LED Illumination Device Light Guide Uniformity
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Solution Overview
Problem
Conventional illumination devices using LEDs suffer from uneven light intensity distribution and light loss due to the narrow-directivity of LEDs, leading to inefficiencies in image scanning applications.
Innovation Solution
An illumination device is designed with a wide-directivity LED and a light guide that satisfies specific conditions for total reflection, ensuring that at least 80% of the light is directed uniformly across the scanning width by optimizing the angle of directivity and refractive indices, thereby enhancing illumination efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a narrow-directivity LED is used as the light source, then energy saving and reliability are improved, but uniform light intensity distribution is deteriorated due to peak occurrence and rippling in the main scanning direction
Solution Approach 1:
A light guide is introduced as an intermediary component between the LED and the document surface. The light guide transforms the narrow-directivity light from the LED into wide-area illumination by guiding light through total internal reflection and extracting it along the side surface, thereby achieving uniform light distribution while maintaining LED energy efficiency
Solution Approach 2:
The patent changes the optical parameters by selecting specific LED viewing angles (60° or more) and configuring the light guide dimensions and refractive indices to satisfy specific mathematical relationships. This transforms the narrow-directivity light into wide-area illumination while maintaining total internal reflection efficiency
2Illumination intensity
If a wide-directivity LED is used to achieve uniform light distribution, then illumination uniformity is improved, but light loss increases due to escape of light rays without total reflection
Solution Approach 1:
The patent precisely controls optical parameters including LED viewing angle (60° or more), light guide length A, LED interval B, and refractive indices to satisfy the mathematical relationship tan−1(B/2A)≦β≦π/2−{sin−1(n1/n2)}. This ensures optimal balance between wide light distribution and total internal reflection efficiency, minimizing light loss while achieving uniform illumination
Solution Approach 2:
The light guide acts as an optical copy mechanism, transferring and redistributing the LED light through total internal reflection. The light pattern is copied and spread uniformly across the document surface while maintaining energy efficiency through controlled reflection
3Area of stationary object
If the LED interval B is increased to cover wider scanning area, then scanning width coverage is improved, but light intensity uniformity is deteriorated due to increased peak occurrence
Solution Approach 1:
The patent establishes a precise mathematical relationship between LED interval B, light guide length A, and LED viewing angle β. By controlling these parameters to satisfy tan−1(B/2A)≦β≦π/2−{sin−1(n1/n2)}, the system achieves optimal balance between coverage area and light uniformity, preventing peak occurrence even when B is increased
Solution Approach 2:
The patent transitions from direct LED-to-document illumination to three-dimensional light guiding through the light guide structure. This dimensional change allows light to be distributed uniformly across the scanning width by utilizing the light guide's side surface extraction, effectively decoupling coverage area from uniformity issues
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 achieves a uniform light intensity distribution and significantly increases illumination efficiency, ensuring that a large portion of the light is effectively used, addressing the issues of rippling and light loss in conventional systems.
Implementation Method 1
the light guide is a rod-like structure composed of a transparent material whose end surface functions as the entrance surface and at least a portion of whose side surface functions as the exit surface. The iris restricts the light beam entering from the entrance surface such that the beam forms an incidence angle, which is equal to or greater than a critical angle the beam forms with the side surface.
Data Source
AI summary
An illumination device that illuminates an original document by propagating an illuminating light beam output from each of a plurality of light emitting diodes from a first end surface of a light guide to a second end surface of the light guide. Assuming that A is a dimension from the first end surface of the light guide to the second end surface of the light guide, B is an interval between adjoining light emitting diodes, the light emitting diodes being arranged in an array format in a main scanning direction, n1 is a refractive index of atmosphere outside of the light guide, and n2 is a refractive index of the light guide, a condition of tan−1(B/2A)≦β≦π/2−{sin−1(n1/n2)} is satisfied.