This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2010-251130, filed Nov. 9, 2010, the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a surface lighting apparatus which can adjust luminance for each of partial regions on a light emission surface thereof.
In recent years, using liquid crystal displays (LCDs) as large-size and thin-shaped television apparatuses and display devices has widely increased. LCDs themselves cannot emit light to perform display, and thus include a surface lighting apparatus (also referred to as a backlight device) corresponding to a light source apparatus.
Backlight devices are broadly classified into a direct type and an edge-light type. In the prior art, backlight devices of the direct type using a cold cathode fluorescent lamp (CCFL) have been used. In recent years, the power of light-emitting diodes (LEDs) has been increased and luminous efficiency of LEDs has been improved, and thus LEDs have become used as a light source for backlight devices.
When LEDs are used as a light source for backlight devices, a plurality of LEDs are connected as one block, the LEDs are independently controlled for each block, and thereby light control for each of partial regions (i.e., local dimming control) can be performed. In addition, luminance of the backlight device is controlled for each partial region in accordance with an image to be displayed, and thereby a contrast ratio between light and dark parts of the image can be increased, and power consumption can be reduced.
However, backlight devices of the direct type using LEDs require a number of LEDs, and thus have the problem of increase in cost. In addition, since LEDs are point light sources, it is necessary to dispose a light diffusion plate between the LEDs and the liquid crystal panel to obtain uniform luminance distribution. To achieve sufficient uniformity of luminance distribution, it is required to secure a certain amount of distance between the LEDs and the light diffusion plate, and thus direct type backlight devices using LEDs are not suitable for achieving reduction in thickness of the LCDs.
Backlight devices of the edge-light type using LEDs and light guide plates in combination can solve the above problems. However, backlight devices of the edge-light type have the problem that uneven luminance is easily generated. In addition, when a number of diffusion sheets are used to prevent uneven luminance, the problem of increase in cost and the problem of reduction in light use efficiency of LEDs are caused.
In general, according to one embodiment, a surface lighting apparatus includes a plurality of surface light source units stacked one on another, and a control unit. Each of the surface light source units includes a light guide plate and a plurality of light-emitting units. The light guide plate includes a light incident surface for introducing light emitted by the light-emitting units, a front surface, a back surface opposed to the front surface, and a light-outputting region configured to output light introduced from the light incident surface through the front surface. The front surface is provided with a light transmission control part to prevent light from diffusing in a direction of arranging the light-emitting units. The light-emitting units are linearly arranged opposite to the light incident surface and configured to emit light toward the light incident surface. The control unit is configured to control a light intensity for each of the light-emitting units. A light guide plate of each surface light source unit other than a lowermost surface light source unit of the surface light source units further includes a window region configured to transmit light which is output from one or more lower surface light source units and is introduced from a back surface thereof.
Hereinafter, surface lighting apparatuses according to various embodiments will be described with reference to the accompanying drawings. The surface lighting apparatus of each embodiment is the edge-light type and is used as, for example, a backlight device of a liquid crystal display. When the surface lighting apparatus is used as the backlight device of a liquid crystal display, the surface lighting apparatus is arranged such that a light emission surface thereof is opposed to a back surface of a liquid crystal panel.
In the following embodiments, like reference numbers denote like elements, and duplication of explanation will be avoided.
The light guide plates 111 and 121 are formed of a transparent material and formed in a thin plate shape. As the material of the light guide plates 111 and 121, it is possible to use, for example, resin material such as acrylic resin and polycarbonate resin.
Each of the light guide plates 111 and 112 has a front surface (also called a main surface), a back surface, and four side surfaces. The front surface and the back surface are opposed to each other in a stacking direction. The stacking direction is a direction in which surface light source units 110 and 120 are stacked or laid one on another, and corresponds to a thickness direction of the light guide plates 111 and 121. In
The line light source 112 is arranged so as to be opposed to a side surface (also referred to as a light incident surface) selected from the side surfaces of the light guide plate 111, and emits light toward the light incident surface. The line light source 122 is arranged in parallel with the line light source 112 and so as to be opposed to a side surface (also referred to as a light incident surface) selected from the side surfaces of the light guide plate 121, and emits light toward the light incident surface. Each of the line light sources 112 and 122 includes a plurality (for example, eight) of light-emitting units 101, and these light-emitting units 101 are linearly arranged along the light incident surface of each of the light guide plates 111 and 121. In addition, each of the light-emitting unit 101 includes one or more light-emitting elements which generate light. In the case where each of the light-emitting units 101 includes a plurality of light-emitting elements, the light-emitting elements of each light-emitting unit 101 are linearly arranged along the direction of arranging the light-emitting units 101.
The light guide plate 111 includes a light-outputting region 113 which upward outputs light emitted by the line light source 112 and introduced from the light incident surface. Further, the light guide plate 111 includes a window region 114 which lets the light output from the surface light source unit 120 pass through and transmits the light. The light guide plate 121 includes a light-outputting region 123 which upward outputs light emitted by the line light source 122 and introduced from the light incident surface. The window region 114 of the light guide plate 111 and the light-outputting region 123 of the light guide plate 121 overlap each other in the stacking direction.
The light-outputting regions 113 and 123 are formed in the light guide plates 111 and 121, respectively, by arranging a number of diffusion marks which diffuse and reflect light. The diffusion marks may be minute concavities and convexities which are formed on the back surfaces of the light guide plates 111 and 121 in a three-dimensional manner. The diffusion marks may be white printing which is formed on the back surfaces of the light guide plates 111 and 121 by silk-screen printing or the like. The diffusion marks may be particles which have light-diffusion characteristic and added to each of the light guide plates 111 and 121.
The light-outputting region 113 guides light emitted by the line light source 112 such that the light is radiated upward from the front surface of the light guide plate 111. On the other hand, light emitted by the line light source 122 is made incident on the light incident surface of the light guide plate 121, reflected and diffused by reflection marks in the light-outputting region 123, and output upward from the light-outputting region 123. The light output from the light-outputting region 123 is transmitted through the window region 114 of the light guide plate 111, and output upward from the front surface of the light guide plate 111.
The linear prisms which are provided in each of the light guide plates 111 and 121 are formed along a direction (light-emitting direction) in which each of the line light sources 112 and 122 emits light. The light-emitting direction of the line light sources 112 and 122 is a direction which is substantially perpendicular to the stacking direction and the direction of arranging the light-emitting units 101. That is, the light-emitting direction is substantially perpendicular to the light incident surface which each of the line light source 112 and 122 faces. Thus, each of the light transmission control parts 301 and 302 has depressed parts and projecting parts which are linearly extended in the light-emitting direction.
A cross-sectional component of the light along line which is transmitted through the light guide plate 111, is subjected to retroreflection by the prism structure. The light which is emitted by the line light source 112 and made incident on the light incident surface of the light guide plate 111 is transmitted while being subjected to retroreflection in the light guide plate 111, thus widely diffused in the light-emitting direction of the line light source 112, and is hardly diffused in the direction of arranging the light-emitting units 101.
In the same manner, a cross-sectional component of the light along line which is transmitted through the light guide plate 121, is subjected to retroreflection by the prism structure. The light which is emitted from the line light source 122 and made incident on the light incident surface of the light guide plate 121 is transmitted while being subjected to retroreflection in the light guide plate 121, thus widely diffused in the light-emitting direction of the line light source 122, and is hardly diffused in the direction of arranging the light-emitting units 101.
The light transmission control parts 301 and 302 are not limited to the example which includes linear prisms that have an isosceles triangle cross section as shown in
Each of the light-emitting elements 401 may be an LED module which generates white light by using LEDs of different colors in combination. For example, the LED module which generates white light includes a red LED, a green LED, and a blue LED.
The light-emitting units 101 are electrically connected to a light control unit 402. The light control unit 402 can turn on/off and control light intensity of the respective light-emitting units 101 independently. For example, the light control unit 402 supplies direct current to each light-emitting unit 101, and controls the light intensity of each light-emitting unit 101 by changing the value of the direct current. As another example, the light control unit 402 supplies high-frequency pulse current to each light-emitting unit 101 to blink on and off the light-emitting unit 101 at high speed, and controls the light intensity of each light-emitting unit 101 by changing a duty ratio of the pulse current.
The number of the light-emitting units 101 which are provided in each of the line light sources 112 and 122 is not limited to eight as shown in
As described above, in the surface light source unit 110, the light guide plate 111 includes the light transmission control part 301, and the line light source 112 includes the plurality of light-emitting units 101. By using the light guide plate 111 and the line light source 112 in combination, a region in which light emitted by each light-emitting unit 101 is output is an elongated rectangular region in the light-outputting region 113, which runs along a linear direction of the prism structure, i.e., the light-emitting direction of the line light source 112. In addition, in the surface light source unit 120, the light guide plate 121 including the light transmission control part 302 and the line light source 122 including the light-emitting units 101. By using the light guide plate 121 and the line light source 122 in combination, a region in which light emitted by each light-emitting unit 101 is output is an elongated region in the light-outputting region 123, which runs along a linear direction of the prism structure, i.e., the light-emitting direction of the line light source 122.
In this transmission, in both the window region 114 and the light-outputting region 113, the light is guided in the light-emitting direction of the line light source 112 by the light transmission control part 301 provided on the front surface of the light guide plate 111, without diffusing in the direction of arranging the light-emitting units 101 of the line light source 112. Thereby, the region from which the light emitted by the light-emitting unit 101 is output can be restricted to the partial region 501 in the light-outputting region 113, which is shaded in
In this transmission, in the light-outputting region 123, the light is guided in the light-emitting direction of the line light source 122 by the light transmission control part 302 provided on the front surface of the light guide plate 121, without diffusing in the direction of arranging the light-emitting units 101 of the line light source 122. Thereby, the region into which the light from the light-emitting unit 101 is output can be restricted to the partial region 502 in the light-outputting region 123, which is shaded in
By stacking these surface light source units 110 and 120, the surface lighting apparatus of
As described above, according to the surface lighting apparatus according to the present embodiment, it is possible to perform light control (local dimming control) for each of a plurality of partial regions, and easily secure uniform luminance. When the surface lighting apparatus of the present embodiment is applied to the backlight device of a liquid crystal display, it is possible to increase a contrast ratio between the light and dark parts of an image to be displayed and improve the image quality, by local dimming control. In addition, the surface lighting apparatus can perform control such as lightening only a necessary part according to the displayed image, therefore reducing the power consumption.
Although the present embodiment shows an example in which the two surface light source units 110 and 120 are stacked, three or more surface light source units may be stacked. In the case where three or more surface light source units are stacked, the window region is more shortened in the light-emitting direction of the line light source, i.e., in a direction perpendicular to the light incident surface. Further, in the surface light source unit of the lower side, the light-outputting region in the surface light source unit is shifted toward the light incident surface.
The case where the surface lighting apparatus has a structure in which three surface light source units are stacked will be explained hereinafter as an example. In the light guide plate of the lowermost surface light source unit, a region of ⅓ of the light guide plate, which is close to the light incident surface, is set as the light-outputting region. In the light guide plate of an intermediate surface light source unit, a region of about ⅓ of the light guide plate, which is close to the light incident surface, is set as the window region, and an about ⅓ region in the center part is set as the light-outputting region. In addition, in the light guide plate of the uppermost surface light source unit, a region of about ⅔ of the light guide plate, which is close to the light incident surface, is set as the window region, and the other region is set as the light-outputting region.
As described above, increasing the number of stacked surface light source units can increase the number of partial regions which can be light-controlled.
Next, a surface lighting apparatus according to a modification of the first embodiment will be explained hereinafter with reference to
In the surface lighting apparatus which can perform local dimming control as described above, there are cases where uniformity of luminance distribution is important when the whole screen is fully lit. To secure uniformity of luminance distribution in full lighting, the surface lighting apparatus according to the modification of the first embodiment is provided with a luminance attenuating region 701 between the light-outputting region 113 and the window region 114 of the light guide plate 111, and the light guide plate 121 is provided with a luminance attenuating region 702 to be superposed on the luminance attenuating region 701, as shown in
Diffusion marks are distributed in the luminance attenuating region 701 of the light guide plate 111, such that luminance gradually increases from the end of the window region 114 toward the end of the light-outputting region 113. Specifically, in the luminance attenuating region 701 of the light guide plate 111, diffusion marks are provided such that distribution density increases in a direction of going away from the line light source 112.
In addition, diffusion marks are distributed in the luminance attenuating region 702 of the light guide plate 121, such that luminance gradually decreases from the end of the light-outputting region 123. Specifically, in the luminance attenuating region 702 of the light guide plate 121, the diffusion marks are provided such that luminance distribution decreases in a direction of going away from the line light source 122.
The diffusion marks of the luminance attenuating regions 701 and 702 may have a minute concavities and convexities which are formed on the back surfaces of the light guide plates 111 and 121 in a three-dimensional manner. Alternatively, the diffusion marks may be white printing which are formed on the back surfaces of the light guide plates 111 and 121 by silk-screen printing or the like.
Further, in order to enhance the effect of an increase and attenuation in luminance, light-absorption marks such as small black printing may be distributed in the luminance attenuating regions 701 and 702 in addition to the diffusion marks. Alternatively, black printing with a specific size may be applied to the luminance attenuating regions 701 and 702.
As shown in
As described above, the surface light source units 110 and 120 are provided with the luminance attenuating regions 701 and 702, respectively, and thereby the luminance uniformity of the whole surface lighting apparatus can be secured when both the surface light source units are lit with the same luminance. In addition, it is possible to increase a margin for manufacturing error of the surface lighting apparatus, such as displacement of the light guide plates 111 and 121.
In the surface lighting apparatus according to the above embodiment and the modification thereof, there are cases where the light emitted from the lower line light source 122 is made incident on the back surface of the upper light guide plate 111, and directly output from the window region 114, as shown in
When there is such a leaking light which is generated by a cause other than diffusion of the diffusion marks of the light-outputting regions 113 and 123, luminance around the line light sources 112 and 112 increases, and unevenness in luminance distribution is generated. To prevent generation of such unevenness in luminance distribution, a light shielding member 902 which blocks light may be provided between the line light source 112 and the line light source 122. Preventing generation of leaking light as described above by the light shielding member 902 enables suppression of generation of unevenness in luminance distribution.
Although the upper light guide plate 111 and the lower light guide plate 121 have the same size in the first embodiment, the lower light guide plate 1021 of the second embodiment is shorter than the upper light guide plate 111 in a light-emitting direction of the line light source 122. Specifically, the light guide plate 1021 is provided by removing a part other than the light-outputting region 123 from the light guide plate 121 of
As shown in
Also in the present embodiment, each of the light guide plates 111 and 1021 may be provided with a luminance attenuating region, as shown in the modification of the first embodiment. In addition, as shown in
As described above, the surface lighting apparatus according to the second embodiment can perform local dimming control and easily secure uniform luminance, like the first embodiment. In addition, the light guide plate of the lower surface light source unit is shortened in the light-emitting direction of the line light source, and thereby weight saving and material saving can be achieved.
The surface lighting apparatus of
As shown in
The window region 114a of the light guide plate 1211 and the light-outputting region 123a of the light guide plate 1221 overlap each other in the stacking direction. In addition; the window region 114b of the light guide plate 1211 and the light-outputting region 123b of the light guide plate 1221 overlap each other in the stacking direction.
Light emitted from the line light source 122a is made incident on the light incident surface of the light guide plate 1221, reflected and diffused by reflection marks in the light-outputting region 123a, and output upward from the light-outputting region 123a. The light output from the light-outputting region 123a is transmitted through the window region 114a of the light guide plate 1211, and output upward from the front surface of the light guide plate 1211.
In addition, light emitted from the line light source 122b is made incident on the light incident surface of the light guide plate 1221, reflected and diffused by reflection marks in the light-outputting region 123b, and output upward from the light-outputting region 123b. The light output from the light-outputting region 123b is transmitted through the window region 114b of the light guide plate 1211, and output upward from the front surface of the light guide plate 1211.
In addition, the front surfaces of the light guide plates 1211 and 1221 are provided with light transmission control parts 301 and 302 as shown in
The light-outputting regions 113a and 113b and the window regions 114a and 114b of the light guide plate 1211 have the same respective functions as those of the light-outputting region 113 and the window region 114 of the light guide plate 111 of
Also in the present embodiment, each of the light guide plates 1211 and 1221 may be provided with a luminance attenuating region, as shown in the modification of the first embodiment. Besides, as shown in
By stacking these surface light source units 1210 and 1220, the surface lighting apparatus of
Although the present embodiment shows the example in which the surface lighting apparatuses of
Also when the surface lighting apparatus of
According to at least one of the above embodiments, it is possible to provide a surface lighting apparatus which can perform light control (local dimming control) for each of a plurality of partial regions, and realizes a thin-shaped and light-weight backlight device which can easily secure uniform luminance.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
Number | Date | Country | Kind |
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2010-251130 | Nov 2010 | JP | national |