Linear Fresnel Lens Facets for Uniform LED Shelf Illumination
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Solution Overview
Problem
Conventional linear Fresnel lenses are inadequate for providing uniform illumination from a linear array of LEDs, especially when light must be bent over large angles, leading to uneven illumination patterns and inefficiencies in handling out-of-plane rays.
Innovation Solution
A method for designing a linear Fresnel lens with adjustable facet angles, using principles of non-imaging optics to achieve uniform illumination by iteratively refining the lens profile and facet angles to match the cumulative flux distribution, allowing for efficient deflection of light across a wide angle, such as 30° shelf illumination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional linear Fresnel lenses are used for LED illumination, then lens thickness is reduced, but illumination uniformity deteriorates due to inability to handle out-of-plane rays
Solution Approach 1:
The patent applies local quality by making the Fresnel facet angles position-dependent rather than uniform. Each facet's angle is specifically optimized for its location on the lens surface, allowing the lens to properly refract both in-plane and out-of-plane rays from the linear LED array. This local optimization of facet angles ensures uniform illumination across the target area while maintaining the thin lens structure.
Solution Approach 2:
The patent changes the parameter of facet angles from constant (conventional design) to variable (optimized design). By adjusting the facet angles as a function of position along the lens, the optical path is optimized for uniform illumination. This parameter change allows the thin lens to effectively redirect light from all LEDs in the array, including out-of-plane rays, achieving both thickness reduction and illumination uniformity.
2Device complexity
If a single extruded lens is used for an array of LEDs, then manufacturing complexity is reduced, but lens thickness increases making extrusion difficult
Solution Approach 1:
The patent applies segmentation by dividing the lens surface into multiple Fresnel facets. This segmentation allows the lens to achieve complex optical functionality with a thin profile that is suitable for extrusion. Instead of requiring a thick monolithic lens, the segmented Fresnel structure provides the necessary light redirection capabilities while maintaining a thin cross-section that can be economically extruded.
Solution Approach 2:
The patent uses curved surfaces in the Fresnel facet design to achieve the desired light redistribution. The faceted surfaces are optimized with specific curvature characteristics that enable effective refraction of light from linear LED arrays. This curved surface approach, combined with Fresnel segmentation, allows the lens to provide uniform illumination while maintaining a thin extrudable profile.
3Measurement precision
If conventional Fresnel lens designs are used, then image fidelity is optimized, but flux distribution uniformity deteriorates for illumination applications
Solution Approach 1:
The patent inverts the design objective from conventional Fresnel lenses. Instead of optimizing for image fidelity (point-to-point correspondence), the design optimizes for uniform flux distribution across the target area. This inversion of the optimization criterion leads to different facet angle selections that prioritize illumination uniformity over image quality, which is the appropriate goal for LED shelf lighting applications.
Solution Approach 2:
The patent uses ray-tracing simulations to model and analyze the optical performance of different Fresnel facet configurations. By creating virtual copies of the optical system in simulation, the designers can iteratively optimize the facet angles to achieve uniform flux distribution before manufacturing. This computational copying and testing approach allows optimization for illumination uniformity without requiring physical prototypes.
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 provides uniform illumination across large areas, reducing aberrations and non-uniformities, and is economically viable for mass production using die-extruded lenses, suitable for applications like supermarket shelves and industrial lighting.
Implementation Method 1
Fresnel facets eliminate the lens thickness required for smooth surfaces by providing the requisite local surface slopes for the desired refractive deflection
Implementation Method 2
A linear Fresnel lens for illumination that handles large amounts of out-of-plane light
Data Source
AI summary
A linear Fresnel lens for LED illumination is configured initially by using a meridional flux-assignment method and is then corrected by assessing the three-dimensional flux distribution of individual facets. The facet angles are slightly altered as required to produce uniformity. A variety of specialized lens shapes are generated, such as for illuminating shelves in commercial refrigerator food-display cases. The lens shapes are suitably thin for economical production by extrusion.