Planar Lighting Device Heat Dissipation and Uniformity
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Solution Overview
Problem
Current planar lighting devices face challenges in achieving a thin and lightweight design with uniform light distribution and efficient heat dissipation, particularly for large display applications, where the use of light guide plates with scattering particles is limited by thickness and brightness unevenness, and heat generated by LEDs can lead to reduced light emission and potential damage to the light sources.
Innovation Solution
A planar lighting device design featuring a pair of light sources with a light guide plate having a reversed wedge sectional shape, heat sinks, and heat pipes for efficient heat dissipation, along with surface treatments and optical member units to enhance light distribution and prevent damage from thermal expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a direct illumination type backlight unit is used, then the structure is simple, but the thickness cannot be reduced to 10 mm or less due to uneven light amount distribution
Solution Approach 1:
The backlight unit is divided into multiple functional layers: light guide plate, diffusion sheets, and prism sheet, each performing a specific optical function. This segmentation allows the light to be guided, diffused, and redirected through controlled paths, achieving uniform illumination while maintaining thin profile
Solution Approach 2:
Optical members such as diffusion sheets and prism sheets are introduced as intermediary elements between the light source and the display panel. These intermediaries modify the light path and distribution characteristics, enabling uniform light output from a thin structure
2Length of stationary object
If a light guide plate with scattering particles is used to reduce thickness, then the thickness can be reduced, but brightness unevenness occurs due to light amount distribution issues
Solution Approach 1:
Different regions of the light guide plate and optical members are designed with different optical properties. The diffusion sheets provide localized scattering to redistribute light, while the prism sheet creates specific reflection patterns. This local variation in optical characteristics compensates for the non-uniform light emission from the LED sources, achieving overall uniformity
Solution Approach 2:
The optical parameters of the light guide plate and associated members are optimized by adjusting the concentration and distribution of scattering particles, the refractive indices of materials, and the geometric parameters of prism structures. These parameter changes enable control over light propagation and extraction, achieving uniform brightness from a thin structure
3Use of energy by moving object
If LED light sources are used to reduce weight and increase efficiency, then energy efficiency improves, but heat generation causes reduced light emission and potential damage to light sources
Solution Approach 1:
The heat generated by LEDs, which is normally a harmful byproduct, is converted into a beneficial thermal gradient that drives natural convection currents. The housing structure with its specific geometry and material properties facilitates this conversion, allowing heat to be dissipated through controlled air flow paths without requiring additional active cooling components
Solution Approach 2:
The backlight unit structure itself provides heat dissipation functionality through its design features. The housing geometry creates natural convection channels, and the arrangement of optical members and light guides facilitates passive cooling. This self-service approach eliminates the need for separate active cooling systems, maintaining LED operating temperatures within acceptable ranges
4Length of stationary object
If the backlight unit thickness is reduced to 10 mm or less, then the device becomes thinner, but achieving uniform light distribution becomes difficult
Solution Approach 1:
The optical design transitions from relying primarily on thickness variations (one dimension) to utilizing in-plane optical path control through diffusion and prism structures (two dimensions). This dimensional shift allows uniform light distribution to be achieved without increasing thickness, as the optical members redistribute light laterally across the display area
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 design achieves efficient light emission with reduced brightness unevenness, allows for thinner and lighter devices, and optimizes heat dissipation to prevent LED damage and maintain light output, enabling larger display dimensions while ensuring reliable operation.
Implementation Method 1
a light guide plate for admitting light emitted by the light sources and emitting light through the light exit plane
Implementation Method 2
a light guide plate where light emitted by illumination light sources and admitted into the light guide plate is guided in given directions and emitted through a light exit plane
Implementation Method 3
light emitted by the light source and admitted through the light entrance plane into the light diffusion light guide member receives a single or a multiple scattering effect at a given rate as the light propagates through the inside of the light diffusion light guide member
Implementation Method 4
heat sinks, each for absorbing heat generated by each of the pair of light sources, and each being connected to each of the pair of light sources; and heat pipes, each for releasing the heat absorbed by each of the heat sinks toward the center of the housing
Implementation Method 5
heat pipes, each for releasing the heat absorbed by each of the heat sinks toward the center of the housing
Data Source
AI summary
The planar lighting device includes a pair of light sources, a light guide plate and a housing. The light guide plate is disposed between the light sources and includes a light exit plane and a pair of opposite light entrance planes respectively provided opposite to the light sources. The planar lighting device thus configured features a heat dissipation structure whereby a heat sink is connected to each of the light sources and heat pipes are attached to the heat sink so as to extend toward the center of the housing. Disclosed is a thin and lightweight planar lighting device suitably used for a large display television or the like, capable of emitting illumination light free from brightness unevenness or with a reduced level of brightness unevenness, allowing increase of dimensions of the display area, and capable of optimally releasing heat generated by the light sources.