DIFFUSER TO IMPROVE UNIFORMITY OF HEAD-UP DISPLAY IMAGE BRIGHTNESS

Abstract

A backlighting arrangement is for a head up display that presents a virtual image to a human driver of a motor vehicle. The arrangement includes a light source emitting light with a non-uniform brightness over a field of view of the human driver. A diffuser includes a surface through which the light emitted by the light source passes. The surface has a texture that varies with position on the surface. The texture scatters the light such that the brightness of the light over a field of view of the human driver is more uniform after passing through the diffuser at a given average brightness than it would be with a diffuser configured to scatter light independent of position after passing through the diffuser.

Claims

1. A backlighting arrangement for a head-up display that presents a virtual image to a human driver of a motor vehicle, the arrangement comprising: a light source configured to emit light with a non-uniform brightness over a field of view of the human driver; and a diffuser including a surface through which the light emitted by the light source passes, the surface having a texture that varies with position on the surface, the texture being configured to scatter the light such that for a virtual image intended to have constant brightness the brightness of the light over the field of view of the head-up display as seen by the human driver is more uniform at a given said non-uniform brightness of the light source than with a diffuser configured to scatter light independent of position.

2. The arrangement of claim 1 wherein the light source is configured to emit light with more brightness in a central portion of the field of view of the head-up display as seen by the human driver than in a peripheral portion of the field of view.

3. The arrangement of claim 1 wherein the light source comprises a plurality of light emitting diodes.

4. The arrangement of claim 1 wherein the surface of the diffuser has a plurality of smooth sections and a plurality of rough sections, the smooth sections being configured to scatter the light to a lesser degree than the rough sections scatter the light.

5. The arrangement of claim 1 wherein the surface of the diffuser comprises a first surface, the diffuser including a second surface having a plurality of micro-prisms.

6. The arrangement of claim 5 wherein the micro-prisms vary by position on the second surface and are configured to vary a bend angle of light passing through the second surface as a function of position on the second surface.

7. The arrangement of claim 6 wherein each said micro-prism has a width and length of approximately between three and 100 microns, and the maximum height of a micro-prism is less than half of the maximum width and length.

8. A method for providing backlighting for a head up display of a motor vehicle, the method comprising: emitting a light field with a non-uniform brightness over a field of view; providing a diffuser including a surface having a texture that varies with position on the surface; and placing the diffuser in a path of the light field such that the varying texture of the diffuser surface scatters the light, and such that for a virtual image intended to have constant brightness the brightness of the light over the field of view as seen by the human driver is more uniform than with a diffuser configured to scatter light independent of position.

9. The method of claim 8 wherein the light field is emitted with more brightness in a central portion of the head-up display field of view than in a peripheral portion of the head-up display field of view.

10. The method of claim 8 wherein the surface of the diffuser has a plurality of smooth sections and a plurality of rough sections.

11. The method of claim 10 wherein the smooth sections scatter the light to a lesser degree than the rough sections scatter the light.

12. The method of claim 8 wherein the surface of the diffuser comprises a first surface, the diffuser including a second surface having a plurality of micro-prisms.

13. The method of claim 12 wherein the micro-prisms vary by position on the second surface and vary a bend angle of light passing through the second surface as a function of position on the second surface.

14. The method of claim 13 wherein each said micro-prism has width and length of approximately between three and 100 microns, and the maximum height of a micro-prism is less than half of the maximum width and length.

15. A backlighting arrangement for a head up display that presents a virtual image to a human driver of a motor vehicle, the arrangement comprising: a light source configured to emit light with a non-uniform brightness over a field of view of the human driver; and a diffuser including: a first surface through which the light emitted by the light source passes, the first surface having a texture that varies with position on the surface; and a second surface through which the light emitted by the light source passes, the second surface having a plurality of micro-prisms that vary with position on the surface, the texture and the micro-prisms being configured to scatter the light such that the brightness of the light over a field of view of the human driver is more uniform at a given said non-uniform brightness of the light source than with a diffuser configured to scatter light independent of position after passing through the diffuser.

16. The arrangement of claim 15 wherein the light source is configured to emit light with more brightness in a central portion of the field of view of the human driver than in a peripheral portion of the field of view of the human driver.

17. The arrangement of claim 15 wherein the light source comprises a plurality of light emitting diodes.

18. The arrangement of claim 15 wherein the first surface of the diffuser has a plurality of smooth sections and a plurality of rough sections, the smooth sections being configured to scatter the light to a lesser degree than the rough sections scatter the light.

19. The arrangement of claim 15 wherein the micro-prisms vary by position on the second surface, and are configured to vary a bend angle of light passing through the second surface as a function of position on the second surface.

20. The arrangement of claim 19 wherein each said micro-prism has a height, width and length of approximately between three and 100 microns, and the maximum height of a micro-prism is less than half of the maximum width and length.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The above-mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

[0014] FIG. 1 is a fragmentary cross-sectional view of one embodiment of a diffuser of the present invention.

[0015] FIG. 2 is an example plot of a diffuser of FIG. 1 with diffuser strength that varies as a function of position on the diffuser to optimize the uniformity of the brightness of the virtual image.

[0016] FIG. 3 is a front schematic view of one embodiment of a head up display LCD backlighting arrangement of the invention including the diffuser of FIG. 1.

[0017] FIG. 4 is a side schematic view of the head up display LCD backlighting arrangement of FIG. 3.

[0018] FIG. 5 is a flow chart of one embodiment of method of the present invention for providing backlighting for a head up display of a motor vehicle.

DETAILED DESCRIPTION

[0019] The embodiments hereinafter disclosed are not intended to be exhaustive or limit the invention to the precise forms disclosed in the following description. Rather the embodiments are chosen and described so that others skilled in the art may utilize its teachings.

[0020] FIG. 1 illustrates one embodiment of a diffuser 10 of the present invention having two outer surfaces 12 and 14. Surface 12 has a texture that varies as a function of position to control the scattering of visible light as a function of position. For example, surface 12 may have smooth sections that scatter light to a lesser degree, and rough or undulating sections that scatter light to a greater degree.

[0021] The other surface 14 is covered with micro-prisms 16 that vary as a function of position to control the bend angle of light passing through the surface as a function of position. Each micro-prism 16 may have a width and length of approximately between three and 100 microns, and the maximum height of a micro-prism is less than half of the maximum width and length.

[0022] Diffuser 10 is conceptually divided into small facets. Within each facet, the light incident on diffuser 10 is directed in a respective predetermined direction by a respective one of prisms 16 as in a Fresnel lens. Prisms 16 are directed so that the bend angle varies with position. The light is also scattered by the surface texture applied at that facet, as the surface is textured so that scattering varies with position.

[0023] The variables of direction and scattering on the entire surfaces 12, 14 may be optimized. As a result, the light from the backlight is directed to obtain a more even distribution of light, as seen by the driver.

[0024] FIG. 2 illustrates an example of an optimized diffuser of FIG. 1. The diffuser has at least one scattering parameter that varies as a function of position on the diffuser. As a specific embodiment, the diffuser is fabricated beginning with a featureless plastic film of an appropriate size to cover the back surface of a liquid crystal display. Both the front and back surface of the film is embossed with a mold. The surface of the mold is composed of a pattern of microstructures of the appropriate dimensions to scatter and direct visible light.

[0025] In the example shown in FIG. 2, only the distribution of scattering properties on the diffuser has been optimized as a function of position. In this example, the scattering as a function of position is optimized by modeling the film as a gradient diffuser in the LightTools program provided by Synopsys Inc.

[0026] The microstructures are defined using one or more variable parameters that determine the scattering distribution of light that interacts with that local area. The mold is designed so the microstructures vary as a function of position on the surface of the mold, so the light scattering, and direction change of light passing through the film varies as intended, as a function of position.

[0027] FIGS. 3-4 present a front view and side view, respectively, of a head up display LCD backlighting arrangement 30 according to one embodiment of the invention, including diffuser 10 of FIG. 1. Arrangement 30 also includes light emitting diodes (LEDs) 32 and free form lenses 34, 36. Although four LEDs 32 are shown in FIG. 3 for ease of illustration, there may be about ten LEDs. As shown, diffuser 10 has a relatively small diffusion angle.

[0028] The texture of surface 12 and the configurations of prisms 16 may be such that luminance is moved from the center of the field of view to the corners of the field of view. For example, light initially directed to the central portion of the field of view may undergo a higher level of scattering to thereby move more of the light to the outer periphery of the field of view.

[0029] In an alternative embodiment (not shown), the diffuser surface includes sub-areas of at least two types of texture. The diffuser is positioned far enough away from the display so variation in the scattering in a sub-area does not cause unwanted structure at the surface of the display. The fraction of at least one type of texture varies as a function of position on the diffuser.

[0030] In yet another embodiment, the scattering texture is provided on the surface of a lens, such as on the surface of at least one of lenses 34, 36, rather than on the surface of the diffuser.

[0031] In still another embodiment, a reflective diffuser is used with scattering and reflection directions that vary as a function of position on the diffuser.

[0032] FIG. 5 illustrates one embodiment of method 500 of the present invention for providing backlighting for a head up display of a motor vehicle. In a first step 502, a light field with a non-uniform brightness is emitted over a field of view. For example, light emitting diodes (LEDs) 32 may conjunctively emit a light field with a brightness that varies depending on the position within a field of view of a human driver of the motor vehicle.

[0033] Next, in step 504, a diffuser is provided including a surface having a texture that varies with position on the surface. For example, diffuser 10 has an outer surface 12 with a texture that varies as a function of position.

[0034] In a final step 506, the diffuser is placed in a path of the light field such that the varying texture of the diffuser surface scatters the light, and such that for a virtual image intended to have constant brightness the brightness of the light over the field of view as seen by the human driver is more uniform at a given brightness than with a diffuser configured to scatter light independent of position. For example, diffuser 10 is placed in a path of the light field such that the varying texture of the diffuser surface 12 scatters the light. For a virtual image that is intended to have constant brightness over the field of view of a viewer, the brightness of the light over the field of view as seen by the human driver is more uniform at a given brightness of LEDs 32 than the brightness of the light over the field of view as seen by the human driver would be with a diffuser that scatters light independent of position. Thus, the light-scattering provided by the varying diffuser surface 12 increases the uniformity of brightness as seen by the driver.

[0035] While this invention has been described as having an exemplary design, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.