Remote Phosphor HUD Illumination for Uniform Local Dimming
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Solution Overview
Problem
Conventional local dimming head-up displays (HUDs) suffer from chromatic aberration, leading to uneven zone brightness and a 'texture' effect in their illumination distribution due to the dispersive properties of lenses used in collimating optics.
Innovation Solution
Implementing a 'remote phosphor' arrangement where blue light from LEDs is collimated without phosphor, and then converted to white light using a phosphor film applied after collimation, thereby avoiding aberrations caused by lens dispersion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If phosphor is applied directly on the LED before collimating optics, then white light is produced for display, but chromatic aberration occurs causing red fringe and uneven zone brightness
Solution Approach 1:
The patent segments the white light generation process into two separate stages: first generating blue light and collimating it, then converting to white light after collimation. This separation eliminates the chromatic aberration that would occur if phosphor were applied before collimation, as the blue light (single wavelength) passes through the collimating lens without dispersion issues.
Solution Approach 2:
The patent performs the collimation action before the phosphor conversion. By preliminarily collimating the blue light from the LED before it interacts with the phosphor, the system ensures that the collimating lens works with monochromatic light, avoiding chromatic aberration. The phosphor conversion to white light occurs after the collimation is already established.
2Illumination intensity
If local dimming is implemented with conventional LED+phosphor setup, then background dimming is achieved, but texture effects appear in illumination distribution
Solution Approach 1:
The patent segments the illumination system into multiple independently controllable zones with separate LED sources. Each zone can be dimmed independently while maintaining uniform illumination within that zone, because the blue LED light is collimated uniformly before phosphor conversion, eliminating the texture effects that would otherwise appear in the illumination distribution.
3Object-affected harmful factors
If blue LED with remote phosphor is used, then chromatic aberration is eliminated, but additional optical path length is required
Solution Approach 1:
The patent places the phosphor conversion in a different spatial dimension relative to the optical path - specifically, after the collimation stage rather than at the LED source. This dimensional repositioning in the optical sequence allows the system to eliminate chromatic aberration while managing the additional path length through proper optical design and compact arrangement of the extended optical train.
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 approach results in a more uniform and homogeneous illumination spot on the LCD, eliminating the red fringe and texture effects associated with chromatic aberration, thereby enhancing the visual clarity and consistency of the HUD.
Implementation Method 1
When white light passes through an optical element, the different wavelengths present refract at slightly different angles as dictated by the dispersion relationship of light in that material, or the change in the index of refraction as a function of the wavelength.
Implementation Method 2
White light LEDs are produced by coating a blue LED with a phosphor that will absorb and re-emit light in a continuous spectrum.
Data Source
AI summary
A head up display arrangement for a motor vehicle includes a picture generation unit having a plurality of light emitters each emitting blue light. A plurality of collimating optics receive the blue light from the light emitters and collimate the received blue light. At least one phosphor element receives the collimated blue light and converts the collimated blue light to diffuse white light. A liquid crystal display receives the diffuse white light and emits a light field dependent upon the diffuse white light. At least one mirror reflects the light field emitted by the liquid crystal display such that the reflected light field is again reflected by a windshield of the motor vehicle so as to be visible by a human driver of the motor vehicle as a virtual image.