Thin LED Flash Module Rectangular Beam Asymmetry
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Solution Overview
Problem
Conventional camera flash modules using phosphor-converted light emitting diodes (pcLEDs) suffer from inefficiencies in light distribution, color uniformity, and module thickness due to the design of the reflector cup and lens, leading to wasted light and non-uniform illumination.
Innovation Solution
A blue flip-chip LED die with a thick transparent substrate for increased side light emission, a conformal phosphor coating, and a rectangular reflector with curved walls to redirect side light into a pyramidal beam, combined with a thin convex lens to minimize thickness and enhance uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional round reflective cup with YAG phosphor is used, then the LED die can be mounted easily, but the light emission pattern is circular which does not match the rectangular camera field of view, causing wasted light
Solution Approach 1:
The patent changes the reflector cup shape from conventional circular to rectangular to match the rectangular camera field of view. This asymmetric modification ensures that light is directed only toward the camera sensor area, eliminating waste light in surrounding areas while maintaining ease of LED die mounting through the reflector cup structure.
2Illumination intensity
If a circular Fresnel lens is used to create conical light emission, then the LED light can be redirected, but the circular beam does not match the rectangular field of view and illuminates unnecessary areas
Solution Approach 1:
The patent replaces the conventional circular Fresnel lens with a rectangular lens that has different refractive indices in orthogonal directions. This asymmetric lens design creates a rectangular light emission pattern that precisely matches the camera field of view, redirecting light efficiently without illuminating unnecessary surrounding areas.
Solution Approach 2:
The patent modifies the lens by creating regions with different refractive indices - specifically, the rectangular lens has a first refractive index in one direction and a second refractive index in the orthogonal direction. This parameter change enables the lens to shape light into a rectangular pattern matching the camera sensor aspect ratio, improving illumination efficiency.
3Illumination intensity
If the lens is spaced away from the LED die by the focal length, then light can be properly redirected, but the flash module thickness significantly increases
Solution Approach 1:
The patent integrates the Fresnel lens directly onto the LED die structure, with the lens positioned in the same plane as the LED die or with minimal spacing. This nesting approach eliminates the need for the conventional focal length spacing, allowing the flash module to achieve a thin profile while still properly redirecting light through the rectangular lens geometry.
4Reliability
If a rigid printed circuit board is used, then electrical connections are stable, but the thinness of the flash module is limited
Solution Approach 1:
The patent replaces the conventional rigid printed circuit board with a flexible circuit board that has sufficient mechanical strength for electrical connections but minimal thickness. This flexible substrate maintains reliable electrical connections between the LED die, reflector cup, and lens while enabling the flash module to achieve a thin overall profile suitable for modern cameras.
5Illumination intensity
If the reflector cup has high walls to redirect angled light, then light collimation improves, but the minimum thickness of the flash module increases
Solution Approach 1:
The patent addresses the light redirection problem by transitioning from a vertical reflector cup structure to a horizontal rectangular lens structure. Instead of using high vertical walls to collimate light, the rectangular lens uses its planar geometry and anisotropic refractive indices to redirect light in the horizontal plane, achieving effective collimation without increasing the vertical thickness of the flash module.
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 results in a thinner, more uniform, and efficient flash module that matches the camera's field of view aspect ratio, reducing back-reflection and improving light distribution across the rectangular beam.
Implementation Method 1
A blue flip-chip LED die has a relatively thick transparent substrate on its top surface. This causes a significant portion of the light emission to be from the sides of the LED die
Implementation Method 2
A conformal coating of phosphor is deposited over the top and side surfaces of the LED die to create a uniform white light
Implementation Method 3
A rectangular reflector with curved walls for redirecting the side LED light into a generally pyramidal beam, having a rectangular cross-section
Implementation Method 4
A thin lens is affixed over the top of the reflector, where the lens has a convex side that faces toward the LED die... there is much less back-reflection
Data Source
AI summary
A thin flash module for a camera uses a flexible circuit as a support surface. A blue GaN-based flip chip LED die is mounted on the flex circuit. The LED die has a thick transparent substrate forming a “top” exit window so at least 40% of the light emitted from the die is side light. A phosphor layer conformally coats the die and a top surface of the flex circuit. A stamped reflector having a knife edge rectangular opening surrounds the die. Curved surfaces extending from the opening reflect the light from the side surfaces to form a generally rectangular beam. A generally rectangular lens is affixed to the top of the reflector. The lens has a generally rectangular convex surface extending toward the die, wherein a beam of light emitted from the lens has a generally rectangular shape corresponding to an aspect ratio of the camera's field of view.