Surface Light Source Device Uniform Luminance at Low Height-to-Pitch Ratio
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Solution Overview
Problem
Conventional direct surface light source devices experience increased luminance unevenness when the height-to-pitch ratio (H/P) is set to 0.2 or less, due to non-optimized light distribution characteristics, leading to inadequate light emission beyond the peak emission angle and resulting in brighter areas near the light emitting devices.
Innovation Solution
A surface light source device with a substrate, light emitting devices having a light emitting element and a light flux controlling member, and a light diffusion plate, where the light diffusion plate is configured to transmit and diffuse light, with specific equations (HP ≤ 0.2, LP > 1, I1/2/I0 > 6) ensuring uniform light distribution by gradually increasing luminous intensity with angle, and the light flux controlling member's shape optimized to emit light in a larger angular range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the height-to-pitch ratio (H/P) is set to 0.2 or less to achieve thinning of the surface light source device, then the device thickness is reduced, but luminance unevenness increases due to non-optimized light distribution characteristics
Solution Approach 1:
The patent changes the light distribution characteristics by adjusting the peak emission angle to 80 degrees or more and controlling the luminous intensity ratio I1/2/I0 to be 6 or more. These parameter changes in the light flux controlling member enable the device to achieve H/P ≤ 0.2 while maintaining uniform luminance distribution across the light emitting surface.
2Illumination intensity
If the peak emission angle is increased to eliminate luminance unevenness, then luminance uniformity improves, but the device cannot be sufficiently thinned (H/P ≤ 0.2) with reduced number of light emitting elements
Solution Approach 1:
The patent achieves both luminance uniformity and thinning by simultaneously optimizing two parameters: setting the peak emission angle to 80 degrees or more and controlling the luminous intensity ratio I1/2/I0 to be 6 or more. This combination of parameter changes enables the light flux controlling member to distribute light effectively even at H/P ≤ 0.2.
Solution Approach 2:
The patent uses a light flux controlling member with an inverted cone shape that copies and redistributes light from the light emitting element in a controlled manner. The specific geometry of the inverted cone enables it to redirect light at the optimized peak emission angle of 80 degrees or more, achieving uniform luminance distribution while allowing device thinning.
3Length of stationary object
If conventional light distribution characteristics are used with H/P ≤ 0.2, then device thinning is achieved, but luminance unevenness occurs with brighter areas near light emitting devices
Solution Approach 1:
The patent resolves the luminance unevenness by changing the light distribution parameters: setting the peak emission angle to 80 degrees or more and controlling the luminous intensity ratio I1/2/I0 to be 6 or more. These parameter changes ensure that light is distributed more toward the center of the light emitting surface, preventing the bright spots that occur with conventional parameters at H/P ≤ 0.2.
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 thin and energy-efficient surface light source device with reduced luminance unevenness, ensuring uniform light emission across the surface even at a height-to-pitch ratio of 0.2 or less, by optimizing the light distribution characteristics and emission angles.
Implementation Method 1
a light diffusion plate disposed substantially parallel to the substrate over the plurality of light emitting devices, the light diffusion plate being configured to transmit light from the light emitting device while diffusing the light
Data Source
AI summary
A surface light source device (100) includes substrate (120), a plurality of light emitting devices (130) disposed at constant intervals on substrate (120), and light diffusion plate (160) disposed substantially parallel to substrate (120) over the plurality of light emitting devices (130). Light emitting device (130) includes light emitting element (140) and light flux controlling member (150). A luminous intensity of light from light emitting device (130) is gradually increased as an angle relative to optical axis (LA) becomes larger in an angular range from a direction along optical axis (LA) of light emitting device (130) to a direction of emission of light with the highest luminous intensity from light emitting device (130). Surface light source device (100) satisfies three Equations of H/P≦0.2, L/P>1, and I1/2/I0>6.