Patent Publication Number: US-2016238777-A1

Title: Light guide plate ,light source module and display device

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part application of U.S. application Ser. No. 14/497,341, filed on Sep. 26, 2014, which claims priority to Taiwan Application Serial Number 103118457, filed May 27, 2014. This application also claims priority to Taiwan Application Serial Number 104116843, filed May 26, 2015. The entire disclosures of all the above applications are hereby incorporated by reference herein. 
    
    
     BACKGROUND 
     1. Field of Invention 
     The present invention relates to a light guide element. More particularly, the present invention relates to a light guide plate, light source module and display device. 
     2. Description of Related Art 
     A conventional light guide plate used in a backlight module has a light-incident surface, a light-emitting surface and a reflecting surface. Light generated by a light source enters the light guide plate from the light-incident surface and is emitted out from the light-emitting surface of the light guide plate. Another conventional light guide plate used in a lamp has two opposite light-emitting surfaces. After entering the light guide plate, light generated by the light source is emitted out from the respective light-emitting surfaces. In order to mix the light passing through the light guide plate uniformly, lateral V-shaped structures are generally disposed on the light-emitting surfaces of the light guide plate. 
     However, such lateral V-shaped structures cause the light guide plate to have high light concentration and directivity, such that obvious dark/bright bands or hot spots are generated on the light-emitting surface of the light guide plate, thus affecting the optical appearance of the light guide plate. 
     SUMMARY 
     One object of the present invention is to provide a light guide plate and a light source module, in which light-emitting angle and directivity of light emitted from a light guide plate can be changed by varying shapes, angles, heights, depths or arrangements of microstructures disposed on a light-emitting surface of the light guide plate, so as to increase light-emitting efficiency and uniformity of the overall light-emitting appearance of the light guide plate. 
     Another object of the present invention is to provide a light guide plate and a light source module, in which light-mixing structures are disposed near a light-incident surface of the light guide plate to be collocated with and the microstructures, so that the problems of non-uniform appearance causing by the dark/bright bands near the light-incident surface of the conventional light guide plate can be improved, thus increasing optical effect of the light guide plate. 
     According to the aforementioned objects, a light guide plate is provided. The light guide plate includes a main body and plural microstructures. The main body includes a light-incident surface and a light-emitting surface connected to the light-incident surface. The microstructures are disposed on the light-emitting surface. Each of the microstructures includes a first optical surface, a second optical surface, a third optical surface and a fourth optical surface. The first optical surface is inclined in relation to the light-incident surface and is connected to the light-emitting surface, in which a first angle is included between the first optical surface and the light-emitting surface. The second optical surface is inclined in relation to the light-incident surface and is connected to the light-emitting surface, in which a second angle is included between the second optical surface and the light-emitting surface. The third optical surface connects the light-emitting surface, the first optical surface and the second optical surface, in which a third angle is included between the third optical surface and the light-emitting surface. The fourth optical surface is opposite to the third optical surface and connects the light-emitting surface, the first optical surface and the second optical surface, in which a fourth angle is included between the fourth optical surface and the light-emitting surface. 
     According to an embodiment of the present invention, the first optical surface and the second optical surface of each of the microstructures are connected to form a ridge line substantially parallel to an edge of the light-incident surface. 
     According to an embodiment of the present invention, each of the microstructures further includes a top surface connecting the first optical surface, the second optical surface, the third optical surface and the fourth optical surface, and an edge of the top surface connected to the first optical surface or the second optical surface is substantially parallel to an edge of the light-incident surface. 
     According to an embodiment of the present invention, each of the top surfaces is a flat surface or an arc surface. 
     According to an embodiment of the present invention, each of the third optical surfaces has one or more flat, angled, faceted or curved reflective or refractive surfaces to change a light output ray angle distribution to a greater extent. 
     According to an embodiment of the present invention, each of the fourth optical surfaces one or more flat, angled, faceted or curved reflective or refractive surfaces to change a light output ray angle distribution to a greater extent. 
     According to an embodiment of the present invention, each of the microstructures is a convex portion or a concave portion. 
     According to an embodiment of the present invention, the light guide plate further includes plural light-mixing structures disposed on the light-emitting surface adjacent to the light-incident surface. 
     According to an embodiment of the present invention, the light-mixing structures are dotted structures. 
     According to an embodiment of the present invention, the light-mixing structures are striped structures, and the light-mixing structures extend along a direction from one side of the light-emitting surface near the light-incident surface to the other side of the light-emitting surface away from the light-incident surface. 
     According to an embodiment of the present invention, the light-mixing structures are striped structures, and each of the light-mixing structures has a width gradually decreasing from one end of the light-mixing structure near the light-incident surface to the other end of the light-mixing structure away from the light-incident surface. 
     According to an embodiment of the present invention, each of the light-mixing structures is a convex portion or a concave portion. 
     According to an embodiment of the present invention, each of the light-mixing structures has a length extending along a direction from one side of the light-emitting surface near the light-incident surface to the other side of the light-emitting surface away from the light-incident surface, and a ratio of the length of the light-mixing structure to an overall length of the main body is greater than or equal to 0.5% and is smaller than or equal to 10%. 
     According to an embodiment of the present invention, a blank portion between the light-mixing structures and the microstructures, and a ratio of a length of the blank portion to an overall length of the main body is greater than 0% and is smaller than or equal to 5%. 
     According to an embodiment of the present invention, the light-mixing structures are connected to the microstructures. 
     According to an embodiment of the present invention, the main body further comprises a surface opposite to the light-emitting surface, and plural optical microstructures are disposed on the surface. 
     According to an embodiment of the present invention, the optical microstructures are dotted structures, striped structures or structures similar to the microstructures. 
     According to an embodiment of the present invention, the third angle and the fourth angle are greater than or equal to −45 degrees and are smaller than or equal to 45 degrees. 
     According to an embodiment of the present invention, the smaller one of the first angle and the second angle faces towards the light-incident surface, and the greater one of the first angle and the second angle faces away from the light-incident surface. 
     According to the aforementioned objects, a light source module is provided. The light source module includes the aforementioned light guide plate and a light source. The light source is disposed adjacent to the light-incident surface of the light guide plate. 
     According to an embodiment of the present invention, the microstructures are arranged to form plural microstructure rows, and each of the microstructure rows has an arrangement density which is greater with increase of a distance between the microstructure row and the light source. 
     According to an embodiment of the present invention, the microstructures are arranged to form plural microstructure rows, and there is a distance between two adjacent microstructure rows, in which the distance is smaller with increase of a distance between the microstructure rows and the light source. 
     According to an embodiment of the present invention, the sizes of the microstructures are greater with increase of a distance between the microstructure row and the light source. 
     According to an embodiment of the present invention, the microstructures are arranged divergently along a light-emitting direction of the light source. 
     It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows: 
         FIG. 1  is a schematic structural diagram showing one type of light guide plate in accordance with a first embodiment of the present invention; 
         FIG. 2  is a schematic cross-sectional view of microstructure viewed along a line A-A in  FIG. 1 ; 
         FIG. 3  is a schematic structural diagram showing one type of microstructure in accordance with the first embodiment of the present invention; 
         FIG. 4A  is a schematic structural diagram showing another type of microstructure in accordance with the first embodiment of the present invention; 
         FIG. 4B  is a schematic structural diagram showing another type of microstructure in accordance with the first embodiment of the present invention; 
         FIG. 5A  is a schematic structural diagram showing one type of microstructure in accordance with a second embodiment of the present invention; 
         FIG. 5B  is a schematic structural diagram showing another type of microstructure in accordance with the second embodiment of the present invention; 
         FIG. 6  is a schematic structural diagram showing one type of microstructure in accordance with a third embodiment of the present invention; 
         FIG. 7  is a schematic structural diagram showing one type of microstructure in accordance with a fourth embodiment of the present invention; 
         FIG. 8  is a schematic structural diagram showing another type of light guide plate in accordance with the first embodiment of the present invention; 
         FIG. 9  is a schematic structural diagram showing another type of light guide plate in accordance with a fifth embodiment of the present invention; 
         FIG. 10  is a schematic cross-sectional view of the microstructure viewed along a line B-B in  FIG. 9 ; 
         FIG. 11  is a schematic structural diagram showing another type of light guide plate in accordance with a sixth embodiment of the present invention; 
         FIG. 12  is a schematic structural diagram showing another type of light guide plate in accordance with a seventh embodiment of the present invention; 
         FIG. 13  is a schematic top view of the light guide plate in accordance with the first embodiment of the present invention; and 
         FIG. 14A - FIG. 14D  are schematic diagrams showing different arrangements of microstructures in accordance with an embodiment of the present invention. 
         FIG. 15  is a schematic structural diagram showing a light source module in accordance with an embodiment of the present invention; 
         FIG. 16  is a schematic side view of the light source module in accordance with an embodiment of the present invention; 
         FIG. 17A  is a schematic diagram showing arrangement densities of first microstructures and second microstructures respectively arranged in relation to a first light source and a second light source; 
         FIG. 17B  is a diagram showing luminance distribution on a light guide plate when one or both of a first light source and a second light source emit light; and 
         FIG. 18  is a schematic structural diagram showing a display device in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     Referring to  FIG. 1 ,  FIG. 1  is a schematic structural diagram showing one type of light guide plate  100  in accordance with a first embodiment of the present invention. The light guide plate  100  is applicable to a backlight module or a lamp. The light guide plate  100  includes a main body  120  and plural microstructures  140 . The microstructures  140  are disposed on the main body  120  for adjusting optical trends and increasing luminance uniformity of the light guide plate  100 . 
     In the light guide plate  100 , the main body  120  is a transparent plate or another equivalent transparent element. The main body  120  mainly includes a light-incident surface  122  and a light-emitting surface  124 . The light-emitting surface  124  is connected to the light-incident surface  122 . A light source  160  can be disposed adjacent to the light-incident surface  122  and light generated by the light source  160  will enter the light guide plate  100  from the light-incident surface  122 . 
     Referring to  FIG. 1  and  FIG. 2 ,  FIG. 2  is a schematic cross-sectional view of the microstructure  140  viewed along a line A-A in  FIG. 1 . In the present embodiment, the microstructures  140  are disposed on the light-emitting surface  124 , and the microstructures  140  are convex portions protruding from the light-emitting surface  124 . Moreover, each of the microstructures  140  includes a first optical surface  141 , a second optical surface  142 , a first side optical surface  143  and a second side optical surface  144 . The first optical surface  141  is connected to the light-emitting surface  124  and inclined in relation to the light-incident surface  122 . A first angle α is included between the first optical surface  141  and the light-emitting surface  124 . Similarly, the second optical surface  142  is connected to the light-emitting surface  124  and inclined in relation to the light-incident surface  122 . A second angle β is included between the second optical surface  142  and the light-emitting surface  124 . Moreover, the first optical surface  141  and the second optical surface  142  of each of the microstructures  140  are connected to form a ridge line  145  which is substantially parallel to an edge of the light-incident surface  122 . In addition, the first angle α and the second angle β are designed corresponding to different optical films collocated with the light guide plate  100 . Meanwhile, the first optical surface  141  and the second optical surface  142  are inclined in relation to the light-incident surface  122 , so that light-emitting angle and light directivity of light emitted from the light guide plate  100  can be changed, thereby increasing light-emitting efficiency and uniformity of the overall light-emitting appearance of the light guide plate  100 . In addition, a shape of each of the microstructures  140  can be varied with a width W, the first angle α and the second angle β thereof, and a height H between a top end of each of the microstructures  140  to the light-emitting surface  124  can be changed by adjusting the first angle α and a top end the second angle β. 
     Referring to  FIG. 1  and  FIG. 2 , in some embodiments, the light guide plate  100  includes a surface  126  opposite to the light-emitting surface  124 . The surface  126  can be a reflecting surface or a light-emitting surface. When the light guide plate  100  is applied to a backlight module, the surface  126  is a reflecting surface. When the light guide plate  100  is applied to a lamp, the surface  126  is a light-emitting surface. 
     Referring to  FIG. 1  and  FIG. 3 ,  FIG. 3  is a schematic structural diagram showing one type of microstructure  140  in accordance with the first embodiment of the present invention. The first side optical surface  143  mainly connects the light-emitting surface  124 , the first optical surface  141  and the second optical surface  142 . Moreover, a first side angle θ is included between the first side optical surface  143  and the light-emitting surface  124 . The second side optical surface  144  is opposite to the first side optical surface  143 . Moreover, the second side optical surface  144  connects the light-emitting surface  124 , the first optical surface  141  and the second optical surface  142 . A second side angle φ is included between the second side optical surface  144  and the light-emitting surface  124 . In some embodiments, each of the first side optical surfaces  143  and the second side optical surfaces  144  has one or more flat, angled, faceted or curved reflective or refractive surfaces. As shown in  FIG. 3 , in the present embodiment, the first side optical surface  143  includes optical units  143   a  and  143   b , and the second side optical surface  144  includes optical units  144   a  and  144   b . The first side optical surface  143  and the second side optical surface  144  are used to change a light output ray angle distribution of the light beam L to a greater extent after the light beam L emitting from the microstructures  140 . Therefore, the light concentration degree of the microstructures  140  can be changed by adjusting the first side angle θ and the second side angle φ. In some embodiments, the first side angle θ and the second side angle φ are in a range from −45 degrees to 45 degrees. 
     In the embodiment of  FIG. 3 , the first side optical surface  143  and the second side optical surface  144  of the microstructures  140  are respectively composed of two optical units. In some embodiments, the microstructures  140  have different designs. Referring to  FIG. 4A ,  FIG. 4A  is a schematic structural diagram showing another type of microstructure in accordance with the first embodiment of the present invention. As shown in  FIG. 4A , a microstructure  200  is similar to the aforementioned microstructure  140 , and the main difference therebetween is that each of a first side optical surface  201  and a second side optical surface  202  of the microstructure  200  is one single surface. Moreover, a first angle α 1  between the first optical surface  141  and a light-emitting surface and a second angle β 1  between the second optical surface  142  and the light-emitting surface of the microstructure  200  are different from the first angle α and the second angle β of the microstructure  140 . 
     Simultaneously referring to  FIG. 4B ,  FIG. 4B  is a schematic structural diagram showing another type of microstructure in accordance with the first embodiment of the present invention. As shown in  FIG. 4B , a microstructure  220  is similar to the aforementioned microstructure  140 , and the main difference therebetween is that a first side optical surface  221  of the microstructure  220  is composed of optical units  221   a ,  221   b  and  221   c , and a second side optical surface  222  is composed of optical units  222   a ,  222   b  and  222   c . It is noted that all of the first side optical surfaces  143 ,  201  and  221  or the second side optical surface  144 ,  202  and  222  composed of two surfaces, one single surface or three surfaces can function to change the light output ray angle distribution of the light beam L to a greater extent. 
     In the present invention, the microstructures  140 ,  200  and  220  are pyramid structures. In some embodiments, the microstructure  200  has different designs. Referring to  FIG. 5A ,  FIG. 5A  is a schematic structural diagram showing one type of microstructure in accordance with a second embodiment of the present invention. As shown in  FIG. 5A , a microstructure  300  is similar to the aforementioned microstructure  200 , and the main difference therebetween is that the microstructure  300  includes a top surface  301 . The top surface  301  connects the first optical surface  141 , the second optical surface  142 , the first side optical surface  201  and the second side optical surface  202 . In other words, the microstructure  300  is a frustum. In the present embodiment, an edge of the top surface  301  connected to the first optical surface  141  or the second optical surface  142  is substantially parallel to an edge of the light-incident surface of the light guide plate. Moreover, a first angle α 2  is included between the first optical surface  141  and the light-emitting surface, and a second angle β 2  is included between the second optical surface  142  and the light-emitting surface of the microstructure  300 , in which the first angle α 2  and the second angle β 2  are different from the first angle α 1  and the second angle β 1  of microstructure  200 . 
     Referring to  FIG. 5B ,  FIG. 5B  is a schematic structural diagram showing another type of microstructure in accordance with the second embodiment of the present invention. As shown in  FIG. 5B , a microstructure  320  is similar to the aforementioned microstructure  300 , and the microstructure  320  is a frustum and has a top surface  321 . The main difference between the microstructure  320  and the microstructure  300  is that a first side optical surface  322  of the microstructure  320  is composed of three optical units  322   a ,  322   b  and  322   c , and a second side optical surface  323  is composed of three optical units  323   a ,  323   b  and  323   c . In addition, as shown in  FIG. 5A  and  FIG. 5B , in some embodiments, the top surfaces  301  and  321  are flat surfaces, and respectively have a width D 1  and a width D 2 . The width D 1  and the width D 2  can be designed corresponding to different optical requirements. Similarly, in the present embodiment, an edge of the top surface  321  connected to the first optical surface  141  or the second optical surface  142  is substantially parallel to an edge of the light-incident surface of the light guide plate. 
     In other embodiments, the microstructure  140  shown in  FIG. 4A  has different designs. Referring to  FIG. 6 ,  FIG. 6  is a schematic structural diagram showing one type of microstructure in accordance with a third embodiment of the present invention. As shown in  FIG. 4A , a microstructure  400  is similar to the aforementioned microstructure  200 , and the main difference therebetween is that each of the microstructures  400  includes a top surface  401 , and the top surface  401  is an arc surface. In the present embodiment, a radian of the top surface  401  can be designed corresponding to different optical requirements. 
     In other embodiments, the microstructure  300  shown in  FIG. 5A  has different designs. Referring to  FIG. 7 ,  FIG. 7  is a schematic structural diagram showing one type of microstructure in accordance with a fourth embodiment of the present invention. In the present embodiment, a microstructure  500  is similar to the aforementioned microstructure  300 , and the main difference therebetween is that the microstructure  500  includes a top surface  501 , and each of the top surface  501 , a first side optical surface  502  and a second side optical surface  503  of the microstructure  500  is one single arc surface. In addition, radians of the top surface  501 , the first side optical surface  502  and the second side optical surface  503  can be designed corresponding to different optical requirements. 
     In other embodiments, the light guide plate  100  shown in  FIG. 1  has different designs. Referring to  FIG. 8 ,  FIG. 8  is a schematic structural diagram showing another type of light guide plate in accordance with the first embodiment of the present invention. As shown in  FIG. 8 , a light guide plate  100   a  is similar to the aforementioned light guide plate  100 , and the main difference therebetween is that the surface  126  of the light guide plate  100   a  is implemented with plural optical microstructures  126   a . Moreover, the optical microstructures  126   a  are dotted structures, striped structures or structures similar to the microstructures  140 , so as to meet different optical requirements. In the present embodiment, the surface  126  is a light-emitting surface, and the optical microstructures  126   a  on the surface  126  are similar to the microstructures  140 . 
     In some embodiments, the light guide plate  100  has different designs. Referring to  FIG. 9  and  FIG. 10 ,  FIG. 9  is a schematic structural diagram showing another type of light guide plate in accordance with a fifth embodiment of the present invention, and  FIG. 10  is a schematic cross-sectional view of microstructure  640  viewed along a line B-B in  FIG. 9 . As shown in  FIG. 9 , a light guide plate  600  is similar to the aforementioned light guide plate  100 , and the main difference therebetween is that microstructures  640  of the light guide plate  600  are concave portions recessed into the light-emitting surface  124  of the light guide plate  600 . Similarly, each of the microstructures  640  includes a first optical surface  641 , a second optical surface  642 , a first side optical surface  643  and a four optical surface  644 . Moreover, the light-emitting angle and light directivity of light emitted from the light guide plate  600  can be changed by adjusting inclined angles of the first optical surface  641  and the second optical surface  642  in relation to the light-incident surface  122 . Meanwhile, the light-diffusing angles of light entering the microstructures  640  can be adjusted by changing the included angles between the first side optical surface  643  and the light-emitting surface or the four optical surface  644  and the light-emitting surface. 
     Simultaneously referring to  FIG. 1  and  FIG. 2 , because the microstructures  140  shown in  FIG. 1  are convex portions, most of the light entering the light guide plate  100  from the light-incident surface  122  is emitted towards the second optical surface  142 . In other words, the second optical surface  142  is a surface which receives light directly. Therefore, in some embodiments, for achieving the purpose of guiding light the area of the second optical surface  142  is greater than that of the first optical surface  141 . In other words, the smaller one of the first angle α and the second angle β faces towards the light-incident surface  122 , and the greater one of the first angle α and the second angle β faces away from the light-incident surface  122 . On the other hand, because the microstructures  640  shown in  FIG. 9  and  FIG. 10  are concave portions, most of the light entering the light guide plate  100  from the light-incident surface  122  is emitted towards the first optical surface  641 . In other words, the first optical surface  641  is a surface which receives light directly. Therefore, in the structural design, the area of the first optical surface  641  is greater than that of the second optical surface  642 , so as to increase the light-emitting efficiency and the uniformity of the overall light-emitting appearance of the light guide plate  600 . 
     Referring to  FIG. 1  and  FIG. 9 , in some embodiments, each of the light guide plates  100  and  600  includes plural light-mixing structures  180 . The light-mixing structures  180  are disposed on the light-emitting surface  124  adjacent to the light-incident surface  122 . Therefore, after being emitted from the light source  160  and entering the light guide plate  100 , the light will pass through the light-mixing structures  180 , such that the problems of non-uniform light appearance causing by the bright bands appearing on the light-incident surface of the conventional light guide plate can be improved. In addition, in the embodiment of  FIG. 1  and  FIG. 9 , the light-mixing structures  180  are striped structures, and the striped structures are convex portions protruding from the light-emitting surface  124  or concave portions recessed into the light-emitting surface  124 . Moreover, the light-mixing structures  180  extend along a direction from one side of the light-emitting surface  124  near the light-incident surface  122  to the other side of the light-emitting surface  124  away from the light-incident surface  122 . 
     Referring to  FIG. 11 ,  FIG. 11  is a schematic structural diagram showing another type of light guide plate in accordance with a sixth embodiment of the present invention. As shown in  FIG. 11 , a light guide plate  700  is similar to the aforementioned light guide plate  100 , and the main difference therebetween is that light-mixing structures  780  of the light guide plate  700  have different shapes. In the present embodiment, each of the light-mixing structures  780  has a width gradually decreasing from one end of the light-mixing structure  780  near the light-incident surface  122  to the other end of the light-mixing structure  780  away from the light-incident surface  122 . In other embodiments, a depth or a height of each of the light-mixing structures  780  can be designed to meet different requirements. For example, the depth or the height of each of the light-mixing structures  780  is gradually decreasing from one end of the light-mixing structure  780  near the light-incident surface  122  to the other end of the light-mixing structure  780  away from the light-incident surface  122 . In other embodiments, as shown in  FIG. 12 ,  FIG. 12  is a schematic structural diagram showing another type of light guide plate  800  in accordance with a seventh embodiment of the present invention. In the shown embodiment of  FIG. 12 , light-mixing structures  880  of the light guide plate  800  are dotted structures. 
     Simultaneously referring to  FIG. 1  and  FIG. 13 ,  FIG. 13  is a schematic top view of the light guide plate  100  in accordance with the first embodiment of the present invention. In the present embodiment, each of the light-mixing structures  180  has a length L 1 , and a ratio of the length L 1  of the light-mixing structure  180  to an overall length of the main body  120  is in a range from 0.5% to 10%. In other embodiments, there is a blank portion  190  between the light-mixing structures  180  and the microstructures  140 , and a ratio of a length L 2  of the blank portion  190  to an overall length of the main body  120  is in a range from 0% to 5%. In other words, the microstructures  140  nearest light-mixing structures  180  can be connected to the light-mixing structures  180  directly, or not directly connected to the light-mixing structures  180  by spaced at a distance from the light-mixing structures  180 . In addition, the length L 1  of the light-mixing structures  180  and the length L 2  of the blank portion  190  can be designed to meet different requirements, thereby generating different light-mixing effects and increase luminance uniformity of the light guide plate  100 . 
     It is noted that, when the light guide plate  100  is applied to a light source module (such as a backlight module), the numbers, sizes and arrangements of the microstructures  140  can be varied corresponding to the distance between the microstructures  140  and the light source  160  or other optical requirements. Referring to  FIG. 14A - FIG. 14D ,  FIG. 14A - FIG. 14D  are schematic diagrams showing different arrangements of the microstructures  140  in accordance with an embodiment of the present invention. In the example shown in  FIG. 14A , the microstructures  140  of the light guide plate  100  have the same size and are arranged to form plural microstructure rows. Each of the microstructure rows is substantially parallel to an edge of the light-incident surface of the light guide plate. Moreover, the microstructure rows near the light source  160  are sparsely arranged, and the microstructure rows away from light source  160  are densely arranged. In other words, the arrangement density of each microstructure row is greater with increase of the distance between the microstructure row and the light source  160 . In addition, in the example shown in  FIG. 14A , every two adjacent microstructure rows are spaced equidistantly. 
     In an example shown in  FIG. 14B , the size of the microstructures  140  in the microstructure rows positioned near the light sources  160  is smaller, and the size of the microstructures  140  in the microstructure rows positioned away from the light sources  160  is greater. In an example shown in  FIG. 14C , each of the microstructures  140  has the same size, and the distance between every two adjacent microstructure rows is smaller with increase of the distance between the microstructure rows and the light source  160 . In an example shown in  FIG. 14D , each of the microstructures  140  has the same size, and the microstructures near the light source  160  are arranged divergently along the light-emitting direction of the light source  160 . Therefore, different arrangements of the microstructures  140  can make the light guide plate  100  emit more uniform light. 
     The light guide plate also can be applied to a light source module with two light sources. Referring to  FIG. 15  and  FIG. 16 ,  FIG. 15  and  FIG. 16  are a schematic structural diagram and a schematic side view showing a light source module  900  in accordance with an embodiment of the present invention. The light source module  900  of the present embodiment mainly includes a light guide plate  920 , a first light source  940  and a second light source  960 . The light guide plate includes a main body  921 , plural first microstructures  923  and plural second microstructures  925 . The main body  921  has a first light-incident surface  921   a , a second light-incident surface  921   b  and a light-emitting surface  921   c . The first light source  940  and the second light source  960  are respectively disposed adjacent to the first light-incident surface  921   a  and the second light-incident surface  921   b . Moreover, the first microstructures  923  and the second microstructures  925  are simultaneously disposed on the light-emitting surface  921   c  of the main body  921 . In the present embodiment, a length, a width and a height of each of the first microstructures  923  and the second structures  925  are smaller than that of the main body  120 . 
     Referring to  FIG. 15  and  FIG. 16  again, structures of the first microstructures  923  and the second structures  925  are similar to that of the aforementioned microstructures  140 . As shown in  FIG. 15 , each of the first microstructures  923  includes a first optical surface  923   a , a second optical surface  923   b , a first side optical surface  923   c  and a second side optical surface  923   d . The first optical surface  923   a  is inclined in relation to the first light-incident surface  921   a  to form a first angle α 3 . It is noted that, the first optical surface  923   a  extends from a bottom portion to a top portion of the first microstructure  923 , and the first angle α 3  is an included angle between the first optical surface  923   a  and a level surface passing through a bottom portion of the first optical surface  923   a , in which the level surface and the light-emitting surface  921   c  are on a same plane. The second optical surface  923   b  is inclined in relation to the first light-incident surface  921   a  to form a second angle β 3 . It is noted that, the second optical surface  923   b  extends from the bottom portion to the top portion of the first microstructure  923 , and the second angle β 3  is an included angle between the second optical surface  923   b  and a level surface passing through a bottom portion of the second optical surface  923   b , in which the level surface and the light-emitting surface  921   c  are on a same plane. In the present embodiment, the smaller one of the first angle α 3  and the second angle β 3  faces towards the first light-incident surface  921   a , and the greater one of the first angle α 3  and the second angle β 3  faces away from the first light-incident surface  921   a . In the present embodiment, the second angle β 3  is smaller than the first angle α 3 . 
     Similarly, each of the second microstructures  925  includes a third optical surface  925   a , a fourth optical surface  925   b , a third side optical surface  925   c  and a fourth side optical surface  925   d . The third optical surface  925   a  is inclined in relation to the second light-incident surface  921   b  to form a third angle α 4 . It is noted that, the third optical surface  925   a  extends from a bottom portion to a top portion of the second microstructure  925 , and the third angle α  4  is an included angle between the third optical surface  925   a  and a level surface passing through a bottom portion of the third optical surface  925   a , in which the level surface and the light-emitting surface  921   c  are on a same plane. The fourth optical surface  925   b  is inclined in relation to the second light-incident surface  921   b  to form a fourth angle β 4 . It is noted that, the fourth optical surface  925   b  extends from the bottom portion to the top portion of the second microstructure  925 , and the fourth angle β 4  is an included angle between the fourth optical surface  925   b  and a level surface passing through a bottom portion of the fourth optical surface  925   b , in which the level surface and the light-emitting surface  921   c  are on a same plane. In the present embodiment, the smaller one of the third angle α 4  and the fourth angle β 4  faces towards the second light-incident surface  921   b , and the greater one of the third angle α  4  and the fourth angle β 4  faces away from the second light-incident surface  921   b . In one embodiment, the fourth angle β 4  is smaller that the third angle α 4 . 
     It is noted that, the first microstructures  923  and the second microstructures  925  shown in  FIG. 15  and  FIG. 16  are merely used as an example for explanation, and embodiments of the present invention are not limited thereto. In other embodiments, the first microstructures  923  and the second microstructures  925  may have different designs. In some examples, each of the first microstructures  923  and the second microstructures  925  can be a convex portion or a concave portion. In other examples, each of the first microstructures  923  and the second microstructures  925  can be structures similar to the aforementioned microstructures  200 ,  220 ,  300 ,  320 ,  400 ,  500  and  640 . 
     Referring to  FIG. 15  and  FIG. 17A ,  FIG. 17A  is a schematic diagram showing arrangement densities of the first microstructures  923  and the second microstructures  925  respectively arranged in relation to the first light source  940  and the second light source  960 . The first microstructures  923  and the second microstructures  925  are arranged on the light-emitting surface  921   c . Moreover, there is a distance between two adjacent first microstructures  923 , in which the distance is smaller with increase of a distance between the first microstructures  923  and the first light-incident surface  921   a  (corresponding to the first light source  940 ). In other words, the first microstructures  923  near the first light-incident surface  921   a  are sparsely arranged, and the first microstructures  923  away from the first light-incident surface  921   a  are densely arranged. Similarly, there is a distance between two adjacent second microstructures  925 , in which the distance is smaller with increase of a distance between the second microstructures  925  and the second light-incident surface  921   b  (corresponding to the second light source  960 ). In other words, the second microstructures  925  near the second light-incident surface  921   b  are sparsely arranged, and the second microstructures  925  away from the second light-incident surface  921   b  are densely arranged. 
     Referring to  FIG. 15  and  FIG. 16  again, the first microstructures  923  are mainly used to change light-emitting angle and directivity of light emitted from the first light source  940 . The second microstructures  925  are mainly used to change light-emitting angle and directivity of light emitted from the second light source  960 . In addition, as shown in  FIG. 15 , because a variation direction of arranging density of the first microstructures  923  arranged in relation to the first light-incident surface  921   a  is opposite to that of the second microstructures  925  arranged in relation to the second light-incident surface  921   b , the first microstructures  923  and the second microstructures  925  can be uniformly arranged on the main body  921 . Therefore, when the first light source  940  and the second light source  960  emits light simultaneously, signally or alternately, light generated by the first light source  940  and the second light source  960  can be reflected and refracted by the light guide plate  920 , so as to achieve the effect of better luminance uniformity. 
     Referring to  FIG. 15  and  FIG. 17B ,  FIG. 17B  is a diagram showing luminance distribution on the light guide plate  920  when one or both of the first light source  940  and the second light source  960  emit light. The first microstructures  923  and the second microstructures  925  are distributed from sparsely to densely along a direction from one side of the light-emitting surface  921   c  to the other side of the light-emitting surface  921   c . Therefore, as shown in  FIG. 15 , an arrangement density of microstructures in a middle area of the light guide plate  920  is smaller than that of microstructures in side areas adjacent to the first light-incident surface  921   a  and the second light-incident surface  921   b , so as to achieve the effect of luminance distribution shown in  FIG. 17B . In other embodiments, with different requirements of luminance distributions, arrangement densities of the first microstructures  923  and second microstructures  925  in the middle area can be adjusted to be higher than or equal to that of the first microstructures  923  and second microstructures  925   n  the side areas. It is noted that the present embodiments should not be construed to limit the scope of the invention. 
     Referring to  FIG. 18 ,  FIG. 18  is a schematic structural diagram showing a display device  980  in accordance with an embodiment of the present invention. The display device  980  of the present embodiment includes a light source module  900  and a display panel  980   a . As shown in  FIG. 18 , the display panel  980   a  is disposed above the light source module  900 . After emitted from the light guide plate  920 , light provided by the first light source  940  and the second light source  960  of the light source module  900  enters the display panel  980   a , so as to achieve the aforementioned objects and will not be described again herein. It is noted that, by emitting light alternately through the first light source  940  and the second light source  960 , the display device  980  can achieve 3D display effect. 
     According to the aforementioned embodiments of the present invention, the light-emitting angle and directivity of the light emitted from the light guide plate can be changed by varying shapes, angles, heights, depths or arrangements of the microstructures, so as to increase light-emitting efficiency and uniformity of the overall light-emitting appearance of the light guide plate. In addition, by collocating the light-mixing structures near the light-incident surface of the light guide plate and the microstructures, the problems of non-uniform appearance causing by the dark/bright bands near the light-incident surface of the conventional light guide plate can be improved, thus increasing the optical effect of the light guide plate. 
     Although the present invention has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims.