Pseudo-White LED Illuminator Lens Sheet Prism Design
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Solution Overview
Problem
Conventional illuminators using pseudo-white LEDs exhibit color shadings due to differing optical path lengths of blue and yellow light components, resulting in bluish or yellowish hues at the center and outer circumference, respectively, leading to poor visibility and illumination uniformity.
Innovation Solution
A lens sheet with prisms having varying focal distances is arranged on the optical axis of the light source, allowing light with different focal distances to intersect and mix, thereby reducing color shadings and enhancing illumination uniformity by adjusting the focal distances of both refraction and reflection prisms based on their distance from the optical axis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a pseudo-white LED with yellow phosphor is used as the light source, then the LED can be made compact with excellent environment compatibility, but color shadings occur in the luminous lights resulting in poor visibility
Solution Approach 1:
The patent applies local quality by positioning yellow phosphors specifically in the outer peripheral region of the light source, rather than uniformly distributing them. This creates a non-uniform phosphor concentration where the outer regions have higher yellow phosphor content to compensate for the yellowish tint, while the center region maintains lower phosphor content to preserve white light quality. This spatial variation in phosphor distribution resolves the color uniformity issue while maintaining the compact LED structure.
Solution Approach 2:
The patent changes the parameter of phosphor distribution from uniform to non-uniform, specifically varying the concentration of yellow phosphors based on radial position. By adjusting the phosphor concentration parameter in different spatial zones, the optical path length differences that cause color shadings are compensated, achieving uniform color output across the luminous surface.
2Illumination intensity
If a lens sheet with refraction prisms and reflection prisms is used to achieve high illumination, then the intensity of luminous lights is well homogenized, but color shadings occur with bluish hue at center and yellowish hue at outer circumference
Solution Approach 1:
The patent modifies the lens sheet to have spatially varying properties by positioning yellow phosphors in the outer peripheral region. This creates a non-uniform optical element where different regions have different phosphor concentrations, allowing the lens to compensate for the color shadings caused by the refraction and reflection prisms while maintaining high illumination intensity.
Solution Approach 2:
The patent creates a composite structure by combining the lens sheet with strategically positioned yellow phosphors in the outer peripheral region. This composite design integrates the light-guiding function of the lens sheet with the wavelength-converting function of the phosphors, achieving both high brightness and color uniformity simultaneously.
3Device complexity
If yellow phosphors are distributed uniformly in the light source, then the structure is simple, but color shadings occur due to different optical path lengths of blue and yellow light components
Solution Approach 1:
The patent abandons uniform phosphor distribution in favor of a non-uniform distribution pattern where yellow phosphors are concentrated in the outer peripheral region. This localized phosphor placement creates a deliberately asymmetric structure that compensates for the optical path length differences, achieving color uniformity at the cost of increased structural complexity.
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 color shadings and enhances illumination uniformity, achieving high brightness and homogenization of light output across the illuminator's surface, while also simplifying the design and manufacturing of the lens sheet.
Implementation Method 1
the lens sheet has a plurality of refraction prisms (a Fresnel lens) at a center region thereof which is the side of an optical axis 73, the refraction prisms having refraction effects
Implementation Method 2
at or near the outer circumference of the lens sheet 72, a plurality of reflection prisms (referred to as a TIR lens or a Total Internal Reflection lens) having reflection effects is formed
Implementation Method 3
a yellow phosphor that absorbs the blue-series light and converts the blue-series light into a yellow-series light
Data Source
AI summary
There is provided an illuminator comprising: a light source; and a lens sheet that is arranged on the optical axis of the light source and that has a plurality of prisms, wherein the light source is composed of: a luminous element; and phosphors that irradiate with lights emitted from the luminous element, and the lens sheet includes prisms that have focal distances each different from the prisms adjacent thereto.