Abstract:
A light source module including light sources and secondary optical lens is proposed. The secondary optical lens includes an incident curved surface, an emitting curved surface, and a bottom of prism. The incident curved surface has a concave area defined as a cavity where the light source is disposed. A light beam generated by the light source is emitted to the inside of the secondary optical lens through the incident curved surface. The light beam is emitted outwards through the emitting curved surface after being reflected by the prism microstructures on the bottom of prism. The light beam reflected by the emitting curved surface can be emitted to the inside of the secondary optical lens again by using the prism microstructures. Therefore, the light source module can reduce the scattering amount of the light beam, thereby improving the utilization of the light beam generated by the light source.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a light source module and a backlight module, and more particularly, to a light source module for reducing light scattering and enhancing use efficiency of light sources and a backlight module using the same. 
         [0003]    2. Description of the Prior Art 
         [0004]    Owing to their low-profile, thin, and lightweight features, liquid crystal display (LCD) devices have replaced cathode ray tubes (CRTs) in many applications and become the mainstream display devices in recent years. LCD screens are widely used in electronic devices such as mobile phones, personal digital assistants (PDAs), digital cameras, computer screens, notebook screens, etc. 
         [0005]    An LCD device comprises a backlight module and an LCD panel. The backlight module is used for supplying light for the LCD device, so that images can be displayed on the LCD panel using the light. Traditionally, fluorescent tubes are used as light sources provided by the backlight module but have been gradually being replaced by light emitting diodes (LEDs) recently. This is because fluorescent tubes are much bulkier than LEDs, which does not conform to the overall trend of lightweight LCD devices. This replacement greatly reduces the thickness and the weight of the backlight module, which reduces the size and the thickness of the LCD devices. 
         [0006]    According to the distribution of light sources provided by a backlight module, there are two main types of configuration for backlight sources: direct-light type and side edge type. The side edge backlight source technology sets the LED chips at sides of the LCD panel; the direct-light backlight technology sets the LED chips at the back of the LCD panel evenly serving as light sources, so that the backlight can be distributed across the LCD panel evenly, creating more delicate and more lifelike images. But it is necessary to use a large number of LED chips in the direct-light backlight source technology, which is a challenge to LCD manufacturers who strive to reduce the number of LEDs while without sacrificing the uniformity of luminance. As generally known in the industry, a certain level of radiation pattern/intensity distribution of LEDs needs to be achieved before a predetermined uniformity of luminance is acquired. However, the number of LEDs is in inverse proportion to the light mixing distance basically. In other words, the number of LEDs has to be increased to satisfy the predetermined uniformity of luminance whenever the light mixing distance is shortened. 
         [0007]    Traditionally, LED emission intensity distribution is usually a Lambertian intensity distribution. The most luminous flux is roughly distributed within a sector region with an angle of ±60 degrees, where the angle θ is defined as the included angle between a light beam and a normal line of an LED emitting surface. 
         [0008]    Referring to  FIG. 1  to  FIG. 3 ,  FIG. 1  shows a perspective view of a light source unit  200  according to the conventional technology,  FIG. 2  shows a top view of the light source unit  200  in  FIG. 1 , and  FIG. 3  is a cross section view of the light source unit  200  along a line e-e′ in  FIG. 2 . In general, the light source unit  200  comprises an LED  210 , a secondary optical lens  220 , and a reflector  230 . To solve mutual constraint dependencies between the number of LEDs and the light mixing distance, a feasible solution is using the secondary optical lens  220  to alter the light intensity distribution in airspace of LEDs. In other words, light energy can be distributed over a wider area through the secondary optical lens  220 . For example, if an angle θ becomes ±75°, it is possible that the uniformity of luminance maintains better while the number of LEDs is reduced. 
         [0009]    Continuing referring to  FIG. 3 , the secondary optical lens  220  comprises a bottom a, an incident curved surface b, and an emitting curved surface c. A light beam is generated by the LED  210  disposed on the bottom a of the secondary optical lens  220 , emitted to the secondary optical lens  220  through the incident curved surface b, and sent outwards through the emitting curved surface c. Because the light beam is refracted twice (i.e., the refraction of the incident curved surface b of the secondary optical lens  220  and the refraction of the emitting curved surface c of the secondary optical lens  220 ), the emitting angle of the light beam is different from the emitting angle of the light beam generated by the LED  210 . Such an arrangement allows the luminous flux θ of the LED  210  to be higher. 
         [0010]    As a light beam  1  shows, the light beam  1  generated by the LED is emitted to the inside of the secondary optical lens  220  through the incident curved surface b; then, the light beam  1  is reflected by the emitting curved surface c of the secondary optical lens  220 ; then, the light beam  1  is emitted to the bottom a at a small angle α; finally, the light beam  1  is emitted outside from the bottom a. However, such a design decreases the use efficiency of the light beam because the scattering effect of the reflector  230  causes the light beam reflected to the reflector  230  to be scattered. The light beam may be emitted to the reflector  230  by the bottom a, or may be reflected to the reflector  230  by the incident curved surface b (not shown in  FIG. 3  because the proportion is small). Thus, the light beam reflected by the reflector  230  cannot be fully utilized; instead, the most portion of the reflected light beam is scattered. 
         [0011]    Therefore, there is a need for a backlight module which is able to reduce light scattering more effectively, thereby enhancing use efficiency of light sources, in order to solve the above-mentioned problem occurring in the prior art. 
       SUMMARY OF THE INVENTION 
       [0012]    Accordingly, the present invention has been made to solve the above-mentioned problem occurring in the prior art, and an object of the present invention is to provide a light source module which can reduce light leakage and thereby can enhance use efficiency of light sources, and a backlight module using the same. 
         [0013]    According to the present invention, a backlight module comprises a light guide plate, at least one light source, a circuit board bearing the at least one light source, and at least one secondary optical lens. The secondary optical lens is disposed on the light source and comprises a bottom, an incident curved surface, and an emitting curved surface. The incident curved surface has a concave area defined as a cavity. The light source is disposed inside the cavity. A plurality of prism microstructures are formed on the bottom. A light beam generated by the light source is emitted to the inside of the secondary optical lens through the incident curved surface, and then is emitted out of the secondary optical lens through the emitting curved surface. The light beam reflected by the emitting curved surface is emitted to the inside of the secondary optical lens again by reflection of the prism microstructures. 
         [0014]    In one aspect of the present invention, a flat zone is disposed on the bottom of prism and is located between the incident curved surface and the bottom, and no prism microstructures are disposed on the flat zone. 
         [0015]    In another aspect of the present invention, each prism microstructure is a bar-like shape, and an extended direction of each of the plurality of prism microstructures and an extended direction of a longer side of the circuit board form an included angle which is between 87 and 93 degrees. 
         [0016]    In still another aspect of the present invention, a vertex angle of each of the plurality of prism microstructures is between 88 and 92 degrees. 
         [0017]    In yet another one aspect of the present invention, a cross section of each of the plurality of prism microstructures is in the shape of an isosceles triangle. A refractive index of materials which each of the plurality of prism microstructures is made of is between 1.45 and 1.7. 
         [0018]    In yet another of the present invention, an emitting surface of the light source is higher than the bottom or is at least parallel to the bottom. 
         [0019]    According to the present, a light source module comprising at least one light source, a circuit board bearing the at least one light source, and at least one secondary optical lens is provided. The secondary optical lens comprises a bottom, an incident curved surface, and an emitting curved surface. The incident curved surface has a concave area defined as a cavity. The light source is disposed inside the cavity. An emitting surface of the light source is higher than the bottom or is at least parallel to the bottom. The light source module further comprises a prism element comprising a plurality of prism microstructures adhered to the bottom. A light beam generated by the light source is emitted to the inside of the secondary optical lens through the incident curved surface. The light beam traveling to the bottom of the secondary optical lens is reflected by the plurality of prism microstructures and is emitted out of the secondary optical lens through the emitting curved surface. 
         [0020]    According to the present, a light source module comprising at least one light source, a circuit board bearing the at least one light source, and at least one secondary optical lens is provided. The secondary optical lens comprises a bottom, an incident curved surface, and an emitting curved surface. The incident curved surface has a concave area defined as a cavity. The light source is disposed inside the cavity. An emitting surface of the light source is higher than the bottom or is at least parallel to the bottom. The light source module further comprises a plurality of prism microstructures disposed on the bottom. A light beam generated by the light source is emitted to the inside of the secondary optical lens through the incident curved surface. The light beam traveling to the bottom of the secondary optical lens is reflected by the plurality of prism microstructures and is emitted out of the secondary optical lens through the emitting curved surface. 
         [0021]    Compared with the prior art, the backlight module according to the present invention utilizes a secondary optical lens comprising a bottom of prism. The light beam reflected by an emitting curved surface of the secondary optical lens can be reflected to the secondary optical lens by the bottom of prism again. In this way, the light beam which would have been scattered can be saved and well used by using the bottom of prism. Accordingly, the backlight module according to the present invention is good at enhancing use efficiency of light sources. 
         [0022]    These and other features, aspects and advantages of the present disclosure will become understood with reference to the following description, appended claims and accompanying figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  shows a perspective view of a conventional light source unit. 
           [0024]      FIG. 2  shows a top view of the light source unit in  FIG. 1 . 
           [0025]      FIG. 3  is a cross section view of the light source unit along a line e-e′ in  FIG. 2 . 
           [0026]      FIG. 4  shows a schematic diagram of a backlight module according to the present invention. 
           [0027]      FIG. 5  shows a top view of the light source module in  FIG. 4 . 
           [0028]      FIG. 6  shows a perspective view of a light source unit in the backlight module according to a first embodiment of the present invention. 
           [0029]      FIG. 7  shows a bottom view of the light source unit in  FIG. 6 . 
           [0030]      FIG. 8  is a cross section view of the light source unit along a line z-z′ in  FIG. 7 . 
           [0031]      FIG. 9  is a cross section view of a light source unit in the backlight module according to a second embodiment. 
           [0032]      FIG. 10  shows a top view of the light source unit in the backlight module according to a third embodiment of the present invention. 
           [0033]      FIG. 11  is a cross section view of the light source unit along a line x-x′ in  FIG. 10 . 
           [0034]      FIG. 12  is a cross section view of the light source unit along a line y-y′ in  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0035]    Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. 
         [0036]    Referring to  FIG. 4 ,  FIG. 4  shows a schematic diagram of a backlight module  400  according to the present invention. The backlight module  400  comprises a light guide plate (LGP)  40  and a light source module  70 . The light source module  70 , disposed on the bottom of the backlight module  400 , comprises a circuit board  30 , a plurality of light source units  600  disposed on the circuit board  30 , and a reflector  50  disposed on the circuit board  30 . Optical elements such as the LGP  40 , a diffusion sheet, and a polarizer film are overlapped and disposed on the plurality of light source units  600 . The backlight module  400  is a direct-light type backlight module. The light source module  70  is placed under the LGP  40  and a light beam generated by the plurality of light source units  600  can be emitted inwards through an incident bottom  401  of the LGP  40 . 
         [0037]    Referring to  FIG. 5  to  FIG. 8 ,  FIG. 5  shows a top view of the light source module  70  in  FIG. 4 ,  FIG. 6  shows a perspective view of a light source unit  600  in the backlight module  400  according to a first embodiment of the present invention,  FIG. 7  shows a bottom view of the light source unit  600  in  FIG. 6 , and  FIG. 8  is a cross section view of the light source unit  600  along a line z-z′ in  FIG. 7 . The light source unit  600  comprises a light source  610  and a secondary optical lens  620 . The light source  610  may be an LED or an organic light emitting diode (OLED). The secondary optical lens  620  comprises a prism bottom  621 , an incident curved surface  622 , and an emitting curved surface  623 . The incident curved surface  622  is projected onto the prism bottom  621 , and the projected area is defined as an opening  626 . The incident curved surface  622  has a concave area defined as a cavity  624 . As shown in  FIG. 8 , the light source  610  having an emitting surface  611  is disposed inside the cavity  624 . The emitting surface  611  needs to be higher than the prism bottom  621 . A distance h exists between the emitting surface  611  and the prism bottom  621 . Or, the emitting surface  611  and the prism bottom  621  are in parallel at least; that is, h=0. The light beam generated by the light source  610  is emitted to the inside of the secondary optical lens  620  through the incident curved surface  622  and is emitted out of the secondary optical lens  620  through the emitting curved surface  623 . Owing to the refraction of the incident curved surface  622  and the refraction of the emitting curved surface  623 , the equivalent luminous flux of the light source  610  becomes higher. The emitting curved surface  623  encompasses the curved surface of the secondary optical lens  620 . 
         [0038]    It is notified that, a plurality of bar-like prism microstructures are formed on the prism bottom  621  of the secondary optical lens  620  of the light source unit  600  according to the present invention. The cross section of each of the plurality of prism microstructures is in the shape of an isosceles triangle. While the secondary optical lens  620  is formed, the prism bottom  621  can be formed simultaneously. In addition, as shown in  FIG. 5 , an angle between an extended direction A of the plurality of bar-like prism microstructures on the prism bottom  621  and an extended direction B of a longer side  301  of the circuit board  30  is in a range between 87 and 93 degrees. Preferably, the included angle is exactly 90 degrees. 
         [0039]    Referring to  FIG. 9 ,  FIG. 9  is a cross section view of a light source unit  800  in the backlight module  400  according to a second embodiment. The light source unit  800  and the light source unit  600  are roughly the same except that the light source unit  800  comprises a prism element  850  and a secondary optical lens  820 . The secondary optical lens  820  has a flat bottom  821 . The prism element  850  comprises a plurality of prism microstructures. The prism element  850  adheres to the lower side of the bottom  821  of the secondary optical lens  820 . Any corresponding modifications and variations can be made without deviating from the scope of the invention. 
         [0040]    As shown in  FIG. 6  to  FIG. 8 , the secondary optical lens  620  according to present invention is a far cry from the conventional secondary optical lens  220 . The prism bottom  621  of the secondary optical lens  620  comprises a plurality of prism microstructures. The function of the prism bottom  621  will be revealed in a subsequent statement. 
         [0041]    Continuing referring to  FIG. 8 , the incident light beam  1  generated by the light source  610  is emitted to the inside of the secondary optical lens  620  through the incident curved surface  622  and is emitted outwards by the emitting curved surface  623 . The incident light beam  1  refracted outwards is referred as the refracted light beam  1 ′. An included angle θ′ formed by the refracted light  1 ′ and the normal line is larger than the angle θ between the incident light beam  1  and the normal line. Therefore, the arrangement of the secondary optical lens  620  can increase the luminous flux. 
         [0042]    On the other hand, while the incident light beam  1  is emitted to the emitting curved surface  623 , some of the incident light beam  1  is reflected by the emitting curved surface  623  and becomes a reflected light beam  3  as shown in  FIG. 8 . The reflected light beam  3  undergoes two total internal reflections by the prism bottom  621  and is emitted into the secondary optical lens  620  again. Then, the reflected light beam  3  is emitted to the emitting curved surface  623  (like a light beam  4 ) and is emitted outwards through the emitting curved surface  623  (like a light beam  4 ′). In this way, the reflected light beam  3  can be prevented from being scattered. Because the reflected light beam  3  can be totally internally reflected by the plurality of prism microstructures, the possibility of scattering of the reflected light beam  3  is decreased, thereby enhancing use efficiency of the light source  610 . 
         [0043]    A less amount of light beam refracted by the prism bottom  621  and the light beam reflected by the incident curved surface  622  are refracted by the prism bottom  621  and then are emitted to the emitting curved surface  623  after being reflected by the reflector  50  (referring to  FIG. 4 ) under the plurality of light source units  600 . 
         [0044]    It is notified that, the prism bottom  621  is preferably designed according to the present embodiment for the purpose that the plurality of prism microstructures of the secondary optical lens  620  is able to match the total internal reflection. For example, the cross section of each of the plurality of prism microstructures is in the shape of an isosceles triangle, so that the light beam can be reflected to the secondary optical lens  620  accurately. In addition, the vertex angle of each of the plurality of prism microstructures and materials which the plurality of prism microstructures are made of have to be modified so as to make sure that the incident angle of the reflected light beam  3  is large enough and that the refractive index of materials is large enough. Preferably, the vertex angle β of each of the plurality of prism microstructures is between 88 and 92 degrees; the refractive index of materials is between 1.45 and 1.7. The distance p between two vertexes of each of the plurality of prism microstructures can be a constant value. Similarly, the vertex angle β of each of the plurality of prism microstructures can be a constant value. Also, the distance p or the vertex angle β varies in a certain trend along the direction B (perpendicular to the extended direction A of the plurality of bar-like prism microstructures shown in  FIG. 5 ). The plurality of prism microstructures may be made of polymethylmethacrylate (PMMA), poly carbonate (PC), or silicon for ensuring that the total internal reflection occurs. However, the above-mentioned design is not to limit the present invention. Operators can adjust materials which the plurality of prism microstructures are made of and the vertex angle of each of the plurality of prism microstructures as long as the total internal reflection occurs. Any corresponding modifications and variations can be made without deviating from the scope of the invention. 
         [0045]    Referring to  FIG. 10  to  FIG. 12 ,  FIG. 10  shows a top view of the light source unit  700  in the backlight module  400  according to a third embodiment of the present invention,  FIG. 11  is a cross section view of the light source unit  700  along a line x-x′ in  FIG. 10 , and  FIG. 12  is a cross section view of the light source unit  700  along a line y-y′ in  FIG. 10 . The light source unit  700  comprises a light source  710  and a secondary optical lens  720 . The light source  710  and the secondary optical lens  720  according to the present embodiment have the same function as the light source  610  and the secondary optical lens  620  according to the first embodiment do, so no further details are released hereafter. Differing from the light source unit  600  according to the first embodiment, the light source unit  700  comprises the secondary optical lens  720  having a bottom of prism  721  comprising a flat zone  725 . The flat zone  725 , located on the bordering area of an incident curved surface  722  and the bottom of prism  721 , may be square-shaped or circle-shaped. No prism microstructures are disposed on the flat zone  725 . An opening  726  is formed when the incident curved surface  722  is projected onto the flat zone  725 . The incident curved surface  722  is projected onto the middle of the flat zone  725  of the bottom of prism  721 . The opening  726  is used for preventing the plurality of prism microstructures from blocking a light beam generated by the light source  710 , or for preventing the light beam from being spayed out from slits of the plurality of prism microstructures. No prism microstructures are disposed on the bordering area of the incident curved surface  722  and the bottom of prism  721  from the cross section along the line x-x′ as shown in  FIG. 11 . Similarly, no prism microstructures are disposed on the bordering area of the incident curved surface  722  and the bottom of prism  721  of the secondary optical lens  720  as shown in  FIG. 12 . 
         [0046]    It is understood that the bottom of prism  721  comprises the flat zone  725  and the opening  726  according to the second embodiment. However, neither the flat zone  725  nor the opening  726  is limited in size and shape according to the present invention. In other words, the shape and size of the opening  726  can be designed at will as long as the size and the shape of the flat zone  725  and the opening  726  are appropriate enough to allow the light beam generated by the light source  710  to be emitted inwards. Any corresponding modifications and variations can be made without deviating from the scope of the invention. 
         [0047]    The light source unit  700  can also be used as a backlight source in the backlight module  400  according to another embodiment. 
         [0048]    While the present invention has been described in connection with what is considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements made without departing from the scope of the broadest interpretation of the appended claims.