JP2007042402A - Lighting system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-directivity and easy-to-produce lighting system allowing easy increase of a luminance and easy equalization of illumination light. <P>SOLUTION: In this lighting system having point light sources and a light guide plate propagating light source light thereof, the light guide plate is formed in a nearly rectangular shape and is formed with grooves, the light sources are light-emitting diodes and are disposed in opposite corners of the light guide plate, and the grooves have ridgelines nearly orthogonal to an advancing direction of emission light of the light-emitting diodes after incidence on the light guide plate. The light guide plate is divided into upper and lower portions by a line connecting the vicinities of the light-emitting diodes disposed in the opposite corners, and the groove on the light guide plate of each the divided portion has a ridgeline nearly orthogonal to the advancing direction of the emission light of the light-emitting diode belonging to the portion. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an illuminating device used as a backlight or a front light of a light receiving display device such as a liquid crystal display device, and more particularly to an illuminating device for a small liquid crystal display such as a mobile phone or a PDA.

In recent years, lighting devices using light emitting diodes (hereinafter abbreviated as LEDs) as light sources have begun to be used because they have advantages such as long life and easy chromaticity adjustment of lighting device light compared to fluorescent display tubes.
3A and 3B are diagrams showing a conventional example when a sidelight type illumination device using a light emitting diode (hereinafter abbreviated as LED) is used as a backlight, wherein FIG. 3A is a plan view and FIG. 3B is a side view. .
The illuminating device in FIG. 3 has a plurality of LED light sources 60-1, 2, 3, 4 arranged on the side surfaces of a substantially rectangular parallelepiped light guide plate 68, and the emitted light from the LED light sources 60-1, 2, 3, 4 is guided. Incident on the light plate 68. A microprism, that is, a groove is formed on the light guide plate 68, and the ridge line connecting the apexes of the microprism is a plurality of LED light sources 60-1, 2, 3, 3, as indicated by a dotted line group 70 in FIG. It was made parallel to the side surface on which 4 is arranged.
As shown in FIG. 3B, the cross-sectional structure is such that the reflection sheet 80 is disposed on the lower surface of the light guide plate 68 and the prism sheet 78 is disposed on the upper surface, and the light guide plate 68, the reflection sheet 80, and the prism sheet 78 are accommodated in the holder 76. The light receiving display device such as a liquid crystal display device placed on the upper side is illuminated.

Light incident from the LED light sources 60-1, 2, 3, and 4 is propagated in the light guide plate 68 by being repeatedly refracted between the upper surface of the light guide plate 68 and the surface of the microprism provided on the lower surface of the light guide plate 68. As the propagation is repeated, the angle formed between the traveling direction of light and the upper surface of the light guide plate 68 becomes smaller than the critical angle, and light is emitted from the upper surface of the light guide plate 68. The light emitted to the lower surface of the light guide plate 68 is reflected by the reflection sheet 80 and returned to the light guide plate 68. The light emitted from the light guide plate 68 is bent by the prism sheet 78 and guided to the display device side.
In the following drawings, the same members are denoted by the same numbers.

However, there is a problem with such a sidelight type illumination device. The light is emitted from the LED light sources 60-1, 2, 3, and 4 in various directions defined by the respective light sources. For example, as shown in FIG. The light 74 thus formed has an angle α with respect to the direction 72 perpendicular to the ridge line 70 of the groove and is not orthogonal.
This situation will be further described with reference to FIGS.
FIG. 4 is a diagram in which the locus of light rays emitted from the LED light sources 60-2, 3 is added to the diagram of the light guide plate 68 and the LED light sources 60-1, 2, 3, 4 in FIG.
The emitted light from the LED light sources 60-1, 2, 3, and 4 that are point light sources needs to have a wide angle to some extent so as not to form a dark portion between the light sources. Further, the light incident on the light guide plate is refracted in the direction of spreading in the width direction of the light guide plate every time it is reflected by the groove. As a result, the light beams 82 and 84 that are substantially orthogonal to the ridge line 70 of the groove and the light beams 86 and 88 that are not orthogonal to the ridge line 70 of the groove are separated.
In this way, when the amount of light whose optical axis and ridge line pattern are not orthogonal to each other increases, it becomes close to the state where the light is scattered at the groove, and is guided among the light refracted at the groove and emitted to the upper surface of the light guide plate 68. The light component that is not perpendicular to the surface of the light plate 68 increases. Therefore, there is a problem that the directivity of the illumination light of the illumination device is deteriorated and the brightness of the illumination device cannot be increased.

This situation is shown in a graph in FIG.
FIG. 5A is a graph showing the optical characteristics of the conventional illumination device as shown in FIG. 3, and FIG. 5B is a diagram for explaining the coordinate axes.
As shown in FIG. 5B, the coordinate axes are the X axis in the vertical direction of the plane of the light guide plate 68, the Z axis in the horizontal direction, and the axes perpendicular to the top surface of the light guide plate 68 and orthogonal to the X axis and the Z axis. The Y axis is assumed. An angle formed between the direction Y ′ in which the illumination light is emitted from the light guide plate 68 and the Y axis is defined as a light emission angle θ.
When the coordinate axes are determined in this way and the optical characteristics of the conventional illumination device are graphed, the result is as shown in FIG.
The horizontal axis in FIG. 5A is the light emission angle θ, the vertical axis is the relative value of the light intensity, and the dotted thick line 90 in the figure is the relationship between the direction of the illumination light and the intensity of the illumination light in the XY plane, A solid thick line 92 indicates the relationship between the direction of the illumination light and the intensity of the illumination light in the ZY plane. Therefore, the point with the horizontal axis θ = 0 indicates the illumination light intensity in the direction orthogonal to the light guide plate 68, and the point θ = 90 indicates the illumination light intensity in the direction parallel to the surface of the light guide plate 68.
As shown in the graph of FIG. 5A, in the conventional lighting device, light in the direction perpendicular to the surface of the light guide plate 68 is the most in both the characteristic 90 on the XY plane and the characteristic 92 on the ZY plane. Although strong, for example, light at an angle of 30 ° from the vertical direction also has a light intensity of about 40% of the vertical direction light on the XY plane and about 10% of the vertical direction light on the ZY plane. The directivity on the XY plane, which is the direction, becomes wide, and the directivity of light as an illumination device is insufficient.

FIG. 6 is a reference diagram provided for explaining the characteristics of the illumination device, and uses the same coordinate axes as those in FIG.
FIG. 6A shows the characteristics in the case of having ideal directivity. As indicated by the solid thick line 94, the characteristics in the XY plane and the characteristics in the ZY plane are all shown. The light is in a direction perpendicular to the surface of the light guide plate where θ = 0.
FIG. 6B shows the characteristics when there is no directivity. The characteristics in the XY plane, the characteristics in the ZY plane, and the angle at each angle with respect to the surface of the light guide plate as indicated by the solid line 96. The light intensity is constant.
The object of the present invention is to realize an illumination device having a characteristic close to the characteristic 94 shown in FIG.

In order to improve the directivity of the illumination light of the illumination device using the LED light source, there is a proposal that the LED light source is placed near the corner portion of the light guide plate, and the groove ridge line is concentric with the LED light source as the center ( For example, see Patent Document 1).
This proposal is excellent for improving the directivity of the lighting device, but in order to increase the luminance of the lighting device, it is necessary to provide one LED light source at the corner of the light guide plate. It has been extremely difficult to make light emitted from the light guide plate uniform over the entire surface of the light guide plate based on the LED light source. In addition, the manufacturing margin has become extremely small.

JP 2001-143512 A

  The problem to be solved is to provide an easy-to-manufacture lighting device having high directivity, high brightness, and uniform illumination light.

  The illuminating device of the present invention is an illuminating device having a point light source and a light guide plate that propagates the light source, wherein the light source is a light emitting diode, the light guide plate has a substantially rectangular shape, and a groove is provided. The groove has a ridge line that is substantially orthogonal to the direction in which the light emitted from the light emitting diode travels after entering the light guide plate, and the light emitting diode is disposed near the diagonal of the light guide plate. To do.

  Moreover, the illuminating device of this invention is characterized by the said ridgeline being substantially concentric with respect to the said light source.

  In the illumination device of the present invention, the light emitting diodes are arranged on the left and right diagonals of the light guide plate, and the light guide plate is divided into upper and lower parts by a line connecting the vicinity of the light emitting diodes arranged on the diagonal. The groove on the light guide plate of each divided part has a ridge line that is substantially orthogonal to the direction in which the light emitted from the light emitting diode belonging to the part travels.

  The illumination device of the present invention is characterized in that ridge lines of the grooves on the divided light guide plates intersect in the vicinity of a line connecting the vicinity of the light emitting diodes.

  In the illuminating device of the present invention, the light emitted from the LED light source and incident on the light guide plate is reflected almost vertically upward. The nature can be narrowed. Therefore, it is possible to increase the brightness and quality of the lighting device. Further, since the LED light source is arranged at the diagonal of the light guide plate, it is possible to realize an illumination device that can easily make illumination light uniform and easy to manufacture.

In an illuminating device having a point light source and a light guide plate that propagates the light source light, the light guide plate has a substantially rectangular shape, a groove is provided, the light source is a light emitting diode, and the light guide plate is disposed diagonally. The light emitting diode is configured to have a ridge line that is substantially orthogonal to a direction in which the light emitted from the light emitting diode travels after entering the light guide plate.
In addition, the light guide plate is divided into upper and lower portions by a line connecting the vicinity of the light emitting diodes arranged diagonally, and the groove on the light guide plate of each of the divided portions is the output of the light emitting diodes belonging to the portions. The ridgeline is almost perpendicular to the direction in which the light travels.

FIG. 1 shows an example of a backlight type according to an embodiment of a lighting device according to the present invention. FIG. 1A is a plan view of the lighting device from which the prism sheet is removed, that is, a view of the XZ plane described in FIG. 5B, and FIG. 1B is a cross-sectional view, that is, Y described in FIG. The figure of -Z surface, (c) is sectional drawing of a light-guide plate.
In the illuminating device of the present invention in FIG. 1A, LED light sources 12 and 14 as point light sources are arranged in the vicinity of diagonal corners of a substantially rectangular light guide plate 10, and emitted light from the LED light sources 12 and 14 is guided. Incident on the light plate 68.
The light guide plate 10 is formed with microprisms, that is, grooves, and is divided into an upper portion 18 and a lower portion 20 by a line 16 connecting the vicinity of the light emitting diodes 12 and 14 arranged diagonally. The ridge line connecting the apexes of the microprisms is substantially concentric with respect to the two LED light sources 12 and 14, as indicated by the dotted line groups 22 and 24 in FIG. Yes. Accordingly, the grooves 22 and 24 on the light guide plate of the respective divided portions 18 and 20 become ridge lines that are substantially orthogonal to the direction in which the light emitted from the light emitting diodes 12 and 14 belonging to the respective portions travels. Yes.

  As shown in FIG. 1B, the cross-sectional structure includes a reflection sheet 34 on the lower surface of the light guide plate 10 and a prism sheet 32 on the upper surface, and the light guide plate 10, the reflection sheet 34, and the prism sheet 32 are accommodated in the holder 30. The light receiving display device such as a liquid crystal display device placed on the upper side is illuminated.

  FIG. 1C is a cross-sectional view of the light guide plate 10, and a microprism is formed on the lower surface of the light guide plate 10 to form a groove. Since the most concave portion 38 and the most convex portion 36 of the microprism are the ridge lines, and the most concave portion 38 and the most convex portion 36 are close to each other, they are drawn with one dotted line in FIG.

FIG. 2 is a diagram for explaining the effect of the illumination device according to the present invention. FIG. 2 (a) is a plan view for explaining the angle formed between the light emitted from the LED light source and the ridge line of the microprism, and FIG. 2 (b) is an optical characteristic. It is the graph showing.
In FIG. 2A, light 40, 42, 44 incident from the LED light source 12 and light 46, 48, 50 incident from the LED light source 14 are the upper surface of the light guide plate 10 and the lower surface of the light guide plate 10 in the light guide plate 10. The light is propagated by being repeatedly refracted with the surface of the microprism provided on the surface.
As the propagation is repeated, the angle formed between the light traveling direction and the upper surface of the light guide plate 10 becomes smaller than the critical angle, and light is emitted from the upper surface of the light guide plate 10. When this propagation is repeated, the traveling direction of the light 40, 42, 44 and the ridgeline 22 of the microprism and the traveling direction of the light 46, 48, 50 and the ridgeline 24 of the microprism are almost orthogonal to each other. Is significantly reduced, and light is emitted in a direction perpendicular to the upper surface of the light guide plate 10 as compared with the prior art. The light emitted to the lower surface of the light guide plate 10 is reflected by the reflection sheet 34 and returned to the light guide plate 10. The light emitted from the light guide plate 10 is further bent by the prism sheet 32 in a direction nearly perpendicular to the upper surface of the light guide plate 10 and guided to the display device side placed on the upper surface of the illumination device.

  The groove ridgelines 22 and 24 on the divided portions 18 and 20 of the light guide plate 10 intersect in the vicinity of the line 16 connecting the vicinity of the light emitting diodes 12 and 14. With this configuration, it is possible to prevent uneven brightness from occurring in the vicinity of the line 16 that connects the vicinity of the light emitting diodes 12 and 14.

Due to such a configuration, the optical characteristics of the illumination device according to the present invention are as shown in FIG.
The coordinate axes are the same as those described with reference to FIG.
The horizontal axis in FIG. 2B is the light emission angle θ, the vertical axis is the relative value of the light intensity, and the dotted thick line 52 in the figure is the relationship between the direction of the illumination light and the intensity of the illumination light in the XY plane, A solid thick line 54 indicates the relationship between the direction of the illumination light and the intensity of the illumination light in the ZY plane. Therefore, the point with the horizontal axis θ = 0 indicates the illumination light intensity in the direction orthogonal to the light guide plate 68, and the point θ = 90 indicates the illumination light intensity in the direction parallel to the surface of the light guide plate 68.
As shown in the graph of FIG. 2B, the lighting device of the present invention has a characteristic 52 in the XY plane and a characteristic 54 in the ZY plane that are perpendicular to the surface of the light guide plate 10 as compared with the conventional case. The light is focused on. For example, light at an angle of 30 ° from the vertical direction has a light intensity of about 10% of the vertical direction light on the XY plane and about several percent of the vertical direction light on the ZY plane, and is particularly in the width direction. The directivity on the XY plane is narrowed, and the directivity of light as an illumination device is improved.

For example, the number of LED chips may be set according to the required brightness of the LED of the light source. However, in the lighting device of the present invention, the LED of the light source is arranged separately on the diagonal of the light guide plate. Compared with the case where it is placed in one place, the number of chips of one LED light source may be half or less, and it is easy to increase the brightness and quality of the lighting device. Further, it is easy to make the luminance uniform over the entire surface of the light guide plate.
Furthermore, since the light sources are arranged in a distributed manner, variations due to manufacturing and assembly conditions can be suppressed, and an illuminating device that is easy to manufacture can be realized as compared with the case where the light sources are arranged in one place.

  Although the present embodiment shows an example in which the illumination device according to the present invention is used as a backlight, it is needless to say that it can be used as a front light by a normal technique.

1 is an embodiment of a lighting device according to the present invention. It is a figure explaining the effect of the illuminating device by this invention. It is a figure which shows the prior art example of the sidelight type illuminating device using a light emitting diode light source. It is the figure which added the locus | trajectory of the light ray radiate | emitted from LED light source to Fig.3 (a). It is a graph showing the optical characteristic of the conventional illuminating device. It is a reference figure provided in order to demonstrate the characteristic of an illuminating device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Light guide plate 18 Light guide plate upper part 20 Light guide plate lower part 12, 14 Light emitting diode 22, 24 Groove ridge line 16 Line 40, 42, 44, 46, 48, 50 which connects the light emitting diode vicinity Emitted light of a light emitting diode

Claims (4)

In an illumination device having a point light source and a light guide plate that propagates the light source light,
The point light source is a light emitting diode;
The light guide plate has a substantially rectangular shape, and is provided with a groove,
The groove has a ridge line that is substantially orthogonal to the direction in which the light emitted from the light emitting diode travels after entering the light guide plate,
The illuminating device, wherein the light emitting diode is disposed in the vicinity of a diagonal of the light guide plate.   The lighting device according to claim 1, wherein the ridge line is formed substantially concentrically with respect to the light source. The light guide plate is divided into upper and lower parts by a line connecting the vicinity of the light emitting diodes arranged diagonally,
3. The illumination device according to claim 2, wherein the groove on the light guide plate of each divided part has a ridge line that is substantially perpendicular to a direction in which light emitted from the light emitting diode belonging to the part travels. . The lighting device according to claim 3, wherein a ridge line of the groove on the light guide plate of each of the divided portions intersects in a vicinity of a line connecting the vicinity of the light emitting diode.

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