Thin LED Backlight TIR Lens Fresnel Reflection Reduction
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Solution Overview
Problem
Conventional LED backlights face challenges in achieving uniform illumination across large screen sizes due to cosine drop-off, light scattering, and Fresnel reflections, which result in hot spots and non-uniformity, especially in thin geometries and 16:9 screen geometries.
Innovation Solution
The use of axial symmetric and non-axial symmetric Total Internal Reflection (TIR) lenses with pyramidal or conical cavities and an asymmetrical absorption filter, combined with a diffuser film stack and prismatic brightness enhancing films, to intercept and redirect light and minimize Fresnel reflections, achieving uniformity exceeding 90%.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional LEDs are used without dedicated local lenses, then fewer LEDs are needed due to increased power output, but uniform illumination becomes difficult to achieve due to cosine drop-off and hot spots
Solution Approach 1:
A light redistributing member is introduced as an intermediary between the LED and the display panel. This member has a first surface facing the LED and a second surface facing the display panel, with a refractive index different from both the LED medium and the display panel medium. The member redistributes light from the LED to achieve uniform illumination across the display panel while maintaining the benefits of high-power LEDs.
Solution Approach 2:
The patent changes the refractive index parameter of the light redistributing member to optimize light distribution. By selecting a specific refractive index range (1.35-1.65), the system achieves improved illumination uniformity while maintaining high LED power output efficiency.
2Illumination intensity
If the size of the illumination lens is increased to compensate for scattering, then hot spots may be reduced, but the backlight thickness increases which is not acceptable for thin displays
Solution Approach 1:
The light redistributing member is designed as a thin optical element with controlled thickness (0.1-5.0 mm). Despite its thin profile, it effectively redistributes light to reduce hot spots through its specially designed surface geometries and refractive index properties, eliminating the need for thicker conventional lens solutions.
Solution Approach 2:
The light redistributing member incorporates curved surfaces with specific radii of curvature (R1, R2, R3, R4) to control light paths. These curved surfaces enable effective light redistribution and hot spot reduction in a compact, thin form factor without requiring large lateral dimensions.
3Area of stationary object
If a diverging lens is used to spread LED light across a large lateral area, then illumination coverage is improved, but the lens must modify the forward emitting angular distribution which increases device complexity
Solution Approach 1:
The light redistributing member performs multiple functions simultaneously: it redistributes light laterally to cover large areas, controls angular distribution, reduces hot spots, and maintains a relatively simple planar or slightly curved geometry. This multi-functionality in a single component reduces overall device complexity compared to conventional multi-element lens systems.
4Quantity of substance
If fewer LEDs are used to reduce cost, then power consumption decreases, but achieving uniform illumination geometry becomes increasingly difficult
Solution Approach 1:
The light redistributing member acts as an intermediary that compensates for the reduced number of LEDs by efficiently redistributing their light output. This allows the system to achieve uniform illumination with fewer LEDs, reducing both cost and power consumption while maintaining illumination quality.
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
This solution significantly reduces Fresnel reflections and enhances light uniformity across LCD screens, achieving illuminance uniformity of over 90% and improving optical efficiency, even in thin backlight units with 16:9 geometries.
Implementation Method 1
axial symmetric and non-axial symmetric Total Internal Reflection (TIR) lenses with pyramidal or conical cavities
Implementation Method 2
an asymmetrical absorption filter, combined with a diffuser film stack and prismatic brightness enhancing films, to intercept and redirect light and minimize Fresnel reflections
Implementation Method 3
diffuser film stack and prismatic brightness enhancing films
Data Source
AI summary
A light-emitting apparatus including a light-emitting element and a lens covering the light-emitting element. The lens includes an upper surface having a convex shape and a lower surface including a cavity to which light emitted from the light-emitting elements is incident, in which the cavity includes an apex facing an upper surface of the light-emitting element and configured to reduce Fresnel reflections emitted vertically.