Optical plate and backlight module using the same

[0001] This application is related to eleven copending U.S. patent applications, which are: application Ser. No. 11/835,425, Ser. No. 11/835,426, Ser. No. 11/835,427, Ser. No. 11/835,428, Ser. No. 11/835,429, Ser. No. 11/835,430, and Ser. No. 11/835,431, filed on Aug. 8, 2007; application Ser. No. 11/836,799, filed on Aug. 10, 2007; application Ser. No. 11/842,170, filed on Aug. 21, 2007; applicants Ser. No. 11/843,669, and Ser. No. 11/843,670, filed on Aug. 23, 2007, and all entitled “OPTICAL PLATE AND BACKLIGHT MODULE USING THE SAME”; In all these copending applications, the inventor is Shao-Han Chang. All of the copending applications have the same assignee as the present application. The disclosures of the above identified applications are incorporated herein by reference.

[0002] 1. Field of the Invention

[0003] The present invention relates to an optical plate for use in, for example, a backlight module, the backlight module typically being employed in a liquid crystal display (LCD).

[0004] 2. Discussion of the Related Art

[0005] In a liquid crystal display device, liquid crystal is a substance that does not itself illuminate light. Instead, the liquid crystal relies on light received from a light source, in order for the liquid crystal to display information. In the case of a typical liquid crystal display device, a backlight module powered by electricity supplies the needed light.

[0006] FIG. 9 represents a typical direct type backlight module 100. The backlight module 100 includes a housing 101, a light reflective plate 102, a light diffusion plate 103, a prism sheet 104, and a plurality of light emitting diode 105 (hereinafter called LED). The housing 101 includes a rectangular base 1011 and four sidewalls 1013 extending from a periphery of the base 1011. The base 1011 and the four sidewalls 1013 cooperatively define a chamber 1017. Each LED 105 includes a base portion 1053 and a light-emitting portion 1051 disposed on the base portion 1053. The LEDs 105 are electrically connected to a printed circuit board 107, and the printed circuit board 107 is fixed to the base 1011 of the housing 101. The light reflective plate 102 is disposed on the LEDs 105 in the chamber 1017. The light reflective plate 102 defines a plurality of through holes (not labeled) that allows the light-emitting portions 1051 of the LED 105 to pass through and to emit light to be transmitted to the light diffusion plate 103. The light diffusion plate 103 is stacked on the prism sheet 104 in the chamber 107. Light emitted from the LEDs 105 is substantially reflected by the light reflective sheet 102 to the light diffusion plate, diffused uniformly in the light diffusion plate 103, and exit the prism sheet 104 as surface light.

[0007] Generally, a plurality of dark areas may occur because of the reduced intensity of light between adjacent LEDs 105. In the backlight module 100, each LED 105 further includes a reflective sheet 106 disposed on the top of the light-emitting portion 1051, configured for decreasing the brightness of a portion of the backlight module 100 above the LED 105. However, the brightness of the backlight module 100 is still not uniform.

[0008] What is needed, therefore, is a new optical plate and a backlight module using the optical plate that can overcome the above-mentioned shortcomings.

[0009] An optical plate according to a preferred embodiment includes at least one transparent plate unit and a diffusion layer. The transparent plate unit includes a light output surface, a bottom surface, a plurality of spherical protrusions, and a lamp-receiving portion. The bottom surface is opposite to the light output surface. The spherical protrusions are formed at the bottom surface. The lamp-receiving portion is defined in the bottom surface. The diffusion layer is integrally formed in immediate contact with the light output surface of the transparent plate, and free of air or gas pockets trapped in an interface therebetween.

[0010] A backlight module according to a preferred embodiment includes a housing, a point light source, a reflective member and an optical plate. The housing includes a base and a plurality of sidewalls extending around a periphery of the base, the base and the sidewalls cooperatively forming an opening. The point light source is disposed on the base, each point light source having a light-emitting portion. The reflective member is positioned above the top of the light-emitting portion. The same optical plate as described in the previous paragraph is employed in this embodiment. The light-emitting portion of the point light source is inserted in the lamp-receiving portion of the optical plate correspondingly. The diffusion layer of the optical plate faces the opening of the housing.

[0011] Other advantages and novel features will become more apparent from the following detailed description of various embodiments, when taken in conjunction with the accompanying drawings.

[0022] Reference will now be made to the drawings to describe preferred embodiments of the present optical plate and backlight module, in detail.

[0023] Referring to FIG. 1, a backlight module 200 in accordance with a first preferred embodiment is shown. The backlight module 200 includes an optical plate 20, a housing 21, a light reflective plate 22, a LED 25, and a reflective member 27. The housing 21 includes a rectangular base 211 and four sidewalls 213 extending around a periphery of the base 211 correspondingly. The base 211 and the sidewalls 213 cooperatively form an opening 217. The optical plate 20, the light reflective plate 22, the LED 25 and the reflective member 27 are received in the housing 21. The light diffusion plate 23 is disposed on the housing 21 over the opening 217.

[0024] Referring to FIGS. 2 and 3, the optical plate 20 can be mounted into the housing 21. The optical plate 20 includes a light output surface 202, a bottom surface 203, a diffusion layer 205, and plurality of spherical protrusions 206. The bottom surface 203 and the light output surface 202 are on opposite sides of the 20. The diffusion layer 205 is formed on the light output surface 202. The spherical protrusions 206 are defined on the bottom surface 203. The diffusion layer 205 forms a ring pattern that includes a plurality of annular rings protruding from the light output surface 202 arranged apart. The optical plate 20 further includes a lamp-receiving portion 204 defined in a center of the bottom surface 203. In this embodiment, the lamp-receiving portion 204 is a through hole that passes through the bottom surface 203 and the light output surface 202. Center axes of the annular rings of the diffusion layer 205 are collinear with the center of the lamp-receiving portion 204. A radial thickness of each of the annular rings of the diffusion layer 205 increases as the radii of the annular rings increases.

[0025] The optical plate 20 can be made from transparent material selected from the group consisting of polycarbonate (PC), polymethyl methacrylate (PMMA), polystyrene (PS), copolymer of methylmethacrylate and styrene (MS), and any suitable combination thereof. The diffusion layer 205 includes transparent resin matrix material 2052, and diffusion particles 2054 uniformly dispersed in the transparent resin matrix material 2052. The light diffusion layer 205 is manufactured by solidifying an ink layer that is coated on the light output surface 202. The ink layer includes a varnish and a plurality of diffusion particles 2054 dispersed in the varnish. The varnish is preferably acrylic varnish. The transparent resin matrix material 2052 is made of acrylic from the varnish. The diffusion particles 2054 are selected from a group consisting of glass beads, silicon dioxide (SiO₂) particles, PMMA particles, and any combination thereof.

[0026] Referring to FIGS. 3 and 4, the spherical protrusions 206 are distributed on the bottom surface 203 in a matrix manner except for an area of the lamp-receiving portion 204. In the preferred embodiment, the spherical protrusions 206 surround the lamp-receiving portion 204 except for an area substantially square. A radius R of the base surface of each spherical protrusion 206 is in a range from about 0.01 millimeters to about 2 millimeters. A depth of each spherical protrusion 206 is preferably greater than 0.01 millimeters and equal to or greater than its radius R. A pitch P of adjacent spherical protrusions 206 is defined by a following formula: 2R≦P≦4R. In this embodiment, each of the spherical protrusions 206 is a hemispherical protrusion.

[0027] Again referring to FIG. 1, in this embodiment, the LED 25 includes a base portion 253, and a light-emitting portion 251 disposed on the base portion 253. The LED 25 is electrically connected to a printed circuit board 26 that is fixed to the base 211 of the housing 21. In this embodiment, the reflective member 27 is a light reflective sheet positioned on the top of the light-emitting portion 251. The optical plate 20 is correspondingly positioned in the housing 21 such that the lamp-receiving portion 204 of the optical plate 20 receives the light-emitting portion 251 of the LED 25 with the reflective member 27. The light output surface 202 of the optical plate 20 faces the opening 217. The light reflective plate 22 defines a through hole (not labeled). The light reflective plate 22 is disposed under the bottom surface 203 of the optical plate 20, the LED 25 passing through the light reflective plate 22 via the through hole.

[0028] In an alternative embodiment, the lamp-receiving portion 205 can be a blind hole that is depressed towards the light output surface 202. The reflective member 27 can be a reflective film formed on the top of the light-emitting portion 251. The reflective member 27 and the LED 25 can be inserted into the blind hole of lamp-receiving portion 204 together.

[0029] In use, light emitted from the light-emitting portion 251 of the LED 25 enters the optical plate 20 via an inner surface of the lamp-receiving portion 204. A significant amount of light transmits to the optical plate 20. An amount of light is reflected at the spherical protrusions 206 and/or the light reflective plate 22, and finally is outputted from the light output surface 202. Accordingly, a light energy utilization rate of the backlight module 200 is increased. In addition, the light from the light output surface 202 can be further diffused in the diffusion layer 205 for improving uniformity of light outputted.

[0030] It should be pointed out that, the light reflective plate 22 can be omitted. In an alternative embodiment, a high reflectivity film can be deposited on inner surfaces of the base 211 and the sidewalls 213 of the housing 21. In other alternative embodiments, the housing 21 is made of metal materials and having high reflectivity inner surfaces.

[0031] It is to be understood that, in order to improve the brightness of the backlight module 200 at a specific range of viewing angles, the backlight module 200 can further include a transparent sheet (not shown) and a prism sheet (not shown) disposed on the top of the housing 21 over the opening 217 in that order. In addition, in order to improve the light energy utilization rate of the backlight module 200, the light reflective plate 22 can further include four reflective sidewalls 223 extending around a periphery thereof. The sidewalls 223 are in contact with the corresponding sidewalls 213 of the housing 21. Furthermore, the spherical protrusions 206 at the bottom 202 may be distributed in other manners, such as, for example, an array of spherical protrusions 206 in the matrix manner can be aligned along a direction slanted with respect to a side surface of the optical plate 20.

[0032] Referring to FIG. 5, an optical plate 30 in accordance with a second preferred embodiment is shown. The optical plate 30 is similar in principle to the optical plate 20. However, a diffusion layer 305 of the optical plate 30 has a uniform thickness and covers the light output surface 202 entirely.

[0033] In the other alternative embodiments, the diffusion layer of the present optical plate can take other forms of diffusion dot patterns or diffusion ring patterns as shown in FIGS. 6 and 7.

[0034] Referring to FIG. 6, a distribution design of a diffusion layer 405 of an optical plate 40 of a third embodiment of the present invention is described below. The diffusion layer 405 is composed of four (or more) substantially square walls arranged apart. The center of the through hole 404 and the points made by the intersections of the diagonals of the square walls of the diffusion layer 405 are collinear. Furthermore, a thickness of each of the square walls is constant, and the length of the sides of the square walls increases along a direction away from the lamp-receiving portion 404.

[0035] Referring to FIG. 7, another distribution design of a diffusion layer 505 of an optical plate 50 of the fourth embodiment of the present invention is described below. The diffusion layer 505 is composed of a plurality of circular dots. The circular dots are substantially identical to each other. The circular dots are arranged separately along a plurality of imaginary circles that have a same center. Centers of the imaginary circles are also the center of a lamp-receiving portion 504 of the optical plate 50. Furthermore, the densities of circular dots of each imaginary circle can increase along a direction away from the lamp-receiving portion 505.

[0036] Referring to FIG. 8, an optical plate 60 in accordance with a fifth preferred embodiment is shown. The optical plate 60 includes four transparent plate units 62. Each transparent plate unit 62 is the same as the optical plate 20 of the first embodiment. The four transparent plate units 62 are tightly arranged side by side to form the assembled optical plate 60. It is to be understood that four side-lighting type LEDs and the combined optical plate 60 can be mounted into a housing to form a larger size backlight module.

[0037] In a backlight module using a plurality of optical plates combined side by side, a plurality of red, green, and blue colored LEDs can be inserted into the lamp-receiving portions of the combined optical plates corresponingly, such that a mixed white surface light can be obtained. It is to be understood that other kinds of point light source, such as field emission lamps and so on, can replace the LEDs in above embodiments.

[0038] Finally, while various embodiments have been described and illustrated, the invention is not to be construed as being limited thereto. Various modifications can be made to the embodiments by those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.