JP2007073364A - Backlight device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backlight device capable of widening the range of angle, within which a light incident on an optical element can be bent via the emission face of the optical element. <P>SOLUTION: The backlight device 1 has a light-emitting diode 3 for emitting light toward a prescribed face 2a of a light guide plate 2, and an optical element 4 having a light-emitting surface 4a facing the prescribed face 2a of a light guide plate 2, substantially uniformizing the irradiation density of the output light irradiated on the prescribed face 2a of an optical member, when the output light output from the light-emitting diode 3 is made incident, by making the incident output light refract and totally reflect toward the prescribed face 2a of a light guide plate 2 via the light-emitting surface 4a, according to the strength of the output light. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention opens to a backlight device that irradiates light toward a predetermined surface of an optical member such as a display panel.

  A conventional backlight device is disclosed in Patent Document 1. The backlight device disclosed in this publication will be described with reference to FIG.

  The LED 202 provided on the base 201 is a monochromatic LED and outputs monochromatic light. The light guide plate 205 emits light incident on the incident surface 206 directly or internally after being reflected from the front of the light guide plate 205.

  In the case where the optical element 203 is not provided, the optical element 203 causes a part of the light incident on the portion where the illuminance on the incident surface 206 is higher than the reference to be incident on the portion where the illuminance on the incident surface 206 is lower than the reference value LED output light) is refracted.

Specifically, the optical element 203 irradiates the incident surface 206 of the light guide plate 205 by changing the refractive characteristics of the LED emitted light incident on the optical element 203 according to the intensity of the light from the LED 202. The density of the irradiated light is made uniform.
JP 2003-297127 A

  However, the conventional backlight device has the following problems.

  That is, as shown in FIG. 6, when the output light A from the LED 202 enters the optical element 203 and exits from the exit surface 302, it is totally reflected when the incident angle θ with respect to the exit surface 302 is greater than or equal to the critical angle θt. The light is not emitted from the emission surface 302 of the optical element 203.

Here, the critical angle θt is expressed as follows: n is the refractive index of the optical element 203 and 1 is the refractive index of the atmosphere.
θt = sin ⁻¹ (1 / n) (1)
Represented as:

  The further away the exit surface 302 of the optical element 203 is from the optical axis 600 (FIG. 5) of the LED 202, the greater the incident angle θ with respect to the exit surface 302 and the closer to the critical angle θt. For this reason, the size of the optical element 203 (particularly, the length of the region orthogonal to the optical axis 600 of the LED 202) is limited to a size that can maintain the incident angle θ with respect to the emission surface 302 below the critical angle θt.

  In other words, when the optical element 203 limited in size is used in a backlight device, a part of the output light from the LED 202 (light incident on the emission surface 302 at a critical angle θt or more) is used. Since the incident surface 206 of the light guide plate 205 is illuminated without any problem, the utilization efficiency of the output light from the LED 202 is reduced.

  In this regard, if the distance between the LED 202 and the optical element 203 is increased, the incident angle θ can be reduced, but there is a risk that it is difficult to reduce the size of the backlight device.

  More specifically, as shown in FIG. 7, the direction of the light 301 incident on the optical element 203 is bent using the refraction of the exit surface (interface with air) 302 of the optical element 203 (reference numeral 301A). In order to bend leftward in the traveling direction of the light 301, the incident normal line 303 of the boundary surface 302 needs to be on the left side in the traveling direction of the light 301.

In this case, the angle δ at which the light 301 bends is α, the incident angle of the light 301 with respect to the boundary surface 302 is α, the emission angle of the light 301A emitted from the boundary surface 302 is β, and the angle of the boundary surface 302 with respect to the traveling direction of the light 301 Is γ,
n · sin α = sln β (2)
δ = β−α (3)
α + γ = 90 ° (4)
The following three formulas hold. From these three formulas (2) to (4), δ is expressed by the following formula (5)
δ = sin ⁻¹ (n · cos γ) + γ−90 ° (5)
Can be expressed as

If the critical angle is θt, it is necessary to satisfy 0 ≦ α <θt in order to use the refraction of the exit surface 302. In this range, the range of γ is 90 ° −θt ≦ γ ≦ from the above equation (5). 90 ° ... (6)
It becomes.

Therefore, the range of the angle δ at which the light 301 is bent is expressed by the following equation (7).
0 ≦ δ <90 ° −θt (7)
It becomes.

  Further, as shown in FIG. 8, in order to bend the direction of the light 301 incident on the optical element 203 to the right side in the traveling direction of the light 301 via the boundary surface 302 of the optical element 203 (see reference numeral 301B). The incident normal 305 of the boundary surface 302 needs to be on the right side in the traveling direction of the light 301.

Therefore, based on the same consideration as in the case of bending light to the left side, the range of the angle δ at which the light 301 bends to the right side via the boundary surface (outgoing surface) 302 is as follows:
0 ≦ δ <90 ° −θt (8)
As is clear from the above equations (7) and (8), the range in which the light 301 incident on the optical element 203 is bent to the left and right with respect to the traveling direction is δ = 0 as the traveling direction of the light 301. If the angle δ when bending to the right side is positive and the angle δ when bending to the left is negative, the following equation (9)
− (90 ° −θt) <δ <90 ° −θt (9)
It is represented by

Here, when the refractive index n of the optical element 203 is 1.5, the range of the angle δ at which the light 301 bends through the boundary surface 302 is sin ⁻¹ ( Since 1 / 1.5) is about 42 °, −48 ° <δ <48 °.

As described above, in the method of obtaining a uniform illumination intensity on the predetermined surface (incident surface) 206 of the optical member (light guide plate) 205 using the refraction characteristics of the light incident on the optical element 203, the optical element 203 is used. The range in which the traveling direction of the light incident on can be refracted to the left and right is the above formula (9) − (90 ° −θt) <δ <90 ° −θt (9)
It will be limited by.

  That is, the light that travels in the direction away from the optical axis 600 in the output light from the LED 202 is bent in the direction of the optical axis 600 of the LED 202 so that the predetermined surface (incident surface) 206 of the optical member (light guide plate) 205 is uniform. It is necessary to make the lighting intensity.

  However, as the distance from the optical axis 600 increases, the angle at which the light 301 is bent through the boundary surface 302 increases, and exceeds the range indicated by the above equation (9) that can be bent by refraction. For this reason, it is difficult to make uniform the intensity of irradiation intensity on the predetermined surface (incident surface) 206 of the optical member (light guide plate) 205 by effectively using the output light from the LED 202.

  The present invention has been made in view of the above-described circumstances. An angle range in which light (incident light) incident on an optical element can be bent through the exit surface of the optical element is compared with a conventional backlight device. The purpose is to improve the utilization efficiency of incident light.

  In order to solve the above-mentioned problem, the invention according to claim 1 has a light emitting diode that outputs light toward a predetermined surface of the optical member, and an emission surface that faces the predetermined surface of the optical member. When the output light that has been output is incident, the incident output light is refracted and totally reflected toward the predetermined surface of the optical member via the emission surface according to the intensity of the output light, An optical element for substantially uniforming the irradiation density of the output light irradiated onto the predetermined surface of the optical member.

 In order to solve the above-described problem, the exit surface of the optical element is configured such that the output light incident on the exit surface is incident on the exit surface at a portion where the incident angle is less than a critical angle. In a part where the output light is refracted toward the predetermined surface of the optical member according to the distance from the optical axis of the light emitting diode, and the incident angle of the output light incident on the output surface is greater than the critical angle. And a total reflection characteristic that totally reflects the incident output light of the portion toward a predetermined surface of the optical member according to a distance from the optical axis of the light emitting diode.

  According to a third aspect of the present invention, in order to solve the above-mentioned problem, a diffraction having a plurality of convex portions whose cross-sectional shape is formed in a substantially serrated shape around the optical axis of the light-emitting diode on the emission surface of the optical element. The grating portion 10 is formed, and the plurality of convex portions respectively have inclined surfaces that are inclined at a predetermined angle with respect to a horizontal direction passing through the one end portion from the one end portion on the optical axis side. Among the inclined surfaces of the convex portions, the inclined surface on which the output light is incident at an incident angle less than the critical angle refracts the incident output light toward the predetermined surface of the optical member, and the plurality of convex portions Among the inclined surfaces, the inclined surface on which the output light is incident at an incident angle greater than or equal to the critical angle is characterized by totally reflecting the incident output light toward the predetermined surface of the optical member.

  In the backlight device according to the present invention, the output light from the light emitting diode incident on the optical element is refracted and totally reflected through the emission surface of the optical element in accordance with the intensity of the output light, thereby providing an optical member. The irradiation density of the output light irradiated on the predetermined surface can be made substantially uniform.

  Preferably, in a portion where the incident angle to the exit surface of the optical element is equal to or greater than the critical angle, by using the total reflection property of the exit surface and emitting the output light to the predetermined surface of the optical member without using the refraction characteristics, The range of the bending angle δ from the traveling direction of the output light can be widened as compared with the case where the refraction characteristics of the exit surface are used.

  Therefore, since output light incident at a critical angle or more can be guided to the predetermined surface side of the optical member by total reflection, generation of return light to the light emitting diode side can be avoided. For this reason, the utilization efficiency of the output light from a light emitting diode can be improved. Moreover, since the angle of the light emitted from the emission surface of the optical element is large, the diffusibility of the emitted light can be improved, and the distance between the light emitting diode and the optical member can be shortened. As a result, downsizing of the backlight device can be easily realized.

  Also, when the red light, blue light, and green light output from the light emitting diode are mixed to generate white light, and the generated white light is irradiated onto a predetermined surface of the optical member, the above diffusibility is improved. The color mixing property of red, blue and green can be improved. As a result, the distance between the light emitting diode and the optical member can be set short, and downsizing of the backlight device can be realized.

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

  First, the principle of the embodiment of the present invention will be described.

  As shown in FIG. 1, when the direction of the light 401 incident on the optical element 2030 is bent using the refraction of the exit surface (interface with air) 402 of the optical element 2030 (see reference numeral 401A), In order to bend leftward in the traveling direction of 401, the incident normal 403 of the boundary surface 402 needs to be on the left side in the traveling direction of the light 401.

In this case, the angle δ at which the light 401 is bent is defined as α where the incident angle of the light 401 to the boundary surface 402 is α.
δ = 180 ° −2α (10)
Represented as:

Assuming that the critical angle is θt, it is necessary that θt ≦ α <90 ° in order to use the total reflection of the emission surface 402. In this range, the range of the angle δ at which the light 401 is bent is expressed by the following equation (11 )
0 ≦ δ <180 ° −2θt (11)
It becomes.

In addition, as shown in FIG. 2, in order to bend the direction of the light 401 incident on the optical element 2030 to the right side in the traveling direction of the light 401 through the boundary surface 402 of the optical element 2030 (see reference numeral 401B), The incident normal 405 of the boundary surface 402 needs to be on the right side in the traveling direction of the light 401. From the same consideration as when light is refracted to the left side, the light 401 passes through the boundary surface (outgoing surface) 402. The range of the angle δ that turns right is expressed by the following equation (12)
0 ≦ δ <180 ° −2θt (12)
As is clear from the above equations (11) and (12), the range in which the light 401 incident on the optical element 2030 is bent to the left and right with respect to the traveling direction is set so that the traveling direction of the light 401 is δ = 0. If the angle δ when bending to the right is positive and the angle δ when bending to the left is negative, the following equation (13)
− (180 ° −2θt) <δ <180 ° −2θt (13)
It is represented by

  For example, when the refractive index n of the optical element 2030 is 1.5, the range of the angle δ at which the light 401 bends through the boundary surface 402 is −98 ° <δ according to the above formulas (1) and (13). <98 °.

  As described above, according to the present embodiment, the range in which the traveling direction of the incident light 401 is bent to the left and right by using the total reflection characteristic with respect to the incident light 401 on the emission surface 402 of the optical element 2030 is the conventional configuration. It can be doubled. In other words, the range of the bending angle δ with respect to the traveling direction of the incident light 401 can be made wider than when refraction is used.

  Preferably, in the present embodiment, according to the incident angle α with respect to the emission surface 402 of the optical element 2030, for example, when the incident angle α is less than the critical angle θt, the incident light 401 is emitted from the emission surface of the optical element 2030. When the incident angle α is greater than or equal to the critical angle θt, the incident light 401 is totally reflected through the exit surface 402 of the optical element 2030, thereby turning the incident light 401 in the direction of travel. The range of the degree δ can be made wider than when only refraction is used.

  An embodiment of the present invention based on the above principle will be described with reference to the drawings.

  FIG. 3 is a diagram showing a schematic configuration of the backlight device 1 according to an embodiment of the present invention.

  As shown in FIG. 3, the backlight device 1 includes, for example, a flat light guide plate 2 that is an optical member that is disposed to face the back surface of a flat display panel (not shown) at a predetermined interval. A light-emitting diode disposed on the optical plate 2 so as to face the optical element 4 with a predetermined interval with respect to the predetermined surface 2a opposite to the surface opposite to the back surface of the display panel, and to be further spaced with a predetermined interval. (LED) 3. The light emitting diode 3 emits light having a predetermined orientation pattern (a portion close to the optical axis center 3a has a dense light beam and a light beam sparse at a portion far from the optical axis center 3a) toward the predetermined surface 2a with the optical axis 3a as a center. And a light emitting diode (LED) 3 that outputs light having a characteristic.

 In the drawing, the optical element 4 whose left half is shown as a vertical cross section has a paired relationship with the light emitting diode 3, and this paired relationship is on the back surface of the light guide plate 2 (on the predetermined surface 2 a side). For example, they are arranged in a honeycomb shape or a matrix shape (not shown).

  In addition, the backlight device 1 is disposed between the light guide plate 2 and the light emitting diode 3, and has an exit surface 4 a that faces the predetermined surface 2 a of the light guide plate 2, and an entrance surface 4 b that faces the exit surface 4 a and the light emitting diode 3. Are provided.

  As the optical element 4, an element capable of bending light via the emission surface 4 a, for example, a refractive lens or a diffraction grating can be used. The optical element 4 has a refractive index n.

  When the output light output from the light emitting diode 3 is incident through the incident surface 4b, the optical element 4 converts the incident output light through the output surface 4a according to the intensity of the output light. By refraction and total reflection, it has a function of making the irradiation density of the output light irradiated onto the predetermined surface 2a of the light guide plate 2 substantially uniform.

  More specifically, on the exit surface 4a of the optical element 4, a plurality of convex portions 10a1, 10a2,... Having a sawtooth shape in cross section around the optical axis 3a and a concentric shape in plan view. Is formed.

  The convex portion 10a1 of the diffraction grating portion 10 has an inclined surface that is inclined at a predetermined angle with respect to a horizontal direction (a direction orthogonal to the optical axis 3a) passing through the one end portion from the one end portion on the optical axis 3a side.

  That is, when the output light passing through the optical path 3a1 is incident on the inclined surface of the convex portion 10a1 through the incident surface 4 at an incident angle less than the critical angle θt, The incident output light is refracted by a predetermined degree of refraction (refractive angle), and when there is no optical element 4, a part other than a part (see reference numeral P1) other than the part that enters the predetermined surface 2a of the light guide plate 2 through the optical path 3a1. When there is no optical element 4 on the predetermined surface 2a, it is configured to guide to a portion where the illuminance is low (see reference numeral A1). The critical angle θt is obtained by the above equation (1).

  Similarly, the convex portion 10a2 is continuously formed radially outward with respect to the convex portion 10a1, and is inclined at a predetermined angle with respect to the horizontal direction passing through the one end portion from the one end portion on the convex portion 10a1 side. Has a surface.

  The inclined surface of the convex portion 10a2 is output when output light passing through the optical path 3a2 of the output light output from the light emitting diode 3 is incident through the incident surface 4 at an incident angle less than the critical angle θt. Light is refracted by a predetermined degree of refraction (a refraction angle), and when there is no optical element 4, a part other than a part (refer to reference numeral P2) that enters the predetermined surface 2a of the light guide plate 2 through the optical path 3a2; When there is no optical element 4 on the surface 2a, it is configured to guide to a portion with low illuminance (see reference A2).

  Furthermore, the convex part 10a3 is continuously formed radially outward with respect to the convex part 10a2, and is an inclined surface that is inclined at a predetermined angle with respect to a horizontal direction passing through the one end part from the one end part on the convex part 10a2 side. have.

  The inclined surface of the convex portion 10a3 is output when output light passing through the optical path 3a3 of the output light output from the light emitting diode 3 is incident through the incident surface 4 at an incident angle less than the critical angle θt. Light is refracted by a predetermined degree of refraction (a refraction angle), and when there is no optical element 4, a part other than a part (see reference numeral P3) other than a part that enters the predetermined surface 2a of the light guide plate 2 through the optical path 3a3, that is, a predetermined part When there is no optical element 4 on the surface 2a, it is configured to guide to a portion with low illuminance (see reference A3).

  In particular, in this embodiment, the closer to the optical axis 3a, the higher the illuminance of light irradiated on the predetermined surface 2a of the light guide plate 2, and the illuminance decreases as the distance from the optical axis 3a increases. The degree of refraction of each of 10a3 is set small according to the distance from the optical axis 3a. In other words, the degree of refraction by the convex part 10a1 is the largest, and the respective inclined surfaces are adjusted so that the degree of refraction of the convex part 10a2 and the convex part 10a3 is small.

  On the other hand, in the present embodiment, the convex portions 10a4 and 10a4 that are further away from the optical axis 3a with respect to the convex portions 10a1 to 10a3 have a total reflection effect that totally reflects incident light, not the refractive action of the convex portions 10a1 to 10a3. It is configured as follows.

  That is, as shown in FIGS. 3 and 4, the convex portion 10a4 of the diffraction grating portion 10 has an inclined surface that is inclined at a predetermined angle with respect to the horizontal direction passing through the one end portion from the one end portion on the optical axis 3a side. ing.

  The inclined surface of the convex portion 10a4 is formed when the output light passing through the optical path 3a4 of the output light output from the light emitting diode 3 is incident through the incident surface 4 at an incident angle α1 equal to or greater than the critical angle θt. (Incident normal 20 of the inclined surface), the output light is totally reflected, and when there is no optical element 4, the portion other than the portion incident on the predetermined surface 2 a of the light guide plate 2 through the optical path 3 a 4 (on the predetermined surface 2 a When there is no optical element 4, it is configured to guide to a portion having a low illuminance.

  Similarly, the convex portion 10a5 of the diffraction grating portion 10 has an inclined surface that is inclined at a predetermined angle with respect to the horizontal direction passing through the one end portion from the one end portion on the optical axis 3a side.

  The inclined surface of the convex portion 10a5 is formed when the output light passing through the optical path 3a5 among the output light output from the light emitting diode 3 is incident through the incident surface 4 at an incident angle α2 equal to or greater than the critical angle θt. (Incident normal 21 of the inclined surface), the output light is totally reflected, and when there is no optical element 4, the portion other than the portion incident on the predetermined surface 2 a of the light guide plate 2 through the optical path 3 a 5 (on the predetermined surface 2 a When there is no optical element 4, it is configured to guide to a portion having a low illuminance.

For example, when the optical element 4 is produced using an acrylic material having a refractive index n = 1.5, sin ⁻¹ (1 / 1.5) is about 42 °, so that the output light when using total reflection The bending angle of
− (180 ° −2 × 42) <δ <180 ° −2 × 42
Finally, the range of the angle δ at which the output light from the light emitting diode 3 bends through the reflecting surfaces of the convex portions 10a4 and 10a5 of the optical element 4 is −98 ° <δ <98 °.

  Here, in the case where the output light from the light emitting diode is bent only by the refractive characteristics using the optical element generated by the material having the same refractive index n = 1.5, which is described as the background art, the above formula ( From 1) and (9), −48 ° <δ <48 °.

  That is, in the present embodiment, the output light output from the light emitting diode and incident on the optical element 4 can be bent toward the predetermined surface 2a of the light guide plate 2 in a range about twice that of the background art.

  As described above, according to the present embodiment, since the light emitting diode output light incident at the critical angle θt or more can be totally reflected toward the predetermined surface 2a side of the light guide plate 2, the return light to the light emitting diode side is reflected. The output light from the light emitting diode can be efficiently used without causing it.

  Moreover, since the angle of the light emitted from the emission surface 4a of the optical element 4 is large, the diffusibility of the emitted light can be improved, and the distance between the light emitting diode 3 and the light guide plate 2 can be shortened. become. As a result, downsizing of the backlight device 1 can be easily realized.

  In the present embodiment, the reflecting surface of each of the convex portions 10a1, 10a2,... Of the diffraction grating portion 10 is a flat surface, but the present invention is not limited to this configuration, and may be a curved surface. Good.

  The present invention is not limited to the above-described embodiments and modifications, and various modifications can be made to the above-described embodiments and modifications within the scope belonging to the present invention.

The figure for demonstrating the principle of this invention. The figure for demonstrating the principle of implementation of this invention. The figure which shows schematic structure of the backlight apparatus concerning one Embodiment of this invention. The figure which expands and shows a part of diffraction grating part of the backlight apparatus shown in FIG. The figure which shows schematic structure of the conventional backlight apparatus. The figure for demonstrating the problem of the conventional backlight apparatus. The figure for demonstrating the problem of the conventional backlight apparatus. The figure for demonstrating the problem of the conventional backlight apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Backlight apparatus 2 Light-guide plate 2a Predetermined surface 3 Light emitting diode 4 Optical element 4a Output surface 10 Diffraction grating part 10a1-10a5 Convex part

Claims (3)

A light emitting diode that outputs light toward a predetermined surface of the optical member;
An output surface that faces the predetermined surface of the optical member, and when the output light output from the light emitting diode is incident, the output light that has been input is changed according to the intensity of the output light. An optical element for making the irradiation density of the output light irradiated on the predetermined surface of the optical member substantially uniform by refraction and total reflection toward the predetermined surface of the optical member via
A backlight device comprising: The exit surface of the optical element is
In a portion where the incident angle of the output light incident on the emission surface is less than a critical angle, the incident output light of the portion is directed toward the predetermined surface of the optical member according to the distance from the light-emitting diode optical axis. Refraction characteristics to refract,
In a part where the incident angle of the output light incident on the exit surface is greater than or equal to the critical angle, the incident output light of the part is directed to the predetermined surface of the optical member in accordance with the distance from the light emitting diode optical axis. Total reflection characteristics that totally reflect
Each of the backlight devices according to claim 1, wherein: A diffraction grating portion 10 having a plurality of convex portions whose cross-sectional shape is formed in a substantially sawtooth shape with the optical axis of the light emitting diode as the center is formed on the emission surface of the optical element. Each having an inclined surface inclined at a predetermined angle with respect to a horizontal direction passing through the one end from the one end on the optical axis side,
Of the inclined surfaces of the plurality of convex portions, the inclined surface on which the output light is incident at an incident angle less than the critical angle refracts the incident output light toward the optical member predetermined surface,
Of the inclined surfaces of each of the plurality of convex portions, the inclined surface on which the output light is incident at an incident angle greater than the critical angle totally reflects the incident output light toward the predetermined surface of the optical member. The backlight device according to claim 2.

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