WO2007029858A1

WO2007029858A1 - Surface lighting device and light source unit using it

Info

Publication number: WO2007029858A1
Application number: PCT/JP2006/317991
Authority: WO
Inventors: Toru Kunimochi
Original assignee: Minebea Co., Ltd.
Priority date: 2005-09-09
Filing date: 2006-09-11
Publication date: 2007-03-15
Also published as: JP2007073469A

Abstract

A surface lighting device having a high front luminance while using an LED and being excellent in luminance uniformity, and a light source unit using the surface lighting device. The surface lighting device (10) comprises a light guide plate (11) having wedge-form section with its thickness gradually decreasing from a side end surface (light entry surface) (11c) on a base end side to a side end surface (11d) on a tip end side, and an LED (12) disposed to face the light entry surface (11c) of the light guide plate (11), and a collector (13) interposed between the light entry surface (11c) of the light guide plate (11) and the LED (12) with its one side surface (13c) facing the light entry surface (11c) of the light guide plate (11) and the other side surface (13d) on the opposite side to the side surface (13c) facing the LED (12), wherein a linear Fresnel lens (14) consisting of a prism group extending in the thickness direction of the light guide plate (11) is provided on the side surface (13c) facing the light entry surface (11c) of the light guide plate (11), and a multi-streak prism (16) extending almost in parallel to the lengthwise direction of the light entry surface (11c) is provided on the reflection surface (11b) of the light guide plate (11).

Description

Surface illumination device and light source unit using the same

Technical field

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 suitably used in a head-up display.

Background art

[0002] In recent years, a head up display (HUD) has been used as a means for providing image information in the forward visual field to an aircraft or vehicle driver. 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 that are arranged inside an 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. Image information O generated by the light source unit 110 is a projection optical system including a concave mirror 104 in the illustrated example. Thus, the image is projected onto the windshield 105, and the driver D can read the information by visually checking the virtual image I with almost no movement of the driving state power.

FIG. 7 is a cross-sectional view showing a conventional configuration example of the light source unit 110 in such a HUD 100 (see, for example, Patent Document 1 and Patent Document 2). In FIG. 7, a light source unit 110 includes a liquid crystal node 103 and an illuminating device 102 for illuminating the liquid crystal panel 103 from behind. As the light source, for example, a discharge lamp 114 such as an ultra-high pressure mercury lamp is provided. Is being used. In addition, a light reflector 115 is disposed behind the discharge lamp 114, and a diffusion plate 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. 117 and a heat ray cut glass 116 for shielding heat rays generated from the discharge lamp 114 are arranged.

[0004] Patent Document 1: Japanese Utility Model Publication No. 6-68957

Patent Document 2: JP-A-8-238955

Disclosure of the invention

Problems to be solved by the invention [0005] 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 for generating a high voltage is required, so that the apparatus configuration is increased in size. In addition, since the discharge lamp generates a large amount of heat, it is often necessary to take heat dissipation measures such as incorporating a heat dissipation fan, and it is difficult to reduce power consumption. Due to these problems, in-vehicle HUDs have traditionally been mounted only on large vehicles with limited mounting space and some limited vehicles. In order to solve such problems, it is possible to simplify the drive circuit as an illumination device in the HUD light source unit, and also consume less power and heat than a discharge lamp. It is preferable to use a planar lighting device using LEDs.

[0006] FIG. 8 shows a 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 121c of the light guide plate 121, and light is emitted onto the output surface 121a of the light guide plate 121. A diffusion sheet 123 for diffusing and leveling 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 is provided. Has been placed. In such a planar illumination device 120, light incident on the light guide plate 121 from the LED 122 propagates through the light guide plate 121 while repeating total reflection, and a part of the light is emitted from the output surface 121a. That is, the liquid crystal panel 103 is illuminated uniformly.

[0007] It should be noted that the prism sheets 124 and 125 are formed by forming multiple triangular prisms on one side thereof, and the two prism sheets 124 and 125 are configured such that the triangular prisms are orthogonal to each other, and The prism 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, the light source unit 110 shown in FIG. In this case, it is difficult to obtain sufficient luminance as a lighting device of a light source unit in the HUD by simply replacing the lighting device 102 with the planar lighting device 120. [0009] 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 an LED, and the surface thereof. It is providing the light source unit using a strip-shaped illuminating device.

Means for solving the problem

[0010] 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 in which the thickness of the side end surface on the base end portion side decreases toward the side end surface on the front end portion side. And an LED disposed to face the side end surface of the light guide plate on the base end portion side, and one side surface of the light guide plate facing the side end surface of the light guide plate on the base end portion side, and one side surface opposite to the one side surface A light condensing body interposed between the LED and a side end surface on the base end side of the light guide plate facing the LED, and the light collector on the base end side of the light guide plate A linear Fresnel lens having a prism group force extending in the thickness direction of the light guide plate is provided on the side surface facing the side end surface, and the light guide plate on the main surface facing the output surface of the light guide plate. A plurality of prisms extending substantially in parallel with the longitudinal direction of the side end surface of the base end portion side are provided.

[0011] According to the present invention, the side end surface force on the base end portion side emits light from the side end surface on the base end portion side of the light guide plate having a wedge-shaped cross section whose thickness is reduced by directing the side end surface on the front end portion side. And the incident light is propagated in the direction in which the thickness of the light guide plate decreases, so that the exit surface force of the light guide plate during the propagation process. The light distribution in the vertical direction (hereinafter simply referred to as the vertical direction) can be narrowed. In addition, a light collector is interposed between the light incident surface of the light guide plate and the LED, and a prism extending in the thickness direction of the light guide plate is formed on the side surface of the light collector that faces the light incident surface of the light guide plate. By providing a linear Fresnel lens that is a group force, it is possible to refract and condense the light emitted radially from the LED force and convert it into light that is substantially parallel 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 characteristics 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 is sufficiently high in an optical system of a head-up display, for example, by using the direction in which the luminance distribution takes a peak value as the front. A planar illumination device having illumination brightness is realized.

[0012] Further, a plurality of prisms 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 are formed on the main surface facing the exit surface of the light guide plate. When the light propagating through the light guide plate is reflected by the main surface (hereinafter referred to as the reflection surface) opposite to the light exit surface of the light guide plate, the light distribution in the horizontal direction described above is completely eliminated. Since it is diffused only in the vertical direction without affecting it, it is possible to eliminate uneven brightness in the vertical direction of the light guide plate.

At this time, in order to make the vertical diffusion slight and reflect it with almost no influence on the vertical light distribution of the emitted light, a multi-row prism extending in the horizontal direction is used. The cross section is preferably a partially cylindrical ridge.

[0013] In one aspect of the present invention, a prism sheet is disposed on the exit surface of the light guide plate, and the surface of the prism sheet facing the exit surface is on the proximal end side of the light guide plate. A multi-triangular triangular prism that extends substantially parallel to the longitudinal direction of the end face is provided, and this makes it possible to broaden the vertical and horizontal light distribution of the light emitted from the light guide plate. Only the direction in which the luminance distribution has a peak value can be converted into a direction substantially perpendicular to the exit surface of the light guide plate. This increases the degree of design freedom for realizing a planar illumination device having sufficiently high illumination brightness, for example, in an optical system of a head-up display.

[0014] In one aspect 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 the linear Fresnel. It is approximately the same as the focal length of the lens, which makes it easy and reliable to place the LED at an appropriate position to narrow the horizontal orientation distribution of the light emitted radially from the LED. be able to.

[0015] In another aspect of the present invention, 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. And a light source unit comprising:

The invention's effect

[0016] Since the present invention is configured as described above, a sidelight type using an LED as a light source is used. In the surface illumination device, it is possible to improve the front luminance without causing luminance unevenness. In addition, since the liquid crystal panel and the planar lighting device according to the present invention arranged 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, the heat dissipation means required for the light source unit can be simplified. Brief Description of Drawings

FIG. 1 is a diagram showing a main part of a planar lighting device according to a first embodiment of the present invention, where (a) is a front view, (b) is a side view, and (c) is (b). FIG.

2 is a side view for explaining the action of the reflecting surface in the planar illumination device shown in FIG.

FIG. 3 is a side view showing a main part of a planar illumination device in a second embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a main part of a light source unit including the planar illumination device shown in FIG. 1 as a third embodiment of the present invention.

FIG. 5 is a cross-sectional view showing a main part of a light source unit including the planar illumination device shown in FIG. 3 as a fourth embodiment of the present invention.

FIG. 6 is a diagram schematically showing a configuration of a conventional head-up display.

7 is a cross-sectional view showing a conventional light source unit used in the head-up display shown in FIG.

FIG. 8 is a side view showing a conventional configuration example of a planar illumination device using LEDs.

Explanation of symbols

[0018] 10, 20: Surface illumination device

11: Light guide plate

11a: Output surface

l ib: Reflecting surface

11c: Incident surface (base end side end surface)

12: LED

13: Light collector

14: Linear Fresnel lens 16: Multiple prism

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a diagram showing a main part of a lighting device according to a first embodiment of the present invention, where (a) is a front view, (b) is a side view, and (c) is an enlarged view of part A of (b). It is.

A planar illumination device 10 shown 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-shaped light guide formed by, for example, injection molding polycarbonate resin, and has a side end surface (hereinafter referred to as a light incident surface) on the base end side 1 lc It is formed so as to have a wedge-shaped cross section whose thickness decreases from the side end surface l id on the distal end side. Similarly to the light guide plate 11, the light collector 13 is a translucent member formed by injection molding of polycarbonate resin, for example, and is formed in a substantially prismatic shape, and its one side surface 13c is made incident on the light guide plate 11. It is arranged to face the surface 11c. In this embodiment, the LED 12 is disposed on the side surface 13d opposite to the side surface 13c of the light collector 13, and faces the light incident surface 1 lc of the light guide plate 11 via the light collector 13. The

[0021] A linear Fresnel lens 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 a side surface 13c of the light collector 13 facing the light incident surface 11c of the light guide plate 11. 14 is provided corresponding to each LED 12. Here, the linear Fresnel lens 14 realizes a curved surface constituting a single cylindrical lens by a set of refractive surfaces of the individual prisms constituting the linear Fresnel lens 14, and has the same effect as that of the cylindrical lens. It has. In the present embodiment, the width dimension d between the side surface 13c and the side surface 13d 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 may be separate from the light collector 13. It may be formed as a member and fixed to the light collector 13. In addition, in the light collector 13, there is an emission angle of light that radiates in the light collector 13 or its luminance distribution at a position facing the LED 12 on the side surface 13 a. You can install a prism!

[0023] Here, a main surface (hereinafter referred to as a reflection surface) l ib that faces the light exit surface 11a of the light guide plate 11 has a longitudinal direction of the light incident surface 1 lc of the light guide plate 11 (hereinafter also referred to as X direction!). U) As shown in FIG. 1 (b), a reflecting plate 15 as a regular reflecting means is disposed on the back surface of the reflecting surface l ib, and this reflecting plate is made of, for example, silver or the like. A metal plate such as a metal-deposited film, a metal plate such as an aluminum plate subjected to specular force, or a film provided with a reflective layer that also has a multilayer structural force of a polymer thin film may be used.

In addition, as shown in FIG. 1 (c), the multi-row prism 16 provided on the reflection surface l ib is composed of a ridge 16 having a partially cylindrical cross section. Constitutes a lens.

Next, with reference to FIG. 1 and FIG. 2, the operation of the planar lighting device 10 in the present embodiment will be described. Here, FIG. 2 is a view showing a side surface of the planar illumination device 10 in order to explain the operation of the protrusion 16 provided on the reflection surface l ib. However, in FIG. 2, it is assumed that the reflecting surface l ib of the light guide plate 11 is configured as a flat surface, and no protrusion 16 as shown in FIG. 1 (c) is provided.

First, as shown in FIG. 1 (b), 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 the output surface 1 la and the reflection surface 1 lb The force that propagates toward the side end surface l id while repeating reflection between the light-emitting plate 11 and the light-emitting surface 11a of the light guide plate 11 formed in a wedge shape and the reflection surface l ib are inclined with each other at an inclination angle Θ. Therefore, the incident angle of light that is reflected by the reflecting surface l ib of the light guide plate 11 and incident on the emitting surface 11a gradually decreases with repeated reflection, and eventually reaches an incident angle that is lower than the critical angle. A part of the light incident on the exit surface 11a exits from the exit surface 11a with a predetermined angle φ corresponding to the incident angle, for example, as the exit light L.

[0027] At this time, in the light guide plate 11 in the present embodiment, the inclination angle Θ is set to be relatively small (for example, within the range of 0 ° <Θ <5 °). Over almost the entire surface of 11a, a lot of 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.

[0028] Here, in order for the light guide plate 11 to have such an action, the reflection surface l ib must be completely flat. However, there are the following problems in making the reflecting surface l ib completely flat. That is, as shown in FIG. 2, when there is a difference in brightness in the luminance distribution of light incident on the side surface 13d of the condenser 13 from the LED 12, if the reflecting surface l ib is a perfectly flat surface, the optical path P1 ( The arrangement relationship between the bright part) and the optical path P2 (dark part) is reflected as it is as a difference in brightness of the outgoing light from the outgoing surface 11a, which causes uneven brightness.

Therefore, in the present embodiment, as shown in FIG. 1 (c), there are provided a plurality of prisms 16 extending in the X direction rather than making the reflecting surface l ib a complete flat surface. is there. As a result, the light incident on the light guide plate 11 is slightly diffused in the YZ plane in the process of repeated reflection between the exit surface 11a and the reflection surface l ib, and therefore the optical path shown in FIG. Luminance unevenness such as Pl and P2 can be eliminated. Here, it is desirable that the unevenness of luminance by the multi-row prism 16 is balanced to the extent that the height and directivity of the emitted light described above are not impaired. For example, in each prism 16 having a cylindrical cross section. Further, the radius of the arc constituting the outer shape of the cross section R = l. 3 mm, and the angle α = 2 ° formed by the arc at the point where the adjacent arc touches the Y direction can be set.

[0030] Note that, as described above, the reflecting surface l ib of the light guide plate 11 has a certain degree of diffusivity, so that the region on the light incident surface 11c side of the light exit surface 11a (shown in FIG. 1 (b)). When leakage light is generated in the area B), the area B may be covered with a reflector similar to the reflector 15. Further, in the present embodiment, as shown in FIG. 1 (a), the force that the multiple prisms 16 are provided on the entire reflection surface l ib of the light guide plate 11 is not necessarily the reflection surface 16 Depending on the shape of the light guide plate 11 that does not need to be provided on the entire surface of 1 lb, 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 l ib.

Here, referring again to FIG. 1 (a), in this 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 collected. It is incident on the light body 13. 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. Since the width d is approximately equal to the focal length of the linear Fresnel lens 14, the light P emitted radially from the LED force is also refracted and collected (in the XY plane) by the action of the linear Fresnel lens 14, Light almost parallel as seen in the front view of Fig. 1 (a) It will be transformed. As a result, the light distribution in the direction parallel to the light incident surface 11 c (that is, in the XZ plane) of the light emitted from the light emission surface l la of the light guide plate 11 can be narrowed. In other words, the light L (see FIG. 1 (b)) emitted from the emission surface lla of the light guide plate can be emitted with high directivity in the Y direction.

Since the multiple prisms 16 formed on the reflection surface l ib of the light guide plate 11 extend in the X direction, they do not affect the characteristics of this light distribution in the XZ plane.

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

Next, the planar lighting device 20 in 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 in the first embodiment described above 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 only the point that the prism sheet 17 is disposed on the light emission surface l la of the light guide plate 11 is used. Are different.

[0035] 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 depends on the length of the light incident surface 11c of the light guide plate 11. The prism surface 17a on which the triangular prism is formed is arranged so as to face the emitting surface lla of the light guide plate 11 so as to coincide with the direction (X direction). Such a prism sheet 17 emits only the emission direction of the light emitted from the light guide plate 11 without spreading the light distribution in the vertical direction (in the YZ plane) and the horizontal direction (in the XZ plane). It is transformed so as to be substantially perpendicular to the plane l la. 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. In order to realize a planar lighting device with sufficiently high illumination brightness, the degree of design freedom increases. Is.

Note that the prism sheet 17 does not necessarily cover the entire exit surface 11a of the light guide plate 11. For example, the region B on the light incident surface 11c side of the light guide plate 11 has a B force total reflection, so that the propagation light is closed inside. If it is trapped and does not function as a substantial light exit surface, it may be covered except for region B. Further, as in the first embodiment described above, when leakage light is generated from this region B, a reflector may be arranged.

[0037] Next, as third and fourth embodiments of the present invention, a light source unit using the planar lighting device according to the present invention will be described. 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 lighting device 10 in the first embodiment disposed behind the liquid crystal panel 33. Further, the planar lighting device 10 is disposed in the housing 35 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. Further, 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 means that holds liquid crystal between a pair of substrates on which electrodes are formed. The light source unit 30 generates image information O by irradiating the liquid crystal panel 33, which is a light modulation means, with the planar illumination device 10 from behind.

[0039] 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. It can be suitably used as a light source for an up display. As a result, the head-up display can be reduced in size and power consumption, and the heat dissipating means can be naturally air-cooled by the radiator 32, so that the heat dissipating means can be simplified.

FIG. 5 is a cross-sectional view showing a main part of the light source unit 40 in the fourth embodiment of the present invention.

The light source unit 40 in the present embodiment includes a liquid crystal panel 33 and the planar lighting device 20 in the third embodiment disposed behind the liquid crystal panel 33. Also planar lighting The device 20 is disposed in a housing 45 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 45 is a well-known light modulation unit that holds liquid crystal between a pair of substrates on which electrodes are formed. The light source unit 40 generates image information O by irradiating the liquid crystal panel 33, which is a light modulation means, with the planar illumination device 20 from behind.

The light source unit 40 in the present embodiment has the same effect as the light source unit 30 described above. In the light source unit 40, the planar illumination device 20 includes the prism sheet 17 and emits emitted light. Since the angle 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.

Claims

The scope of the claims

[1] A 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 front end side, and is arranged to face the side end surface on the base end side of the light guide plate A side end surface on the base end side of the light guide plate, with one side surface facing the side end surface on the base end side of the light guide plate and one side surface on the opposite side of the one side surface facing the LED And a light collector interposed between the LED and the LED,

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 collector that faces the side end surface of the light guide plate on the base end side. The main surface facing the light exit surface of the light plate is provided with a multi-row prism extending substantially parallel to the longitudinal direction of the side end surface on the base end side of the light guide plate. Lighting device.

[2] The multi-line prism extending substantially parallel to the longitudinal direction of the side end surface on the base end side of the light guide plate is a convex line having a partially cylindrical cross section. Planar lighting device.

[3] A prism sheet is disposed on the exit surface of the light guide plate, and a surface facing the exit surface of the prism sheet is substantially the same as 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-row triangular prism extending in parallel is provided.

[4] The width of the light collector between the side surface facing the side end surface on the base end side of the light guide plate and the side surface facing the LED substantially matches the focal length of the linear Fresnel lens. The planar illumination device according to any one of claims 1 to 3, wherein:

[5] A liquid crystal panel in which liquid crystal is held between a pair of substrates on which electrodes are formed, and the planar illumination device according to any one of claims 1 to 4, which is disposed behind the liquid crystal panel. A light source unit comprising: