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Patent for Sale:

Methods and structures for improved spatial color uniformity in LEDs    

The patented technology provides methods and structures for improving the spatial color uniformity in phosphor-converted LEDs


Phosphor-converted LEDs exhibit spatial (angular) color non-uniformity resulting from differences in the intensity of the pump source (the LED) and the intensity of the down-converted light emitted from the phosphor. In phosphor-converted LEDs a portion of the light from the pump LED (generally blue light) is absorbed by the phosphor and emitted in a broad longer wavelength region (generally in the yellow-red wavelength range) and the combination of these is perceived as white light. Angular color differences can result from (i) different light distribution patterns of the pump and down-converted light (generally the intensity distribution pattern from the LED is Lambertian while that from the phosphor is isotropic) and (ii) variations in the ratio of the blue and down-converted light resulting from varying path lengths through the phosphor and variations in the spatial distribution of the phosphor concentration around the LED. In many cases the color is bluer or has a higher CCT on-axis, compared to off axis.

Spatial color uniformity (SCU) is required for a wide range of lighting applications. In general lighting, it is unacceptable to have easily visible variations in color with angle. The United States Department of Energy EnergyStar program for certification of energy efficient products has a requirement for spatial color uniformity for lighting products. High SCU is required in a wide range of other applications where the color is important, either in providing information or in terms of visibility and color rendering. Examples of such applications include automotive lighting, illumination for inspection and testing, medical illumination, for example in hospitals, and emergency lighting and indicators.

The impact of poor SCU can be magnified when LEDs are combined with optical systems. In certain situations the optics will “image out” only a portion of the solid angle of light emitted by the LED. This can result in an easily perceptible shift in the color or CCT as well as degrading the angular color uniformity. Additionally, optical systems may capture only a portion of the light emitted by the LED, resulting in a shift in color or CCT compared to without the optic.

The available technology includes two patent families. The first family has 5 issued US patents while the second family has 8 issued US patents. The approaches of these patents are applicable to a wide range of LED structures. The first family focuses on the use of concentration grading of the phosphor particles to achieve improved SCU, while the second family focuses on shaping of the phosphor over the LED to achieve improved SCU. The second approach is particularly amenable to LED packages in which the phosphor is molded over the LED. In both cases the methods and structures are engineered to improve the angular match between the spatial intensity distribution of the light from the LED and the down-converted light, to improve the SCU. The first family includes claims for methods and structures, while the second family includes claims for structures.

The key benefits of these approaches are the ability to improve the spatial color uniformity of LEDs without making large changes to the incumbent manufacturing process and with little impact on cost.

Primary Application of the Technology

The target markets for the technology are any LED applications that have requirements for high spatial color uniformity. These include general illumination, automotive lighting, illumination for inspection and testing, medical illumination, for example in hospitals, and emergency lighting and indicators.

The seller would like to be granted a license back.

Patent Summary

U.S. Patent Classes & Classifications Covered in this listing:

Class 257: Active Solid-State Devices (E.G., Transistors, Solid-State Diodes)

This class provides for active solid-state electronic devices, that is, electronic devices or components that are made up primarily of solid materials, usually semiconductors, which operate by the movement of charge carriers - electrons or holes - which undergo energy level changes within the material and can modify an input voltage to achieve rectification, amplification, or switching action, and are not classified elsewhere.

Subclass 100: Encapsulated
Subclass 96: Plural heterojunctions in same device
Subclass 98: With reflector, opaque mask, or optical element (e.g., lens, optical fiber, index of refraction matching layer, luminescent material layer, filter) integral with device or device enclosure or package

Class 313: Electric Lamp And Discharge Devices

This is the generic class for electric lamp and electric space discharge device structure. Examples of such devices are electric incandescent lamps, gas or vapor filled electric discharge tubes, including lamps, mercury arc devices, vacuum discharge tubes, radio tubes, cyclotrons, cathode-ray tubes, photosensitive discharge devices, secondary emission electron multipliers, spark plugs, and open air arc and spark devices.

Subclass 484: With gaseous discharge medium
Subclass 501: Light conversion
Subclass 512: With envelope or encapsulation

Class 438: Semiconductor Device Manufacturing: Process

This class provides for manufacturing a semiconductor containing a solid-state device for the following purposes: (a) conducting or modifying an electrical current, (b) storing electrical energy for subsequent discharge within a microelectronic integrated circuit, or (c) converting electromagnetic wave energy to electrical energy or electrical energy to electromagnetic energy. Also operations involving: (1) coating a substrate with a semiconductive material, or (2) coating a semiconductive substrate or substrate containing a semiconductive region. It also provides for operations involving etching a semiconductive substrate or etching a substrate containing a semiconductive region. The class provides for packaging or treatment of packaged semiconductor.

Subclass 29: Including integrally formed optical element (e.g., reflective layer, luminescent material, contoured surface, etc.)