Thin Flash Module Using Side-Emitting LED and Light Guide
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Solution Overview
Problem
Conventional flash modules for cameras, especially in cell phones, are too thick and expensive due to the use of xenon bulbs or point-source LEDs, which are not suitable for extreme thinness and result in an intense point of light that is objectionable to the subject being photographed.
Innovation Solution
A side-emitting LED with a flip chip configuration, a planar phosphor layer, and a thin light guide with reflective surfaces is used to redirect light sideways, eliminating the need for lenses and creating a very thin flash module that spreads light over a large area, reducing the module's thickness to less than 1 mm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional point-source LEDs or xenon bulbs are used in flash modules, then light output intensity is sufficient, but the module thickness becomes too large for thin camera applications
Solution Approach 1:
The patent transitions from vertical light emission (point-source LED or bulb) to lateral light emission by removing the growth substrate and directing light through the side of the LED structure. This dimensional change allows the light to propagate horizontally into a light guide rather than vertically, enabling a much thinner overall module profile while maintaining sufficient light output intensity for flash applications.
Solution Approach 2:
The growth substrate is completely removed from the LED structure, extracting the bulky base that traditionally supported the LED from below. This extraction eliminates the need for a deep mounting structure and allows the LED to be mounted in a flip-chip configuration with light emission directed laterally, significantly reducing the vertical thickness of the flash module.
2Illumination intensity
If point-source LEDs are used, then light output is concentrated and intense, but the light appears as an objectionable point source to the subject being photographed
Solution Approach 1:
A light guide is introduced as an intermediary component between the side-emitting LED and the subject being photographed. The light guide receives the concentrated lateral light emission from the LED and redistributes it across its extended surface area, transforming the intense point source into a diffuse area light source that illuminates the subject evenly without creating an objectionable bright spot in photographs.
Solution Approach 2:
The light emission is redirected from a vertical point source into lateral propagation along a light guide. This dimensional transformation spreads the light across a larger surface area in the horizontal plane, converting the concentrated point source into a distributed area source that eliminates the harmful point source effect while maintaining total light output.
3Object-affected harmful factors
If diffusing lenses are added to spread light from point sources, then light diffusion improves, but the module thickness increases significantly
Solution Approach 1:
Instead of adding vertical diffusion elements that increase thickness, the patent achieves light diffusion by changing the emission dimension to lateral. The side-emitting LED coupled with a planar light guide provides area light emission inherently, eliminating the need for separate diffusing lenses and maintaining a thin module profile.
4Ease of operation
If conventional LED packages with reflectors and lenses are used, then light directionality is improved, but the package thickness becomes approximately 5mm
Solution Approach 1:
The growth substrate is extracted from the LED structure, removing the traditional base that requires significant vertical space. This allows the LED to be mounted in a flip-chip configuration where the active emission layer is positioned close to the light guide, enabling effective light directionality through lateral emission without requiring a 5mm thick conventional package.
Solution Approach 2:
The light emission is redirected from vertical to lateral direction, allowing the use of a thin planar light guide with reflective surfaces to achieve proper light directionality. This dimensional change eliminates the need for bulky conventional packaging while maintaining effective light control.
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 a reliable, cost-effective, and thin flash module that diffuses light evenly, making the light source appear as a large surface area rather than a point source, improving user experience and camera performance without increasing module thickness.
Implementation Method 1
A uniform reflective film is formed on the phosphor layer... such that substantially all light impinging on the reflector is redirected back into the LED
Implementation Method 2
The side-emitting LEDs are relatively thick. US2006/227546 A1 discloses side-emitting LEDs being in a backlight, where the side emission is due to special transparent lenses over the LEDs, which lenses reflect light, using total internal reflection.
Implementation Method 3
A planar phosphor layer is formed over the second semiconductor layer
Data Source
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AI summary
Very thin flash modules for cameras are described that do not appear as a point source of light to the illuminated subject. Therefore, the flash is less objectionable to the subject. In one embodiment, the light emitting surface area is about 5 mm x 10 mm. Low profile, side-emitting LEDs optically coupled to solid light guides enable the flash module to be thinner than 2 mm. The flash module may also be continuously energized for video recording. The module is particularly useful for cell phone cameras and other thin cameras.