Backlight module and display apparatus

A backlight module includes a light guide plate, a light source, a first optical film, and a second optical film. The light source is disposed on one side of a light incident surface of the light guide plate. The first optical film is disposed between the light guide plate and the second optical film. An illumination beam from the light source has a first polarization component and a second polarization component perpendicular to the first polarization component. A ratio of the first polarization component to the second polarization component is greater than or equal to 1.2 and less than or equal to 10. The second optical film includes a substrate and a plurality of prism structures disposed between the substrate and the light guide plate. An included angle between an extending direction of the prism structures and the light incident surface is less than 5 degrees.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of China application serial no. 202110750325.1, filed on Jul. 2, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND

Technical Field

The invention relates to a display technique, and in particularly, relates to a backlight module and a display apparatus.

Description of Related Art

Along with increasing applications of non-self-luminous displays such as liquid crystal displays, the design of backlight modules also needs to be adjusted for different purposes. In order to improve the light energy utilization rate of a light source, backlight modules equipped with optical brightness enhancement film (BEF) have become one of the mainstreams in the market. Generally, this type of backlight module is equipped with a laminated structure of two optical BEFs (for example, two prism sheets with prism extending directions to be orthogonal to each other), which may guide a light beam emitted from a light guide plate at a large angle to cover a specific angle range (for example, −60 degrees to 60 degrees) of a normal viewing angle to increase the light intensity of the backlight module near the normal viewing angle.

In order to further improve high light collection of the backlight modules, a high light collection type backlight module using reverse prism sheets to replace the two laminated optical BEFs is developed. This type of the backlight module may further increase the total light output near the normal viewing angle (i.e., having a light converging characteristic of a smaller angle range). However, since prism structures of the reverse prism sheet needs to be arranged opposite to the light guide plate, the light emitting surface of the light guide plate may be easily scratched by the prism structures of the reverse prism sheet, which affects the production yield of the backlight module. On the other hand, since the illumination beam generated by such backlight module has a low light beam polarizability, the loss of light energy after passing through a display panel with a polarizer is large, resulting in a poor light energy utilization rate of the display apparatus.

SUMMARY

The invention is directed to a backlight module adapted to generate an illumination beam with a relatively high proportion of a specific polarization component.

The invention is directed to a display apparatus providing a favorable light energy utilization rate.

In order to achieve one or a portion of or all of the objects or other objects, an embodiment of the invention provides a backlight module. The backlight module includes a light guide plate, a light source, a first optical film, and a second optical film. The light guide plate has a light incident surface and a light emitting surface connected to each other. The light source is disposed on one side of the light incident surface of the light guide plate, and is configured to emit an illumination beam. The first optical film is disposed on one side of the light emitting surface of the light guide plate. The illumination beam has a first polarization component parallel to a virtual surface and a second polarization component perpendicular to the virtual surface after passing through the first optical film. The virtual surface is perpendicular to the light incident surface and the light emitting surface. A ratio of the first polarization component to the second polarization component is greater than or equal to 1.2 and less than or equal to 10. The second optical film is disposed on one side of the first optical film facing away from the light guide plate, and includes a substrate and a plurality of prism structures. The prism structures are disposed on one side of the substrate of the second optical film facing the light guide plate, and an included angle between an extending direction of the prism structures and the light incident surface of the light guide plate is less than 5 degrees.

In order to achieve one or a portion of or all of the objects or other objects, an embodiment of the invention further provides a display apparatus. The display apparatus includes a display panel and a backlight module. The backlight module is disposed in overlap with the display panel, and includes a light guide plate, a light source, a first optical film, and a second optical film. The light guide plate has a light incident surface and a light emitting surface connected to each other. The light source is disposed on one side of the light incident surface of the light guide plate, and is configured to emit an illumination beam. The first optical film is disposed on one side of the light emitting surface of the light guide plate. The illumination beam has a first polarization component parallel to a virtual surface and a second polarization component perpendicular to the virtual surface after passing through the first optical film. The virtual surface is perpendicular to the light incident surface and the light emitting surface. A ratio of the first polarization component to the second polarization component is greater than or equal to 1.2 and less than or equal to 10. The second optical film is disposed on one side of the first optical film facing away from the light guide plate, and includes a substrate and a plurality of prism structures. The prism structures are disposed on one side of the substrate facing the light guide plate, and an included angle between an extending direction of the prism structures and the light incident surface of the light guide plate is less than 5 degrees.

Based on the above descriptions, in the backlight module and the display apparatus of an embodiment of the invention, the first optical film and the second optical film are disposed on one side of the light emitting surface of the light guide plate. One side of the second optical film facing the light guide plate is provided with a plurality of prism structures with the extending direction substantially parallel to the light incident surface of the light guide plate. The first optical film located between the prism structures and the light guide plate may increase a polarization component of the illumination beam from the light guide plate in a specific direction, which is beneficial to an increase in the light energy utilization rate of the display apparatus. Moreover, through arrangement of the first optical film, the light emitting surface of the light guide plate is prevented from being scratched by the prism structures of the second optical film, so the production yield of the backlight module is prevented from being affected.

DESCRIPTION OF THE EMBODIMENTS

FIG.1is a schematic diagram of a display apparatus according to a first embodiment of the invention.FIGS.2A and2Bare schematic cross-sectional views of the display apparatus ofFIG.1.FIG.3is a schematic top view of a backlight module ofFIG.1.FIG.4AandFIG.4Bare light intensity distribution diagrams after an illumination beam exits from a light guide plate ofFIG.1.FIG.5Ais a partial enlarged schematic view of a second optical film ofFIG.2A.FIG.5Bis a partial enlarged schematic view of a second optical film according to another embodiment of the invention.FIG.5Cis a partial enlarged schematic view of a second optical film according to still another embodiment of the invention. For clarity's sake,FIG.3only illustrates a light guide plate100, a light source110, and a second optical film130of a backlight module50inFIG.1.

Referring toFIG.1toFIG.2B, a display apparatus10includes the backlight module50. The backlight module50includes the light guide plate100, the light source110, a first optical film120, and the second optical film130. The light guide plate100has a light incident surface100b, a light emitting surface100a, and a bottom surface100c. The light incident surface100bis connected to the light emitting surface100aand the bottom surface100c. The light emitting surface100ais opposite to the bottom surface100c. The light source110is disposed on one side of the light incident surface100bof the light guide plate100, and is configured to emit an illumination beam IB. Namely, the backlight module50of the embodiment is an edge-type backlight module. It should be noted that in the embodiment, a number of the light sources110is, for example, four, which does not mean that the invention is limited to the content disclosed in the drawings. In other embodiments, the number of the light sources110may be adjusted according to an optical design of the backlight module.

In this embodiment, the light emitting surface100aof the light guide plate100may be selectively provided with a plurality of lenticular lens structures100m1, and the bottom surface100cof the light guide plate100may be selectively provided with a plurality of optical microstructures100m2. For example, the lenticular lens structures100m1are arranged in a direction Y and extend in a direction X, and the optical microstructures100m2are arranged in the direction X and extend in the direction Y. Namely, an extending direction of the lenticular lens structures100m1intersects an extending direction of the optical microstructures100m2. Particularly, the extending direction of the lenticular lens structures100m1is substantially perpendicular to the light incident surface100bof the light guide plate100. However, the invention is not limited thereto. In other embodiments, a plurality of optical microstructures may be provided on at least one of the light emitting surface and the bottom surface of the light guide plate according to actual light shape requirements.

In this embodiments, each of the lenticular lens structures100m1of the light guide plate100has a height H1parallel to a normal direction (for example, a direction Z) of the light emitting surface100aand a width W parallel to the light incident surface100band the light emitting surface100a, and a ratio of the height H1to the width W is greater than 0.15. The optical microstructures100m2of the light guide plate100respectively have a light-facing surface100m2r. In the embodiment, by setting an included angle α between the light-facing surface100m2rof the optical microstructure100m2and the bottom surface100cis between 1 degree and 10 degrees, the illumination beam IB may be emitted out from the light emitting surface100aof the light guide plate100at a relatively large angle (for example, greater than 50 degrees). In an exemplary embodiment, the included angle α between the light-facing surface100m2rand the bottom surface100cof the light guide plate100may be between 4 degrees and 10 degrees.

To be more specific, a light exit type of the light guide plate100of the embodiment has concentricity and directivity, and a transmission direction of the illumination beam IB emitted from the light guide plate100is substantially deflected toward a normal direction of the light incident surface100b(for example, a direction opposite to the direction X). For example, a light intensity of the illumination beam IB emitted from the light guide plate100is mostly concentrated on a side of the light guide plate100relative to the light source110(a region near an azimuth angle of 90 degrees inFIG.4A), and the light intensity is more concentrated in an exit angle range of 50 degrees to 85 degrees on this azimuth (as shown inFIG.4B). Therefore, the illumination beam IB from the light guide plate100may enter the first optical film120at a relatively large angle (as shown inFIG.2A). For example, an included angle θ (i.e., an incident angle) between the illumination beam IB incident to the first optical film120and a normal direction of the first optical film120toward a first surface120sof the light guide plate100is greater than 50 degrees.

Furthermore, the first optical film120is disposed on one side of the light emitting surface100aof the light guide plate100. The illumination beam IB from the light guide plate100has a first polarization component P1parallel to a virtual surface (not shown in the figure) and a second polarization component P2perpendicular to the virtual surface, and the virtual surface here is, for example, an XZ plane, i.e., the virtual surface is perpendicular to the light incident surface110band the light emitting surface110a. Particularly, after the illumination beam IB passes through the first optical film120, it also has the first polarization component P1parallel to the aforementioned virtual surface and the second polarization component P2perpendicular to the virtual surface, wherein a ratio of the first polarization component P1to the second polarization component P2is greater than or equal to 1.2 and less than or equal to 10. In an exemplary embodiment, the ratio of the first polarization component P1to the second polarization component P2of the illumination beam IB after passing through the first optical film120may be greater than or equal to 1.2 and less than or equal to 4.

In this embodiment, a material of the first optical film120is, for example, polymethyl methacrylate (PMMA). Therefore, if the illumination beam IB from the light guide plate100enters the first optical film120at an angle greater than 50 degrees, a transmittance difference of the first polarization component P1and the second polarization component P2of the illumination beam IB at a light incident surface (i.e., the first surface120sinFIG.2A) of the first optical film120may be greater than 10%, and a good polarization separation effect is thereby provided.

Referring toFIG.3andFIG.5Atogether, the second optical film130is disposed on a side of the first optical film120facing away from the light guide plate100and includes a substrate131and a plurality of prism structures132. The substrate131has a surface131afacing the light guide plate100and a surface131bopposite to the surface131a. The prism structures132of the second optical film130are arranged on the surface131aof the substrate131in the direction X and extend in the direction Y. Namely, an extending direction of the prism structures132of the embodiment is parallel to the light incident surface100bof the light guide plate100, but the invention is not limited thereto. In other embodiments, in order to avoid a moiré pattern produced by the prism structures132and the periodic structures of other film layers, the extending direction of the prism structures132may not be parallel to the light incident surface100bof the light guide plate100, for example, an included angle between the extending direction of the prism structures132and the light incident surface100bof the light guide plate100may be less than 15 degrees. In an exemplary embodiment, the included angle between the extending direction of the prism structures132and the light incident surface100bof the light guide plate100may be less than 5 degrees.

In detail, each of the prism structures132has a prism light-facing surface132rfacing the light source110and a shady surface132bfacing away from the light source110. Here, the prism light-facing surface132rand the shady surface132bdefine a ridge line132RL of the prism structure132, and an extending direction of the ridge line132RL is parallel to the light incident surface100bof the light guide plate100. The shady surface132bof the prism structure132may be divided into two parts, i.e., a first part132b1and a second part132b2. The first part132b1is connected between the substrate131and the second part132b2. The second part132bis connected between the prism light-facing surface132rand the first part132b1.

Particularly, in this embodiment, an included angle β1between the first part132b1of the shady surface132bof the prism structure132and the prism light-facing surface132ris between 62 degrees and 68 degrees, and an included angle β2between the second part132b2of the shady surface132band a virtual extending surface of the first part132b1is between 2 degrees and 4 degrees. Namely, the shady surface132bof the prism structure132is a bent surface. The illumination beam IB from the first optical film120is deflected toward the normal direction (for example, the direction Z) of the light emitting surface100aafter entering the prism structure132of the second optical film130, thereby increasing an output brightness value of the backlight module50near the normal viewing angle, and forming a light shape with high light collection.

Although the embodiment ofFIG.5Ais configured to illustrate that the shady surface132bof the prism structure132of the second optical film130has a break angle, the invention is not limited thereto. In other embodiments that are not shown, it is also possible that the prism light-facing surface132rof the prism structure132of the second optical film130has a break angle, i.e., the prism structure132of the second optical film130has a break angle on one side surface. In an embodiment, besides that the shady surface132bof a prism structure132A of a second optical film130″ has a break angle, a prism light-facing surface132r″ of the prism structure132A of a second optical film130″ may also be divided into two parts, i.e., a third part132r1and a fourth part132r2(as shown inFIG.5B). The third part132r1is connected between the substrate131and the fourth part132r2. The fourth part132r2is connected between the second part132b2of the shady surface132band the third part132r1. Similar to the shady surface132b, an included angle β3between the fourth part132r2of the prism light-facing surface132r″ and a virtual extending surface of the third part132r1is between 2 degrees and 4 degrees. Therefore, both sides surfaces of the prism structure132A of the second optical film130illustrated inFIG.5Bhave the break angles.

In some other embodiments, the prism light-facing surface and the shady surface of the prism structure of the second optical film may also be planar surfaces without break angles. For example, in a prism structure132C of a second optical film130C of an embodiment shown inFIG.5C, neither a prism light-facing surface132r′ nor a shady surface132b′ has a break angle. Particularly, an included angle γ1between the prism light-facing surface132r′ and the substrate131is not equal to an included angle γ2between the shady surface132b′ and the substrate131, and an included angle β1′ between the prism light-facing surface132r′ and the shady surface132b′ of the prism structure132C is preferably between 48 degrees and 74 degrees, and is optimally between 48 degrees and 64 degrees. However, the invention is not limited thereto. In an embodiment that is not shown, the included angle between the prism light-facing surface of the prism structure and the substrate of the second optical film may also be equal to the included angle between the shady surface and the substrate, and the included angle between the prism light-facing surface and the shady surface of the prism structure is preferably between 59 degrees and 67 degrees, and is optimally between 60 degrees and 64 degrees.

On the other hand, since an apex angle of the prism structure132of the second optical film130is an acute angle, it is easy to scratch the light emitting surface100aof the light guide plate100to form bright marks or bright spots. By disposing the first optical film120between the light guide plate100and the second optical film130, the prism structures132on the second optical film130may also be prevented from directly contacting the light emitting surface100bof the light guide plate100, thereby improving production yield of the backlight module50.

In this embodiment, a material of the substrate of the first optical film120(such as the substrate121ofFIG.6) and the substrate131of the second optical film130may be a low complex refractive index material, and the low complex refractive index material includes, for example, polycarbonate (PC), polymethyl methacrylate (PMMA), cyclic olefin polymer (COP) and cellulose triacetate (TAC), but the invention is not limited thereto. In other embodiments, the material of the substrate of the first optical film120and/or the substrate131of the second optical film130may also be a high complex refractive index material, and the high complex refractive index material includes, for example, polyethylene terephthalate (PET), polycarbonate (PC) or a stretched film of cyclic olefin copolymer (COP). Particularly, if the high complex refractive index material is configured to fabricate the substrate of the first optical film120and the substrate131of the second optical film130(i.e., the substrate of the optical film has birefringence), an axial direction of an optical axis (or a material stretching axis) of the substrate of the optical film should be parallel or perpendicular to the light incident surface100bof the light guide plate100to avoid phase retardation of the illumination beam IB after passing through these films. Such phase retardation may cause a change of the ratio of the first polarization component P1to the second polarization component P2of the illumination beam IB, which results in deterioration of the aforementioned polarization separation effect.

Referring toFIG.1toFIG.2Bagain, the display apparatus10further includes a display panel200that is overlapped and disposed on the backlight module50. The display panel200is located on one side of the surface131bof the second optical film130and includes two polarizers211and212and a liquid crystal cell220. Where, the polarizer211is arranged between the liquid crystal cell220and the backlight module50, and the liquid crystal cell220is arranged between the polarizer211and the polarizer212. For example, in the embodiment, the polarizer211and the polarizer212respectively have an absorption axis AX1and an absorption axis AX2, and axial directions of the two absorption axes AX1and AX2are orthogonal to each other, but the invention is not limited thereto. In other embodiments, a relative arrangement relationship of the axial directions of the two absorption axes of the two polarizers of the display panel may be adjusted according to an electric control mode of the liquid crystal cell, which is not limited by the invention.

In this embodiment, the axial direction of the absorption axis AX1of the polarizer211closer to the backlight module50in the display panel200is perpendicular to the first polarization component P1of the illumination beam IB (or parallel to the light incident surface100bof the light guide plate100). Namely, the first polarization component P1of the illumination beam IB may pass through the polarizer211of the display panel200. Therefore, due to the polarization separation effect of the first optical film120, the first polarization component P1of the illumination beam IB incident on the display panel20may be increased, thereby improving the light energy utilization rate of the display apparatus10.

In order to further increase the light energy utilization rate of the display apparatus10, the backlight module50may also optionally include a reflector140. The reflector140is arranged on one side of the bottom surface100cof the light guide plate100. For example, in the embodiment, the reflector140may be a silver reflector or a white reflector with a reflectivity greater than 95%, but the invention is not limited thereto. In an exemplary embodiment, the reflectivity of the reflector140may be greater than 98%.

Other embodiments are listed below to describe the invention in detail, where the same components are denoted by the same symbols, and the description of the same technical content is omitted. The aforementioned embodiment may be referred for descriptions of the omitted parts, and detailed descriptions thereof are not repeated in the following embodiment.

FIG.6is a schematic diagram of a display apparatus according to a second embodiment of the invention.FIG.7is a schematic top view of a backlight module ofFIG.6.FIG.8Ais a partial enlarged schematic diagram of a first optical film ofFIG.6.FIG.8Bis a partial enlarged schematic view of a first optical film according to another embodiment of the invention.FIG.9Ais a light intensity distribution diagram of an illumination beam after exiting from the first optical film ofFIG.8A.FIG.9Bis a light intensity distribution diagram of the illumination beam after exiting from the first optical film ofFIG.8B.

Referring toFIG.6andFIG.7, a difference between a display apparatus10A of the embodiment and the display apparatus10ofFIG.1lies in a different configuration of the first optical film. In the embodiment, a first optical film120A of a backlight module50A includes a substrate121and a plurality of optical microstructures122. The substrate121has a first surface121afacing the light guide plate100and a second surface121bfacing the second optical film130. The optical microstructures122are provided on the second surface121bof the substrate121of the first optical film120A. In the embodiment, the optical microstructures122are arranged in the direction Y and extend in the direction X. Namely, a long axis direction (an extending direction of a ridge line122RL) of the optical microstructures122of the first optical film120A is substantially perpendicular to the light incident surface100bof the light guide plate100and an extending direction of a ridge line132RL of the prism structure132of the second optical film130.

Based on the above configuration relationship, the light collection of the backlight module50A in the extending direction of the prism structure132of the second optical film130may be further enhanced, thereby increasing the output brightness value of the backlight module50A near the normal viewing angle. However, the invention is not limited thereto, and in other embodiments, in order to increase a viewing angle of the backlight module in an arrangement direction of the prism structures132of the second optical film130(or a direction perpendicular to the light incident surface100bof the light guide plate100), the extending direction of the plurality of optical microstructures122of the first optical film120A may also be parallel to the extending direction of the prism structures132of the second optical film130.

Referring toFIG.8A, in this embodiment, the optical microstructures122of the first optical film120A are prisms. The prism has an apex angle122V close to the second optical film130, and a range A1of the apex angle122V is between 120 degrees and 160 degrees. In an exemplary embodiment, the value of the apex angle122V may be between 140 degrees and 160 degrees. However, the invention is not limited thereto. According to other embodiments, the optical microstructures of the first optical film may also be lenticular lens structures, elliptical lens structures or elongated concave-convex structures.

Referring toFIG.9A, since the apex angle122V of the optical microstructure122of the first optical film120A of the embodiment is a sharp angle, a light shape of the illumination beam IB from the light guide plate100after passing through the first optical film120A is relatively asymmetric in a direction perpendicular to the light incident surface100bof the light guide plate100(i.e., an azimuth at a 90-degree angle inFIG.9A), and the illumination beam IB has a higher output brightness value near the normal viewing angle after passing through the second optical film130. However, the invention is not limited thereto, and in other embodiments, an apex angle122V′ of an optical microstructure122A of a first optical film120A′ may be an arc angle (as shown inFIG.8B). Therefore, the light shape of the illumination beam IB from the light guide plate100after passing through the first optical film is relatively symmetric in the direction perpendicular to the light incident surface100bof the light guide plate100(as shown inFIG.9B), and the illumination beam IB has a lower output brightness value near the normal viewing angle after passing through the second optical film130.

FIG.10is a schematic diagram of a display apparatus according to a third embodiment of the invention.FIG.11is a schematic top view of a backlight module ofFIG.10.FIG.12is a partial enlarged side view of a first optical film ofFIG.10. Referring toFIG.10toFIG.12, a difference between a display apparatus10B of the embodiment and the display apparatus10ofFIG.1lies in a different configuration of the optical microstructures of the first optical film. In the embodiment, an optical microstructure123of a first optical film120B of a backlight module50B is an elliptical lens structure.

Particularly, the elliptical lens structure respectively has a first length L1and a second length L2in a long axis direction and a short axis direction, and a ratio of the first length L1to the second length L2is greater than 2. In an exemplary embodiment, the ratio of the first length L1to the second length L2of the elliptical lens structure may be greater than 5. In the embodiment, the long axis direction of the elliptical lens structure is a direction perpendicular to the light incident surface100bof the light guide plate100, such as the direction X. The short axis direction (for example, the direction Y) is perpendicular to the long axis direction. On the other hand, the elliptical lens structure has a height H2in a normal direction of the second surface121bof the substrate121, and a ratio of the second length L2to the height H2is between 1 and 50. In an exemplary embodiment, the ratio of the second length L2to the height H2of the elliptical lens structure may be between 2 and 30.

Based on the above configuration relationship, the light collection of the backlight module50B in the extending direction of the prism structures132of the second optical film130may be further enhanced, thereby increasing the output brightness value of the backlight module50B near the normal viewing angle. However, the invention is not limited thereto, and in other embodiments, in order to increase a viewing angle of the backlight module in the arrangement direction of the prism structures132of the second optical film130(or the direction perpendicular to the light incident surface100bof the light guide plate100), the long axis direction of the plurality of elliptical lens structures (i.e., the optical microstructures123) of the first optical film120B may also be parallel to the extending direction of the prism structures132of the second optical film130.

On the other hand, by arranging the elliptical lens structures, the second optical film130and the first optical film120B may also be prevented from being adsorbed to cause adsorption marks or Newton's rings. However, the invention is not limited thereto. In other embodiments, the elliptical lens structures may also be arranged on the first surface121aof the substrate121of the first optical film facing the light guide plate100, so as to avoid the first optical film and the light emitting surface100aof the light guide plate100from being adsorbed to cause adsorption marks or Newton's rings.

FIG.13is a schematic diagram of a display apparatus according to a fourth embodiment of the invention.FIG.14is a schematic top view of a backlight module ofFIG.13. For clarity's sake,FIG.14only illustrates the light guide plate100, the light source110, and the second optical film130A of a backlight module50C inFIG.13.

Referring toFIG.13andFIG.14, a difference between a display apparatus10C of the embodiment and the display apparatus10ofFIG.1lies in a different structural composition of the second optical film. To be specific, in order to increase a viewing angle of the backlight module50C in the arrangement direction of the prism structures132of the second optical film130A (or the direction perpendicular to the light incident surface100bof the light guide plate100), the surface131bof the substrate131of the second optical film130A facing away from the light guide plate100is further provided with a plurality of optical microstructures133, and an extending direction or a long axis direction of the optical microstructures133is parallel to the extending direction of the prism structures132.

In this embodiment, the optical microstructure133of the second optical film130A is an elliptical lens structure, and the long axis direction of the elliptical lens structure is parallel to the light incident surface100bof the light guide plate100. Particularly, the long axis direction of the elliptical lens structure is parallel to the direction of the light incident surface100bof the light guide plate100, such as the direction Y. A short axis direction (for example, the direction X) is perpendicular to the long axis direction. The elliptical lens structure respectively has a first length L1′ and a second length L2′ in the long axis direction and the short axis direction, and a ratio of the first length L1′ to the second length L2′ is greater than 2. In an exemplary embodiment, the ratio of the first length L1′ to the second length L2′ of the elliptical lens structure may be greater than 5.

However, the invention is not limited thereto, and in other embodiments, the optical microstructures of the second optical film disposed on the surface131bof the substrate131facing away from the light guide plate100may also be prisms, lenticular lens structures, or elongated concave-convex structures. Particularly, in this embodiment, the optical microstructures133of the second optical film130A also have a haze value less than 80%, so as to avoid the viewing angle of the backlight module50C in the arrangement direction of the prism structures132of the second optical film130A (or the direction perpendicular to the light incident surface100bof the light guide plate100) to be too large to reduce the output brightness value near the normal viewing angle. In an exemplary embodiment, the haze value of the optical microstructures133of the second optical film130A may be between 30% and 60%.

FIG.15is a schematic diagram of a display apparatus of a fifth embodiment of the invention. Referring toFIG.15, a difference between a display apparatus10D of the embodiment and the display apparatus10C ofFIG.13lies in a different configuration of the optical microstructures of the second optical film. In the embodiment, in the second optical film130B of the backlight module50D, the plurality of optical microstructures134arranged on the surface131bof the substrate131facing away from the light guide plate100are a plurality of prism structures, and an extending direction of the prism structures are parallel to the light incident surface100bof the light guide plate100and the extending direction of the prism structures132(for example, the direction Y). Since a function of the optical microstructures134of the second optical film130B of the embodiment is similar to that of the optical microstructures133of the second optical film130A ofFIG.13, a detailed description thereof may be deduced by referring to the relevant paragraphs of the above embodiment, which is not repeated.

FIG.16is a schematic diagram of a display apparatus according to a sixth embodiment of the invention.FIG.17is a schematic diagram of a display apparatus according to a seventh embodiment of the invention. Referring toFIG.16, a difference between a display apparatus10E of the embodiment and the display apparatus10A ofFIG.6lies in a different structural composition of the first optical film. To be specific, in order to prevent a first optical film120C of a backlight module50E from being adsorbed to the light emitting surface100aof the light guide plate100, an optical film layer125may be provided on the first surface121aof the substrate121of the first optical film120C facing the light guide plate100. For example, in the embodiment, a haze value of the optical film layer125may be less than 20%. In an exemplary embodiment, the haze value of the optical film layer125may be less than 5%. However, the invention is not limited thereto, and according to other embodiments, the optical film layer125may have a pencil hardness greater than 2H and a surface energy lower than that of the substrate121.

Referring toFIG.17, in another embodiment, in a first optical film120D of a backlight module50F of a display apparatus10F, the optical film layer125of the first optical film120C ofFIG.16may be replaced by a plurality of prisms124, but the invention is not limited thereto. In another embodiment, the first surface121aof the substrate121of the first optical film facing the light guide plate100may also be provided with a plurality of elliptical lens structures, a plurality of lenticular lens structures, or a plurality of elongated concave-convex structures, and a long axis direction (or an extending direction) of these structures may be perpendicular or parallel to the light incident surface100bof the light guide plate100to adjust a light shape of the backlight module, for example, to increase light collection or a viewing angle in a specific direction.

FIG.18is a schematic diagram of a display apparatus of an eighth embodiment of the invention. Referring toFIG.18, a difference between a display apparatus10G of the embodiment and the display apparatus10ofFIG.1is that the display apparatus10G further includes a reflective polarizer170disposed between the polarizer211and a backlight module50G. By means of a reflection axis RX of the reflective polarizer170being parallel to the light incident surface100bof the light guide plate100, a proportion of the first polarization component P1of the illumination beam IB incident to the display panel200may be further increased, thereby increasing a light energy utilization rate of the display apparatus10G.

On the other hand, the backlight module50G of the embodiment may also selectively include a third optical film150disposed between the light guide plate100and the reflector140. The third optical film150includes a substrate151and a plurality of prism structures152disposed on a third surface151sof the substrate151facing the light guide plate100. The prism structures152are arranged in the direction Y and extend in the direction X. Namely, an extending direction of the prism structures152is perpendicular to the light incident surface100bof the light guide plate100. In the embodiment, each of the prism structures152has an apex angle152V closer to the light guide plate100, and a range A2of the apex angle152V is between 80 degrees and 100 degrees.

It should be noted that through the arrangement of the third optical film150, selection flexibility of the reflector140may be increased. For example, in order to obtain a cost advantage, the reflector140may be a white reflector with a lower cost, and the third optical film150may be set to compensate for the loss of a part of the output brightness value of the backlight module50G generated due to the selection of the white reflector.

FIG.19is a schematic diagram of a display apparatus according to a ninth embodiment of the invention. Referring toFIG.19, a difference between a display apparatus10H of the embodiment and the display apparatus10ofFIG.1lies in a different composition of a backlight module. In the embodiment, a backlight module50H further includes a fourth optical film160disposed between the second optical film130and the display panel200. The fourth optical film160includes a substrate161and a plurality of prism structures162. The substrate161has a surface161afacing the light guide plate100and a surface161bopposite to the surface161a. In the embodiment, the prism structures162may be selectively disposed on the surface161bof the substrate161. However, the invention is not limited thereto, and in other embodiments, the prism structures162may also be replaced by the optical microstructures133(i.e., the elliptical lens structures) ofFIG.13, and in another embodiment, the prism structures162may be further changed to be disposed on the surface161aof the substrate161.

In this embodiment, the extending direction of the prism structures132of the second optical film130may be parallel to an extending direction of the prism structures162of the fourth optical film160, but the invention is not limited thereto. Since a function of a combination of the second optical film130and the fourth optical film160of the embodiment is similar to that of the second optical film130B ofFIG.15, detailed description thereof may be deduced by referring to the related paragraphs of the aforementioned embodiments and is not repeated herein.

FIG.20is a schematic diagram of a display apparatus according to a tenth embodiment of the invention. Referring toFIG.20, a difference between a display apparatus10I of the embodiment and the display apparatus10D ofFIG.15is that a backlight module50I of the display apparatus10I further includes a fourth optical film disposed between the second optical film130B and the display panel200. The fourth optical film160A includes a substrate161and a plurality of optical microstructures162A. The substrate161has a surface161afacing the light guide plate100and a surface161bopposite to the surface161a. In the embodiment, the optical microstructures162A are, for example, a plurality of prism structures. The prism structures may be selectively disposed on the surface161bof the substrate161, and an extending direction thereof is perpendicular to the light incident surface100bof the light guide plate100.

Through the arrangement of the optical microstructures162A, the viewing angle of the backlight module501in the extending direction (for example, the direction Y) of the plurality of prism structures132(or the plurality of optical microstructures134) of the second optical film130B may be increased. However, the invention is not limited thereto. According to other embodiments, the optical microstructures162A of the fourth optical film may also be replaced by a plurality of elliptical lens structures (such as the optical microstructures123inFIG.10), and in another embodiment, the prism structures162may be further changed to be disposed on the surface161aof the substrate161.

In view of the foregoing, in the backlight module and the display apparatus of the embodiments of the invention, the first optical film and the second optical film are disposed on one side of the light emitting surface of the light guide plate. One side of the second optical film facing the light guide plate is provided with a plurality of prism structures with the extending direction substantially parallel to the light incident surface of the light guide plate. The first optical film located between the prism structures and the light guide plate may increase a polarization component of the illumination beam from the light guide plate in a specific direction, which is beneficial to an increase in the light energy utilization rate of the display apparatus. Moreover, through the arrangement of the first optical film, the light emitting surface of the light guide plate is prevented from being scratched by the prism structures of the second optical film, so the production yield of the backlight module is prevented from being affected.