Windshield Reflective Polarizer for HUD Color Shift Control
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Solution Overview
Problem
Conventional reflective polarizers used in display systems, such as heads-up displays, suffer from significant variations in optical reflectivity due to multiple notches or bands of high and low reflectivity, leading to color shifts at different angles of incidence, which compromises the transmission and reflection of light.
Innovation Solution
A reflective polarizer for windshields with a configuration that includes distinct and spaced-apart reflection bands, limited to two in the visible wavelength range, and a controlled reflectance ratio between maximum and minimum reflectance values, along with polymeric layers and skin layers, to minimize optical reflectivity variations and reduce color shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional reflective polarizers with multiple notches or bands are used to achieve high reflectivity, then the reflectivity for specific wavelengths is improved, but the optical reflectivity varies significantly at different angles of incidence causing color shifts
Solution Approach 1:
The patent changes the structural parameters of the reflective polarizer by limiting the number of reflection bands in the visible range to no more than two, and controlling the reflectance ratios (R1max/R1min between 2:1 and 10:1, R2max/R2min between 1:1.5 and 1:3). This parameter optimization reduces angular dependence and color shifts while maintaining sufficient reflectivity for HUD applications.
Solution Approach 2:
The patent applies different reflectance characteristics to different wavelength ranges: in the visible range, it limits reflection bands to reduce color shifts, while in the infrared range, it allows more reflection bands for heat rejection. This localized optimization of optical properties resolves the contradiction between reflectivity and color consistency.
2Object-affected harmful factors
If multiple reflection bands are used to reject infrared radiation, then the infrared rejection capability is improved, but the complexity of the reflective polarizer structure increases
Solution Approach 1:
The patent segments the spectral control function by treating visible and infrared ranges differently: visible range uses limited reflection bands (≤2) for color consistency, while infrared range uses multiple reflection bands for heat rejection. This segmentation allows independent optimization of each wavelength range without excessive overall complexity.
3Stability of the object's composition
If the reflectance ratio between maximum and minimum reflectance is reduced to minimize color shifts, then the color consistency is improved, but the overall reflectivity may decrease
Solution Approach 1:
The patent optimizes the reflectance ratio parameters to specific ranges (R1max/R1min between 2:1 and 10:1, R2max/R2min between 1:1.5 and 1:3) that balance color consistency and overall reflectivity. These parameter values are chosen to minimize color shifts while maintaining sufficient reflectivity for HUD image brightness.
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 ensures consistent light transmission and reflection, reducing color shifts and maintaining brightness of the reflected image, while ensuring sufficient light transmission in the visible wavelength range.
Implementation Method 1
Reflective polarizers are optical elements that allow light of one polarization to be substantially transmitted through the reflective polarizer for a wavelength range, while substantially reflecting light of another polarization for the same wavelength range
Implementation Method 2
The reflective polarizer is configured to receive the image light at a first incident angle of greater than about 30 degrees and reflect the received image light for viewing by the passenger
Data Source
AI summary
A windshield of a vehicle includes a reflective polarizer. The windshield is configured to receive and reflect an image light emitted by a display toward a passenger of the vehicle, such that for a substantially normally incident light, the windshield has first and second reflection spectra versus wavelength for the incident light polarized along respective first and second directions. The first reflection spectrum includes a plurality of reflection bands. Each of the reflection bands has a maximum reflectance R1max between 20% and 80%. Between each pair of adjacent reflection bands in the plurality of reflection bands, the first reflection spectrum has a minimum reflectance R1min between 5% and 25%. In the visible wavelength range, the second reflection spectrum has a maximum reflectance R2max and a minimum reflectance R2min, such that R2max and R2min are within 15% of each other.