JP2007188645A - Backlight unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight unit improved in display quality in the vicinity of a light source by efficiently taking the light from the light source into a light guide plate. <P>SOLUTION: In the backlight unit 40 constituted of an LED 20 and a light guide plate 30, the incident end face 31 of the light guide plate 30 facing the LED 20 is constructed of a rough surface of crimp-like in rounded shape. The roughness of the rough surface in the incident end face 31 is not uniform and the face in nearly parallel to the LED 20 is made roughest, and the roughness of the face most inclined to the LED 20 side is made smallest. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a backlight unit used for a mobile phone, a vehicle-mounted display, and the like. In detail, it is related with the backlight unit which improved the display quality of the light source vicinity.

  In general, a mobile phone, an in-vehicle display, and the like display a desired screen by an LCD (Liquid Crystal Display). Such a cellular phone or the like is provided with a backlight unit on the back of the LCD in order to display a screen even in a dark place.

  Such a backlight unit is required to emit light uniformly over the entire screen.

Therefore, conventionally, in an illuminating device having a light emitting diode, a light guide, and a lens, the lens is arranged so that the light emission boundary line from adjacent light emitting diodes intersects with the outer edge line shape of the effective light emitting area in the light emitting surface. Is disclosed in which the size or the curved shape thereof is set (for example, Patent Document 1 below).
Japanese Laid-Open Patent Publication No. 10-260404

  However, in the above prior art, since the effective light emitting area is located away from the light emitting diode, the light guide does not enter into a small casing such as a mobile phone, and the size of the light guide is large. I had to take a large casing.

  Further, when the size of the LCD is extended to the entire light guide, the light emitting regions do not intersect with each other in the light guide near the light emitting diode, and a dark place is generated. Therefore, a dark place is generated in the vicinity of the light emitting diode, and the display quality is not necessarily good.

  Accordingly, the present invention has been made in view of the above problems, and an object thereof is to provide a backlight unit in which light from a light source is efficiently taken into a light guide plate and display quality in the vicinity of the light source is improved.

  In order to achieve the above object, the present invention provides a backlight unit including a light emitting diode and a light guide plate that emits light point-emitted from the light emitting diode over the entire surface, the light guide plate facing the light emitting diode. And an R-shaped light incident end surface, and the light incident end surface is formed of a rough surface so as to scatter the light from the light emitting diode.

  Further, the present invention is characterized in that, in the backlight unit, the roughness of the rough surface of the light incident end surface is changed.

  Furthermore, the present invention provides the backlight unit, wherein the light incident end surface is composed of a plurality of surfaces such that the surface is inclined from the first surface substantially parallel to the light emitting surface of the light emitting diode toward the light emitting diode. Each of the plurality of surfaces is constituted by the rough surface, and the roughness of the rough surface is gradually reduced from the first surface.

  Furthermore, the present invention is characterized in that, in the backlight unit, a surface inclined to the light emitting diode side among the surfaces is the mirror surface having the least roughness.

  Furthermore, the present invention provides the backlight unit, wherein the light incident end surface is composed of a plurality of surfaces such that the surface is inclined from the first surface substantially parallel to the light emitting surface of the light emitting diode toward the light emitting diode. Each surface of the plurality of surfaces is constituted by the rough surface, and the roughness of the rough surface is substantially the same as each surface.

  Furthermore, the present invention is characterized in that, in the backlight unit, the light emitting diode is disposed inside the R shape of the light guide plate.

  ADVANTAGE OF THE INVENTION According to this invention, the backlight unit which took in the light from a light source efficiently to a light-guide plate, and improved the display quality of the vicinity of a light source can be provided.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing an external configuration of a display unit 1 to which the present invention is applied.

  The display unit 1 includes a reflection sheet 10, an LED (Light Emitting Diode) 20, an LED holding plate 21, a light guide plate 30, and an LCD (Liquid Crystal Display) 50. In the drawing, the uppermost LCD 50 is the position closest to the human viewpoint position.

  The LED 20, the LED holding plate 21, and the light guide plate 30 constitute a backlight unit 40.

  The reflection sheet 10 is located at the lowermost part and reflects the light leaking from the light guide plate 30 to illuminate the LCD 50. The reflective sheet 10 also has a function of illuminating the LCD 50 by reflecting sunlight when the mobile phone is used outside.

  The LED 20 is a light emitting element and serves as a light source that illuminates the LCD 50. The LED 20 has various shapes such as a horizontally long shape, a vertically long shape, and a square shape.

  The LED holding plate 21 holds the LEDs 20 such that the LEDs 20 are arranged along the side surfaces of the light guide plate 30.

  The light guide plate 30 is provided between the reflective sheet 10 and the LCD 50. The light guide plate 30 irradiates the entire surface of the LCD 50 by reflecting the light point-emitted from the LED 20 inside. Therefore, the light guide plate 30 has a wedge shape in which the thickness gradually decreases as the distance from the side surface on which the LED 20 is located, and a flat plate shape. A part of the light reflected by the light guide plate 30 is directed toward the reflection sheet 10, but is reflected by the reflection sheet 10 and irradiates the LCD 50.

  The light guide plate 30 includes an R-shaped light incident end face 31 at a position facing the LED 20. The light incident end surface 31 is a surface of the light guide plate 30 on which light emitted from the LEDs 20 enters the light guide plate 30, and is formed in a concave shape with respect to the light guide plate 30 as shown in FIG. 1.

  The LED 20 is arranged in this R shape as shown in FIG. Since the LEDs 20 are arranged inside the light guide plate 30, the display unit 1 can be arranged in a narrow housing such as a mobile phone.

  Further, in the display unit 1 of FIG. 1, a diffusion sheet or a lens sheet may be provided between the light guide plate 30 and the LCD 50.

  Next, the light incident end face 31 of the light guide plate 30 will be described in detail. In the present embodiment, the end surface 31 is formed of a rough rough surface. Incident light from the LED 20 is scattered in the light guide plate 30 by this rough surface. Therefore, since the scattered light passes through the entire light guide plate 30, no dark place is generated between the adjacent LEDs 20.

  FIG. 3A is a diagram illustrating an example of an optical path for incident light when the light incident end surface 31 of the light guide plate 30 is a mirror surface. The arrow indicates the optical path. The light emitted from the LED 20 enters the light guide plate 30 via the mirror surface. Although the optical path entering the light guide plate 30 depends on the refractive index of the mirror surface, the optical path is formed in a substantially straight line with respect to the incident light. Therefore, there is a region where the optical path does not reach between the adjacent LEDs 20, and the dark place 32 is generated.

  FIG. 3B is a diagram illustrating an example of an optical path for incident light when the light incident end surface 31 of the light guide plate 30 is formed into a rough rough surface. As in FIG. 3A, an arrow indicates an optical path. Incident light from the LED 20 is scattered by the rough surface in the light guide plate 30. Accordingly, since the optical path in the light guide plate 30 is formed in all directions, the dark place 32 does not occur between the LEDs 20. Therefore, display quality due to light and dark in the vicinity of the light source can be improved.

  In addition, since the shape of the light incident end face 31 is an R shape, the light emitted from the LED 20 is incident so as to be substantially orthogonal at any position on the light incident end face 31, and the probability that incident light is reflected is reduced. . Therefore, the light emitted from the LED 20 can be effectively guided to the light guide plate 30.

  In addition, by making the light incident end face 31 into an R shape, the distance between the light incident end face 31 and the LED 20 becomes very short, and the height is higher than that in the case of a semicircular shape as shown in FIG. The situation where the light emitted in the direction does not enter the light guide plate 30 can be avoided.

  When the grain-like rough surface in the present embodiment is viewed in detail, irregularities are present randomly, and further, there are fine crater-shaped irregularities on the irregularities. The light incident end face 31 having such a rough surface is formed by molding a mold by special processing.

  A simulation was performed on how light is scattered when the light incident end face 31 is formed into a rough rough surface. This result will be described below.

  In this simulation, the light incident end face 31 of the light guide plate 30 is divided into a plurality of areas, and how the light intensity changes in a plurality of patterns each having a rough surface with a different diffusion degree in each area is examined. It was. 4A and 4B show this condition.

  FIG. 4A is a diagram showing the positional relationship of each light incident surface area. That is, the light incident end face 31 is divided into four areas symmetrically. A surface substantially orthogonal to the light emitted from the LED 20 is defined as an input surface area 1, and a surface facing the LED 20 with an inclination of about “10 degrees” relative to the area 1 is defined as a light incident surface area 2. Further, a surface inclined about “20 degrees” with respect to the light incident surface area 2 is referred to as a light incident surface area 3, and a surface inclined further about “20 degrees” with respect to the light incident surface area 3 is referred to as a light incident surface area 4. .

  FIG. 4B is a diagram showing the relationship between each light incident surface area and the degree of diffusion in each pattern. The vertical axis represents the degree of diffusion, and the horizontal axis represents the light incident surface area.

  “Type A” is a type having a rough surface with the same diffusion degree “100%” in the light incident surface areas 1 to 4.

  “Type B” is a type having a rough surface with a diffusion degree of “100%” in the light incident surface area 1 and gradually decreasing in the light incident surface area 2 to 4.

  In “Type C”, the incident surface area 1 has a diffusion degree “100%”, and the diffusion degree gradually decreases toward the area 4, but the diffusion degree is lower than that of “Type B”. Has a rough surface.

  “Type D” and “Type E” are almost the same, and the degree of diffusion decreases toward the area 4, but “Type E” has the lowest ratio, and in the light incident surface area 4, the degree of diffusion is “0%”. (Substantially mirror surface).

  This simulation is a simulation of how the intensity of light changes in each type, that is, on the light incident end face 31 having different rough surfaces.

  The “diffusion degree” will be described. FIGS. 5A to 5C show examples thereof. The diffusion degree “100%” is a case where the incident light 70 is scattered by about “100%”. However, actually, “95%” of the reflected light 71 excluding “5%” is scattered in the light guide plate 30 as shown in FIG.

  Further, the diffusion degree “50%” is a case where “50%” is diffused in-plane with respect to the incident light 70 as shown in FIG. “5%” of the incident light 70 is reflected as reflected light 71, and the remaining “45%” travels straight through the light guide plate 30.

  Further, the diffusion degree “0%” is a case where the incident light 70 is not scattered in the plane as shown in FIG. “5%” of the incident light 70 is reflected as the reflected light 71, and “95%” travels straight through the light guide plate 30. It is almost the same state as the mirror surface.

  In other words, the “diffusion degree” is an index indicating the roughness of the surface, and the ratio of how much light that is orthogonal to the surface diffuses in the surface without going straight when entering the surface. It shows that.

  Next, the simulation result under such conditions will be described. FIG. 6 shows the light intensity (“cd”) at each angle (“deg”) of “Type A”. The vertical axis represents the light intensity, and the horizontal axis represents the angle. Here, as shown in FIG. 7, the angle is an angle with respect to the center line 33 of the light guide plate 30, and the clockwise direction in the drawing is “+” and the counterclockwise direction is “−”.

  As a comparison target, a case where all the light incident surface areas are mirror surfaces (diffuse degree “0%”) is shown. All mirror types are indicated by solid lines, and "Type A" is indicated by dotted lines.

  As shown in FIG. 6, in the vicinity of the angle “0”, the intensity of light is higher in all the mirror surfaces than in “Type A”. In other words, the intensity of the light traveling straight through the light guide plate 30 becomes larger when all the mirror surfaces are used.

  However, from the angle “40 degrees” to “50 degrees”, the light intensity of “Type A” gradually decreases, but in the case of all mirror surfaces, it decreases rapidly. The sharp drop in light intensity in this angular region causes light and darkness in human vision just near the light source.

  That is, when the light incident end face 31 of the light guide plate 30 is roughened with a diffusion degree of “100%”, the light intensity in the vicinity of the light source by the LED 20 is reduced more than when the light incident end faces 31 are all mirrored. Can be lowered. Therefore, the display quality of the image displayed on the LCD 50 in the vicinity of the light source is better when the rough surface is used than when the mirror surface is used.

  FIG. 8 is a simulation result showing the intensity of light with respect to each angle of “type B”. As described above, “Type B” is a type in which the surface substantially perpendicular to the incident light (light incident surface area 1) has the largest diffusion degree, and the degree of diffusion decreases as the surface is gradually inclined toward the LED 20 side. belongs to.

  Also in this case, the intensity of light changes gently in the region of the angle “40 degrees” to “50 degrees” as compared with the case where all are mirror surfaces. Accordingly, the display quality of the video in the vicinity of the light source is kept high.

  Compare this "Type B" with "Type A". Similarly, paying attention to the region from the angle “40 degrees” to “50 degrees”, the light intensity of “type B” is slightly higher than that of “type A”.

  That is, the intensity of light in this angular region is higher as “Type B” is higher. Therefore, even when the same number of LEDs 20 are present, the brightness near the light source is higher when the rough surface is gradually mirrored.

  This is because FIG. 9 shows the result of “type C”, FIG. 10 shows the result of “type D”, FIG. 10 shows the result of “type D”, and FIG. 11 shows the result of “type E”. The trend is clear when you look at.

  That is, the light intensity, that is, the luminance gradually increases in the region of the angle “40 degrees” to “50 degrees” where the light source exists as it becomes “type C”, “type D”, and “type E”. Go.

  The roughness of the rough surface of the light incident end face 31 is not uniform, and the diffusion degree of the surface (surface substantially parallel to the light emitting surface of the LED 20) in which the incident light from the LED 20 is substantially orthogonal is made highest (most roughened). The degree of diffusion of the surface is lowered (gradually lowering the roughness) as it is inclined to the side, and the degree of diffusion on the surface most inclined to the LED 20 side is made the lowest (by making the roughness the lowest) ), The luminance of light in the vicinity of the light source can be gradually increased.

  Since the brightness is high when a rough surface of “Type E” is used, the pitch between the LEDs 20 can be made wider than that of “Type A”. A constant light intensity can be obtained even when the pitches of the LEDs 20 are separated. Therefore, since the number of LEDs 20 can be reduced, the cost of the backlight unit 40, and thus the display unit 1, can be reduced. Such type of rough surface is preferably used for portable information terminals such as mobile phones and PDAs.

  On the other hand, even if a “type A” rough surface is used, the brightness increases by narrowing the pitch between the LEDs 20. In particular, although not shown in FIGS. 6 to 11, since the light from the adjacent LED 20 reaches the region of the angle “40 degrees” to “50 degrees”, a considerably high luminance is obtained as a whole.

  Therefore, in consideration of the light from the adjacent LED 20, even if a “type A” rough surface is used, the pitch can be narrowed to obtain a luminance sufficient to display an image such as a moving image on the LCD 50. . Such a rough surface is preferably used for a display of a car navigation device, for example.

  From the above, by making the light incident end face 31 of the light guide plate 30 rough, it is possible to improve the display quality by eliminating the brightness near the light source. Furthermore, by changing the roughness of the rough surface according to the angle of the surface, the luminance of the image displayed on the LCD 50 in the vicinity of the light source can be changed, and the display quality can be improved.

  In the above example, with respect to the positional relationship of the light incident surface area, the light incident surface area 2 is inclined by about “10 degrees” with respect to the light incident surface area 1, and the light incident surface area 3 is approximately equal to the light incident surface area 2. In the example described above, “20 degrees” and the light incident surface area 4 are inclined by about “20 degrees” with respect to the light incident surface area 3. Of course, each light incident surface of the light incident end surface 31 is not limited to this, and may be any angle as long as it can be gradually inclined toward the LED 20 side. Further, the number of the light incident surface areas is not limited to “4” in the above-described example, and may be any number as long as it is plural. In either case, the same operational effects as the above-described example are obtained.

  In the above-described example, the LED 20 has been described as being disposed on one side surface of the light guide plate 30. However, for example, the backlight unit 40 may be configured such that the LED 20 is disposed on both side surfaces. If there is an R-shaped textured rough surface at a position facing the LED 20, the same effect as the above-described example is achieved.

  This display unit is used for, for example, a display of a portable information terminal such as a mobile phone or a PDA, or an in-vehicle display such as a car navigation device.

FIG. 1 is a diagram illustrating an external configuration example of a display unit. FIG. 2 is a diagram showing an example in which LEDs are arranged on the light incident end face of the light guide plate. FIG. 3A shows an example of an optical path when the light incident end face is a mirror surface, and FIG. 3B shows an example of an optical path when the light incident end face is an R-shaped embossed surface. FIG. 4A is a diagram showing the positional relationship between each light incident surface area, and FIG. 4B is a diagram showing the relationship between each type of light incident surface area and the degree of diffusion. 5A shows an example of an optical path when the degree of diffusion is “100%”, FIG. 5B shows an example of an optical path of “50%”, and FIG. 5C shows an example of an optical path of “0%”. . FIG. 6 is a diagram showing the relationship between the angle of type A and the light intensity. FIG. 7 is a conceptual diagram for explaining the angle. FIG. 8 is a diagram showing the relationship between the angle of type B and the light intensity. FIG. 9 is a diagram showing the relationship between the angle of type C and the light intensity. FIG. 10 is a diagram showing the relationship between the angle of type D and the intensity of light. FIG. 11 is a diagram showing the relationship between the angle of type E and the light intensity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Display unit, 10 Reflective sheet, 20 LED (light emitting diode), 21 LED holding plate, 30 Light guide plate, 31 Light incident end surface, 32 Dark place, 33 Center line, 40 Backlight unit, 50 LCD, 70 Incident light, 71 reflected light

Claims (6)

In a backlight unit comprising a light emitting diode and a light guide plate that emits light point-emitted from the light emitting diode over the entire surface,
The light guide plate has an R-shaped light incident end face at a position facing the light emitting diode, and the light incident end face is formed of a rough surface so as to scatter the light from the light emitting diode. Backlight unit to be used.   The backlight unit according to claim 1, wherein the rough surface of the light incident end surface is configured to change its roughness.   The light incident end surface is composed of a plurality of surfaces such that the surface is inclined from the first surface substantially parallel to the light emitting surface of the light emitting diode toward the light emitting diode, and each surface of the plurality of surfaces is the rough surface. The backlight unit according to claim 2, wherein the backlight unit is configured so that the roughness of the rough surface gradually decreases from the first surface.   4. The backlight unit according to claim 3, wherein a surface inclined to the light emitting diode side among the surfaces is the mirror surface having the least roughness.   The light incident end surface is composed of a plurality of surfaces such that the surface is inclined from the first surface substantially parallel to the light emitting surface of the light emitting diode toward the light emitting diode, and each surface of the plurality of surfaces is the rough surface. The backlight unit according to claim 1, wherein the roughness of the rough surface is substantially the same for each of the surfaces.   The backlight unit according to claim 1, wherein the light emitting diode is disposed inside the R shape of the light guide plate.

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