JP4560653B2 - Light guide plate and backlight unit - Google Patents

Description

  The present invention relates to a backlight unit incorporated in a field-sequential color liquid crystal display device and a light guide plate used therefor.

  A color liquid crystal display can consume much less power than a conventional display using a cathode ray tube or the like, and can make the entire display thinner and lighter. For this reason, the application has been expanded especially for displays that require a large display area. However, in a liquid crystal display, a backlight is used to increase the display brightness, and illumination light is transmitted from the back of the liquid crystal display panel. There is a need. In addition, since the liquid crystal display has a slower response speed of the liquid crystal compared to a cathode ray tube or the like, it is necessary to drive the liquid crystal by a field sequential method, particularly when displaying a moving image or the like, to overcome the drawbacks related to the response speed.

  As an example of such a backlight, linear light sources that emit red light, green light, and blue light are incorporated at equal intervals on the outer peripheral surface of the rotating body, and these are arranged directly under a field sequential type liquid crystal display panel. Japanese Patent Application Laid-Open No. H10-228707 discloses a light guide plate disposed on the side of the light guide plate.

  On the other hand, when an analog television image is displayed on a liquid crystal, the image for one frame is separated into three primary colors, for example, the red image for one frame is first scanned and displayed, and then the green image for the same frame is scanned and displayed. Finally, it is necessary to scan and display a blue image. In this case, when the next color scan display is performed during the scan display of a specific color by the field sequential method, a plurality of colors of light are simultaneously irradiated on the same screen, and the preceding image and the subsequent image are followed. There is a problem that color mixing occurs between the images and the sharpness of the displayed image is lowered. For this reason, when an image of an analog television or the like is displayed on a liquid crystal, it is substantially difficult to display an image of the next color until the display of a specific color in one frame image is completed, and a high-speed moving image is displayed. Could not be displayed clearly.

  The present patent applicant has proposed a backlight unit that can solve such problems in Patent Document 2. This is formed between a pair of partition walls that face each other in the first direction and whose light-reflecting surfaces face each other, and a second wall that is formed between the pair of partition walls and intersects the first direction. A housing having an elongated rectangular opening along the direction of the housing, and at least one end along the second direction of the housing, and red light toward the other end along the second direction of the housing. , At least three light sources that respectively emit blue light and green light, a reflector that is attached to the housing and has a reflecting surface that reflects the light emitted from the light source toward the opening of the housing, and a plurality of housings in the first And a frame that is held in alignment along the direction.

JP 2004-055563 A JP 2006-147398 A

  The backlight disclosed in Patent Document 1 requires power for rotationally driving a rotating body, and uses a fluorescent tube as a linear light source. Have. In addition, it is necessary to increase the diameter of the rotating body so that light from the three linear light sources attached to the rotating body does not mix, and to increase the circumferential interval between the two adjacent linear light sources, The display cannot be made so thin.

  The backlight unit disclosed in the cited document 2 needs to prepare a large number of housings and a large number of reflectors, and has a drawback that the number of parts increases.

  An object of the present invention is to provide a very simple backlight unit that can be incorporated into a field sequential type color liquid crystal display device and can reduce the number of components thereof, and a light guide plate incorporated in the backlight. .

  The first aspect of the present invention comprises a front surface portion from which light is emitted, a back surface portion positioned on the opposite side of the front surface portion, and a plurality of side surface portions positioned between the front surface portion and the back surface portion. A light guide plate in which at least one of the side surface portions is a light incident end surface portion on which light to be emitted from the surface portion is incident, and has a pair of slope portions and a ridge portion where the pair of slope portions intersect, One end of the ridge portion is located on the light incident end surface portion, and further includes a plurality of partition grooves formed on the back surface portion so that the ridge portions are arranged in parallel to each other. It is.

  In the present invention, the light incident from the light incident end face part is totally reflected by the partition groove inside the light guide plate, so that the surface part of the light guide plate is optically partitioned into individual fields by the partition groove. Emanating from the surface.

  In the light guide plate according to the first aspect of the present invention, it is preferable that the side surface portion parallel to the ridge portion of the partition groove includes an inclined surface opposite to the slope portion of the nearest partition groove.

  The inclined surface of the partition groove and the inclined surface of the side surface portion can be formed as a flat surface or a curved surface.

  The back surface portion has a pair of slope portions and a ridge portion where the pair of slope portions intersect, and a plurality of prism bodies formed continuously on the back surface portion so that the ridge portion is parallel to the ridge portion of the partition groove. Can have.

  The back surface portion has a pair of slope portions and a ridge portion where the pair of slope portions intersect, and a plurality of prism bodies formed continuously on the back surface portion so that the ridge portion is parallel to the ridge portion of the partition groove. Can have. In this case, the height of the inclined surface portion of the prism body is set higher as it is farther from the light incident end surface portion, the interval between adjacent prism bodies is set shorter as it is farther from the light incident end surface portion, or a pair of inclined surface portions. For example, it is effective to set the apex angle of the prism body made smaller as the distance from the light incident end face portion decreases.

  It is also possible to form an optical element having an arbitrary contour shape and cross-sectional shape instead of the prism body described above.

  A large number of light deflection elements randomly formed on at least one of the front surface portion and the back surface portion can be provided. This optical deflecting element can also have an arbitrary contour shape and cross-sectional shape depending on the purpose.

  A second aspect of the present invention is a backlight unit incorporated in a field sequential type color liquid crystal display device, the light guide plate according to the first aspect of the present invention, the surface portion of the light guide plate, and the light incident end face A plurality of light emitting portions that are arranged so as to oppose the light incident end face portion partitioned by the light guide sheet partitioning grooves and the light incident end face portions, and emit light guided into the light guide plate. It is characterized by comprising a light source unit having

  In the present invention, the light incident from the light incident end face part is totally reflected by the partition groove inside the light guide plate, so that the surface part of the light guide plate is optically partitioned into individual fields by the partition groove. Then, it is emitted from the surface portion and becomes transmitted illumination light of the liquid crystal display panel. When paying attention to any one area partitioned by the partition groove of the light guide plate, it is possible to substantially display a high-speed moving image by sequentially lighting three colors of light according to the response speed of the liquid crystal shutter. Become.

  In the backlight unit according to the second embodiment of the present invention, each light emitting unit may include at least red light, blue light and green light semiconductor light emitting elements.

  According to the light guide plate of the present invention, a plurality of partition grooves are formed on the back surface portion of the light guide plate in parallel with each other, and each partition groove has a pair of slope portions and a ridge portion where the pair of slope portions intersect. In addition, since one end of the ridge is positioned at the light incident end face, it is possible to obtain a simple light guide plate that can be used in a backlight unit of a field sequential color liquid crystal display device.

  When the side surface parallel to the ridge of the partition groove includes an inclined surface opposite to the slope of the nearest partition groove, it is possible to have the same function as the partition groove on the side surface intersecting the light incident end surface. The entire surface portion of the light guide plate can be used effectively.

  When the inclined surface of the partition groove and the inclined surface of the side surface portion are formed as a flat surface or a curved surface, particularly in the case of a flat surface, the partition groove can be brought close to the surface portion, so that from the adjacent region across the partition groove The leakage of light can be further suppressed.

  A plurality of prism bodies are continuously formed on the back surface, and each prism body has a pair of slope portions and a ridge portion where the pair of slope portions intersect, and this ridge portion is set parallel to the ridge portion of the partition groove. In this case, light propagating in the light guide plate can be guided along the ridge portion, and light with high luminance that is strongly deflected in a predetermined direction can be emitted from the surface portion.

  A plurality of prism bodies are continuously formed on the back surface portion, and each prism body has a pair of slope portions and a ridge portion where the pair of slope portions intersect, and this ridge portion is set in parallel with the light incident end face portion. In this case, the light incident on the light guide plate can be temporarily emitted from the back surface portion to the outside of the light guide plate. As a result, by using a reflector or the like together, light with uniform illuminance can be emitted from the entire surface portion of the light guide plate.

  In particular, when the height of the slope portion of the prism body is set higher as the distance from the light incident end surface portion increases, the light from the back surface portion is temporarily emitted out of the light guide plate as the distance from the light incident end surface portion increases. The light is again incident on the light guide plate from the back surface portion, so that the light can be emitted more uniformly from the entire front surface portion.

  Similarly, when the distance between the adjacent prism bodies is set shorter as the distance from the light incident end face portion becomes shorter, the distance from the light incident end face portion causes light to be temporarily emitted from the back surface portion to the outside of the light guide plate. Light can be emitted more uniformly from the whole.

  Similarly, when the apex angle of the prism body formed by the pair of slope portions is set to be smaller as the distance from the light incident end face portion is increased, light can be emitted more uniformly from the entire surface portion.

  When at least one of the front surface portion and the back surface portion includes a large number of minute light deflecting elements randomly arranged, the light emitted from the front surface portion and the back surface portion can be deflected in a desired direction. Light with more uniform luminance can be emitted in a desired direction.

According to the backlight unit of the present invention, a plurality of partition grooves are formed on the back surface portion of the light guide plate so as to be spaced apart from each other in parallel, and each partition groove has a pair of slope portions and a ridge portion where the pair of slope portions intersect. And having one end of the ridge portion positioned at the light incident end surface portion, and the light source has a plurality of light emitting portions respectively arranged with respect to the light incident end surface portion of the light guide plate partitioned by the partition groove. The regions adjacent to each other function as a single light guide member. As a result, a light guide plate having a very small number of parts in a state in which a plurality of housings and reflectors are combined into one can be used for the backlight unit. In particular, it is possible to use as a backlight unit, such as OCB (O ptically C ompensated B irefringence or O ptically C ompensated B end) liquid crystal having a high response speed.

  When each light emitting portion includes at least three color semiconductor light emitting elements, it can be incorporated into a field sequential color liquid crystal image display device by switching emitted light having different emission colors at high speed.

  Embodiments in which the light guide plate according to the present invention is applied to a backlight unit incorporated in a field-sequential color liquid crystal display device will be described in detail with reference to FIGS. 1 to 8, but the present invention is limited to these embodiments. The present invention is not limited to this, and can be further combined as necessary, or can be applied to any other technique belonging to the spirit of the present invention.

  The appearance of the backlight unit in this embodiment is shown in FIG. 1 in an exploded state, the appearance of the back surface portion of the light guide plate is extracted and enlarged, and shown in FIG. 2, and the appearance of the light incident end face portion of the light guide plate is extracted and enlarged. FIG. 4 shows the sectional shape shown in FIG. That is, the backlight unit 10 in the present embodiment accommodates a single light guide plate 11, a light source unit 13 attached to the light incident end surface portion 12 of the light guide plate 11, and the light source unit 13 together with the light guide plate 11. A casing 14 as a light reflecting sheet of the present invention is provided.

  The light guide plate 11 having a rectangular plate shape includes a front surface portion 15 from which light is emitted, a back surface portion 16 located on the opposite side of the front surface portion 15, and a plurality of ( 4) in the illustrated example, and is for emitting light incident from the previous incident end surface portion 12 from the surface portion 15. In the present embodiment, the two opposing side surface portions 17 of these side surface portions 17 are used as the light incident end surface portion 12. However, when the intensity of light from the light source unit 13 is sufficient, or the surface portion 15 of the light guide plate 11. When the area is relatively small, only one of the side surface portions 17 may be used as the light incident end surface portion 12. In the present embodiment, the light incident end face portion 12 is formed with a flat surface, but it can also be formed with a cylindrical lens-shaped curved surface.

  On the surface portion 15 of the light guide plate 11, light deflection elements 18 (not shown) for deflecting light emitted from the surface portion 15 of the light guide plate 11 in a predetermined direction are randomly formed. As this optical deflection element 18, for example, those disclosed in Japanese Patent Application No. 11-102609, Japanese Patent Application No. 11-250713, Japanese Patent Application Laid-Open No. 2000-193826, Japanese Patent Application Laid-Open No. 2000-227522, etc. are used as they are. Is possible. These light deflecting elements 18 are arranged so that the distribution density thereof increases as the distance from the light incident end face portion 12, in other words, toward the central portion of the surface portion 15 is increased.

  On the back surface portion 16 of the light guide plate 11, a plurality of partition grooves 19 having a V-groove shape are formed in parallel with each other at predetermined intervals, and light incident from the incident end surface portion 12 is arranged in the arrangement direction of the partition grooves 19. Care is taken not to spread significantly along. Each partition groove 19 has a pair of slope portions 19a and a ridge portion 19b where the pair of slope portions 19a intersect. One end of the ridge portion 19b is located on the light incident end face portion 12 and the ridge portions 19b are mutually connected. They are arranged in parallel. The angle formed by the pair of inclined surfaces 19a, that is, the stagnation angle α is preferably an acute angle so that light propagating in the light guide plate 11 is totally reflected as much as possible. The depth of the partition groove 19 is preferably set as deep as possible as long as the strength required for the light guide plate 11 can be maintained. It can be set up to about 95%. The number of partition grooves 19 formed in the light guide plate 11 is the size of an image of one frame (generally corresponding to the area of the surface portion 15 of the light guide plate 11) and the liquid crystal display panel used. It is necessary to set based on the number of time divisions according to the response speed.

  The side surface portion 17 parallel to the ridge portion 19 b of the partition groove 19 has an inclined surface 17 a opposite to the inclined surface portion 19 a of the nearest partition groove 19, and the region of the light incident end surface portion 12 sandwiched between the partition grooves 19 Consideration is given so that the same function can be obtained in the region of the light incident end surface portion 12 between the inclined surface 19a and the inclined surface 17a of the partition groove 19 closest to the side surface portion 17. That is, the inclined surface portion 19a and the inclined surface 17a are composed of a region in which light incident from the light incident end surface portion 12 of the light guide plate 11 is surrounded by the inclined surface portion 19a and the inclined surface 17a adjacent thereto, and two adjacent ones. It mainly functions as a total reflection surface for light propagating in the light guide plate 11 so as to propagate in the region surrounded by the partition groove 19. In the present specification, a region surrounded by the inclined surface portion 19a and the inclined surface 17a adjacent thereto and a region surrounded by the two adjacent partition grooves 19 are referred to as individual illumination regions, and the partition described above. The groove 19 defines these individual illumination areas. This individual illumination area corresponds to an individual housing part in Patent Document 2.

  In addition, although the slope part 19a of the partition groove | channel 19 in this embodiment and the inclined surface 17a of the side part 17 are formed in the plane, they are formed in the curved surface continuous with respect to the back surface part 16, and are linear ridges. It is also possible to make the shape as shown in FIG. 5 without the portion 19b or the groove bottom. In particular, when the groove bottom of the partition groove 19 is formed with a curved surface, the bending strength of the light guide plate 11 along the direction orthogonal to the ridge portion 19b of the partition groove 19 can be increased.

  A plurality of V-groove prism bodies 20 perpendicular to the extending direction of the partition groove 19 are formed on the back surface portion 16 of the light guide plate 11 at a predetermined interval. The prism body 20 in this embodiment has a pair of slope portions 20a and ridge portions 20b where the pair of slope portions 20a intersect, and the ridge portions 20b are set in parallel to the light incident end face portion 12, respectively. These prism bodies 20 mainly function as windows, that is, openings, for temporarily emitting the light incident from the light incident end surface portion 12 of the light guide plate 11 from the back surface portion 16. For this reason, in this embodiment, the distance between the adjacent prism bodies 20 is set to be shorter as it is farther from the light incident end surface portion 12, and the light emitted from the central portion of the surface portion 15 of the light guide plate 11 farthest from the light incident end surface portion 12. By forcibly increasing the ratio, the light emission distribution from the surface portion 15 along the longitudinal direction of the partition groove 19 is considered to be uniform.

  If the light emission distribution from the surface portion 15 along the longitudinal direction of the partition groove 19 can be made uniform, it can be set at equal intervals as shown in FIG. In the embodiment shown in FIG. 6, the angle formed by the pair of slope portions 20a, that is, the stagnation angle β is set to be smaller as the prism body 20 is farther from the light incident end face portion, and the depth of the slope portion 20a is set. Is set deeper as it is located farther from the light incident end face portion 12, but is preferably set shallower than the depth of the partition groove 19 described above. In addition, as shown in FIG. 7, the prism body 20 can be formed on the back surface portion 16 in parallel with the partition groove 19. In this case, you may make it form the slope part 20a of the adjacent prism body 20 continuously.

  It is also possible to form the prism body 20 in a triangular prism shape protruding from the back surface portion 16 instead of the V groove shape recessed from the back surface portion 16.

  The light source unit 13 disposed so as to face the light incident end surface portion 12 of the light guide plate 11 includes the light incident end surface portion 12 sandwiched between the inclined surface 17a and the partition groove 19 of the side surface portion 17 and the partition grooves 19 adjacent to each other. For each individual illumination area, each has a plurality of light emitting sections 22 each including a set of at least three LEDs 21 each emitting red light, green light, and blue light toward the light guide plate 11. When the length of the light guide plate 11 along the extending direction of the partition groove 19 is relatively short with respect to the amount of light of the LEDs 21, the light emitting part 22 is arranged with only one side face part 17 as the light incident end face part 12. However, in order to increase the amount of emitted light and the luminance, it is effective to arrange the light emitting unit 22 with the pair of side surface portions 17 facing each other as the light incident end surface portion 12 as in the present embodiment. In order to increase the amount of emitted light, it is also effective to add a white LED that emits white light in addition to at least three pairs of LEDs 21 that respectively emit red light, green light, and blue light.

  The casing 14 having a rectangular frame shape functions as a light reflecting surface for reflecting light by the inner wall 14a. The light reflecting surface is optically rough and has a function of weakening the directivity of the reflected light. Therefore, the light emitted from the portion other than the surface portion 15 of the light guide plate 11 is diffusely reflected by the inner wall 14a of the casing 14, enters the light guide plate 11 again, and finally exits from the surface portion 15. It becomes. The entire back surface 16 of the light guide plate 11 including the partition groove 19 and the prism body 20 can be vapor-deposited with a light reflecting film. In this case, the inner wall 14a of the casing 14 has a light reflecting function. The casing 14 itself can be omitted in some cases.

  When such a backlight unit 10 is incorporated in a field sequential type color liquid crystal display device, a liquid crystal display panel (not shown) decomposes a color image of one frame into a red image, a blue image, and a green image, and corresponding pixels. Since it is used as a simple liquid crystal shutter that opens and closes, an OCB liquid crystal capable of high-speed response can be used, and high definition of pixels can be achieved at the same time.

  FIG. 8 shows a timing chart of the liquid crystal display device in this embodiment. This schematically shows a timing chart in the first block when the screen of the liquid crystal display device is divided into, for example, 10 blocks corresponding to the positions of the partition grooves 19 of the light guide plate 11. That is, the LEDs 21 are sequentially turned on for each light emitting unit 22 in a field sequential manner in synchronization with the liquid crystal gate pulse of the liquid crystal display panel. In this embodiment, a color image of one frame is generated every 16.67 milliseconds, and this is decomposed into a red image, a blue image, and a green image, and each image for each color is divided every 5.56 milliseconds. The LED 21 of each light-emitting unit 22 in the individual illumination area of the 10-block liquid crystal display panel is sequentially driven every 5.56 milliseconds so that it can be combined and displayed as a color image of one frame. When attention is paid to one light emitting unit 22, the LED 21 emitting red light in synchronization with the liquid crystal gate pulse of the liquid crystal display panel in the block is lit every 1.00 millisecond every 16.67 milliseconds. The LED 21 that emits green light after 56 milliseconds is turned on every 1.00 millisecond with a period of 16.67 milliseconds, and the LED 21 that emits blue light after another 5.56 milliseconds is 1 with a period of 16.67 milliseconds. Lights up for .00 milliseconds. The liquid crystal constituting each block of the liquid crystal display panel corresponding to the light emitting unit 22 is scanned and driven as a liquid crystal gate pulse by 0.556 milliseconds with a period of 5.56 milliseconds, but in each field per block. Each gate scan time is set to complete in 0.556 milliseconds.

  Although it is ideal that the liquid crystal responds accurately to the data signal, as a practical matter, the opening of the liquid crystal shutter according to the magnitude of the data signal depends on the change in the magnitude of the data signal. There is a tendency for operation delay to occur. For this reason, in this embodiment, the operation timing of the liquid crystal is anticipated, and the lighting timing of the corresponding LED 21 is delayed by a predetermined time in advance with respect to the driving timing of the liquid crystal gate pulse. About 4.00 milliseconds after the pulse output).

  In any case, when attention is paid to one light emitting unit 22, red light, green light, and blue light LEDs 21 correspond to the response speed of the liquid crystal shutter used in the corresponding liquid crystal display panel every 5.56 milliseconds. After the liquid crystal gate pulse is output, the lights are sequentially turned on. In the present embodiment, illumination lights of different colors are emitted simultaneously by the individual light emitting sections 22 in a plurality of blocks. However, these illumination lights are separated by the partition grooves 19 that define the individual illumination areas. There is no fear of color mixing on the liquid crystal display panel side, and an image with high definition can be formed.

  It should be noted that the present invention should be construed only from the matters described in the claims, and in the above-described embodiment, all the changes and modifications included in the concept of the present invention are other than those described. Is possible. That is, all matters in the above-described embodiment are not intended to limit the present invention, and include any configuration not directly related to the present invention. To get.

It is the stereographic projection figure showing the external appearance of one Embodiment of the backlight unit by this invention in a decomposition | disassembly state. FIG. 3 is a three-dimensional projection view in which a part of the external appearance of the light guide plate of the backlight unit shown in FIG. It is a front view of the light-guide plate of the backlight unit shown in FIG. FIG. 4 is a cross-sectional view taken along arrow IV-IV in FIG. 3. It is the front view which extracted and expanded some other embodiments of the light-guide plate by this invention. It is sectional drawing corresponding to FIG. 4 in further another embodiment of the light-guide plate by this invention. It is the front view which extracted and expanded a part of another embodiment of the light-guide plate by this invention. 2 is a timing chart illustrating an example when the backlight unit illustrated in FIG. 1 is driven by a field sequential method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Backlight unit 11 Light-guide plate 12 Light-incidence end surface part 13 Light source unit 14 Casing 14a Inner wall 15 Front surface part 16 Back surface part 17 Side part 17a Inclined surface 18 Light deflection element 19 Partition groove 19a Slope part 19b Ridge part 20 Prism body 20a Slope part 20b Ridge 21 LED
22 Light emitting part α, β Angle formed by a pair of slopes (stagnation angle)

Claims (11)

A front surface portion from which light is emitted; a back surface portion positioned on the opposite side of the front surface portion; and a plurality of side surface portions positioned between the front surface portion and the back surface portion, wherein at least one of the side surface portions is the surface portion. A light guide plate that is a light incident end face portion on which light for emitting light is incident,
A pair of slope portions and a ridge portion where the pair of slope portions intersect, and one end of the ridge portion is positioned on the light incident end surface portion, and the ridge portions are arranged in parallel with each other. A light guide plate, further comprising a plurality of partition grooves formed.   2. The light guide plate according to claim 1, wherein the side surface portion parallel to the ridge portion of the partition groove includes an inclined surface opposite to a slope portion of the most recent partition groove.   The light guide plate according to claim 2, wherein the inclined surface of the partition groove and the inclined surface of the side surface portion are formed as a flat surface or a curved surface.   The back surface portion has a pair of slope portions and a ridge portion where the pair of slope portions intersect, and is formed in a continuous state on the back surface portion so that the ridge portion is parallel to the ridge portion of the partition groove. The light guide plate according to claim 1, further comprising a plurality of prism bodies.   The back surface portion includes a pair of slope portions and a ridge portion where the pair of slope portions intersect, and the ridge portion includes a plurality of prism bodies formed so as to be parallel to the light incident end face portion. The light guide plate according to any one of claims 1 to 3.   The light guide plate according to claim 5, wherein a height of the slope portion of the prism body is set to be higher as the distance from the light incident end surface portion is increased.   The light guide plate according to claim 5 or 6, wherein an interval between the adjacent prism bodies is set to be shorter as the distance from the light incident end face portion is increased.   8. The light guide plate according to claim 5, wherein a stagnation angle formed by the pair of slope portions of the prism body is set to be smaller as the distance from the light incident end surface portion is increased.   The light guide plate according to any one of claims 1 to 3, further comprising a large number of light deflection elements randomly formed on at least one of the front surface portion and the back surface portion. A backlight unit incorporated in a field sequential type color liquid crystal display device,
The light guide plate according to any one of claims 1 to 9,
A light reflecting sheet covering a portion other than the surface portion of the light guide plate and the light incident end face portion;
A light source unit having a plurality of light emitting portions arranged so as to face the light incident end face portions partitioned by the partition grooves of the light guide plate and emitting light guided into the light guide plate. Characteristic backlight unit.   The backlight unit according to claim 10, wherein each of the light emitting units includes at least a semiconductor light emitting element of at least red light, blue light, and green light.

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