BACKLIGHT MODULE AND DISPLAY DEVICE

A backlight module includes a light source, an optical film, and a light control film. The light control film has a first reference surface and a plurality of first optical structures disposed on the first reference surface. Each of the first optical structures has a first optical surface and a second optical surface. A first included angle is formed between the first optical surface and the first reference surface. A second included angle is formed between the second optical surface and the first reference surface. The first included angle is an acute angle and is smaller than the second included angle. Thereby, the light can be deflected to one side and the light output of the other side can be suppressed. This invention also provides a display device including the backlight module.

FIELD OF THE INVENTION

The present invention relates to an optical element, particularly referring to a backlight module and display device capable of deflecting light field distributions.

BACKGROUND OF THE INVENTION

For automotive display devices, such as the Center Informative Display (CID), a wide viewing angle in horizontal is required to ensure that passengers on both the left and right sides can see the displayed content on the screen.

However, the backlight module used in the CID is difficult to apply to the display in front of the driver's seat (Driver Information Display, DID) or the display in front of the co-driver's seat (Co-Driver Display, CDD). The reason is that the wide-angle light of automotive display devices may be reflected by the car windows and affecting the driver. Therefore, conventional backlight module structures cannot meet the specific viewing angle requirements of automotive display devices.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a backlight module capable of directing light field distributions towards one side.

The backlight module comprises a surface light source, an optical film, and a light control film. The optical film is disposed on an emitting side of the surface light source. The light control film comprises a first reference surface and multiple first optical structures positioned on the first reference surface, wherein the first reference surface is located on one side of the light control film facing away from the optical film. Each of said first optical structures comprises a first optical surface and a second optical surface, wherein the first optical surface and the second optical surface are arranged along a first direction. The first optical surface and the first reference surface form a first included angle θ1, the second optical surface and the first reference surface form a second included angle θ2, the first included angle θ1 is an acute angle, and the first included angle θ1 is smaller than the second included angle θ2.

In a preferable embodiment, the light emitted by the surface light source has an angular range of 8 relative to the normal direction of the backlight module when passing through the optical film, the transmittance of the light is at least 50%, and the light deflects in the direction away from the first optical surface after entering the light control film.

In a preferable embodiment, the light deflects at an angle μ away from the first optical surface of the film when it exits the light control film, and the angle μ is determined by the following relationship: μ=0.52*θ1+29.7.

In a preferable embodiment, the light emission angle δ of the optical film, the first included angle θ1 of the light control film, and the critical angle θc of the light control film satisfy the following relationship: δ+θ1<θc.

In a preferable embodiment, the optical film is a louver film with multiple blocking sections spaced along the first direction and multiple light-transmitting sections located between adjacent blocking sections. Each of the first optical structures extends along a second direction, where the first direction is not parallel to the second direction, and the blocking sections and the light-transmitting sections extend along the second direction.

In a preferable embodiment, the backlight module further includes a prism positioned between the surface light source and the optical film, and the prism has multiple linear microstructures extending along the first direction.

In a preferable embodiment, the backlight module further includes a prism positioned between the surface light source and the optical film, each of the first optical structures extends along a second direction, where the first direction is not parallel to the second direction, and the prism has multiple linear microstructures extending along the second direction.

In a preferable embodiment, the light control film further comprises a second reference surface relative to the first reference surface and multiple second optical structures arranged along the first direction on the second reference surface. Each of the first optical structures extends along a second direction, where the first direction is not parallel to the second direction. Each of the second optical structures extends along the second direction. Each of the second optical structures consists of a third optical surface and a fourth optical surface. The third optical surface and the second reference surface form a third included angle θ3, the fourth optical surface and the second reference surface form a fourth included angle θ4, and the third included angle θ3 is acute and smaller than the fourth included angle θ4.

In a preferable embodiment, the light emission angle δ of the optical film, the first included angle θ1 of the light control film, the third included angle θ3, and the critical angle θc of the light control film satisfy the following relationship: δ+(θ1+θ3)<θc.

In a preferable embodiment, the first included angle θ1 of the first optical structure and the third included angle θ3 of the second optical structure are oriented towards the same side of the light control film. Both the first included angle θ1 and the third included angle θ3 are less than 45 degrees, and both the second included angle θ2 and the fourth included angle θ4 are greater than 45 degrees.

In a preferable embodiment, the first included angle θ1 is greater than the third included angle θ3.

In a preferable embodiment, the surface light source comprises a light guide plate and a light bar. The light guide plate has a light incident side and a light exit side connected to the light incident side. The light bar is positioned on the light incident side of the light guide plate, and the light exit side faces the optical film.

In a preferable embodiment, the light bar comprises of a circuit board and multiple light-emitting elements, the circuit board extends along the first direction, and the light-emitting elements are arranged along the same direction.

In a preferable embodiment, the surface light source comprises a circuit board parallel to the optical film and multiple light-emitting elements positioned on the circuit board.

In a preferable embodiment, the surface light source further comprises a diffuser plate, which has a bottom surface and a top surface opposite to the bottom surface, the bottom surface faces the circuit board, and the top surface faces the optical film.

Another object of the present invention is to provide a display device which comprises the backlight module as described above, and a display panel arranged on the backlight module.

The characteristic of the present invention is that due to the asymmetrical nature of the first prism structure in the light control film, light passing through the film is deflected to one side by its asymmetrical microstructure, thereby suppressing the transmittance on the other side. As a result, when applied to displays such as the Driver Information Display (DID) or Co-Driver Display (CDD) positioned in front of the driver's or co-driver's seat, the light distribution can be biased to one side, making it less susceptible to reflection from the left-side or right-side windows.

DETAILED DESCRIPTION OF THE INVENTION

The detailed description and preferred embodiments of the invention will be set forth in the following content and provided for people skilled in the art to understand the characteristics of the invention.

The light field distribution diagram disclosed in the present invention is obtained by observing the brightness level of the 360-degree direction of the light-emitting surface (perpendicular to the light-emitting plane) from the normal direction of the backlight module. Therefore, the light field distribution diagram is a circle, and the scale around the circle is an angle. The scales marked on each concentric circle inside represent the tilt angle between the viewing direction and the normal direction of the backlight module.

Secondly, the words “approximately”, “approximately”, “approximately” or “substantially” appearing in the content of this case not only cover the clearly stated numerical values and numerical ranges, but also covers the allowable deviation range that can be understood by a person with ordinary knowledge in the technical field to which the invention belongs. The deviation range can be determined by the error generated during measurement, and this error is caused, for example, by limitations of the measurement system or process conditions. In addition, “about” may mean within one or more standard deviations of the above numerical value, such as within ±5%, ±3%, or ±1%. Words such as “about”, “approximately”, “approximately” or “substantially” appearing in this text may be used to select acceptable deviation ranges or standard deviations based on optical properties, etching properties, mechanical properties, or other properties. Therefore, a single standard deviation is not applied to all the above optical properties, etching properties, mechanical properties, and other properties.

Referring toFIG.1andFIG.2, it is a first preferred embodiment of the backlight module of the present invention. The backlight module comprises a surface light source2, a prism3, an optical film4, and a light control film5. A display panel (not shown) is provided in the light emitting direction of the light control film5to form a display device.

The optical film4is defined to have a first direction X, and a second direction Y that is not parallel to the first direction X. In this embodiment, the second direction Y is perpendicular to the first direction. X, but it is not limited to this. In this embodiment, the optical film4is a louver film and has a plurality of blocking sections41spaced apart along the first direction X, and a plurality of light-transmitting sections42located between adjacent blocking sections41. The blocking sections41and the light-transmitting sections42extend along the second direction Y. In other embodiments, the optical film4may be a light-transmitting film having a prism structure or a light splitting structure instead of a louver film, so the description of this embodiment should not be limited.

Referring toFIG.2andFIG.3, the light control film5has a first reference surface51facing away from the optical film4, and a plurality of first optical structures52disposed on the first reference surface51along the first direction X. Each of the first optical structures52extends along the second direction Y. That is to say, the blocking sections41and the light-transmitting sections42of the optical film4are arranged parallel to the first optical structures52of the light control film5. Each of the first optical structures52has a first optical surface521and a second optical surface522. In this embodiment, the first optical surface521, the second optical surface522, and the first reference surface51together form a triangle, so that each first optical structure52has a triangular cross-section. However, in other embodiments, one or both of the first optical surface521and the second optical surface522can be designed as a compound slope and without causing each first optical structure52to have a triangular cross-section. It should not be limited to the description of this embodiment. As shown inFIG.3, the first optical surface521and the second optical surface522are arranged along the first direction X. The first optical surface521and the first reference surface51form a first included angle θ1, and the second optical surface522and the first reference surface51form a second included angle θ2. The first included angle θ1 is an acute angle, and the first included angle θ1 is smaller than the second included angle θ2. In the first preferred embodiment of the present invention, the first included angle θ1 is 20°, and the second included angle θ2 is 80°. Therefore, each first optical structure52has a triangular cross-section in which the first included angle θ1 and the second included angle θ2 are angularly asymmetric.

The optical film4disclosed in this embodiment is used to change the light field distribution of the surface light source2to a single direction first. Then, the first optical structure52of the light control film5extending in the same direction as the blocking portion41of the optical film4is used to adjust the light field distribution that has become a single direction. Since each of the first optical structures52of the light control film5is an angularly asymmetric microstructure in which the first included angle θ1 is smaller than the second included angle θ2, therefore, when light passes through the light control film5, its angularly asymmetric microstructure will effectively deflect and guide the light to a specific side for light extraction, while effectively suppressing the light extraction efficiency on the other side. As a result, when applied to displays such as the Driver Information Display (DID) or Co-Driver Display (CDD) positioned in front of the driver's or co-driver's seat, the light distribution can be biased to one side, making it less susceptible to reflection from the left-side or right-side windows.

As shown inFIG.4, it is a light field distribution diagram without using the light control film5of the present invention. The dark area is in the center and does not produce any offset effect. In addition, as shown inFIG.5, even if the light control film5of the present invention is used, the extension direction of the first optical structure52of the light control film5and the extension direction of the blocking portion41and the light-transmitting portion42of the optical film4are perpendicular to each other, and the offset effect is still unable to be produced, and a large amount of noise will be generated on both sides. Therefore, as shown inFIG.1, the present invention must use the light control film5and the optical film4at the same time, and the extension direction of the first optical structure52of the light control film5and the extension direction of the blocking portion41and the light-transmitting portion42of the optical film4must be parallel to each other. In this way, as shown inFIG.6, the dark area can be deviated from the center, producing the required offset effect.

It should be noted that, the prism3is between the surface light source2and the optical film4to assist in converging the light field distribution of the surface light source2, so that the light can enter the optical film4above the prism3in a more concentrated manner to avoid loss of light energy or brightness. In addition, the prism3has a plurality of strip-shaped or linear microstructures31, and the strip-shaped microstructures31may extend along the first direction X as shown inFIG.1. The corresponding light field distribution is shown inFIG.6, which can produce a good offset effect. The strip-shaped microstructure31may also extend along the second direction Y as shown inFIG.7, and its corresponding light field distribution is shown inFIG.8, which can also produce a good offset effect. ComparingFIG.6andFIG.8, the extension direction of the strip-shaped microstructures31of the prism3will not affect the offset effect.

Referring toFIG.9, which is a second preferred embodiment of the backlight module of the present invention. The difference from the first preferred embodiment is that the first included angle of the light control film5is less than 45 degrees, and the second included angle is a right angle. InFIG.9, the first included angle θ1 is 10°, and the second included angle θ2 is 90°, so that each of the first optical structures52has a right-angled triangle cross-section. However, the second included angle θ2 can also be an acute angle to improve the problem of difficulty in mold release at right angles. The light field distribution diagram inFIG.10shows that offset effects can also be produced. Compared withFIG.6,FIG.10shows that there are significantly fewer light-colored striped areas on the left, which means that energy or brightness loss can be effectively reduced and resulting in better offset effects.

Referring toFIG.1andFIG.2, in the first preferred embodiment, the surface light source2is side-lit and includes a light guide plate21, a diffusion film22, and a light bar23. The light guide plate21has a light incident side211and a light exit side212connected to the light incident side211. The diffusion film22is disposed on the light exit side212of the light guide plate21. The light bar23is disposed on the light incident side211of the light guide plate21, and the light exit side212faces the optical film4. The light bar23has a circuit board231(not shown inFIG.2) and a plurality of light-emitting elements232. The circuit board231extends along the first direction X, and the light-emitting elements232are arranged along the first direction X. Therefore, the arrangement directions of the circuit board231and the light-emitting elements232are different from the extending directions of the blocking portion41of the optical film4and the first optical structure52of the light control film5. In this embodiment, they are perpendicular to each other. In this way, the light can be effectively deflected and guided to a specific side, while effectively suppressing the light efficiency on the other side. On the contrary, if the arrangement direction of the circuit board231and the light-emitting elements232is the same as the direction of the blocking sections41of the optical film4and the first optical structures52of the light control film5, the light emission on the other side cannot be suppressed.

Furthermore, the surface light source2can also be a direct lit as shown inFIG.11, including a circuit board231parallel to the optical film4, a plurality of light emitting elements232arranged on the circuit board231, and a diffuser plate24. The diffuser plate24has a bottom surface241and a top surface242opposite to the bottom surface241. The bottom surface241faces the circuit board231, and the top surface242faces the optical film4. In the present invention, the surface light source2can be either side-lit or direct-lit.

Referring toFIG.12, a third preferred embodiment of the backlight module of the present invention. The backlight module comprises a light source2, a prism3, an optical film4, and a light control film5. The difference from the first preferred embodiment is that the light control film5further comprises a plurality of optical structures54facing the optical film4and disposed along the first direction X. The first optical structures52and the second optical structures54extend along the second direction Y.

Referring toFIG.13, in more detail, the light control film5further comprises a second reference surface53relative to the first reference surface51and facing the optical film4. The second optical structures54are disposed on the second reference surface53along the first direction X. Each of the first optical structures52has a first optical surface521and a second optical surface522. The first optical surface521and the first reference surface51have a first included angle θ1, and the second optical surface522and the first reference surface51have a second included angle θ2. The first included angle θ1 is an acute angle, and the first included angle θ1 is smaller than the second included angle θ2. Each of the second optical structures54has a third optical surface541and a fourth optical surface542. The third optical surface541and the second reference surface53form a third included angle θ3, and the fourth optical surface542and the second reference surface53form a fourth included angle θ4. The third included angle θ3 is an acute angle, and the third included angle θ3 is smaller than the fourth included angle θ4. The first included angle θ1 of the first optical structures52and the third included angle θ3 of the second optical structures54are toward the same side of the light control film5. The first included angle θ1 and the third included angle θ3 are both less than 45 degrees, and the second included angle θ2 and the fourth included angle θ4 are both greater than 45 degrees. The first included angle θ1 is greater than the third included angle θ3, the fourth included angle θ4 is greater than the second included angle θ2, and the fourth included angle θ4 is a right angle. In this embodiment, the first included angle θ1 is 20°, the second included angle θ2 is 80°, the third included angle θ3 is 10°, and the fourth included angle θ4 is 90°. The light field distribution diagram inFIG.14can also produce a offset effect, and compared withFIG.6, the dark area inFIG.14is further away from the center, resulting in more obvious offset effect. In short, compared with the first optical structures52being provided on only one side of the light control film5, this embodiment uses the light control film5with the second optical structures54on the second reference surface53, the light field deflection effect can finely adjust to meet different usage situations or customer requirements. In addition, the first optical structures52and the second optical structures54are convex structures. In other embodiments, concave structures can also be used, and their light field deflection effects are still basically the same or similar. Therefore, it should not be limited to the description of this embodiment.

Referring toFIG.15, it is a graph that quantifies the light field distribution values of various embodiments. Wherein, the dotted line represents the control group using only the optical film4. The dashed line represents the first preferred embodiment. The dash-dotted line represents the second preferred embodiment. The solid line represents the third preferred embodiment.FIG.15shows that compared with the control group, the third preferred embodiment can most effectively suppress the light output at the viewing angle of −30° to −15° and shift the light output to the viewing angle of 15° to 30°, which can effectively suppress the light extraction of one side and produce an offset effect. It should be noted that each included angle of the light control film5can be adjusted to adjust the light deflection range according to different application environments to obtain the best offset effect.

In the first preferred embodiment of the backlight module of the present invention, the light control film5is arranged so that after the light passes through and leaves the light control film5, it is deflected in a direction away from the first optical surface521. In this way, the light is deflected to one side and the light emission of the other side is suppressed, so it can be applied to the environments that require asymmetric light fields. However, if there is only the light control film5but not the optical film4, there will still be significant stray light in the viewing angle distribution in the horizontal between +60 and +90 degrees, as shown inFIG.16. In order to eliminate large-angle stray light caused by total reflection, the first preferred embodiment of the backlight module of the present invention also needs to dispose the optical film4between the light control film5and the surface light source2. In this way, the light that is prone to total reflection in the light control film5(that is, the light with an incident angle greater than the critical angle θc of the light control film5) is eliminated (or cut-off) before entering the light control film5. InFIG.16, the dotted line represents the control group using only the light control film5. The dashed line represents the first preferred embodiment. As shown inFIG.16, only when the light control film5and the optical film4are combined, the light can be deflected to one side and the light emission from the other side can be suppressed. At the same time, it can also avoid the generation of stray light at large angles and significantly reduce the light energy or luminance in the viewing angle area between ±60 and ±90 degrees.

In more detail, the light emission angle δ of the optical film4, the first included angle θ1 of the light control film5, and the critical angle θc of the light control film5must comply with the following relationship: δ+θ1<θc.

Referring toFIG.17, when the light emitted by the surface light source2passes through the optical film4, the light emission angle δ is an angle range relative to the normal direction of the backlight module, and the transmittance is at least 50%. That is, the viewing angle is between approximately −17° to −18° and +24° to +25°. In order to deflect the viewing angle light at negative angles, the value of 8 is designed to be 17 in this embodiment. The light control film5is made of polycarbonate (PC), and its critical angle θc is 39°. Therefore, the first included angle θ1 of the light control film5is designed to be less than 22° to comply with the relationship of δ+θ1<θc. In the first preferred embodiment of the present invention, the first included angle θ1 is 20°, which is less than 22°. In addition, although the light control film5in this embodiment is made of PC, it can also be made of Optically Clear Adhesives (OCA), Polyethylene terephthalate (PET), Poly methyl methacrylate (PMMA). Therefore, the critical angle θc will be different and should not be limited to the description of this embodiment.

Referring toFIG.18, the dotted line represents the control group using only the optical film4. The dashed line represents the first preferred embodiment. In this embodiment, when the light leaves the light control film5, it is directed away from the first optical surface521by a deflection angle μ. The angle μ conforms to the following relationship: μ=0.52*θ1+29.7. When the first included angle θ1 is 20°, the deflection angle μ is approximately 40° (0.52*20°+29.7=40.1°). That is to say, when the light control film5and the optical film4are not combined, the light emitting position of 50% of the light energy or luminance corresponds to a viewing angle of approximately −52° (the dotted line). Compared with the case where the light control film5and the optical film4are combined, the light emitting position of 50% of the light energy or luminance corresponds to a viewing angle of approximately −10° (the dashed line), and the difference between the two is 42°, which is quite close to the above calculation result of the formula. In other embodiments, when the first included angle θ1 is 10°, the deflection angle μ is approximately) 35° (0.52*10°+29.7=34.9°. When the first included angle θ1 is 40°, the deflection angle μ is approximately 50° (0.52*) 40°+29.7=50.5°. In other embodiments, when the first included angle θ1 is 10°, the deflection angle μ is approximately 35° (0.52*10°+29.7=34.9°). When the first included angle θ1 is 40°, the deflection angle μ is approximately 50° (0.52*) 40°+29.7=50.5°. Therefore, the above formula can effectively represent the relationship between the deflection angle μ and the first included angle θ1.

When the light control film5is adopted as a double-sided microstructure similar to the third preferred embodiment of the backlight module of the present invention, the light emission angle & of the optical film4, the first included angle θ1 of the light control film5, the third included angle θ3, and the critical angle θc of the light control film5must meet the following formula: δ+(θ1+θ3)<θc. Referring toFIG.19, when the light control film5with single-sided microstructures and the first internal angle θ1 is 20° (the dashed line), the light emitting position of 50% of the light energy or luminance corresponds to a viewing angle of approximately −10°. When the light control film5with double-sided microstructures as the first internal angle θ1 is 10° and the third included angle θ3 is 10° (the solid line), the light emitting position of 50% of the light energy or luminance also corresponds to a viewing angle of approximately −10°. Both the single-sided microstructures of the first preferred embodiment and the double-sided microstructures of the third preferred embodiment can deflect light to one side and suppress the light extraction of the other side. At the same time, they can also avoid large-angle stray light. Wherein, the double-sided microstructures of the third preferred embodiment can further reduce the energy or luminance at viewing angles between −30° to −60° and +70° to +90°.

Through the above design, when the backlight module of the present invention is used in vehicle-mounted equipment, as shown inFIG.20, the image of the dashboard91located on the driver's seat side can be projected to the driver's seat and passenger seat, and it will not be reflected by the window on the driver's side. Alternatively, as shown inFIG.21, the image of the display screen92located on the passenger's seat side can be projected to the driver's seat and the passenger's seat but will not be reflected by the window on the passenger's side, reducing interference caused by image reflections.

To sum up, the backlight module of the present invention can deflect light to one side and suppress the light emission rate of the other side through the combination of the optical film and the light control film, and it can be applied to environments that require anisotropic light fields.