JP2005235661A - Backlight - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase luminance by condensing the outgoing light from a backlight with a prism sheet. <P>SOLUTION: On the lower surface side of the prism sheet 4 of the backlight 1, prisms composed of two prism surfaces 4a and 4b parallel to the X-direction are continuously formed in the Z-direction. One prism surface 4a near to a light source among two prism surfaces is a flat surface, and the other prism surface 4b in the opposite direction of the light source is a curved surface where the longitudinal section of a lengthwise direction has a convex shape on the opposite side from the light source. As shown in the figure, the outgoing light from a light guide plate 3 of the backlight 1 is reflected on the prism sheet 4, condensed and travels in the Y-direction of an irradiation direction because the prism surface 4b of a convex shape makes the spread in the Z-direction narrower. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a backlight which is an illumination device that irradiates a small liquid crystal display used in a mobile phone, a PDA, or the like from the back.

  In recent years, backlights, which are illumination devices for small liquid crystal displays (hereinafter abbreviated as LCDs) such as mobile phones and PDAs, have been demanded for high brightness, high viewing angle, thinness, light weight, and low power consumption as well as cost reduction. Is getting tougher. As a light source of such a backlight, a light emitting diode (hereinafter abbreviated as LED) that consumes less power and generates less heat is used. The light emitted from the LED first enters from the side surface of the light guide plate, and is propagated by being repeatedly reflected in the light guide plate. And the light which came out from the lower surface of the light-guide plate is reflected by a reflection sheet, and is returned in a light-guide plate. Light reflected by a convex shape or a saw shape provided on the lower surface of the light guide plate is emitted from the upper surface of the light guide plate. The light emitted from the light guide plate changes its traveling direction depending on the prism sheet, and irradiates the LCD from the back side. Since the LED is a point light source, it is difficult to make the luminance uniform, and various ideas have been made to make the display easy to see by making the display surface bright without any unevenness in luminance (see, for example, Patent Document 1). .

  An example of such a conventional backlight will be described with reference to the drawings. FIG. 3 is a plan view and a side view of a conventional backlight. FIG. 4 is a ray tracing diagram of the light guide plate of the backlight. FIG. 5A is a luminance distribution diagram in the longitudinal section showing the directivity of the light guide plate, and FIG. 5B is a luminance distribution diagram in the sectional direction in the same manner. FIG. 6 is a ray tracing diagram from the light guide plate. FIG. 7A is a luminance distribution diagram of the longitudinal section showing the directivity of the illuminance of the backlight, and FIG. 7B is a luminance distribution diagram of the sectional view of the width direction.

  First, the configuration of the backlight will be described. In FIG. 3, 11 indicates an edge light type backlight, and 2 indicates an LED as a light source. Reference numeral 3 denotes a light guide plate, and a plurality of LEDs 2 are disposed in the vicinity of the end surface 3 a of the light guide plate 3. X indicates the width direction of the backlight 11, which is the arrangement direction of the LEDs 2, Y indicates the irradiation direction, and Z indicates the length direction perpendicular to X. Reference numeral 14 denotes a prism sheet in which a microprism composed of two prism surfaces 14 a and 14 b parallel to the X direction is formed continuously in the Z direction on the lower surface, and is disposed close to the upper surface 3 b of the light guide plate 3. . Reference numeral 5 denotes a reflection sheet, which is disposed close to the lower surface 3 c of the light guide plate 3. As shown in FIG. 4, on the lower surface 3c of the light guide plate 3, a slope having a narrow width of an angle α in the Z direction and parallel to the X direction is continuously formed in a step shape. The angle α is set in order to efficiently direct light from the light source toward the upper surface of the light guide plate.

Next, the operation of the backlight 11 will be described. As shown in FIG. 4, the light emitted from the LED 2 with an angle θ slightly downward in the Z direction enters the inside from the end surface 3 a of the light guide plate 3 and is totally reflected when the incident angle exceeds the critical angle and enters the lower surface 3 b. To the upper surface 3b. When the incident angle exceeds the critical angle and enters the upper surface 3b, the light is totally reflected and travels toward the lower surface 3c again. The light is repeatedly reflected on the lower surface 3c and the upper surface 3b, but the light whose incident angle is less than the critical angle due to the effect of the stepped slope is emitted upward from the upper surface 3b with the emission angle φ. The light emitted outward from the lower surface 3 c is returned into the light guide plate 3 by the reflection sheet 5. As shown in FIGS. 5A and 5B, the light emitted from the upper surface 3b of the light guide plate 3 is inclined in the length direction, and the spread of the light intensity is wide in the width direction. It is narrow and unbalanced in the vertical direction. As shown in FIG. 6, the light emitted from the light guide plate 3 in the Z direction is transmitted through the prism surface 14 a of the prism sheet 14, reflected by the prism surface 14 b, and the traveling direction is changed upward to change the upper surface of the prism sheet 14. To the back of the LCD (not shown).
JP 2003-59321 (FIG. 1, paragraphs 0012 to 0016)

  However, as described above, in the case where the prism sheet 14 having the conventional two-plane prism surface is used, the prism sheet 14 has only a function of changing the traveling direction of light. The directivity of the light 11 greatly depends on the directivity of the emitted light from the light guide plate 3 alone. That is, the light emitted from the light guide plate is not condensed, and the intensity becomes the luminance of the backlight 11 as it is. Therefore, as shown in FIGS. 7 (a) and 7 (b), the emitted light from the backlight travels vertically in the Y direction, that is, toward the LCD display surface, but does not collect light, resulting in insufficient brightness. There was a problem.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems and provide a backlight capable of increasing luminance by condensing light emitted from a light guide plate with a prism sheet.

  The means of the present invention for achieving the above-described object includes a light source that is a light emitting diode, a light guide plate in which the light source is disposed in the vicinity of the end surface, and a reflection sheet that is disposed in the vicinity of the lower surface of the light guide plate. And a prism sheet disposed close to the upper surface of the light guide plate, and a backlight for illuminating the liquid crystal display device from the back side, the lower surface of the prism sheet being in the width direction of the end surface of the light guide plate A microprism composed of two prism surfaces parallel to each other is formed continuously in the length direction of the light guide plate, and the prism surface facing the light source of the prism sheet is curved. In the backlight, the prism surface having the curved surface is characterized in that a longitudinal section in a length direction of the light guide plate has a convex shape opposite to the light source.

  Further, the prism surface facing the light source among the two prism surfaces of the prism sheet is a flat surface.

  According to the present invention, a light source that is a light emitting diode, a light guide plate in which the light source is disposed close to the end surface, a reflection sheet that is disposed in proximity to the lower surface of the light guide plate, and an upper surface of the light guide plate And a prism sheet arranged in proximity to the backlight for illuminating the liquid crystal display device from the back side, and the lower surface of the prism sheet includes two prism surfaces parallel to the width direction of the end surface of the light guide plate. In the backlight in which the microprism is formed continuously in the length direction of the light guide plate, and the prism surface facing the light source of the prism sheet is curved, the curved surface In the prism surface, the longitudinal section in the length direction of the light guide plate has a convex shape opposite to the light source, so that the range of the light traveling direction is narrowed on the curved surface. Since is it condenses, it is possible to increase the brightness of the backlight.

  Hereinafter, a backlight which is the best mode for carrying out the present invention will be described in detail with reference to the drawings. FIG. 1 is a ray tracing diagram from a light guide plate of a backlight according to an embodiment of the present invention. FIG. 2A is a luminance distribution diagram in the longitudinal section showing the directivity of the light emitted from the light guide plate, and FIG. 2B is a luminance distribution diagram in the same width direction.

  In FIG. 1, reference numeral 1 denotes a backlight which is an embodiment of the present invention. Reference numeral 4 denotes a prism sheet of the backlight 1. On the lower surface side of the prism sheet 4, microprisms composed of two prism surfaces 4 a and 4 b parallel to the X direction are continuously formed in the Z direction. Of the two prism surfaces 4a and 4b, the prism surface 4a close to the light source is a flat surface, and the prism surface 4b facing the opposite side of the light source has a longitudinal section that is convex to the opposite side of the light source. It is a curved surface. Since other configurations are the same as those of the conventional backlight, the same reference numerals and names are used for the same components, and detailed description thereof is omitted.

  Next, the operation of the embodiment of the present invention will be described. Since the configuration of the light guide plate 3 of the backlight 1 is the same as the conventional one, the luminance distribution is also as shown in FIGS. 5 (a) and 5 (b). When the light emitted from the light guide plate 3 is traced, as shown in FIG. 1, the incident light is incident on the prism surface 4a of the prism sheet 4 and reflected by the prism surface 4b to change the traveling direction. Head in the direction.

  The effect of the backlight 1 which is embodiment of this invention is demonstrated. The light emitted from the light guide plate 3 is incident on the prism surface 4b without being reflected because the prism surface 4a of the prism sheet 4 is flat, and is reflected by the convexity of the prism surface 4b when reflected by the prism surface 4b. The range in the length direction is narrowed. Therefore, as shown in FIG. 2A and FIG. 2B, the emitted light in the length direction of the backlight 1 is condensed and the luminance can be increased.

  The backlight of the present invention can be widely applied to small electronic devices such as mobile phones and PDAs.

It is a ray tracing figure in the prism sheet of the backlight which is embodiment of this invention. It is a luminance distribution figure of the section of the length direction which shows the directivity of the light guide plate which is an embodiment of the invention. It is a luminance distribution figure of the cross section in the width direction which shows the directivity of the light guide plate which is an embodiment of the invention. It is the top view and side view of the conventional backlight. It is a ray tracing figure in the light guide plate of the conventional backlight. It is a luminance distribution figure of the section of the length direction which shows the directivity of the conventional light guide plate. It is a luminance distribution figure of the cross section in the width direction which shows the directivity of the conventional light-guide plate. It is a ray tracing figure in the prism sheet of the conventional backlight. It is a luminance distribution figure of the section of the length direction which shows the directivity of the conventional backlight. It is a brightness | luminance distribution figure of the cross section in the width direction which shows the directivity of the conventional backlight.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Backlight 2 Light emitting diode 3 Light guide plate 3a End surface 3b Upper surface 3c Lower surface 4 Prism sheet 4a, 4b Prism surface 5 Reflective sheet X Width direction Z Length direction

Claims (2)

  A light source that is a light emitting diode, a light guide plate in which the light source is disposed close to the end surface, a reflection sheet that is disposed in proximity to the lower surface of the light guide plate, and a surface that is disposed in proximity to the upper surface of the light guide plate A prism sheet that illuminates the liquid crystal display device from the back side, and a microprism composed of two prism surfaces parallel to the width direction of the end face of the light guide plate is provided on the lower surface of the prism sheet. In the backlight which is formed continuously in the length direction of the optical plate and the prism surface facing the opposite side of the light source of the prism sheet is curved, the prism which is curved The surface is characterized in that the longitudinal section of the light guide plate in the longitudinal direction has a convex shape opposite to the light source. The backlight according to claim 1, wherein the prism surface facing the light source among the two prism surfaces of the prism sheet is a flat surface.

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