JP2021051963A - Planar light unit - Google Patents

Abstract

To provide a planar light unit which can express a high-quality image with no light emission unevenness by facilitating local dimming by making the directivity of light emitting elements arranged corresponding to a plurality of pixels constituting a display panel adjustable so that it becomes substantially a square shape.SOLUTION: A planar light unit includes: a substrate; a light emitting element 13 arranged on the substrate; a diffusion plate arranged above the light emitting element 13; and a prism sheet 17 arranged above the diffusion plate, and having a plurality of prism lines 17c. The light emitting element 13 has directivity in the shorter direction and the longer direction, and in each directivity, a light distribution pattern D2 becomes substantially a square shape by adjusting the direction of the prism sheet 17 in which the plurality of prism lines 17c are formed.SELECTED DRAWING: Figure 7

Description

The present invention relates to a direct type planar light unit using an LED as a light source.

A planar light unit using a light emitting element (LED) as a direct type backlight on the back surface of a liquid crystal panel is used in a liquid crystal display device used for a liquid crystal television, a car navigation system for a vehicle, or the like. Such a planar light unit includes LEDs that are a plurality of point-shaped light sources arranged on a substrate, and a diffuser plate and a prism sheet arranged above the LEDs (Patent Document 1).

In the liquid crystal display device having the above configuration, when the light emitted from directly above the LED, which is a point light source, passes through the prism sheet, the obliquely incident light is refracted in the direction directly above by a plurality of prism lines and emitted. , Create bright areas at multiple locations separated from directly above the light source. Therefore, the light is diffused by the diffusing plate using the bright part generated at a plurality of places as a pseudo light source, so that the brightness unevenness can be reduced over a wide range and the appearance can be improved.

Japanese Unexamined Patent Publication No. 2010-123551

By providing a prism sheet as in the liquid crystal display device, it is possible to reduce uneven brightness of light emitted from a plurality of LEDs. Since each LED controls the contrast and the like in units of a plurality of pixels formed on the display panel by local dimming, a substantially square directivity without bias is required. However, the shape of the LED may be rectangular with a lateral direction and a longitudinal direction depending on its structure, terminal arrangement, etc., and if the prism sheet is not arranged according to the shape, the display in pixel units will vary. There was a problem that local dimming became difficult.

Therefore, the problem to be solved by the present invention is that local dimming can be achieved by making it possible to adjust the directivity of the light emitting elements arranged corresponding to the plurality of pixels constituting the display panel so as to have a substantially square shape. An object of the present invention is to provide a planar light unit capable of easily expressing a high-quality image without uneven light emission.

The present invention includes a substrate, a light emitting element arranged on the substrate, a diffuser plate arranged above the light emitting element, and a prism sheet arranged above the diffuser plate and having a plurality of prism lines. In the planar light unit, the light emitting element has directivity in the lateral direction and the longitudinal direction, and each directivity is arranged by adjusting the orientation of the prism sheet on which the plurality of prism lines are formed. The light pattern is adjusted to be substantially square.

According to the planar light unit of the present invention, by adjusting the direction of the prism line of the prism sheet and the arrangement position of the light emitting element, a substantially square shape corresponding to a plurality of pixel units constituting a display panel such as a liquid crystal is formed. A light distribution pattern can be obtained. This facilitates local dimming and allows the display panel to display still images and moving images with optimum contrast.

It is an exploded perspective view of the planar light unit of 1st Embodiment. It is sectional drawing of the planar light unit of the said 1st Embodiment. It is a perspective view of a prism sheet. (A) is a plan view showing the directivity of the LED corresponding to a pixel, and (b) is a plan view of a prism sheet having a plurality of prism lines. FIG. 4 is a cross-sectional view of FIG. (A) A plan view of the LED, (b) a directivity diagram in the lateral direction of the LED, and (c) a directivity diagram in the longitudinal direction of the LED. It is a top view of the planar light unit adjusted to the directivity of a square shape by a prism sheet. (A) A diagram showing the directivity when the LED is arranged so as to be parallel to the prism line, and (b) Directivity when the LED is arranged so as to be orthogonal to the prism line. It is a figure which shows. It is an exploded perspective view of the planar light unit of the 2nd Embodiment. It is a top view of the planar light unit of the 2nd Embodiment.

Hereinafter, embodiments of the planar light unit according to the present invention will be described in detail with reference to the drawings. The drawings schematically represent the planar light unit of the present invention. The dimensions and dimensional ratios of these physical objects do not always match the dimensions and dimensional ratios on the drawings. Further, the duplicate description may be omitted as appropriate, and the same member may be given the same reference numeral. Furthermore, it should be noted that the technical scope of the present invention is not limited to the embodiments described below, but extends to the inventions described in the claims and their equivalents.

1 and 2 show the configuration of the planar light unit 11 according to the first embodiment of the present invention. The planar light unit 11 includes a rectangular substrate 12 made of resin, metal, alloy, or the like, and a plurality of light emitting elements (LEDs) 13 mounted on the upper surface of the substrate 12 by a die bond, a wire bond, a flip chip, or the like. A diffuser plate 14 arranged above the LED 13 facing the LED 13 and a prism sheet 17 arranged above the diffuser plate 14 are provided. Further, the planar light unit 11 includes a reflective sheet 15 that is in close contact with the upper surface of the substrate 12. The reflective sheet 15 has an opening 16 in a portion corresponding to the LED 13 mounted on the substrate 12. The opening 16 is formed to be larger than the planar shape of the LED 13 and substantially similar to the planar shape so as not to interfere with the light emitted upward from the light emitting surface of the LED 13. The substrate 12, the LED 13, the diffusion plate 14, the reflective sheet 15, and the prism sheet 17 are housed in a box-shaped back case 19, and are unitized by covering the frame-shaped front case 20 from above.

The diffuser plate 14 is made of a translucent base material such as frosted glass, and is arranged above the substrate 12 so as to cover a plurality of LEDs 13 arranged on the upper surface of the substrate 12. A predetermined diffusion pattern 14a corresponding to each LED 13 is formed on the diffusion plate 14. The diffusion plate 14 is supported by a resin frame 21 arranged on the peripheral edge of the substrate 12 so as to face the substrate 12 at a predetermined distance.

The light diffused by the diffuser plate 14 is adjusted to the directivity so that the prism sheet 17 has a desired viewing angle. As shown in FIG. 3, the prism sheet 17 is formed of a polyester base material 17a and an acrylic resin 17b formed on the polyester base material 17a and composed of a plurality of prism lines 17c having a triangular cross section. .. Each prism line 17c extends linearly in one direction at a predetermined pitch P. The pitch P is set to about 50 μm. As such a prism sheet 17, for example, a BEF (Brightness Enhancement Film: trade name) sheet manufactured by Sumitomo 3M Ltd. can be adopted.

As shown in FIG. 2, the planar light unit 11 having the above configuration is used as a backlight source for the display panel 18 arranged above the planar light unit 11. As the display panel 18, a flat panel formed of a liquid crystal, an organic EL, or the like is used. This flat panel is formed by an aggregate of a plurality of pixels (not shown), and is entirely divided into several square-shaped local dimming regions 18a as shown in FIGS. 4 (a) and 5 (a). .. An LED 13 is arranged in each local dimming area 18a.

As the LED 13, a thin and small LED 13 is used in response to the thinning of the planar light unit 11. Since the anode terminal connection portion, the cathode terminal connection portion, the semiconductor chip, and the like are arranged in a rectangular shape inside the LED 13, as shown in FIG. 6A, the LED 13 is composed of a lateral direction L1 and a longitudinal direction L2. It has a rectangular shape. FIG. 6B shows the directivity of the LED 13 in the lateral direction L1, and FIG. 6C shows the directivity of the LED 13 in the longitudinal direction L2. In this embodiment, as an example, a top light emitting LED (manufactured by Citizen Electronics Co., Ltd.) having one element, a single white light emitting, a size of 2.5 mm in length, 1.4 mm in width, and 0.75 mm in height was used. In the LED 13 of this embodiment, as described above, since the lengths of the lateral direction L1 and the longitudinal direction L2 are different, the lateral direction L1 tends to be wide and the longitudinal direction L2 tends to have a narrow rectangular directional characteristic. It is in. When the local dimming region 18a is irradiated with the LED 13 having both directivities, as shown in FIG. 4A, an elliptical light distribution pattern D1 is obtained, and a plurality of pixel units constituting the display panel 18 are obtained. In some cases, the contrast and the like may vary, and the quality of the image or the like displayed on the display panel 18 may deteriorate. In the present invention, this problem is solved by using the prism sheet 17 described later.

The resolution of the display panel 18 can be increased by increasing the number of pixels. For example, by dividing a pixel having a normal resolution into one square and dividing it into four evenly, the number of squares having a quarter size becomes four, and the overall resolution can be improved. At this time, if the directivity of the LED 13 that irradiates the pixels before division is square, it is relatively easy to convert from here to small square pixels having the same ratio. However, if the directivity of the LED 13 that irradiates the pixel before the division is rectangular as shown in FIGS. 4A and 6, the local dimming adjustment when the pixel is divided into a plurality of small pixels can be adjusted. It gets complicated.

In this way, in increasing the resolution of the display panel 18, due to the ease of calculation when dividing a pixel into a plurality of blocks, one square, four squares that are four times as large as that, and one square that is twice as large as that square. In many cases, there are eight squares that are eight times as large as a square, and 16 squares that are twice as large as one square. The resolution of many displays currently in use is a multiple of 4, such as 7680 pixels wide x 4320 pixels high for 8k TVs, 3840 pixels wide x 2160 pixels high for 4k TVs, 1920 pixels wide x 1080 pixels high for 2k TVs. Therefore, it is generally considered that the pixels are divided into squares.

In the present invention, in order to improve the problem corresponding to such adjustment of local dimming on a pixel-by-pixel basis, the orientation of the LED 13 shown in FIG. 4 (a) is oriented with respect to the arrangement of the LED 13 shown in FIG. 4 (a). A prism sheet 17 having a prism line 17c was arranged. As a result, the directivity in the lateral direction and the longitudinal direction changes, and as shown in FIG. 7, a substantially square light distribution pattern D2 corresponding to the local dimming region 18a composed of a plurality of pixels can be obtained. In this way, by arranging the prism sheets 17 in a direction in which the plurality of prism lines 17c are orthogonal to the longitudinal direction of the LED 13, the directivity in the lateral direction and the longitudinal direction of the LED 13 can be polarized respectively. As a result, local dimming of a plurality of pixels on the display panel 18 becomes easy, and an image can be displayed with an optimum contrast.

FIG. 8 compares the directivity in the relationship between the prism line 17c and the orientation of the LED 13 by a simulation using LightTools manufactured by SYNOPSYS. The LED 13 used as a light source was a top light emitting LED shown in FIG. 6, and the prism sheet 17 was a BEF (Brightness Enhancement Film: trade name) sheet manufactured by Sumitomo 3M Ltd. One LED 13 was arranged at the center of the prism sheet 17. Further, the distance from the prism sheet 17 was set to 3.0 mm, and the illuminance in the range of 20 mm around the LED 13 was measured.

FIG. 8A shows the LED 13 arranged so that the longitudinal direction is parallel to the prism line 17c. In this case, since the LED 13 has a directivity that spreads in the lateral direction, the light distribution pattern has an elliptical shape with respect to the local dimming region 18a set in a square shape.

On the other hand, as shown in FIG. 8B, if the LED 13 is arranged so that the longitudinal direction is orthogonal to the prism line 17c, the directivity in the lateral direction is suppressed, so that the LED 13 has a substantially square shape. A spreading light distribution pattern D2 can be obtained.

The plurality of pixels constituting the display panel 18 are the minimum units such as color information of the displayed image. Therefore, as shown in FIG. 8B, the light distribution pattern of the local dimming region 18a corresponding to each LED 13 is made substantially square, so that the contrast and the like can be easily controlled, and the overall display quality can be improved. Can be improved.

Further, as shown in FIG. 2, the directivity characteristic of the LED 13 itself can be adjusted by the diffusion pattern 14a formed on the diffusion plate 14. By further adjusting the directivity adjusted by the diffusion pattern 14a via the prism sheet 17, it becomes easy to make the light distribution pattern D2 closer to a square shape. In this way, by combining with the diffusion pattern 14a, the processing accuracy of the prism line 17c formed on the prism sheet 17 can be complemented, and the cost and man-hours required for adjustment can be reduced.

The structure of the diffusion pattern 14a may be an aggregate of fine dots. In particular, when a minute-sized dot that is almost invisible to humans is used as the diffusion pattern 14a, a natural gradation effect can be obtained, and the in-plane uniformity of light irradiation of the planar light unit 11 is further improved. The micro-sized dots preferably have a diameter of 0.35 mm or less, preferably 0.087 mm or less in diameter, and more preferably 0.058 mm or less in diameter.

FIG. 9 shows the configuration of the planar light unit 11'of the second embodiment of the present invention. The planar light unit 11'has a circular shape as a whole. Since the configuration is a circular shape of each component shown in FIG. 1, detailed description thereof will be omitted. FIG. 10 shows a configuration of a substrate 12'in which a plurality of LEDs 13 can be arranged along the outer peripheral edge of a circle and a circular prism sheet 17'in place of the rectangular substrate 12 in FIG. 7, and a light distribution pattern thereof. It shows D2. As shown in FIG. 10, even if it has a circular shape, it can be arranged so that the spacing X1 in the X direction and the spacing Y1 in the Y direction of the adjacent LEDs 13 are substantially equal. Further, the light distribution pattern D2 of each LED 13 can be adjusted to have a square shape depending on the orientation of the LED 13 and the orientation of the prism line 17c of the prism sheet 17. As a result, the visibility and appearance do not change even if the viewing angle is rotated by 90 degrees. Therefore, it is suitable as a display device for watch-type wearable devices and the like. Since such wearable devices are frequently used outdoors, visibility in sunlight is required, but it is sufficient because a plurality of LEDs 13 are evenly arranged in a circular space. Brightness can be ensured.

The prism sheet 17 used in the present embodiment is formed by cutting a large-sized sheet material in which a plurality of grooves serving as prism lines are formed in one direction to a size capable of forming a plurality of planar light units 11. be able to. Then, as shown in FIG. 4, the prism sheet 17 cut to substantially the same size as the planar light unit 11 is arranged according to the orientation of the LED 13. If the size of the sheet material of the prism sheet 17 and the size of the planar light unit 11 are not an integral multiple, cutting the sheet material will generate a surplus, but if the direction of the LED 13 is rotated by 90 °, the groove directions will differ by 90 °. A sheet can be formed. As a result, the cost can be reduced without wasting the sheet material. That is, adjusting the orientations of the LED 13 and the prism sheet 17 to make the light distribution pattern substantially square contributes to the effective use of the prism sheet. Even if the orientation of the LED 13 with respect to the substrate is not an accurate 90 ° or 180 °, for example, an angle of about 45 °, a light distribution pattern having a substantially square shape can be obtained.

In each of the above embodiments, the prism sheets 17 and 17'are formed according to the shapes of the substrates 12 and 12', but the prism sheet may be arranged only above the LED 13. Alternatively, the prism line 17c formed on the prism sheet may be formed only above the LED 13. In this way, by providing the prism sheet or the prism line only above the LED 13, the directivity can be changed for each LED 13, and a substantially square light distribution pattern can be obtained. As a result, the number of prism sheets and prism lines in the portion where the LED 13 is not arranged can be reduced, and the cost can be reduced.

As described above, when the LED 13 is arranged on the outer periphery of the display area of the planar light unit 11, the directivity may not be square but rectangular like the shape of the LED 13. In such a case, the arrangement of the LED 13 must be adjusted to a position corresponding to the directivity, but the prism sheet 17 makes the directivity closer to a square shape, which facilitates the design. That is, by making the directivity substantially square, it becomes easy to control the contrast and the like, and the effect of improving the display quality as a whole can be obtained.

D1, D2 Light distribution pattern 11 Planar light unit 12 Board 13 LED (light emitting element)
14 Diffusion plate 14a Diffusion pattern 15 Reflective sheet 16 Opening 17 Prism sheet 17a Polyester base material 17b Acrylic resin 17c Prism line 18 Display panel 18a Local dimming area 19 Back case 20 Front case 21 Resin frame

Claims (5)

A planar light unit including a substrate, a light emitting element arranged on the substrate, a diffuser plate arranged above the light emitting element, and a prism sheet arranged above the diffuser plate and having a plurality of prism lines. In
The light emitting element has directivity in the lateral direction and the longitudinal direction, and the light distribution pattern has a substantially square shape by adjusting the direction of the prism sheet on which the plurality of prism lines are formed. A planar light unit that is adjusted to be. The planar light unit according to claim 1, wherein the prism sheet is arranged so that the prism lines are orthogonal to either the lateral direction or the longitudinal direction of the light emitting element, whichever is narrower in directivity. The planar light unit according to claim 1 or 2, wherein a plurality of prism lines are formed in parallel at a predetermined pitch. The planar light unit according to claim 1 or 2, wherein a display panel composed of an aggregate of a plurality of pixels is arranged above the prism sheet, and the light emitting element is arranged corresponding to each pixel. The planar light unit according to claim 4, wherein the prism sheet is adjusted in the direction of the prism lines so that the light distribution pattern by the light emitting element has a substantially square shape corresponding to the pixels.

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