Virtual Image Display Backlight Prism Layout for External Light Separation
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Solution Overview
Problem
Virtual image display devices for vehicles face challenges in preventing external light, such as sunlight, from overlapping with the virtual image due to the limited angle between the reflection direction of external light and the image light path, which can lead to inefficiencies in illumination transmission and increased dead space in the backlight as the image display panel size increases.
Innovation Solution
Incorporating a deflection prism array between the light source unit and the image display panel to deflect the illumination light, increasing the angle between the unit normal vector of the display screen and the after-transmission vector, thereby separating the external light from the image light path without tilting the image display panel excessively, thus maintaining efficient light transmission and reducing dead space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the image display panel size is increased, then the display area is improved, but the angle between the reflection direction of external light and the image light path is reduced, causing external light to overlap with the virtual image
Solution Approach 1:
A light separating element is introduced as an intermediary component between the image display panel and the backlight. This element selectively separates external light from the image light path while allowing the virtual image to pass through unchanged. The light separating element includes light separating portions positioned at specific locations to block external light reflections without interfering with the displayed image, thus resolving the overlap problem while maintaining large display area.
2Object-affected harmful factors
If the image display panel is tilted to increase the angle between reflection direction and image light path, then external light separation is improved, but the illumination light transmission efficiency is reduced and dead space in the backlight increases
Solution Approach 1:
Instead of tilting the image display panel, a light separating element is positioned between the panel and backlight to perform the separation function. This intermediary approach achieves external light separation without requiring panel tilt, thereby maintaining optimal illumination light transmission efficiency and minimizing dead space in the backlight assembly.
Solution Approach 2:
The light separating element is divided into multiple light separating portions positioned at specific locations corresponding to different viewing angles and external light sources. This segmentation allows selective blocking of external light reflections from different directions while maintaining overall transmission efficiency and avoiding the need for excessive panel tilting.
3Object-affected harmful factors
If a light separating element is added to separate external light, then external light overlap is suppressed, but the device complexity increases
Solution Approach 1:
The light separating element is designed to perform multiple functions: it separates external light from the image light path, maintains the virtual image quality, and integrates with the existing backlight structure. By combining these functions into a single component, the design achieves external light suppression without proportionally increasing overall device complexity.
Solution Approach 2:
The light separating element is positioned within the existing backlight assembly structure, nesting it between the image display panel and the backlight. This nested arrangement utilizes the existing spatial configuration, minimizing additional space requirements and reducing the overall complexity increase compared to adding a separate external light separation system.
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 effectively suppresses the overlap of external light with the virtual image, maintains efficient illumination transmission, and ensures a compact backlight design suitable for vehicle applications.
Implementation Method 1
The deflection prism array includes deflection prism elements arranged to deflect the illumination light from the light source unit while transmitting the illumination light. The deflection prism array deflects a direction of an after-transmission vector corresponding to a Poynting vector of the illumination light immediately after transmitting the deflection prism array with respect to a direction of a before-transmission vector corresponding to a Poynting vector of the illumination light immediately before transmitting the deflection prism array.
Implementation Method 2
The image display panel transmits an illumination light from the backlight and displays an image to be imaged as a virtual image on a display screen.
Data Source
AI summary
A virtual image display device includes a backlight and an image display panel that displays an image to be imaged as a virtual image on a display screen. The backlight has a deflection prism array on an optical path between a light source unit and the image display panel. The deflection prism array includes deflection prism elements to deflect the illumination light, and deflects a direction of an after-transmission vector corresponding to a Poynting vector of the illumination light immediately after passing through the deflection prism array with respect to a direction of a before-transmission vector corresponding to a Poynting vector of the illumination light immediately before passing through the deflection prism array. An angle between a unit normal vector of the display screen and the after-transmission vector is larger than an angle between the unit normal vector of the display screen and the before-transmission vector.