Head-Up Display Backlight Asymmetric Illuminance
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Solution Overview
Problem
Head-up display devices experience luminance inconsistency due to vertical movement of the driver's viewpoint, causing changes in the brightness of the projected image on the windshield.
Innovation Solution
A head-up display device with a transmission-type liquid-crystal display element and a backlight unit featuring a single light source, optical condenser, and a diffuser with a light emission face optically conjugated to the driver's visible area, allowing for adjustable illuminance distribution to maintain constant luminance across the vertical direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional backlight unit with uniform illuminance is used, then the liquid crystal panel receives consistent light, but the luminance distribution in the driver's visible area becomes non-uniform due to vertical viewpoint movement
Solution Approach 1:
The patent applies local quality by creating non-uniform illuminance distribution in the light emission face of the optical condenser. Specifically, the upper side has different illuminance characteristics than the lower side, with the maximum illuminance position shifted from the center toward the upper side. This local variation in illuminance quality compensates for the luminance non-uniformity caused by vertical viewpoint movement, ensuring consistent perceived brightness across different viewing positions.
Solution Approach 2:
The patent employs asymmetry in the optical condenser design by intentionally creating an asymmetric illuminance distribution pattern. The light emission face is designed so that the illuminance maximum is not at the center but shifted toward the upper side, and the illuminance values at the upper and lower sides are deliberately made different. This asymmetric configuration counteracts the symmetric problem of vertical viewpoint movement, maintaining constant luminance perception regardless of vertical eye position.
2Illumination intensity
If multiple light sources are used to achieve uniform luminance distribution, then brightness consistency improves, but device complexity and cost increase
Solution Approach 1:
The patent applies parameter changes by modifying the illuminance distribution parameters of a single light source system. Instead of using multiple light sources, the invention changes the illuminance parameters (intensity distribution, maximum position, asymmetry ratio) of the optical condenser's light emission face. This single-parameter approach (controlling illuminance distribution shape and position) achieves uniform luminance output with simpler hardware, reducing device complexity while maintaining luminance uniformity.
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 suppresses brightness changes caused by the driver's viewpoint movement, ensuring a consistent display image luminance and reducing component costs by using a single light source and asymmetric optical condenser design.
Implementation Method 1
an optical condenser that condenses light emitted from the light source toward the liquid-crystal display element
Implementation Method 2
an optical member arranged in an optical path between the optical condenser and the liquid-crystal display element to diffuse the light condensed by the optical condenser
Data Source
AI summary
A head-up display device has a backlight unit configured to illuminate a liquid crystal panel from a back side. The backlight unit has an optical condenser configured to condense the light emitted from a light source toward the liquid crystal panel, and a microlens array arranged in an optical path between the optical condenser and the liquid crystal panel to diffuse the light condensed by the optical condenser. The microlens array has a light emission face arranged in a position optically conjugated with an eyebox to emit the light incident from the optical condenser.