High-Power White LEDs Using Scattered Photon Extraction
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Solution Overview
Problem
Current phosphor-converted LED (pc-LED) technology is inefficient in the visible spectrum, with light output below that of incandescent lamps, requiring larger LED chips or multiple chips, and suffers from reduced efficiency and increased temperature, leading to declining performance as temperature rises above 90°C.
Innovation Solution
The implementation of a technique called Scattered Photon Extraction (SPE) where the down-conversion material is moved away from the LED die, and a tailored optic device is used to extract back-transferred radiation, allowing more light to exit the device and improving efficiency by preventing radiation feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If phosphor particles are randomly oriented and interspersed throughout the epoxy, then the device structure is simple, but light transmission efficiency is reduced due to scattering and absorption
Solution Approach 1:
The patent extracts the phosphor particles from the epoxy matrix and places them on the reflector cup surface, separating the phosphor conversion function from the light transmission path. This allows light to travel through the epoxy without encountering scattered phosphor particles, improving transmission efficiency while maintaining the simplicity of mixing phosphor into epoxy for phosphor application
Solution Approach 2:
The reflector cup serves as an intermediary surface that holds the phosphor particles in a controlled position. Instead of phosphor particles being randomly distributed in the epoxy, they are concentrated on the reflector cup where they can be efficiently excited by LED light and redirect converted light back toward the LED, improving overall light extraction efficiency
2Illumination intensity
If a larger LED chip or multiple chips are used to increase light output, then luminous output increases, but device complexity and cost increase
Solution Approach 1:
The patent implements an optical feedback mechanism where phosphor particles convert some LED light to longer wavelengths and redirect this converted light back toward the LED chip. This back-transferred light undergoes multiple passes through the phosphor layer, increasing the probability of conversion and extracting more total light from the same LED chip, thereby increasing light output without requiring larger or multiple chips
Solution Approach 2:
The patent creates a continuous optical path where light from the LED chip passes through the phosphor layer, unconverted light exits the device, and converted light is redirected back to the LED chip for further conversion opportunities. This continuous circulation of light maximizes the utilization of each photon generated by the LED, improving luminous output efficiency
3Temperature
If direct energy absorbing cooling is incorporated to handle temperature rise, then thermal management is improved, but device complexity increases
Solution Approach 1:
The patent converts the previously harmful back-transferred light (which caused heating and efficiency loss) into a beneficial resource. By placing phosphor particles on the reflector cup, the system captures back-transferred light and uses it for additional phosphor conversion, turning what was waste energy into useful light output. This reduces the need for aggressive cooling measures while maintaining or improving performance
4Loss of energy
If phosphor conversion efficiency is maintained at high temperatures, then luminous efficacy is preserved, but this contradicts the natural tendency of phosphor efficiency to drop above 90°C
Solution Approach 1:
The patent creates a continuous conversion process where light that exits the device can re-enter and undergo additional conversion passes. This continuous circulation ensures that phosphor particles are constantly utilized for light conversion, maximizing their effectiveness even at elevated temperatures by ensuring every photon has multiple opportunities for conversion rather than a single pass
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 significantly increases light output and luminous efficacy, achieving a 1500-lumen package at 150 lm/W, while extending the life of the LED and improving uniformity of the white light source.
Implementation Method 1
a down conversion material receives and down converts at least some of the short wavelength radiation emitted by the LED
Implementation Method 2
Scattered Photon Extraction (SPE) where the down-conversion material is moved away from the LED die, and a tailored optic device is used to extract back-transferred radiation
Data Source
AI summary
A light emitting apparatus includes a first radiation source without a dome, a substantially transparent and light transmissive optic device, a lens, a down conversion material, and a heat sink. The optic device is devoid of scattering particles and phosphor, and includes a planar top surface distal the first radiation source, a bottom surface proximal the first radiation sources, and a transparent sidewall extending between the top surface and the bottom surface. The down conversion material includes a flat layer including phosphor that is disposed on the planar top surface of the optic device between the lens and the radiation source. The heat sink, upon which the radiation source is mounted, has a recess formed therein in which an air space is defined between a boundary of the recess and the optic device.