Reflective Sheet Aperture Layout for LED Luminance Uniformity
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Solution Overview
Problem
Light emitting devices with reflective sheets experience decreased luminance uniformity due to irreversible heat shrinkage of the reflective sheet material over time, caused by temperature changes, which is not addressed in existing technologies.
Innovation Solution
A light emitting device design where the reflective sheet's apertures are configured with a first spacing larger than a second spacing, both initially and after heat shrinkage, to maintain luminance uniformity by adjusting the relative positions of light emitting elements and apertures, considering both reversible expansion and irreversible shrinkage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the reflective sheet is made from resin material to achieve reflectivity and cost-effectiveness, then the device can be manufactured economically, but the sheet undergoes irreversible heat shrinkage over time causing luminance uniformity to deteriorate
Solution Approach 1:
The patent applies preliminary action by pre-compensating for the expected heat shrinkage in the aperture positioning design. The apertures are intentionally positioned at asymmetric distances from the light emitting elements - with the first distance being greater than the second distance - so that after the resin sheet shrinks during operation, the apertures will naturally shift to the correct positions relative to the light emitting elements, maintaining luminance uniformity throughout the device's operational life
2Reliability
If the aperture area is enlarged to prevent contact with light emitting elements due to positional shift, then reliability is improved, but the spacing between apertures and light emitting elements increases affecting luminance distribution
Solution Approach 1:
The patent applies asymmetry by designing the aperture positioning with unequal distances - the first distance from the aperture to the light emitting element is intentionally made greater than the second distance. This asymmetric configuration allows the aperture to accommodate positional shifts from heat shrinkage and linear expansion while maintaining appropriate spacing relationships, preventing contact with light emitting elements while preserving optimal luminance distribution characteristics
3Manufacturing precision
If symmetric aperture positioning is used to simplify manufacturing, then manufacturing precision is improved, but luminance uniformity deteriorates due to heat shrinkage induced positional shifts
Solution Approach 1:
The patent applies preliminary action by pre-compensating for the expected heat shrinkage in the aperture positioning design. The apertures are intentionally positioned at asymmetric distances from the light emitting elements - with the first distance being greater than the second distance - so that after the resin sheet shrinks during operation, the apertures will naturally shift to the correct positions relative to the light emitting elements, maintaining luminance uniformity throughout the device's operational life
Solution Approach 2:
The patent applies asymmetry by designing the aperture positioning with unequal distances - the first distance from the aperture to the light emitting element is intentionally made greater than the second distance. This asymmetric configuration allows the aperture to accommodate positional shifts from heat shrinkage and linear expansion while maintaining appropriate spacing relationships, preventing contact with light emitting elements while preserving optimal luminance distribution characteristics
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 configuration maintains or improves luminance uniformity over the device's lifespan by minimizing the difference between the initial and final spacings, reducing the impact of heat-induced positional changes and linear expansion coefficient differences between the substrate and reflective sheet.
Implementation Method 1
the difference in linear expansion coefficients due to the different materials between the substrate and the reflective sheet causes relative positional shift between the substrate and the apertures of the reflective sheet due to temperature changes
Implementation Method 2
when such a resin sheet is used for a long period of time in a high temperature environment, it shrinks and crystallizes, and irreversible heat shrinkage occurs in which the shrinkage does not return to its original state even when the temperature is lowered
Data Source
AI summary
A light emitting device comprises a substrate a plurality of light emitting elements provided on the substrate, and a reflective sheet provided to be positioned at a predetermined reference position on the substrate and having a plurality of apertures that expose the light emitting elements therethrough, respectively. The apertures are configured such that a first spacing that is located between each of the apertures and a respective one of the light emitting elements and farther than the respective one of the light emitting elements from the reference position is larger than a second spacing that is located between each of the apertures and the respective one of the light emitting elements and closer than the respective one of the light emitting elements to the reference position.