Cold Mirror Phase Difference Control for HUD Color Consistency
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional head-up display (HUD) apparatuses using cold mirrors suffer from a change in image color tone when viewed from different positions due to variations in reflection phase difference across the visible wavelength range, leading to inconsistent image appearance for drivers and passengers.
Innovation Solution
A cold mirror is designed to maintain a reflection phase difference within 180±60 degrees across the visible wavelength range of 420 to 680 nm, ensuring consistent image color tone by optimizing the relationship between incident wavelength and reflection phase difference, while maintaining high average reflectivity above 90% for a bright display.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a conventional cold mirror is used to block infrared light, then the display is protected from heating, but the image color tone changes depending on the viewing position
Solution Approach 1:
The patent changes the optical parameters of the cold mirror by controlling the thickness of the low-refractive-index layer to be 1/4 wavelength or less. This parameter change modifies the phase difference characteristics of reflected light, ensuring the reflection phase difference remains within 180±60 degrees across the visible spectrum, thereby eliminating color tone variations at different viewing positions while maintaining infrared blocking functionality
Solution Approach 2:
The patent uses a composite thin film structure consisting of alternating high-refractive-index and low-refractive-index layers. This composite structure allows simultaneous optimization of infrared reflection and visible light phase characteristics, achieving both thermal protection and color consistency that single-layer structures cannot provide
2Stability of the object's composition
If the reflection phase difference is controlled within 180±60 degrees across the visible wavelength range, then color tone consistency is improved, but the design complexity increases
Solution Approach 1:
The patent simplifies the design by establishing a clear parameter rule: the low-refractive-index layer thickness should be 1/4 wavelength or less. This parameter specification provides a straightforward design guideline that achieves the desired phase difference control without requiring complex optimization processes
Solution Approach 2:
The patent applies different thickness requirements to different layers: the low-refractive-index layer is constrained to 1/4 wavelength or less, while the high-refractive-index layer has a standard quarter-wave thickness. This localized quality control achieves overall phase difference management through targeted layer optimization
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 effectively reduces color tone variations when viewing the image from different positions, ensuring a consistent appearance for both drivers and passengers, with minimal impact on reflectivity characteristics, and is particularly effective within incident angle ranges of 20 to 60 degrees.
Implementation Method 1
a cold mirror for forming the mirror has conventionally been proposed... infrared components included in the sun light are absorbed by the cold mirror
Implementation Method 2
infrared components included in the sun light are absorbed by the cold mirror and the display is thus prevented from being heated
Implementation Method 3
when a difference between an amount of variation in phase of p-polarized light reflected by the cold mirror between before and after the reflection and an amount of variation in phase of s-polarized light reflected by the cold mirror between before and after the reflection is defined as a reflection phase difference, a relationship between an incident wavelength and the reflection phase difference is set so that the reflection phase difference falls within a range of 180±60 degrees for an entire visible wavelength range of 420 to 680 nm
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
This invention relates to a cold mirror for a head-up display apparatus and provides a cold mirror that enables suppression of a phenomenon of change in color tone of an image depending on a position from which the image is viewed. This invention also provides a head-up display apparatus including the cold mirror. In a head-up display apparatus 10, display light 20 of an image displayed on a display 16 is reflected by a cold mirror 12 and a reflected image of the image is viewed by a viewer. A relationship between an incident wavelength and a reflection phase difference in the cold mirror 12 is set so that the reflection phase difference falls within a range of 180±60 degrees for an entire visible wavelength range of 420 to 680 nm.