Backlight unit, display screen and motor vehicle

Abstract

A mode switchable backlight unit includes first and second arrays of one or more light sources and a transparent light guide including an array of extraction features forming a light output surface, the extraction features including an asymmetric shape. The mode-switchable backlight unit has at least two switchable operating modes that provide an output beam having first and second divergence angles, the second divergence angle being greater than the first divergence angle. This allows a single light guide backlight unit to provide at least two different and switchable beam angle distributions. The mode-switchable backlight unit has a number of advantages, including reduced thickness and improved energy efficiency.

Description

Technical Field

[0001] This invention relates to an active privacy backlight (also known as a mode-switchable backlight unit) and a display screen. Background Technology

[0002] In the automotive industry, car displays require switchable privacy modes for certain user experiences, such as preventing the driver from being distracted by the content displayed. Such displays preferably have switchable beam angles, allowing the screen to be seen or switched to a mode where it cannot be seen from certain positions. For example, in one mode, the screen can be seen by both the driver and passengers, but in another mode, the screen can be seen only by the passengers.

[0003] Displays in this art typically employ a two-layer side-lit light guide design. For example, International Patent Publication No. WO2020185264 describes a mode-switchable backlight comprising: a first directional backlight including a narrow-angle emitter array configured to provide narrow-angle emitted light during a first mode and a second mode; and a second directional backlight including a bidirectional emitter array configured to provide bidirectional emitted light only during the second mode, the bidirectional emitted light having a bifurcation angle range complementary to the angular range of the narrow-angle emitted light. During the second mode, the combination of the narrow-angle emitted light and the bidirectional emitted light is configured to provide wide-angle emitted light having an angular range that is the sum of the angular range of the narrow-angle emitted light and the bifurcation angle range of the bidirectional emitted light.

[0004] US Patent Publication No. 2018259799 describes a display device having a privacy mode and an open mode, which uses a light-blocking arrangement (including elements formed of photochromic materials) to block laterally guided light in privacy mode, but does not block laterally guided light in open mode.

[0005] The displays described in the aforementioned literature have significant cost, thickness, and / or power efficiency issues. Summary of the Invention

[0006] Typically, an apparatus and method are needed to solve one or more of the problems mentioned above.

[0007] One aspect of the present invention is to provide a mode-switchable backlight unit that eliminates or at least mitigates one or more of the aforementioned disadvantages of arrangements known in the prior art.

[0008] Further objects and objectives of the present invention will become apparent from the following description.

[0009] According to a first aspect of the present invention, a mode-switchable backlight unit is provided, the mode-switchable backlight unit comprising:

[0010] a. A first array of one or more light sources;

[0011] b. A second array of one or more light sources, independent of a first array of one or more light sources; and

[0012] c. A transparent light guide for guiding light emitted from a first array and a second array of light sources, the transparent light guide comprising an array of extraction features forming the light output surface of a mode-switchable backlight unit, the extraction features comprising an asymmetrical shape.

[0013] The switchable backlight unit has the following features:

[0014] A first operating mode, corresponding to a first array of one or more light sources, the first array of one or more light sources illuminating an array of extracted features to provide an output beam having a first divergence angle from a light output surface; and

[0015] The second operating mode corresponds to a second array of one or more light sources, which illuminates an array of extraction feature sections to provide an output beam with a second divergence angle from the light output surface, the second divergence angle being greater than the first divergence angle.

[0016] The mode-switchable backlight unit of the present invention advantageously allows at least two different and switchable beam angle distributions (i.e., divergence angles) to be delivered by a single light-guided backlight unit. The divergence angle is preferably quantized by the full width at half maximum (FWHM) of the output beam.

[0017] Compared to arrangements in the prior art, the backlight unit of the present invention has lower cost (due to fewer components and reduced complexity) and is easier to integrate into the system.

[0018] Furthermore, the backlight unit of the present invention is more energy-efficient than the arrangement in the prior art. This is because the backlight unit can have fewer layers. Compared to, for example, International Patent Publication No. WO2020185264, the number of light guide layers can be reduced from two to one. This results in higher optical efficiency and therefore lower system power consumption. In addition, the backlight unit of the present invention is advantageously thinner than the arrangement in the prior art.

[0019] In the context of a first array and a second array of one or more light sources, "independent" means that the second array of one or more light sources can be turned on and off without affecting the first array of one or more light sources, and vice versa. In other words, the first array of one or more light sources can be turned on while the second array of one or more light sources can be turned off, and vice versa.

[0020] In the context of optical guides, "transparent" means that, according to the test standard ASTM D-1003 (Standard Test Method for Haze and Transmittance of Transparent Plastics), the visible light transmittance is greater than 80%, and preferably greater than 90%.

[0021] The extracted feature may include a first surface profile and a second surface profile. Light from a first array of one or more light sources may preferably interact substantially with the first surface profile. Light from a second array of one or more light sources may preferably interact substantially with the second surface profile. In this context, "substantially" means that at least 85%, at least 90%, or at least 95% of the light emitted from one or more light sources interacts with the surface profile.

[0022] The first divergence angle may be less than about 90°, or less than about 80°, or less than about 70°, or less than about 60°, or about 40°.

[0023] The second divergence angle may be greater than approximately 90°, or greater than approximately 100°, or approximately 110°.

[0024] The relative normal intensity in the first operating mode can be approximately twice that in the second operating mode.

[0025] The first array of one or more light sources and the second array of one or more light sources are preferably coplanar. Additionally, the first and second arrays of one or more light sources are preferably coplanar with a transparent light guide.

[0026] Preferably, the backlight unit comprises a single transparent light guide (i.e., no more than one transparent light guide). This advantageously provides a thinner backlight unit than those disclosed in the art.

[0027] A transparent light guide may include a transparent sheet, and an array layer of extraction features may be mounted on the transparent sheet. In some embodiments, the extraction features include refractive extraction features. In some embodiments, the extraction features include reflective extraction features.

[0028] The extracted feature may include a transparent prism structure, wherein at least one face of the prism is curved. In these embodiments, the curved surface of the prism is a second surface profile, and the flat / straight surface of the prism is a first surface profile.

[0029] The mode-switchable backlight unit may not have any symmetrical extraction features.

[0030] One or more light sources can be any light source known to those skilled in the art, particularly those suitable for backlighting. Such light sources include one or more light-emitting diodes (LEDs), cold cathode fluorescent lamps, laser diodes, organic light-emitting diodes, and other electroluminescent devices. The light can be non-directional.

[0031] Preferably, the light source includes an LED. The LED can be any design known to those skilled in the art, including edge-emitting LEDs, side-emitting LEDs, top-emitting LEDs, or die LEDs.

[0032] The mode-switchable backlight unit may also include a substrate for supporting a first array of one or more light sources and a second array of one or more light sources.

[0033] Transparent light guides can be mounted on the substrate.

[0034] The transparent light guide can have a width of about 0.1 mm to about 10 mm. Preferably, the transparent light guide is planar.

[0035] The extracted feature portion can have a height of approximately 1µm to approximately 100µm.

[0036] The mode-switchable backlight unit can have a width of approximately 0.1 mm to approximately 10 mm.

[0037] The light source can be encapsulated within a transparent light guide and / or a cavity within a transparent light guide.

[0038] Alternatively, or otherwise, the light source can be adjacent to a transparent light guide. Such implementations may be referred to as "side-lit".

[0039] Alternatively or otherwise, the light sources can be distributed throughout the entire transparent light guide. For example, each light source (from left to right in the transparent light guide) can alternate between a first array and a second array (i.e., arranged in an ABABAB pattern). Such an implementation can be referred to as "full array incident light." This advantageously provides different light emission angles from the light sources.

[0040] The mode-switchable backlight unit may also include a specular reflector. The purpose of the reflector is to reflect the output beam back through the backlight unit. The reflector can be positioned such that an array of extracted features is positioned between the reflector and the transparent light guide. Alternatively, the reflector can be positioned adjacent to the surface of the transparent light guide opposite the light output surface.

[0041] The mode-switching backlight unit may also include a diffuser, which advantageously improves the output beam quality. The diffuser may be positioned between the light output surface and the observer of the mode-switching backlight unit, and in some cases adjacent to the light output surface. The diffuser may be a weak Gaussian diffuser.

[0042] Implementations including diffusers and / or reflectors may be considered suboptimal because they simultaneously increase the thickness of the backlight unit. However, the advantages provided by diffusers and / or reflectors can be particularly beneficial in certain applications. For example, when using refracted light to extract features, mode-switchable backlight units preferably include specular reflectors.

[0043] According to a second aspect of the present invention, a display screen is provided, comprising an image display element and a mode-switchable backlight unit as described above, the mode-switchable backlight unit being disposed below the image display element for backlighting the image display element.

[0044] The display screen of the present invention, with its switchable beam angle, advantageously allows the screen to be seen or switched to a mode that is not visible from certain positions. Therefore, the display screen of the present invention is suitable for switching between a public mode and a private mode, while being cheaper and more energy-efficient than displays in the art. Thus, the display can be an automotive display.

[0045] Image display elements may include thin-film transistor (TFT) displays. Display devices may be liquid crystal display devices, and therefore may include liquid crystal cells, which may also be referred to as liquid crystal panels.

[0046] The second aspect of the invention may include one or more features of the first aspect or an embodiment thereof, or vice versa.

[0047] According to a third aspect of the invention, the use of a mode-switchable backlight unit or a display screen as described above in a motor vehicle is provided.

[0048] The inventors have found that this invention is particularly beneficial to the automotive industry.

[0049] The third aspect of the invention may include one or more features of the first or second aspect or embodiments thereof, or vice versa.

[0050] According to a fourth aspect of the present invention, a method for manufacturing a mode-switchable backlight unit as described above is provided, the method comprising the following steps:

[0051] • Provide a first array of one or more light sources and a second array of one or more light sources, wherein the second array of one or more light sources is independent of the first array of one or more light sources;

[0052] • Provides a transparent light guide suitable for guiding light emitted from a first array and a second array of light sources; and

[0053] • An array of extraction features for forming the light output surface of the mode-switchable backlight unit is positioned on a transparent light guide, the extraction features including an asymmetrical shape.

[0054] in

[0055] The mode-switchable backlight unit has: a first operating mode corresponding to a first array of one or more light sources, the first array of one or more light sources illuminating an array of extraction features to provide an output beam with a first divergence angle from a light output surface; and a second operating mode corresponding to a second array of one or more light sources, the second array of one or more light sources illuminating an array of extraction features to provide an output beam with a second divergence angle from a light output surface, the second divergence angle being greater than the first divergence angle.

[0056] The mode-switching backlight unit can be manufactured by replicating a master. The master can be manufactured using one or more of laser processing, 3D lithography, and diamond molds. The master can be replicated using one or more of imprinting (including UV imprinting) and microimprinting. Alternatively, the mode-switching backlight unit can be manufactured using any suitable method known in the art for micro-optical films.

[0057] Suitable materials for the transparent light guide, the array for extracting features, and (if present) the substrate are conventional and will be known to those skilled in the art.

[0058] The method may also include forming a display device from mode-switchable backlight units.

[0059] An embodiment of the fourth aspect of the present invention may include one or more features of the first to third aspects of the present invention or embodiments thereof, or vice versa.

[0060] According to a fifth aspect of the present invention, a mode-switchable backlight unit is provided, the mode-switchable backlight unit comprising:

[0061] a. A first array of one or more light sources;

[0062] b. A second array of one or more light sources, independent of a first array of one or more light sources; and

[0063] c. A transparent light guide for guiding light emitted from a first array and a second array of light sources, the transparent light guide comprising an array of extraction features forming the light output surface of a mode-switchable backlight unit, the extraction features comprising an asymmetrical shape.

[0064] Wherein, when the array of extracted features is illuminated by a first array of one or more light sources, the light beam emitted from the output surface has a first divergence angle, and

[0065] When the array of extracted features is illuminated by a second array of one or more light sources, the light beam emitted from the output surface has a second divergence angle greater than the first divergence angle.

[0066] The mode-switchable backlight unit can advantageously switch between two modes: one mode with a first divergence angle and another mode with a second divergence angle.

[0067] In some embodiments of the fifth aspect, the mode-switchable backlight unit has a first operating mode corresponding to a first array of one or more light sources, the first array of one or more light sources illuminating an array of extraction features to provide an output beam with a first divergence angle from a light output surface; and a second operating mode corresponding to a second array of one or more light sources, the second array of one or more light sources illuminating an array of extraction features to provide an output beam with a second divergence angle from a light output surface, the second divergence angle being greater than the first divergence angle.

[0068] The fifth aspect of the invention may include one or more features of the first to fourth aspects or embodiments thereof, or vice versa. Attached Figure Description

[0069] Various embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, wherein:

[0070] Figure 1 This is a side view of a mode-switchable backlight unit according to an embodiment of the present invention;

[0071] Figure 2 It is in the first operating mode. Figure 1 The mode allows switching the side view of the backlight unit;

[0072] Figure 3 It is in the second operating mode. Figure 1 The mode allows switching the side view of the backlight unit;

[0073] Figure 4 This is a side view of a mode-switchable backlight unit according to an embodiment of the present invention;

[0074] Figure 5 This is a side view of a mode-switchable backlight unit according to an embodiment of the present invention;

[0075] Figure 6 This is a side view of a mode-switchable backlight unit according to an embodiment of the present invention;

[0076] Figure 7 This is a side view of a display screen according to one embodiment of the present invention;

[0077] Figure 8 is a side view providing an exemplary surface profile of an output beam with a first divergence angle; and

[0078] Figure 9 is a side view of an exemplary surface profile providing an output beam with a second divergence angle. Detailed Implementation

[0079] Now refer to Figure 1 The invention is described up to Figure 9.

[0080] See Figure 1 The diagram shows a side view of a mode-switching backlight unit 1a according to an embodiment of the present invention. It can be seen that the mode-switching backlight unit 1a includes a first array 2 of light sources in the form of light-emitting diodes (LEDs) and a second array 3 of light sources, also in the form of LEDs. The first array 2 and the second array 3 of light sources are coplanar. Both the first array 2 and the second array 3 of light sources are coupled to the edge of a transparent planar light guide 4. Light is guided within the transparent light guide 4 until it encounters a change in the surface profile. The surface of the transparent light guide 4 forms the light output surface 5 of the mode-switching backlight unit 1a. The thickness of the transparent light guide 4 is in the range of 0.1 mm to 10 mm.

[0081] An array of extraction features 6 with asymmetrical shapes is positioned across the outer surface of the transparent light guide 4. In this embodiment, each extraction feature 6 has a transparent asymmetrical prism structure, such that at least one face of the prism is straight 7 and at least one face of the prism is curved 8. Each extraction feature 6 on the transparent light guide 4 is identical. However, it should be understood that the extraction features 6 need not be identical, as long as each extraction feature 6 has an asymmetrical shape.

[0082] In this embodiment, the extraction feature 6 is a refractive extraction feature and is therefore positioned across the light output surface 5. However, it should be understood that the extraction feature 6 can be a reflective extraction feature and can therefore be located on the surface of the transparent light guide 4 opposite to the light output surface 5.

[0083] Figure 2 The first operating mode is shown. Figure 1 The side view of the switchable backlight unit 1a is shown in the mode. In this mode, the first array 2 of the light source is turned on and the second array 3 of the light source is turned off. When turned on, the first array 2 of the light source illuminates the array of the extraction feature section 6, and the light interacts with the surface 7 of the extraction feature section 6 to provide an output beam 9 with a first divergence angle (α) from the light output surface 5.

[0084] Figure 3 The second operating mode is shown. Figure 1The side view of the switchable backlight unit 1a shows a mode in which the second array 3 of the light source is turned on and the first array 2 of the light source is turned off. When turned on, the second array 3 of the light source illuminates the array of the extraction feature section 6, and the light interacts with the curved surface 8 of the extraction feature section 6 to provide an output beam 9 with a second divergence angle (β) from the light output surface 5. (Comparison) Figure 3 and Figure 2 It can be seen that the second divergence angle (β) is greater than the first divergence angle (α).

[0085] Therefore, through selective illumination of light source arrays 2 and 3 (i.e., which array is turned on and which is turned off), the divergence angle can be (e.g.) Figure 3 The relatively wide angle of the middle and (such as) Figure 2 The angles are switched between relatively narrow angles. In these embodiments, the first divergence angle (α) has a half-maximum full width (FWHM) of ±20° (i.e., α equals 40°), and the second divergence angle (β) has an FWHM of ±55° (i.e., α equals 110°). However, it should be understood that the first and second divergence angles do not need to be exactly these values, as long as the second divergence angle (β) is greater than the first divergence angle (α).

[0086] Figure 4 A side view of a mode-switchable backlight unit 1b according to an embodiment of the present invention is shown. This embodiment includes... Figure 1 All features of the illustrated embodiment are used, and the embodiment operates in a similar manner. However, the first array 2 and the second array 3 of the light sources are not positioned adjacent to the transparent light guide 4 (i.e., side-lit); instead, the light sources 2 and 3 are encapsulated within the transparent light guide 4. It should be understood that the light sources 2 and 3 can alternatively be located in cavitation within the transparent light guide 4, or a combination of both, or a combination of all three (i.e., encapsulated, cavitated, and side-lit).

[0087] Figure 5 A side view of a mode-switchable backlight unit 1c according to an embodiment of the present invention is shown. This embodiment includes... Figure 4 All features of the illustrated embodiment are present, and the embodiment operates in a similar manner. However, the mode-switchable backlight unit 1c also includes a substrate 10 for supporting a first array 2 of one or more light sources and a second array 3 of one or more light sources. A transparent light guide 4 is disposed on the support 10, and the light sources 2 and 3 are positioned on the support 10 such that the light sources 2 and 3 are encapsulated by the combination of the support 10 and the transparent light guide 4.

[0088] Figure 6 A side view of a mode-switchable backlight unit 1d according to an embodiment of the present invention is shown. This embodiment includes... Figure 4The illustrated embodiment features all the characteristics of the light source and operates in a similar manner. However, a first array 2 and a second array 3 of one or more light sources are distributed throughout the transparent light guide 4. This arrangement is referred to as a "full array". In this embodiment, each light source 2, 3 (from left to right in the transparent light guide) alternates between the first and second arrays (i.e., arranged in an ABABAB pattern). Distributing the light sources 2, 3 throughout the transparent light guide 4 provides different light emission angles.

[0089] Figure 7 A side view of a display screen 11 according to an embodiment of the present invention is shown. The display screen includes, as... Figure 1 The switchable backlight unit 1 and liquid crystal panel 12 are shown. It should be understood that any switchable backlight unit described herein can be used with the liquid crystal panel 12. The liquid crystal panel 12 is positioned adjacent to the light output surface 5 of the switchable backlight unit 1. Arrow 13 indicates the direction in which the display screen 11 is viewed. Therefore, the switchable backlight unit 1 illuminates the liquid crystal panel 12. By switching between these two operating modes, the range in which the display screen 11 can be seen is changed. That is, the display screen 11 can be switched to a mode in which it is not visible from certain positions.

[0090] Additionally, the mode-switchable backlight unit 1 includes a specular reflector 14 adjacent to the surface of the transparent light guide 4 opposite to the light output surface 5. The purpose of the specular reflector 14 is to ensure that as much light as possible (preferably all light) is guided through the liquid crystal panel 12.

[0091] Figure 8A and Figure 8B A side view is shown of an exemplary surface profile providing an output beam 9 with a first divergence angle (α). Both have flat surfaces that produce light with a relatively narrow divergence angle.

[0092] Figure 9A and Figure 9B A side view is shown of an exemplary surface profile providing an output beam 9 with a second divergence angle (β). Figure 9A A smooth surface is shown that produces non-scattered light with a relatively wide divergence angle. Figure 9B The jagged surface that produces scattered light with a relatively wide divergence angle is shown.

[0093] Typically, each feature extraction unit 6 will include, for example: Figure 8A or Figure 8B The surface profile shown and as Figure 9A or Figure 9B The surface contour shown makes the extracted feature 6 have an overall asymmetrical shape.

[0094] As previously stated, the mode-switchable backlight unit 1 has several advantages over the prior art. The backlight unit 1 of the present invention has lower cost (due to fewer components and reduced complexity), easier system integration, is thinner, and more energy-efficient than arrangements in the prior art. This is because the backlight unit 1 has fewer layers. This results in higher optical efficiency and therefore lower system power consumption.

[0095] A mode-switchable backlight unit 1 is disclosed, comprising a first array 2 and a second array 3 of one or more light sources and a transparent light guide 4, wherein the transparent light guide 4 includes an array of extraction features 6 forming a light output surface 5, the extraction features 6 having an asymmetrical shape. The mode-switchable backlight unit 1 has at least two switchable operating modes that provide an output beam 9 having a first divergence angle (α) and a second divergence angle (β), the second divergence angle (β) being greater than the first divergence angle (α). This allows at least two different and switchable beam angle distributions to be delivered by a single light guide backlight unit 1. The mode-switchable backlight unit 1 has several advantages, including reduced thickness and improved energy efficiency.

[0096] Throughout this specification, unless the context otherwise requires, the terms “comprising” or “covering” or variations thereof such as “having” or “with,” “including” or “containing” will be understood to imply inclusion of the said integers or groups of integers, but not to exclude any other integers or groups of integers. Furthermore, unless the context explicitly requires otherwise, the term “or” will be interpreted as inclusive rather than exclusive.

[0097] The foregoing description of the invention is for illustrative and descriptive purposes and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to best utilize the invention in the various embodiments and to make various modifications according to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the invention as defined by the appended claims.

Claims

1. A mode-switchable backlight unit comprising: a. a first array of one or more light sources; b. a second array of one or more light sources, the second array of one or more light sources being independent of the first array of one or more light sources; and c. a transparent light guide for guiding light emitted from the first and second arrays of light sources, the transparent light guide comprising an array of extraction features forming a light output surface of the mode-switchable backlight unit, the extraction features comprising an asymmetric shape, wherein the mode-switchable backlight unit has: a first mode of operation corresponding to the first array of one or more light sources illuminating the array of extraction features to provide an output light beam from the light output surface having a first angle of divergence; and a second mode of operation corresponding to the second array of one or more light sources illuminating the array of extraction features to provide an output light beam from the light output surface having a second angle of divergence, the second angle of divergence being greater than the first angle of divergence. The extraction features comprise a first surface profile and a second surface profile. Light from the first array of one or more light sources interacts with the first surface profile and light from the second array of one or more light sources interacts with the second surface profile.

2. The mode-switchable backlight unit of claim 1, wherein, The first angle of divergence is less than 90°, or less than 80°, or less than 70°, or less than 60°, or 40°.

3. The mode-switchable backlight unit of claim 2, wherein, The second angle of divergence is greater than 90°, or greater than 100°, or 110°.

4. The mode-switchable backlight unit of claim 1, wherein, The first array of one or more light sources and the second array of one or more light sources are co-planar.

5. The mode-switchable backlight unit of claim 1, wherein, The transparent light guide comprises a transparent sheet and an array layer of the extraction features mounted on the transparent sheet.

6. The mode-switchable backlight unit of claim 1, wherein, The extraction features comprise a transparent prismatic structure, wherein at least one face of the prisms is curved.

7. The mode-switchable backlight unit of claim 1, wherein, The mode-switchable backlight unit further comprises a substrate for supporting the first array of one or more light sources and the second array of one or more light sources, wherein the transparent light guide is disposed on the substrate.

8. The mode-switchable backlight unit of claim 1, wherein, The light sources are encapsulated within the transparent light guide and / or in an air pocket within the transparent light guide.

9. The mode-switchable backlight unit of claim 1, wherein, The mode-switchable backlight unit further comprises a specular reflector positioned adjacent to a surface of the transparent light guide opposite the light output surface.

10. The mode-switchable backlight unit of claim 1, wherein, 12. A display screen comprising an image display element and a mode-switchable backlight unit according to claim 1 disposed beneath the image display element for back-lighting the image display element.

11. The mode-switchable backlight unit of claim 1, wherein, 13. A motor vehicle comprising a mode-switchable backlight unit according to claim 1 or a display screen according to claim 12. ​ ​

Images