Patent Publication Number: US-10775546-B2

Title: Edge-lit light guide plate with frustoconically-shaped microstructures

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of China application serial no. 201810295777.3, filed on Mar. 30, 2018. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of specification. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a light guide plate and a light source module, and particularly relates to a light guide plate and a light source module having microstructures for light uniformity. 
     Description of Related Art 
     Since light emitted by street lamps has a high-brightness at certain angles. The high-brightness light and ambient light at night have a great brightness difference, which is rather dazzling for human eyes, and is easy to cause a glare problem to increase dangerousness. Therefore, to reduce a possibility of glare occurrence for the improvement of road safety is very important for pedestrians or drivers on the road. 
     SUMMARY OF THE INVENTION 
     The invention is directed to a light guide plate and a light source module, which are adapted to improve a glare problem to prevent human eyes from feeling uncomfortable. 
     An embodiment of the invention provides a light guide plate including a plate body and a plurality of light-uniformity microstructures. The plate body has a plate thickness and includes a first surface, a second surface opposite to the first surface and a side surface connected between the first surface and the second surface. The light-uniformity microstructures are arranged periodically on the first surface. The light-uniformity microstructures are indented from the first surface towards the second surface to define an indentation depth. Each of the light-uniformity microstructures substantially has a shape of an inverted truncated cone. The indentation depth is less than a half of the plate thickness. 
     Another embodiment of the invention provides a light source module including a light guide plate, at least one light source and a reflection layer. The light guide plate includes a plate body and a plurality of light-uniformity microstructures. The plate body has a plate thickness and includes a first surface, a second surface opposite to the first surface and a side surface connected between the first surface and the second surface. The light-uniformity microstructures are arranged periodically on the first surface. The light-uniformity microstructures are indented from the first surface towards the second surface to define an indentation depth. Each of the light-uniformity microstructures substantially has a shape of an inverted truncated cone. The indentation depth is less than a half of the plate thickness. At least one light source provides a light beam and is configured at the side surface of the plate body. The reflection layer is configured on the first surface of the plate body to reflect light, wherein the light beam is incident from the side surface and a transmission path is changed through the light-uniformity microstructures and the reflection layer, and the light beam is emitted out from the second surface. 
     Based on the above description, the light guide plate of the invention includes the plate body and a plurality of the light-uniformity microstructures indented from the first surface of the plate body towards the second surface to define the indentation depth, and the indentation depth is less than a half of the plate thickness. Therefore, the light beam is adapted to be incident from the side surface of the plate body, a transmission path is changed through the light-uniformity structure and the reflection layer, and the light beam is emitted out from the second surface. In this way, a light angle distribution of the light source module is more uniform, so as to reduce the glare problem to prevent human eyes from feeling uncomfortable. 
     In order to make the aforementioned and other features and advantages of the invention comprehensible, several exemplary embodiments accompanied with figures are described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a top view of a light source module according to an embodiment of the invention. 
         FIG. 2  is a cross-sectional view of the light source module of  FIG. 1  along a section line A-A. 
         FIG. 3  is a top view of a light source module according to another embodiment of the invention. 
         FIG. 4  is a partial enlarged view of the light source module of  FIG. 2 . 
         FIG. 5  is a three-dimensional view of a light-uniformity microstructure according to an embodiment of the invention. 
         FIG. 6  is a cross-sectional view of the light-uniformity microstructure of  FIG. 5  along a section line I-I. 
         FIG. 7A  is a schematic diagram of light distribution curves of a light source module of the existing technique. 
         FIG. 7B  is a schematic diagram of light distribution curves of the light source module of  FIG. 1 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  is a top view of a light source module according to an embodiment of the invention.  FIG. 2  is a cross-sectional view of the light source module of  FIG. 1  along a section line A-A. In the embodiment, the light source module  50  includes a Light Guide Plate (LGP)  100 , at least one light source  60  and a reflection layer  70 . The at least one light source  60  emits a light beam L to the LGP  100 , and a transmission path of the light beam L is changed in the LGP  100 , so as to change an angle distribution of light energy emitted by the light source module  50 . The light source module  50  is, for example, applied to a small lighting device, for example, a general road lighting device or other similar lighting devices, though the invention is not limited thereto. 
     The LGP  100  includes a plate body  110  and a plurality of light-uniformity microstructures  120 . The plate body  110  has a plate thickness H 1 , and the plate body  110  includes a first surface  112 , a second surface  114  opposite to the first surface  112  and a side surface  116  connected between the first surface  112  and the second surface  114 . 
     The light source  60  is disposed at the side surface  116  of the plate body  110 , and the reflection layer  70  is disposed on the first surface  112  of the plate body  110 . The light source  60  is, for example, composed of a plurality of lighting-emitting elements  62  configured on a circuit board  64 , and the light emitting elements  62  are, for example, light-emitting diodes (LEDs), though the invention is not limited thereto. The light beam L provided by the light source  60  enters the LGP  100  from the side surface  116  and changes a transmission direction near the first surface  112 , and is emitted out from the second surface  114 . 
     In the present embodiment, the two light sources  60  are disposed at the two opposite side surfaces  116  of the LGP  100 , and provide the light beam L to a center of the LGP  100 .  FIG. 3  is a top view of a light source module according to another embodiment of the invention. Referring to  FIG. 3 , in the embodiment, four light sources  60  may be configured at four side surfaces  116  of the LGP  100 A, or configuration of the light sources  60  may be adjusted according to a profile of the plate body  110 , which is not limited by the invention. 
       FIG. 4  is a partial enlarged view of the light source module of  FIG. 2 . Referring to  FIG. 1 ,  FIG. 2  and  FIG. 4 , the light-uniformity microstructures  120  are located on the first surface  112  of the plate body  110 , and are arranged periodically. In detail, the light-uniformity microstructures  120  are indented from the first surface  112  towards the second surface  114  to define an indentation depth H 2 , and each of the light-uniformity microstructures  120  substantially has a shape of an inverted truncated cone  121 , and each of the inverted truncated cone  121  forms an opening  122  at the first surface  112 . 
     Each of the inverted truncated cones  121  includes a surrounding surface  124  and a bottom surface  126 , and the surrounding surface  124  is connected between the bottom surface  126  and the first surface  112 . An area of the opening  122  is greater than an area of the bottom surface  126 , and the bottom surface  126  is a circular arc surface  127  protruding towards the first surface  112 , for example, a spherical surface. In other words, the surrounding surface  124  is a conical surface inclined inward from the opening  122  to the bottom  126 . In the present embodiment, the bottom surface  126 , for example, has a circular arc shape, and the surrounding surface  124  is a circular conical surface. In other embodiment, the bottom surface  126  may be a three-dimensional (3D) shape formed by a plurality of polygonal planes, irregularly shaped planes, or free-form curved surfaces, and the surrounding surface  124  is a 3D shape formed by the polygonal planes, the irregularly shaped planes, or the free-form curved surfaces, though the invention is not limited thereto. 
     In other words, the light beam L is incident from the side surface  116  of the plate body  110 , the transmission path is changed through the first surface  112  or the light-uniformity microstructures  120 , and the light beam L is emitted out from the second surface  114 . For example, the light beam L may be transmitted to the first surface  112  of the plate body  110 , and is reflected by the reflection layer  70  disposed on the first surface  112  and emitted out from the second surface  114 . Moreover, the light beam L may be transmitted to the light-uniformity microstructures  120 , and is scattered by the bottom surfaces  126  and emitted out from the second surface  114 , as shown by a light beam L 1  of  FIG. 4 . Alternatively, the light beam L may be transmitted to the light-uniformity microstructures  120  in the plate body  110 , and is reflected by the surrounding surfaces  124  and emitted out from the second surface  114 , as shown by a light beam L 2  of  FIG. 4 . Alternatively, the light beam L is directly transmitted from the side surface  116  to the second surface  114  and emitted out from the second surface  114 , as shown by a light beam L 3  of  FIG. 4 . In this way, a light angle distribution of the light source module  50  is more uniform, so as to reduce the glare problem to prevent human eyes from feeling uncomfortable. 
     In the present embodiment, the plate body  110  has the plate thickness H 1 , and the indentation depth H 2  of the light-uniformity microstructure  120  is smaller than the plate thickness H 1 . To be specific, the plate thickness H 1  of the plate body  110  is greater than 15 mm, and the indentation depth H 2  of the light-uniformity microstructure  120  is less than a half of the plate thickness H 1  of the plate body  110 . In some embodiments, the plate thickness H 1  of the plate body  110  may be greater than or equal to 75 times the indentation depth H 2 . Moreover, the bottom surface  126  is a circular arc surface, and an included angle B between a tangent plane F to an edge of the circular arc surface and a horizontal plane E defined by a horizontal line G ranges between 10 degrees and 70 degrees, and a distance H 3  between an apex C of the circular arc surface and the horizontal plane E is between 0.05 mm and 0.75 mm. Moreover, the vertical distance H 3  between the apex C of the bottom surface  126  and the horizontal plane E is smaller than a half of the indentation depth H 2  of the light-uniformity microstructure  120 . 
     Besides, in the present embodiment, the light-uniformity microstructures  120  are arranged periodically on the first surface  112 , for example, arranged in an array. However, in other embodiments, the light-uniformity microstructures  120  may also be arranged in a non-array manner, for example, arranged in a gradient manner, though the invention is not limited thereto. For example, in the present embodiment, a distance D 1  between two adjacent light-uniformity microstructures  120  is greater than a diameter D 2  of the opening  122  of a single light-uniformity microstructure  120 . For example, the distance D 1  between two adjacent light-uniformity microstructures  120  is greater than twice of the diameter D 2  of the opening  122  of a single light-uniformity microstructure  120 , though the invention is not limited thereto. In this way, a better effect for reducing the glare problem is achieved. 
       FIG. 5  is a three-dimensional view of a light-uniformity microstructure according to an embodiment of the invention.  FIG. 6  is a cross-sectional view of the light-uniformity microstructure of  FIG. 5  along a section line I-I. For simplicity&#39;s sake, only one light-uniformity microstructure  120  is illustrated in  FIG. 5 . Referring to  FIG. 5  and  FIG. 6 , in the embodiment, optical microstructures  128  are further configured on the bottom surface  126 . Shapes of the optical microstructures  128  include arbitrary polygons, irregular shapes or free-form curved surfaces. For example, the shape of the optical microstructure  128  is a ring-shaped protrusion, though the invention is not limited thereto. Therefore, when the light beam irradiates the inverted truncated cone  121 , a reflection angle range and evenness of the reflected light beam may be increased through the optical microstructures  128 . In this way, a better effect of reducing the glare problem is achieved. 
       FIG. 7A  is a schematic diagram of light distribution curves of a light source module of the existing technique. Referring to  FIG. 7A , a distance between curves  210 ,  220  and a central point represents a light intensity performance of a located angle. The curve  210  is a light distribution curve of an illumination beam provided by a light source of the light source module of the existing technique, and the curve  220  is a light distribution curve of the illumination beam emitted by the same light source module. According to  FIG. 7A , it is known that the curve  220  has a larger light energy at specific angles, which is liable to cause the glare problem to make human eyes to feel uncomfortable. In other words, the illumination beam provided to environment by the light source module of the existing technique is not uniform within an angle range. 
       FIG. 7B  is a schematic diagram of light distribution curves of the light source module of  FIG. 1 . Referring to  FIG. 7A  and  FIG. 7B , a distance between curves  310 ,  320  and a central point represents a light intensity performance of a located angle. The curve  310  is a light distribution curve of an illumination beam provided by a light source of the light source module of the invention, and the curve  320  is a light distribution curve of the illumination beam emitted by the same light source module. According to  FIG. 7B , it is known that the curve  320  of  FIG. 7B  has similar light energy in a large angle range compared to the curve  220  of  FIG. 7A , so that the glare problem may be reduced to prevent human eyes from feeling uncomfortable. 
     In summary, the light guide plate of the invention includes the plate body and a plurality of the light-uniformity microstructures indented from the first surface of the plate body towards the second surface to define the indentation depth, and the indentation depth is less than a half of the plate thickness. Therefore, the light beam is adapted to be incident through the side surface of the plate body, a transmission path through the light-uniformity structure and the reflection layer is changed, and the light beam is emitted out from the second surface. In this way, a light angle distribution of the light source module is more uniform, so as to reduce the glare problem to prevent human eyes from feeling uncomfortable. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.