Light-emitting device with cover layer for blue light leakage
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Solution Overview
Problem
Conventional red LEDs used in light-emitting devices suffer from inferior temperature characteristics and increased blue light leakage at high temperatures, leading to reduced color purity when viewed from oblique angles due to the dielectric multilayer film's inefficiency in reflecting blue light.
Innovation Solution
A light-emitting device configuration featuring a light-transmissive member, a phosphor layer, a dielectric multilayer film, and a cover layer, where the cover layer is either a phosphor or pigment layer disposed on the lateral surfaces to absorb blue light and convert it into yellow-red to red light, minimizing light leakage and maintaining color purity across viewing angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a dielectric multilayer film is used to reflect blue light in a light-emitting device, then blue light reflection efficiency is improved at normal viewing angles, but blue light leakage increases at oblique angles due to reduced reflection efficiency
Solution Approach 1:
The patent extracts the blue light reflection function from the dielectric multilayer film by introducing a separate reflective member (such as a metal reflector or high-reflection coating) positioned at the bottom of the light-emitting device. This reflective member specifically targets and reflects blue light that would otherwise leak at oblique angles, while the dielectric multilayer film continues to handle wavelength conversion and overall light management. This separation allows the system to maintain high blue light reflection efficiency across all viewing angles without compromising the phosphor conversion function.
Solution Approach 2:
The patent introduces a reflective member as an intermediary element between the light-emitting element and the external environment. This reflective member acts as a mediator that intercepts blue light attempting to escape at oblique angles and redirects it back into the optical path, where it can be converted to red light by the phosphor layer or directed toward the viewer. This intermediary approach resolves the contradiction by adding a dedicated component for blue light management without interfering with the existing dielectric multilayer film's wavelength conversion function.
2Illumination intensity
If red LEDs are used to provide red light emission, then red light output is achieved, but temperature characteristics deteriorate and output decreases at high temperatures
Solution Approach 1:
The patent replaces the direct red LED emission mechanism with an indirect approach using blue light-emitting LEDs combined with phosphor wavelength conversion. Instead of relying on red LEDs that suffer from poor temperature characteristics, the system uses blue LEDs (which have excellent temperature stability) to excite red phosphor materials, thereby generating red light through photoluminescence. This substitution transfers the light generation function from a thermally sensitive direct emission mechanism to a thermally stable indirect conversion mechanism.
Solution Approach 2:
The patent employs composite material systems consisting of blue light-emitting semiconductor materials combined with red phosphor materials. This composite approach allows the system to leverage the thermal stability of blue LED materials while achieving red light emission through the phosphor conversion process. The composite structure of blue LED chip plus red phosphor layer creates a hybrid system that overcomes the temperature sensitivity inherent in pure red LED materials.
3Use of energy by moving object
If the dielectric multilayer film allows increased blue light transmission at larger angles of incidence, then more blue light reaches the phosphor layer, but color purity deteriorates due to blue light blending with red emitted light
Solution Approach 1:
The patent segments the light management functions by separating the wavelength conversion function (handled by the dielectric multilayer film and phosphor layer) from the blue light reflection function (handled by the dedicated reflective member). The reflective member is positioned and configured to specifically target blue light at oblique angles, reflecting it back into the optical path before it can reach the viewer. This segmentation allows the dielectric multilayer film to maintain high blue light transmission for phosphor excitation while the reflective member prevents blue light leakage that would compromise color purity.
Solution Approach 2:
The patent applies local quality by positioning the reflective member specifically at regions where oblique blue light leakage occurs, rather than uniformly treating all light paths. The reflective member is strategically placed at the bottom and/or lateral surfaces of the light-emitting device, creating localized blue light reflection zones that address oblique angle issues without interfering with the primary optical path. This localized approach maintains high color purity in the forward direction while correcting blue light leakage at oblique angles.
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 effectively reduces blue light leakage and maintains uniform red color purity even at oblique angles, enhancing the light-emitting device's performance and color consistency.
Implementation Method 1
a dielectric multilayer film interposed therebetween to reflect blue light
Implementation Method 2
The first phosphor layer absorbs at least a portion of the blue light emitted by the light-emitting element
Implementation Method 3
The first phosphor layer absorbs at least a portion of the blue light emitted by the light-emitting element and emits yellow-red to red light
Implementation Method 4
the cover layer is either: a second phosphor layer that absorbs at least a portion of the blue light emitted by the light-emitting element
Implementation Method 5
a second phosphor layer that absorbs at least a portion of the blue light emitted by the light-emitting element and emits yellow-red to red light
Data Source
AI summary
A light-emitting device includes: a set of layers including (i) a light-transmissive member having a top surface, a bottom surface, and a lateral surface contiguous with the top surface and the bottom surface, (ii) a first phosphor layer disposed below the bottom surface, and (iii) a dielectric multilayer film between the light-transmissive member and the first phosphor layer; a cover layer disposed on a lateral surface of the set of layers; and a light-emitting element disposed below the first phosphor layer. The light-emitting element emits blue light. The first phosphor layer absorbs at least a portion of the blue light and emits yellow-red to red light. The cover layer is either: a second phosphor layer that absorbs at least a portion of the blue light emitted by the light-emitting element and emits yellow-red to red light, or a pigment layer that presents yellow-red to red light.