Double-Molded LED Lens with Dual-Index Silicone for Backlight Mixing
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Solution Overview
Problem
Backlight waveguides for LCDs experience non-uniform light mixing near the edge due to total internal reflection, leading to a wider mixing region and inefficiencies, which cannot be effectively addressed by decreasing LED pitch without increasing cost.
Innovation Solution
A double-molded lens system for LEDs, where a low-index silicone outer lens is molded around the periphery and a high-index silicone inner lens is molded within, collimating light and reducing the mixing region by eliminating air gaps and optimizing light emission patterns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a conventional domed lens with high index of refraction is used to increase light extraction from the LED die, then light extraction efficiency is improved, but the mixing region depth increases and the waveguide width increases
Solution Approach 1:
The lens is divided into two distinct segments: an outer lens with low index of refraction (n=1.33-1.47) and an inner lens with high index of refraction (n=1.54-1.76). Each segment performs a different optical function - the outer lens controls side emission while the inner lens collimates forward light, thereby achieving high light extraction without increasing mixing region depth
Solution Approach 2:
Different regions of the lens system are assigned different optical properties. The outer lens region has low index material optimized for side light extraction, while the inner lens region has high index material optimized for forward collimation. This local differentiation allows simultaneous optimization of both light extraction efficiency and mixing region control
2Length of stationary object
If the pitch of LEDs is decreased to reduce the mixing region width, then the mixing region is shortened, but manufacturing cost increases
Solution Approach 1:
The invention changes the optical parameters of the lens system by using dual-index materials with specific refractive indices (outer: n=1.33-1.47, inner: n=1.54-1.76). This parameter optimization enables the lens to control light emission patterns more efficiently, shortening the mixing region without requiring reduced LED pitch, thereby avoiding increased manufacturing costs
3Ease of operation
If a reflector is added around the LEDs to direct side light toward the waveguide edge, then light direction is improved, but device complexity and space requirements increase
Solution Approach 1:
The dual-index lens system performs multiple optical functions simultaneously: the outer lens extracts side light while the inner lens collimates forward light. This multi-functional integration eliminates the need for separate reflector components, reducing device complexity and space requirements while maintaining effective light direction 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 double-molded lens system shortens the mixing region, allows for thinner waveguides without efficiency loss, and tailors light emission patterns for uniform illumination, enhancing light utilization and reducing costs.
Implementation Method 1
The inner lens is formed of a higher index silicone, such as n=1.54-1.76. The light emitted from the top surface of the LED die is collimated by the inner lens, since there is TIR within the inner lens due to its index of refraction being higher than that of the outer lens.
Implementation Method 2
Light from the LED die striking the inner lens sidewall at less than the critical angle for TIR is transmitted into the outer lens.
Data Source
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AI summary
A double-molded lens for an LED includes an outer lens molded around the periphery of an LED die and a collimating inner lens molded over the top surface of the LED die and partially defined by a central opening in the outer lens. The outer lens is formed using silicone having a relatively low index of refraction such as n=1.33-1.47, and the inner lens is formed of a higher index silicone, such as n=1.54-1.76, to cause TIR within the inner lens. Light not internally reflected by the inner lens is transmitted into the outer lens. The shape of the outer lens determines the side emission pattern of the light. The front and side emission patterns separately created by the two lenses may be tailored for a particular backlight or automotive application.