LED-Light Guide Coupling Apparatus with Parabolic Reflector
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Solution Overview
Problem
Current coupling arrangements between LEDs and light guides in compact fluorescent lamps (CFLs) suffer from low coupling efficiency due to geometric incompatibility between the radiation mode of the LED and the guided mode, resulting in significant light loss and limited red color rendering, with efficiencies ranging from 35% to 50%.
Innovation Solution
The proposed solution involves a coupling apparatus with a support and reflector surface that positions the LED in a central recessed portion adjacent to a substantially planar end of the light guide, using a coupler with parabolic or aspheric inner reflector surfaces to enhance light transfer, and optionally filling the cavity with a material matching the refractive index of the light guide to minimize Fresnel reflections and maximize total internal reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If butt coupling or contact between polished end of light guide and LED is used, then device complexity is reduced, but coupling efficiency remains low (35%-50%)
Solution Approach 1:
The patent introduces a coupler as an intermediary component between the LED and light guide. This coupler includes a reflector surface that actively redirects light, serving as a mediator to improve coupling efficiency from 35-50% to 70-96% without significantly increasing device complexity
Solution Approach 2:
The coupler employs curved or spherical reflector surfaces to redirect light from the LED into the light guide. The curved geometry helps concentrate and redirect light rays that would otherwise be lost, improving coupling efficiency while maintaining relatively simple device structure
2Loss of energy
If lens coupling with special geometry lens is used, then coupling efficiency is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The coupler acts as an intermediary that combines reflective surfaces with the light guide, avoiding the need for complex lens systems while achieving similar or better coupling efficiency (70-96% versus 60-80% for lens coupling)
Solution Approach 2:
The coupler design uses simpler, potentially cheaper materials and manufacturing processes compared to precision lens coupling. The reflector surface can be implemented with standard materials and techniques, reducing manufacturing cost while maintaining high coupling efficiency
3Illumination intensity
If reflector with air gap is used, then light reflection is enhanced, but Fresnel reflections occur at interfaces
Solution Approach 1:
The patent changes the optical parameter (refractive index) by filling the cavity with material matching the light guide's refractive index. This eliminates the air gap and associated Fresnel reflections, reducing light loss while maintaining enhanced reflection through the coupler's reflector surface
4Illumination intensity
If LED is positioned close to discharge tube for color mixing, then red color rendering is improved, but LED temperature increases
Solution Approach 1:
The light guide serves as an intermediary that transports red light from the LED to the discharge tube region. This allows the LED to be positioned in the base (away from heat) while still achieving effective color mixing at the discharge tube, maintaining both low LED temperature and good red color rendering
Solution Approach 2:
The system separates the LED positioning function (in the cool base) from the color mixing function (at the discharge tube). The light guide divides the light path into separate segments, allowing thermal and optical functions to be decoupled
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 arrangement achieves coupling efficiencies of up to 96%, significantly improving red color rendering by reducing light loss and allowing for easier assembly and lower manufacturing costs, while maintaining the LED's operating temperature.
Implementation Method 1
The support includes a reflector surface for transferring a high ratio of light from the LED to the light guide
Implementation Method 2
Eliminating an air gap between the light source and the light guide is desirable because such a structure would reduce the Fresnel reflections on the LED-air and air-light guide interfaces
Implementation Method 3
Eliminating an air gap between the light source and the light guide is desirable because such a structure would reduce the Fresnel reflections on the LED-air and air-light guide interfaces, and also enhances the application of total internal reflection (TIR) on the reflecting surface
Data Source
AI summary
Different arrangements for improving the coupling-in efficiency between an LED assembly and a light guide are disclosed. In a first arrangement, a substantially planar end of a light guide is seated on a perimeter wall of a support that encloses a LED assembly, and a reflecting surface enhances coupling efficiency of a light guide. Alternative arrangements use a separate coupler disposed between the LED assembly and the light guide, which coupler has a paraboloid or aspheroid conformation to develop substantially collimated light that is directed into the light guide. The cavity around the LED assembly and within the coupler, may be air or a material having an index of refraction that closely matches the index of refraction of the light guide material.