Shallow Rectangular LED Cup with Conformal Phosphor
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Solution Overview
Problem
Packaged LEDs suffer from a wide light emission profile due to the phosphor halo effect caused by the conical cup design, leading to poor color uniformity and increased package height, which is not aesthetically pleasing and inefficient in light extraction.
Innovation Solution
A shallow, rectangular reflective cup with four flat walls sloping upward at a 33-degree angle is used, featuring a conformal phosphor coating and a clear encapsulant with a smooth flat top surface to minimize total internal reflection and redirect light efficiently, eliminating the need for a lens and allowing for a more compact package.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conical cup is filled with phosphor to convert LED light, then phosphor conversion is achieved, but a phosphor halo effect occurs causing poor color uniformity
Solution Approach 1:
The patent changes the symmetric conical cup shape to an asymmetric shallow rectangular cup with flat bottom and vertical sides. This asymmetric geometry prevents the phosphor from accumulating at the center and eliminates the phosphor halo effect, achieving uniform color distribution across the light output.
Solution Approach 2:
The patent changes the geometric parameters of the cup from a deep conical shape to a shallow rectangular shape with specific dimensions (flat bottom, vertical sides, shallow depth). This parameter change allows the phosphor to be distributed uniformly without forming a concentrated halo at the center.
2Productivity
If a hemispherical lens is added to improve light extraction, then light extraction efficiency increases, but package height increases
Solution Approach 1:
The patent removes the hemispherical lens component from the package structure. Instead of adding a lens to improve light extraction, the invention uses the shallow rectangular cup geometry combined with phosphor coating on the inner surfaces to achieve efficient light extraction without increasing package height.
Solution Approach 2:
The patent uses thin phosphor coatings applied to the inner surfaces of the shallow cup instead of a bulky hemispherical lens. This thin-film approach maintains compact package height while still achieving effective light extraction and color conversion.
3Reliability
If a deep conical cup is used to hold phosphor, then phosphor conversion is effective, but the package becomes taller and less aesthetically pleasing
Solution Approach 1:
The patent replaces the deep conical shape with a shallow rectangular shape featuring flat bottom and vertical sides. This asymmetric design achieves effective phosphor conversion in a shallow configuration, eliminating the need for deep cup structures and reducing overall package height.
Solution Approach 2:
The patent transitions from a deep vertical conical structure to a shallow horizontal rectangular structure. By changing the dimensional distribution (from deep-vertical to shallow-horizontal), the invention maintains phosphor conversion effectiveness while significantly reducing package height.
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 solution results in improved color uniformity and light extraction efficiency with a well-defined rectangular beam, enabling a shallower package that can be arrayed closely without gaps, providing a flat and aesthetically pleasing surface with reduced phosphor halo effect.
Implementation Method 1
For phosphor conversion, the cup is then completely filled with a viscous phosphor mixture and cured to encapsulate the LED die. The combination of the LED die light and the phosphor light creates the desired overall light color, such as white light.
Implementation Method 2
The encapsulation shape is also designed to minimize the TIR at the encapsulant-air interface. Dome-shaped encapsulation is popular since the rays of light emitted by the LED die impinge on the surface of the dome generally at right angles. This minimizes TIR.
Implementation Method 3
The cup somewhat limits the side light emission of the LED die and redirects the side light in a generally forward direction.
Data Source
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AI summary
An LED die (26) conformally coated with phosphor (28) is mounted at the base (24) of a shallow, square reflector cup (16). The cup has flat reflective walls (20) that slope upward from its base to its rim at a shallow angle of approximately 33 degrees. A clear encapsulant (30) completely fills the cup to form a smooth flat top surface. Any emissions from the LED die or phosphor at a low angle (48, 50) are totally internally reflected at the flat air-encapsulant interface toward the cup walls. This combined LED/phosphor light is then reflected upward by the walls (20) and out of the package. Since a large percentage of the light emitted by the LED and phosphor is mixed by the TIR and the walls prior to exiting the package, the color and brightness of the reflected light is fairly uniform across the beam. The encapsulant is intentionally designed to enhance TIR to help mix the light.