LED Light Guide With Refractive Index Apertures
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Solution Overview
Problem
Light emitting diodes (LEDs) emit light in a Lambertian radiation pattern, resulting in a wide angular spread, making it difficult to increase extraction efficiency and direct light effectively, especially when additional optics are bulky and struggle to collect and redirect the emitted light.
Innovation Solution
A light guide is coupled to the LED, featuring a first material with a grid of apertures filled with a second material of higher refractive index, forming frustrated cones to redirect light rays more directionally, with the apertures extending from a small diameter at the LED to a larger diameter and angled sides to achieve total internal reflection and refraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If additional optics such as lenses and reflectors are used to redirect light rays, then the light output directionality is improved, but the device becomes bulky and complex
Solution Approach 1:
The patent combines the light guiding function and the directional control function into a single integrated light guide structure. The light guide includes a transparent substrate with multiple light guides formed directly on it, eliminating the need for separate lenses and reflectors. This merging of functions reduces device complexity while maintaining directional light output.
Solution Approach 2:
The light guide uses a thin transparent substrate with light guides formed as elongated structures on its surface. This thin-film approach replaces bulky traditional optics with a compact, planar structure that achieves the same light redirection function with minimal thickness and reduced overall device size.
2Shape
If additional optics are used to shape light output, then light directionality is improved, but the amount of light collected and directed is reduced due to emission direction
Solution Approach 1:
The light guide structure implements local quality by creating regions with different refractive indices through the light guides formed on the substrate. The light guides have specific geometric configurations (elongated shapes with particular cross-sections) that locally modify light propagation characteristics, enabling efficient light collection and directional control without energy loss.
Solution Approach 2:
The patent changes the refractive index parameter by using light guide materials with different refractive indices than the surrounding medium. This parameter change enables total internal reflection at the light guide boundaries, efficiently directing light rays that would otherwise be lost, thereby improving light extraction efficiency while maintaining directional output.
3Loss of energy
If the LED emits light in a Lambertian pattern, then light extraction from the small emissive surface is maximized, but the angular spread is too wide for many applications
Solution Approach 1:
The light guide acts as an intermediary between the LED emissive surface and the final light output. It receives light from the small LED surface in all directions (maintaining extraction efficiency) and transforms this omnidirectional light into a directional beam through total internal reflection at the light guide boundaries, effectively decoupling extraction efficiency from angular spread.
Solution Approach 2:
The light guide structure adds a spatial dimension to light control by using elongated three-dimensional structures on the substrate surface. These elongated light guides extend in specific directions and use their length and cross-sectional geometry to control light propagation, transforming the two-dimensional Lambertian emission pattern into a directional three-dimensional light output.
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
The light guide effectively directs a greater portion of the LED's light output closer to perpendicular, enhancing directional emission and increasing the forward light output, thereby improving light extraction efficiency.
Implementation Method 1
A light guide includes a first material having a first index of refraction with a plurality of apertures arranged in a grid. A second material having a second index of refraction that is larger than the first index of refraction fills the plurality of apertures.
Implementation Method 2
Each aperture extends from a first end adjacent the LED die to a larger second end. The first end may be a circle of approximately 1 to 2 μm in diameter. The distance between the first and second ends may be from approximately 10 to 20 μm.
Data Source
AI summary
A device to emit light includes a light emitting diode (LED) die and a light guide coupled to the LED die. The light guide includes a first material having a first index of refraction with a plurality of apertures arranged in a grid. A second material having a second index of refraction that is larger than the first index of refraction fills the plurality of apertures. Each aperture extends from a first end adjacent the LED die to a larger second end. The first end may be a circle of approximately 1 to 2 μm in diameter. The distance between the first and second ends may be from approximately 10 to 20 μm. Each aperture may be in the form of a frustrated cone having an included angle between the sides from approximately 3 to 7 degrees. The light guide may be formed on a transparent substrate.