weak refractive medium. This low efficiency is mainly due to the total internal reflection of the light emitted by the active layer.
Implementation Method 2
said side face is frosted to produce a diffused light during use
Data Source
AI summary
The present invention concerns a display assembly comprising an organic light-emitting diode display device comprising at least one OLED comprising an emitting stack placed on a transparent substrate, whose back face is placed on the emitting surface of the OLED, and a secondary object to be illuminated, said transparent substrate comprising a front face and at least one side face arranged to light a secondary object.