Abstract:
A scattering module and a backlight module comprising the scattering module are provided. The backlight module includes a plurality of light sources, while the scattering module includes a plurality of scattering elements. The scattering elements are disposed correspondingly to the light sources so that the scattering elements have different linearly arranged densities in different directions. Thereby, the light generated from the backlight module would be projected onto the display panel evenly with a uniform brightness.

Description:
This application claims priority to Taiwan Patent Application No. 096130752 filed on Aug. 20, 2007, the disclosures of which are incorporated herein by reference in their entirety. 
   CROSS-REFERENCES TO RELATED APPLICATIONS 
   Not applicable. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a scattering module and a backlight module comprising the same and more particularly, the present invention relates to a scattering module structure capable of rendering the brightness of a backlight module more uniform without incurring a non uniform distribution of brightness on a display panel. 
   2. Descriptions of the Related Art 
   Liquid crystal displays (LCDs) are full color display devices that utilize the liquid crystal technology with advantages such as low power consumption, low radiation, small footprints, is lightweight and is flexible in size. Therefore, LCDs have been used in many electronic products that incorporate display screens, such as digital cameras, personal digital assistants (PDAS) and TV sets. LCDs differ from conventional cathode ray tube (CRT) display devices in that the liquid crystal layer of an LCD does not emit light by itself. As a result, an additional light source is needed to obtain an image on the screen. Generally, the additional light source is known as a backlight module. 
   Backlight modules fall into two categories according to the location of the light sources disposed therein: the edge lighting type and the direct lighting type. Generally, direct lighting light sources are the most commonly used type in large-sized backlight modules. The direct lighting type backlight module comprises a plurality of light source devices and a set of optical films. The light emitted from the light source devices is modulated via the optical films and then propagated to a color filter for display on a display panel. Generally, the set of optical films includes one or more layers of brightness enhancement films (BEFs), a diffuser sheet, a diffuser plate and a reflector. A plurality of dot patterns are arranged beneath the diffuser plate, so that when light impinges on the dot patterns, a portion of the light will be transmitted through the dot patterns while the remaining portion is reflected off the dot patterns. By reflecting a portion of the light, an increased number of reflections will occur between the diffuser plate and the back plate. By transmitting the other portion of the light, a dark band prevented from forming above the dot patterns. As a result, a more uniform emergent light beam and thereby an improved overall performance of the backlight module are obtained. 
   As shown in a cross-sectional view of  FIG. 1 , a prior art backlight module  1  comprises a set of optical films and a plurality of light sources  11 . The set of optical films includes, from top to bottom, a BEF  10 , a diffuser sheet  12 , a diffuser plate  14  and a reflector  16 . The plurality of light sources  11  are disposed on the reflector  16 . The light sources may be light emitting diodes (LEDs). Since light emitted from a light source  11  is concentrated in the very front of the light source  11 , if the brightness of the light transmitted through the diffuser plate  14  is not uniform, alternate latticed dark and bright streaks or even latticed dark and bright dots tend to arise on the display panel between the individual light sources.  FIG. 2  depicts the simulation results of a brightness distribution on a display panel incorporating the backlight module  1 . The dark areas as indicated by the ellipse are shown between the individual LED light sources in the display panel. Furthermore, among the current backlight modules of a direct lighting structure, there is a decreased number of light sources as an effort to reduce the cost. In this case, the latticed dark streaks will become more obvious. 
   To mitigate the latticed dark streaks, a backlight module shown in  FIG. 3  has been proposed. As seen in the cross-sectional view of  FIG. 3 , in order for the light emitted from the light sources to be diffused uniformly, the backlight module  3  has additional dot patterns at the bottom of the diffuser sheet. Accordingly, the set of optical films in the backlight module  3  includes a BEF  30 , a diffuser sheet  32 , a diffuser plate  34 , a plurality of dot patterns  31  and a reflector  36 . A plurality of light sources  33  (e.g., LEDs) are disposed on the reflector  36 , while the dot patterns  31  are disposed on the bottom surface of the diffuser plate  34 . More specifically, the plurality of dot patterns  31  are centered around a point where the light emitting center of the light sources  33  is projected on the diffuser plate  34 . By adjusting the size of the individual dot patterns  31  and spacing therebetween in such a way that the linearly density of the dot patterns  31  decreases as the dot patterns  31  are located further away from the central point, the brightness of the light sources  33  is redistributed through the diffusion of the dot patterns  31 , thus mitigating the latticed dark streaks arising from a non uniform brightness distribution of the light sources. However, in such a prior art structure, the dot pattern arrangement only takes into account the relative relationships between the individual light sources arranged along the same horizontal or vertical axis, but ignores the fact that the maximum distance between the individual light sources exists in the diagonal direction, thus causing a larger linearly density along the horizontal or vertical axis than that along the diagonal direction. Consequently, when the spacing between the light sources and the interval between the light sources and the diffuser plates are enlarged to a certain extent, the dark areas still arose between the light sources. For example, if LED light sources are used and the spacing between the light sources are enlarged to 26-27 mm while the interval between the LED light sources and the diffuser plates is enlarged to 20 mm, a light transmission plot as shown in  FIG. 4  is obtained through an experiment and simulation results. It can be seen from this plot that, although the arrangement of the dot patterns mitigates latticed dark streaks, dark areas still arose between four the LED light sources (as shown by the ellipse). 
   Accordingly, it is important to provide a new dot pattern arrangement with such a linearly density so that the brightness of the light sources are distributed uniformly in the display panel. 
   SUMMARY OF THE INVENTION 
   One objective of this invention is to provide a scattering module adapted for a backlight module. The backlight module includes a plurality of light sources. The light sources are located on a side of the scattering module, and include a first light source, a second light source and a third light source. The second light source is arranged along a first direction of the first light source with a first spacing formed therebetween. The third light source is arranged along a second direction of the first light source with a second spacing formed therebetween. The first spacing is smaller than the second spacing, while the first direction is different from but is substantially not perpendicular to the second direction. The scattering module of this invention comprises a plurality of scattering elements. The scattering elements present a first linearly arranged density in the first direction and a second linearly arranged density in the second direction, with the first linearly arranged density is smaller than the second linearly arranged density. In this way, the light from the backlight module is projected to the display panel uniformly without incurring a non uniform brightness distribution. 
   Another objective of this invention is to provide a backlight module, which comprises a plurality of light sources and the aforesaid scattering module. The light sources are disposed on a side of the scattering module and include a first light source, a second light source and a third light source. The second light source is arranged along a first direction of the first light source with a first spacing formed therebetween. The third light source is arranged along a second direction of the first light source with a second spacing formed therebetween. The first spacing is smaller than the second spacing, while the first direction is different from but is substantially not perpendicular to the second direction. The scattering module comprises a plurality of the scattering elements, which present a first linearly arranged density and a second linearly arranged density in directions parallel to the first direction and the second direction respectively, with the first linearly arranged density smaller than the second linearly arranged density. In this way, the light from the backlight module is projected onto the display panel uniformly without incurring a non uniform brightness distribution. 
   The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view of a backlight module of the prior art; 
       FIG. 2  depicts the simulation plot of the light transmission in the backlight module of  FIG. 1 ; 
       FIG. 3  is a schematic view of another backlight module of the prior art; 
       FIG. 4  depicts the simulation plot of the light transmission in the backlight module of  FIG. 3 ; 
       FIG. 5  is a cross-sectional view of a backlight module in accordance with the first embodiment of this invention; 
       FIG. 6  is a top view showing the relative positions of the light sources on a reflector in the backlight module in accordance with the first embodiment of this invention; 
       FIG. 7  is a bottom view showing the relative positions of the dot patterns on a diffuser plate in the backlight module in accordance with the first embodiment of this invention; 
       FIG. 8  depicts the simulation plot of the light transmission in the backlight module in accordance with the first embodiment of this invention; and 
       FIG. 9  is a bottom view showing the relative positions of the dot patterns on a diffuser plate in a backlight module in accordance with the second embodiment of this invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The first embodiment of this invention is a backlight module  5 , of which a cross-sectional view is depicted in  FIG. 5 . The backlight module  5  comprises a brightness enhancement film (BEF)  50 , a diffuser sheet (DS)  52 , a diffuser plate (DP)  54 , a scattering module  51 , a plurality of light sources  53  and a reflector  56  from top to bottom in  FIG. 5 . The scattering module  51  further comprises a plurality of scattering elements. In this embodiment, these scattering elements are a plurality of dot patterns  51   a  disposed on the bottom surface of the diffuser plate  54 . The plurality of light sources  53  are light emitting diodes (LEDs) disposed on the reflector  56  facing towards the scattering elements. In other words, the plurality of light sources  53  are disposed on a side of the scattering module  51 . 
   The top view of the reflector  56  and the light sources  53  in the backlight module  5  is depicted in  FIG. 6 . The plurality of light sources  53  include a first light source  530 , a second light source  532  and a third light source  534 . The second light source  532  is arranged along a first direction  531  of the first light source  530 , with a first spacing a defined therebetween. The third light source  534  is arranged along a second direction  533  of the first light source  530 , with a second spacing b defined therebetween. It should be noted that the first direction  531  is different from and is substantially not perpendicular to the second direction  533 . In this embodiment, the first direction  531  is in a vertical direction while the second direction  533  is in a diagonal direction, so that the first spacing a is smaller than the second spacing b. In other embodiments, the first direction  531  may be in the horizontal direction instead, which is not depicted in the drawings but can be imagined by those skilled in the art. 
   A bottom view of the diffuser plate  54  and the dot patterns  51  in the backlight module  5  are depicted in  FIG. 7 . The plurality of dot patterns  51  include a first dot pattern  510 , a second dot pattern  512  and a third dot pattern  514 . In this embodiment, these dot patterns  510 ,  512 ,  514  all have an equal area and the same profile. When viewed from a direction parallel to the first direction  531 , the dot patterns  510 ,  512 ,  514  are all in a lozenge form. The first dot pattern  510 , the second dot pattern  512  and the third dot pattern  514  correspond to the first light source  530 , the second light source  532  and the third light source  534  respectively. The line connecting the first dot pattern  510  and the second dot pattern  512  is parallel to the first direction  531 . The dot patterns located along this line have a first linearly arranged density. A line connecting the first dot pattern  512  and third dot pattern  514  is parallel to the second direction  533 . The dot patterns located along this line have a second linearly arranged density. Here, the first and second linearly arranged densities are each defined as a length occupied by the dot patterns in a unit length c along the first direction  531  and the second direction  533  respectively. The dot patterns located in a unit length c along the first direction  531  present a first total area, and those located in the unit length c along the second direction  533  present a second total area which is larger than the first total area. Since each individual dot pattern has the same area, it can be inferred that the first linearly arranged density along the first direction  531  is smaller than the second linearly arranged density along the second direction  533 . Consequently, because the larger dot pattern area is arranged along the second direction  533 , the light emitted from the light sources  530 ,  532 ,  534  may be diffused in a more effective way and distributed more uniformly on the display panel. 
   The simulation plot of the light transmission presented by the display panel of a display apparatus adopting such a backlight module is depicted in  FIG. 8 . As can be seen, the different dot pattern arrangement of this embodiment results in an increased linearly arranged density of dot patterns along the diagonal direction, thus preventing a non uniform brightness. Therefore, even if the spacing between individual light sources is enlarged, uniform light can still be provided to the display panel of the display apparatus adopting such a backlight module. 
   In reference to  FIG. 7 , when viewed from the first direction  531 , the first dot pattern  510  and the second dot pattern  512  may be considered as the arrangement of the lozenge dot pattern along the first direction  531 . However, when viewed from the second direction  533 , the first dot pattern  510  and the third dot pattern  514  may be considered as the arrangement of the square dot pattern. The different arrangement of the dot patterns in the different directions results in an increased linearly arranged density of the dot patterns along the second direction  533 , so that the first linearly arranged density of the lozenge dot patterns along the first direction  531  is smaller than the second linearly arranged density of the square dot patterns along the second direction  533 . As a consequence, uniform light, obviating the brightness with a non uniform distribution is obtained. 
   In other preferred examples of the first embodiment, the dot patterns may vary in area according to the distance to the light sources. For example, the area of the dot patterns may be designed in such a way that the further the dot pattern is located from a light source, the smaller the area thereof will be. In this case, the dot patterns located midway between the two light sources will have the minimum area. On the other hand, the light sources are not merely limited to the arrangement in an array form, and examples with other arrangement or random distribution forms may readily occur to those skilled in the art. 
   The second embodiment of this invention is also a backlight module. The scattering module  51 ′ of this backlight module comprises scattering elements different from those in the previous embodiments.  FIG. 9  depicts the bottom view of a diffusion plate  54  and the scattering elements  51   a ′ of this backlight module. As shown, the scattering elements  51   a ′ of the scattering module  51 ′ all have an equal area and a circular shape. The scattering elements includes a first dot pattern  510 ′, a second dot pattern  512 ′ and a third dot pattern  514 ′, which correspond to a first light source  530 , a second light source  532  and a third light source  534  respectively. The line connecting the first dot pattern  510 ′ and the second dot pattern  512 ′ is parallel to a first direction  531 , with two adjacent dot patterns along the first direction  531  with a first distance x, i.e., the first dot pattern  510 ′ and the second dot pattern  512 ′ has the first distance x. The line connecting the first dot pattern  510 ′ and the third dot pattern  514 ′ is parallel to a second direction  533 , with two adjacent dot patterns along the second direction  533  with a second distance y, i.e., the first dot pattern  510 ′ and the third dot pattern  514 ′ has the first distance y. Since the first distance x is greater than the second distance y, the light emitted from the light sources in the second direction  533  will be effectively diffused due to the more closely arranged dot patterns. As a consequence, the light becomes uniform and further obviates brightness with a non uniform distribution. 
   In the other preferred examples of the second embodiment, the dot patterns may vary in area according to the distance to the light sources. For example, the area of the dot patterns may be designed in such a way that the further the dot pattern is located from a light source, the smaller the area thereof will be. In this case, the dot patterns located in the midway between the two light sources will have the minimum area. On the other hand, the light sources are not merely limited to the arrangement in an array form. Examples with other arrangement or random distribution forms may readily occur to those skilled in the art. 
   In conclusion, this invention provides a larger linearly arranged density in the diagonal direction than those in the horizontal or vertical direction, thereby enhancing the light diffusion effect in the diagonal direction presenting a longer distance and rendering the light distribution more uniform. With this invention, even when the number of the light sources is reduced and the interval between light sources is increased due to cost, the brightness can be more uniform despite the inadequate reducing reflection arising from the low linearly arranged density of the dot patterns resulting in the brightness with a non uniform distribution. 
   The above disclosure is related to the detailed technical contents and inventive features thereof. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Nevertheless, although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.