JP2007073469A - Planar illuminator and light source unit using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a planar illuminator that uses LEDs, has high front luminance, and has improved uniformity in luminance, and to provide a light source unit using the planar illuminator. <P>SOLUTION: The planar illuminator 10 comprises a light guide plate 11 having a wedge-like section, where the thickness decreases from a side end face (light-incident surface) 11c at the side of a base end section to a side end face 11d at the tip section side; an LED 12 arranged opposite to the light-incident surface 11c of the light guide plate 11; and a light collecting body 13 interposed between the light-incident surface 11c of the light guide plate 11 and the LED 12 while one side surface opposes the light-incident surface 11c of the light guide plate 11 and one side surface 11d at a side opposite to the side 11c opposes the LED 12. A linear Fresnel lens 14 comprising a group of prisms extended in the thickness direction of the light guide plate 11 is provided on a side 13c that opposes the light-incident surface 11c of the light guide plate 11 of the light collecting body 13. A multiple stripe prism 16 extended in a direction nearly in parallel with the longitudinal direction of the light-incident surface 11c is provided on a reflection surface 11b of the light guide plate 11. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a planar illumination device and a light source unit using the same, and more particularly to a light source unit preferably used in a head-up display.

  In recent years, a head-up display (HUD) has been used as a means for providing image information in the forward field of view to a driver of an aircraft or a vehicle. FIG. 6 is a diagram schematically showing the configuration of an in-vehicle HUD as an example. In FIG. 6, the HUD 100 includes a light source unit 110 and a projection optical system 104 arranged inside the instrument panel 101. In general, the light source unit 110 includes a transmissive liquid crystal panel 103 and an illumination device 102 disposed behind the transmissive liquid crystal panel 103, and image information O generated by the light source unit 110 is a projection optical system including a concave mirror 104 in the illustrated example. Is projected onto the windshield 105, and the driver D can read the information from the driving state with almost no eye movement by visually recognizing the virtual image I.

  FIG. 7 is a cross-sectional view showing a conventional configuration example of the light source unit 110 in the HUD 100 (see, for example, Patent Document 1 and Patent Document 2). In FIG. 7, the light source unit 110 includes a liquid crystal panel 103 and an illumination device 102 for illuminating the liquid crystal panel 103 from behind. As the light source, a discharge lamp 114 such as an ultrahigh pressure mercury lamp is used. Has been. A light reflecting plate 115 is disposed behind the discharge lamp 114, and a diffusion plate 117 for scattering light from the discharge lamp 114 to emit light in a plane between the discharge lamp 114 and the liquid crystal panel 103. And the heat ray cut glass 116 for shielding the heat ray which generate | occur | produces from the discharge lamp 114 is arrange | positioned.

Japanese Utility Model Publication No. 6-68957 JP-A-8-238955

  In the HUD light source unit as described above, the use of a discharge lamp as the light source of the illumination device has the following problems. In other words, in order to light the discharge lamp, a drive circuit that generates a high voltage is required, so that the apparatus configuration is increased in size. Further, since the discharge lamp generates a large amount of heat, in many cases, it is necessary to take heat dissipation measures such as incorporating a heat dissipation fan or the like, and it is difficult to reduce power consumption. Due to such problems, conventionally, in-vehicle HUDs are mainly mounted on large vehicles with a sufficient mounting space and some limited vehicles. In order to solve such a problem, as a lighting device in a HUD light source unit, it is possible to simplify the drive circuit and to use an LED that consumes less power and generates less heat than a discharge lamp. It is preferable to use the planar lighting device used.

  FIG. 8 shows the configuration of a conventional typical planar illumination device using LEDs. In FIG. 8, the planar illumination device 120 includes a light-transmitting light guide plate 121 and an LED 122 disposed on one end surface 121 c of the light guide plate 121, and light is emitted onto the light exit surface 121 a of the light guide plate 121. A diffusion sheet 123 for diffusing and making uniform and prism sheets 124 and 125 for condensing light and improving the front luminance are laminated. In addition, a pattern for diffusing and reflecting light is usually formed on the back surface 121b of the light guide plate 121, and a reflection plate 126 for reflecting light leaking from the back surface 121b of the light guide plate and returning it to the light guide plate 121. Has been placed. In such a planar illumination device 120, the light incident on the light guide plate 121 from the light source 122 propagates while repeating total reflection in the light guide plate 121, and a part of the light exits from the output surface 121a. The liquid crystal panel 103 is illuminated uniformly.

  The prism sheets 124 and 125 are formed by forming multiple triangular prisms on one surface side, and the two prism sheets 124 and 125 have the triangular prisms orthogonal to each other and each prism sheet. The sheets 124 and 125 are laminated so that the prism forming surfaces face the liquid crystal panel 103 side.

  However, such a planar illumination device 120 has a problem that the front luminance is low due to the wide light distribution of the emitted light. For example, in the light source unit 110 shown in FIG. It is difficult to obtain sufficient luminance as a lighting device of a light source unit in HUD by simply replacing lighting device 120.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a planar illumination device having high front luminance and excellent luminance uniformity while using LEDs, and the planar illumination device. It is providing the light source unit using.

  In order to solve the above problems, a planar lighting device according to the present invention includes a light guide plate having a wedge-shaped cross section whose thickness decreases from a side end surface on the base end side toward a side end surface on the front end side, and the light guide plate. The LED arranged to face the side end surface of the light plate on the base end side, and one side face to the side end surface on the base end side of the light guide plate, and one side surface opposite to the one side surface to the LED A condensing body interposed between the LED and the side end surface on the base end side of the light guide plate opposed to the side end surface of the light collector on the base end side of the light guide plate A linear Fresnel lens composed of a prism group extending in the thickness direction of the light guide plate is provided on a side surface of the light guide plate, and a main surface opposite to an output surface of the light guide plate is on a base end side of the light guide plate A plurality of prisms extending substantially in parallel with the longitudinal direction of the side end surfaces of the prisms are provided.

  According to the present invention, light is incident from the side end surface on the base end side of the light guide plate having a wedge-shaped cross section whose thickness decreases from the side end surface on the base end side toward the side end surface on the tip end side. By propagating incident light in the direction in which the thickness of the light guide plate decreases, the side end surface of the light guide plate on the base end side of the light guide plate (hereinafter referred to as the light incident surface) of light emitted from the light guide plate in the propagation process The light distribution in the vertical direction (hereinafter simply referred to as the vertical direction) can be narrowed. Further, a condensing body is interposed between the light incident surface of the light guide plate and the LED, and a prism group extending in the thickness direction of the light guide plate on a side surface of the light condensing member facing the light incident surface of the light guide plate. By providing a linear Fresnel lens consisting of refracting and condensing light emitted radially from the LED, it becomes possible to convert the light into substantially parallel light when viewed from the main surface direction of the light guide plate. The light distribution in the direction parallel to the light incident surface of the light guide plate (hereinafter referred to as the horizontal direction) can be narrowed. Therefore, the light emitted from the light guide plate is emitted with high directivity in a predetermined direction from the light emission surface of the light guide plate, and the peak value of the luminance distribution can be improved. The planar illumination device according to the present invention realizes a planar illumination device having sufficiently high illumination brightness, for example, in an optical system of a head-up display, by using the direction in which the luminance distribution takes a peak value as the front. It is.

Furthermore, a multi-surface prism extending substantially parallel to the longitudinal direction of the side end surface (light incident surface) on the base end portion side of the light guide plate is provided on the main surface facing the light exit surface of the light guide plate. Therefore, when the light propagating through the light guide plate is reflected by a main surface (hereinafter referred to as a reflection surface) opposite to the light exit surface of the light guide plate, the light distribution in the horizontal direction described above is not affected at all. Since the light is diffused only in the vertical direction, the uneven luminance in the vertical direction of the light guide plate can be eliminated.
At this time, in order to make the vertical diffusion slight and reflect the light distribution in the vertical direction with little effect on the vertical light distribution, the cross section of a multi-row prism extending in the horizontal direction is partially It is preferable to use a cylindrical ridge.

  In one aspect of the present invention, a prism sheet is disposed on the light exit surface of the light guide plate, and a surface of the prism sheet facing the light exit surface has a length of a side end surface on the base end side of the light guide plate. A multi-triangular prism that extends substantially parallel to the direction is provided, and this allows the luminance distribution to have a peak value without widening the vertical and horizontal light distribution of the light emitted from the light guide plate. Only the direction in which the light is taken can be converted into a substantially vertical direction with respect to the exit surface of the light guide plate. This increases the degree of design freedom for realizing a planar illumination device having a sufficiently high illumination brightness, for example, in an optical system of a head-up display.

  In one embodiment of the present invention, the width between the side surface of the light collector facing the side end surface on the base end side of the light guide plate and the side surface facing the LED is a focal point of the linear Fresnel lens. The LED substantially coincides with the distance, whereby the LED can be easily and reliably arranged at an appropriate position for narrowing the horizontal orientation distribution of the light emitted radially from the LED.

  According to another aspect of the present invention, there is provided a liquid crystal panel in which liquid crystal is held between a pair of substrates on which electrodes are formed, and a planar lighting device according to the present invention disposed behind the liquid crystal panel. A light source unit is provided.

  Since the present invention is configured as described above, it is possible to improve the front luminance of the sidelight type planar illumination device using LEDs as a light source without causing uneven luminance. In addition, since the liquid crystal panel and the planar lighting device according to the present invention disposed behind the liquid crystal panel can constitute a high-intensity light source unit that can be used in a head-up display, In addition to contributing to downsizing and low power consumption, it is possible to simplify the heat dissipating means required for the light source unit.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
1A and 1B are diagrams showing a main part of a lighting device according to a first embodiment of the present invention, where FIG. 1A is a front view, FIG. 1B is a side view, and FIG. 1C is an enlarged view of a portion A in FIG. It is.

  A planar illumination device 10 illustrated in FIG. 1 includes a light guide plate 11, two LEDs 12, and a light collector 13. In the planar lighting device 10, the light guide plate 11 is a plate-like light guide formed by, for example, polycarbonate resin injection molding, and a distal end portion from a side end surface (hereinafter referred to as a light incident surface) 11 c on the base end side. It is formed to have a wedge-shaped cross section whose thickness decreases toward the side end face 11d. Similarly to the light guide plate 11, the light collector 13 is a translucent member formed by injection molding, for example, a polycarbonate resin, and is formed in a substantially prismatic shape, and its one side surface 13 c is formed as a light incident surface of the light guide plate 11. It is arranged to face 11c. In the present embodiment, the LED 12 is disposed on the side surface 13 d opposite to the side surface 13 c of the light collector 13, and faces the light incident surface 11 c of the light guide plate 11 through the light collector 13.

  A linear Fresnel lens 14 composed of a prism group extending in the thickness direction of the light guide plate 11 (hereinafter also referred to as Z direction) is provided on the side surface 13c of the light collector 13 facing the light incident surface 11c of the light guide plate 11. Each LED 12 is provided correspondingly. Here, the linear Fresnel lens 14 realizes a curved surface constituting one cylindrical lens by a set of refracting surfaces of individual prisms constituting the linear Fresnel lens 14, and has the same operation as that of such a cylindrical lens. It is what has. In the present embodiment, the width dimension d between the side surface 13 c and the side surface 13 d of the light collector 13 is formed so as to substantially match the focal length of the linear Fresnel lens 14.

  In the planar illumination device according to the present invention, the linear Fresnel lens 14 may be formed integrally with the light collector 13 or formed as a separate member from the light collector 13. Thus, it may be fixed to the light collector 13. Further, in the light collector 13, a light incident prism for adjusting the radiation angle of the light spreading radially in the light collector 13 and / or the luminance distribution thereof may be provided at a position facing the LED 12 on the side surface 13 a. Good.

  Here, a main surface (hereinafter referred to as a reflective surface) 11b facing the light exit surface 11a of the light guide plate 11 extends substantially parallel to the longitudinal direction (hereinafter also referred to as the X direction) of the light incident surface 11c of the light guide plate 11. A plurality of existing prisms 16 are provided, and on the back surface of the reflecting surface 11b, as shown in FIG. 1 (b), a reflecting plate 15 as a regular reflecting means is disposed. For example, it may be made of a film on which a metal such as silver is vapor-deposited, a metal plate such as a mirror-finished aluminum plate, or a film having a reflective layer having a multilayer structure of polymer thin films.

  Further, as shown in FIG. 1C, the multiple prisms 16 provided on the reflecting surface 11b are composed of convex ridges 16 having a partially cylindrical cross section, and these convex ridges 16 constitute a so-called lenticular lens. ing.

  Next, with reference to FIG. 1 and FIG. 2, the effect | action of the planar illuminating device 10 in this embodiment is demonstrated. Here, FIG. 2 is a view showing a side surface of the planar illumination device 10 in order to explain the operation of the ridges 16 provided on the reflection surface 11b. However, in FIG. 2, it is assumed that the reflection surface 11 b of the light guide plate 11 is configured as a flat surface, and no ridge 16 as shown in FIG.

  First, as shown in FIG. 1B, the outgoing light P from the LED 12 enters the light guide plate 11 from the light incident surface 11c of the light guide plate 11, and is reflected between the output surface 11a and the reflective surface 11b. Although it propagates toward the side end face 11d while repeating, the exit surface 11a and the reflecting surface 11b of the light guide plate 11 formed in a wedge shape are inclined with respect to each other at an inclination angle θ. The incident angle of the light reflected by the surface 11b and incident on the exit surface 11a is gradually reduced by repeating the reflection, and eventually a part of the light incident on the exit surface 11a at an incident angle lower than the critical angle is obtained. For example, the outgoing light L is emitted from the outgoing surface 11a at a predetermined angle φ corresponding to the incident angle.

  At this time, in the light guide plate 11 according to the present embodiment, the inclination angle θ is set to be relatively small (for example, within a range of 0 ° <θ <5 °), and thereby, almost the entire surface of the emission surface 11a. As a result, much light is incident on the exit surface 11a at an incident angle that is slightly below the critical angle. As a result, the light distribution of the emitted light in the direction perpendicular to the light incident surface 11c of the light guide plate 11 (that is, in the YZ plane) can be narrowed. In other words, the light L emitted from the emission surface 11a of the light guide plate can be emitted with high directivity in the φ direction in the YZ plane.

  Here, in order for the light guide plate 11 to have such an action, the reflecting surface 11b is preferably a completely flat surface. However, to make the reflecting surface 11b a completely flat surface, There is a problem. That is, as shown in FIG. 2, when there is a difference in brightness in the luminance distribution of the light incident from the LED 12 to the side surface 13d of the light collector 13, if the reflecting surface 11b is a completely flat surface, the optical path P1 (bright Portion) and the optical path P2 (dark portion) are reflected as they are as the difference in brightness of the light emitted from the light exit surface 11a, which causes uneven brightness.

  Therefore, in this embodiment, as shown in FIG. 1C, the reflecting surface 11b is not a completely flat surface, but is provided with a plurality of prisms 16 extending in the X direction. Accordingly, the light incident on the light guide plate 11 is slightly diffused in the YZ plane in the process of repeated reflection between the emission surface 11a and the reflection surface 11b, so that the optical paths P1 and P2 shown in FIG. Such brightness unevenness can be eliminated. Here, it is desirable to balance the effect of eliminating the uneven brightness by the multiple prisms 16 to such an extent that the high directivity of the emitted light is not impaired. Further, the radius R of the arc that constitutes R = 1.3 mm, and the angle α = 2 ° between the arcs and the Y direction at the point where the adjacent arcs touch each other can be set.

  As described above, since the reflecting surface 11b of the light guide plate 11 has a certain degree of diffusivity, light leaks into the region on the light incident surface 11c side of the light emitting surface 11a (region B shown in FIG. 1B). When this occurs, the region B may be covered with a reflector similar to the reflector 15. In the present embodiment, as shown in FIG. 1A, the multi-prism 16 is provided on the entire reflecting surface 11b of the light guide plate 11. However, the multi-prism 16 is not necessarily a reflecting surface. It is not necessary to provide the entire surface of the light guide plate 11b. Depending on the shape of the light guide plate 11, the object can be achieved even if the light guide plate 11 is provided only in the region on the light incident surface 11c side of the reflective surface 11b.

Here, referring to FIG. 1A again, in the present embodiment, the LED 12 is disposed on the side surface 13d of the light collector 13, and the emitted light P from the LED 12 is emitted radially and the light collector 13. Is incident on. Here, in the planar illumination device 10, the linear Fresnel lens 14 including a prism group extending in the thickness direction of the light guide plate 11 is provided on the side surface 13 c of the light collector 13, and the width of the light collector 13. Since d substantially matches the focal length of the linear Fresnel lens 14, the light P emitted radially from the LED is refracted and collected (in the XY plane) by the action of the linear Fresnel lens 14, It is converted into light P ′ that is substantially parallel as seen in the front view of FIG. Thereby, the light distribution in the direction parallel to the light incident surface 11c (that is, in the XZ plane) of the light emitted from the light emission surface 11a of the light guide plate 11 can be narrowed. In other words, the light L (see FIG. 1B) emitted from the emission surface 11a of the light guide plate can be emitted with high directivity in the Y direction.
The multiple prisms 16 formed on the reflecting surface 11b of the light guide plate 11 extend in the X direction, and thus do not affect the characteristics of the light distribution in the XZ plane.

  In this manner, in the planar illumination device 10 according to the present embodiment, the emitted light from the light guide plate 11 is highly directional in a predetermined direction (that is, the φ direction in the YZ plane) from the output surface 11a of the light guide plate 11. And the peak value of the luminance distribution in that direction is increased.

  Next, the planar lighting device 20 according to the second embodiment of the present invention will be described with reference to FIG. However, in the following description, the same or similar parts as those of the above-described first embodiment will be referred to with the same reference numerals, and the description of the overlapping parts will be omitted as appropriate, and the differences will be described.

  FIG. 3 is a side view showing a main part of the planar illumination device 20 in the present embodiment. The planar illumination device 20 has basically the same configuration and function as the planar illumination device 10 described above, and is different only in that the prism sheet 17 is disposed on the light exit surface 11a of the light guide plate 11. To do.

  In the present embodiment, the prism sheet 17 is formed by forming multiple triangular prisms on the one surface 17a side, and the direction in which the triangular prisms extend is the longitudinal direction of the light incident surface 11c of the light guide plate 11 (X direction). The prism surface 17a on which the triangular prism is formed is disposed so as to oppose the light exit surface 11a of the light guide plate 11. Such a prism sheet 17 does not spread the light distribution of the light emitted from the light guide plate 11 in the vertical direction (in the YZ plane) and the horizontal direction (in the XZ plane), and only the light emission direction of the light guide plate 11 The conversion is performed so as to be substantially perpendicular to the emission surface 11a. At this time, for example, the emission angle Ψ of the emitted light L can be controlled in accordance with the apex angle γ of the triangular prism included in the prism sheet 17 and the inclination angle θ of the light guide plate 11. The degree of freedom in design for realizing a planar lighting device having sufficiently high illumination brightness is increased.

  The prism sheet 17 does not necessarily need to cover the entire exit surface 11a of the light guide plate 11. For example, in the region B on the light incident surface 11c side of the light guide plate 11, the propagation light is confined inside by total reflection. In the case where it does not function as a substantial light emitting surface, it may be anything except that it covers the region B. Further, as in the first embodiment described above, when leakage light is generated from this region B, a reflecting plate may be arranged.

  Next, light source units using the planar illumination device according to the present invention will be described as third and fourth embodiments of the present invention. FIG. 4 is a cross-sectional view showing a main part of the light source unit 30 in the third embodiment of the present invention.

  The light source unit 30 in the present embodiment includes a liquid crystal panel 33 and the planar illumination device 10 in the first embodiment disposed behind the liquid crystal panel 33. The planar lighting device 10 is disposed in a housing 35 together with an aluminum plate 31 for heat dissipation, and the aluminum plate 31 is coupled to a radiator 32 that is partially exposed to the outside. In addition, the liquid crystal panel 33 assembled to the support 34 disposed on the front surface of the housing 35 is a well-known light modulation unit that holds liquid crystal between a pair of substrates on which electrodes are formed. The unit 30 generates image information O by irradiating the liquid crystal panel 33, which is a light modulator, with the planar illumination device 10 from behind.

  In the light source unit 30, the planar illumination device 10 functions as an illumination device having sufficient front luminance due to the high directivity of the emitted light, and the light source unit 30 is, for example, an in-vehicle head-up display. Therefore, it can be suitably used as a light source. Thereby, while contributing to size reduction and low power consumption of the head-up display, the heat dissipating means can be natural air-cooled by the heat dissipator 32, so that the heat dissipating means can be simplified.

  Moreover, FIG. 5 is sectional drawing which shows the principal part of the light source unit 40 in the 4th Embodiment of this invention.

  The light source unit 40 in the present embodiment includes a liquid crystal panel 33 and the planar illumination device 20 in the third embodiment disposed behind the liquid crystal panel 33. Moreover, the planar lighting device 20 is disposed in the housing 45 together with the aluminum plate 31 for heat dissipation, and the aluminum plate 31 is coupled to a radiator 32 that is partially exposed to the outside. In addition, the liquid crystal panel 33 assembled to the support 34 disposed on the front surface of the housing 45 is a well-known light modulation unit that holds liquid crystal between a pair of substrates on which electrodes are formed. The unit 40 generates image information O by irradiating the liquid crystal panel 33, which is a light modulator, with the planar illumination device 20 from behind.

  The light source unit 40 in the present embodiment has the same operations and effects as the light source unit 30 described above. However, in the light source unit 40, the planar illumination device 20 includes the prism sheet 17 and the emission angle of the emitted light. Since ψ is converted in a direction substantially perpendicular to the exit surface 11a of the light guide plate 11, the housing 45 can be further downsized.

It is a figure which shows the principal part of the planar illuminating device in the 1st Embodiment of this invention, (a) is a front view, (b) is a side view, (c) is the A section enlarged view of (b). . In the planar illumination device shown in FIG. 1, it is a side view for demonstrating the effect | action of the reflective surface. It is a side view which shows the principal part of the planar illuminating device in the 2nd Embodiment of this invention. It is sectional drawing which shows the principal part of a light source unit provided with the planar illuminating device shown in FIG. 1 as the 3rd Embodiment of this invention. It is sectional drawing which shows the principal part of a light source unit provided with the planar illuminating device shown in FIG. 3 as the 4th Embodiment of this invention. It is a figure which shows typically the structure of the conventional head-up display. It is sectional drawing which shows the conventional light source unit used with the head-up display shown in FIG. It is a side view which shows the example of a conventional structure of the planar illuminating device using LED.

Explanation of symbols

10, 20: planar illumination device, 11: light guide plate, 11a: exit surface, 11b: reflection surface, 11c: light incident surface (side end surface on the base end side), 12: LED, 13: light collector, 14 : Linear Fresnel lens, 16: Plural prism

Claims (5)

A light guide plate having a wedge-shaped cross section whose thickness decreases from a side end surface on the base end side toward a side end surface on the front end side; and an LED disposed to face the side end surface on the base end side of the light guide plate; The side surface on the base end portion side of the light guide plate and the LED, the one side surface facing the side end surface on the base end portion side of the light guide plate, and the one side surface on the opposite side of the one side surface facing the LED And a condensing body interposed between
A linear Fresnel lens consisting of a prism group extending in the thickness direction of the light guide plate is provided on a side surface of the light collector that faces the side end surface of the light guide plate on the base end side.
The main surface facing the exit surface of the light guide plate is provided with a plurality of prisms extending substantially in parallel with the longitudinal direction of the side end surface on the base end side of the light guide plate. Illuminator.   2. The planar shape according to claim 1, wherein the multiple prisms extending substantially parallel to the longitudinal direction of the side end surface on the proximal end side of the light guide plate are convex strips having a partially cylindrical cross section. Lighting device.   A prism sheet is disposed on the exit surface of the light guide plate, and the surface facing the exit surface of the prism sheet extends substantially parallel to the longitudinal direction of the side end surface on the base end side of the light guide plate. The planar illumination device according to claim 1, wherein a multi-triangular triangular prism is provided.   The width between the side surface of the light collector facing the side end surface on the base end side of the light guide plate and the side surface facing the LED is substantially equal to the focal length of the linear Fresnel lens. The planar illumination device according to any one of claims 1 to 3. A liquid crystal panel that holds liquid crystal between a pair of substrates on which electrodes are formed, and the planar illumination device according to any one of claims 1 to 4 disposed behind the liquid crystal panel. A featured light source unit.

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