JP2018073673A - Planar light unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a planar light unit in which a positional deviation does not occur between an LED and a light guide plate, even when a transparent member is interposed between the LED and an incident surface of the light guide plate for close contact.SOLUTION: A case 18 for accommodating an LED 14 and a light guide plate 12 comprises a back frame 17 and a front frame 11. An elastomer 15 is interposed between an incident surface 12g of the light guide plate 12 and an emission surface of the LED 14. When covered by the front frame 11 in which a spring mechanism 11g extending downward from an upper surface 11e is provided, the spring mechanism 11g pushes a side surface 11c of the light guide plate 12, and the light guide plate 12 is fixed to the back frame 17.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a planar light unit that illuminates a liquid crystal panel or the like from the back, and more specifically, a transparent flexible member is disposed between a light source and an incident surface of a light guide plate to improve the incident efficiency to the light guide plate. The present invention relates to a side edge type planar light unit.

  2. Description of the Related Art A side edge type planar light unit including a light guide plate that emits light incident from one side surface (incident surface) from one main surface (exit surface) is known. In this planar light unit, the light source and the light guide plate may be brought into close contact with each other so as to suppress reflection at the interface as much as possible to improve the light emission efficiency. For example, FIG. 1 of Patent Document 1 describes a planar light unit including a light source, a light guide plate, and an intermediate layer that closely contacts the light source and the light guide plate.

  Further, in a side edge type planar light unit, a light source, a light guide plate, and the like are housed in a frame-like case, and a side surface of the light guide plate is pushed by an elastic member, and these are fixed to the case. For example, in FIG. 1 of Patent Document 2, an elastic holding portion provided between a side surface opposite to a side surface serving as a light receiving portion of a light guide plate and an inner wall surface of a frame body facing the side surface is provided with a light guide plate. A planar light unit for fixing the frame to the frame is described.

Japanese Patent Laying-Open No. 2007-103101 (FIG. 1) JP 2006-318830 A (FIG. 1)

  However, if a transparent member is interposed between the LED serving as the light source and the incident surface of the light guide plate as an intermediate layer for adhesion, the LED is displaced relative to the light guide plate when the LED and the light guide plate are stored in the case. Is likely to occur. This misalignment not only lowers the light emission efficiency but also causes uneven brightness on the exit surface.

  Accordingly, the present invention has been made in view of the above problems, and even if a transparent member is interposed between the LED and the incident surface of the light guide plate for close contact, the positional deviation between the LED and the light guide plate. It aims at providing the planar light unit which does not generate | occur | produce.

  In order to solve the above problems, a planar light unit of the present invention is a planar light unit in which an LED and a light guide plate are housed in a case. The case includes a back frame and a front frame that covers the back frame, The front frame includes a spring mechanism extending downward from the upper surface, the light guide plate has an incident surface and an output surface orthogonal to the incident surface, and a transparent flexible member is interposed between the LED and the incident surface. The spring mechanism pushes a side surface of the light guide plate that faces the incident surface toward the incident surface.

  The light guide plate may include a support portion that protrudes from both sides of the incident surface and extends in parallel with the emission surface, and the spring mechanism may cause the support portion to contact the side wall of the back frame.

  The light guide plate may include an incident portion reflecting surface having a bowl-shaped cross section between the incident surface and the emitting surface.

  The spring mechanism may be made of metal, made of a part of the front frame, and may have a U-shaped cross section.

  The spring mechanism may be made of resin and integrated with the front frame.

  The spring mechanism has an inclined surface, the light guide plate has an inclined surface on the side surface facing the incident surface, and when the front frame is put on the back frame, the inclined surfaces slide to each other. A light guide plate may be fixed to the back frame.

  In the planar light unit of the present invention, first, a light guide plate equipped with a transparent flexible member is inserted into the back frame. At this time, no stress is applied to the LED, the transparent flexible member, and the backlight. In this state, the LED, the transparent flexible member, and the backlight are positioned. Next, when the front frame is put on the back frame, the spring mechanism pushes one side surface of the light guide plate. The spring mechanism moves the light guide plate in parallel to the bottom surface of the back frame, so that the LED and the incident surface of the light guide plate are in close contact with the transparent flexible member. As a result, the light guide plate is fixed to the back frame. That is, since the parallel movement of the light guide plate by the spring mechanism is slight, the LED, the transparent flexible member, and the light guide plate are positioned and fixed without causing a positional shift.

  As described above, in the planar light unit of the present invention, even when the transparent flexible member is interposed between the LED and the light guide plate, no positional deviation occurs between the LED and the light guide plate.

It is a disassembled perspective view of the planar light unit shown as 1st Embodiment of this invention. It is a top view of the planar light unit shown in FIG. It is a top view which shows the internal structure of the planar light unit shown in FIG. It is sectional drawing of the planar light unit shown in FIG. It is sectional drawing of the planar light unit shown as 2nd Embodiment of this invention. It is sectional drawing of the planar light unit shown as 3rd Embodiment of this invention. It is sectional drawing of the planar light unit shown as 4th Embodiment of this invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. In the description of the drawings, the same or equivalent elements will be denoted by the same reference numerals, and redundant description will be omitted. The scale and the like of the drawings are changed as appropriate for explanation. The invention specific matters shown in the scope of claims are described in ().

(First embodiment)
FIG. 1 is an exploded perspective view of a planar light unit 10 shown as the first embodiment of the present invention. The planar light unit 10 includes a front frame 11, a light guide plate 12, a circuit board 13, an LED 14, an elastomer 15 (transparent flexible member), a reflective sheet 16 and a back frame 17. An optical sheet 19 (see FIG. 2 and FIG. 4) (not shown) is laminated on the light guide plate 12. The case 18 (reference numeral is not shown) includes a front frame 11 and a back frame 17. Other members are accommodated in the case 18.

The front frame 11 includes side walls 11a, 11b, 11c, and 11d on four sides of the upper surface 11e. In addition, a part of the side wall 11c is observed through the cut and bent hole 11g. The side wall 11d is hidden behind the upper surface 11e of the front frame 11 and is not observed. The upper surface 11e is open at the center, and includes a spring mechanism 11f and a cut hole 11g for forming the spring mechanism 11f on the side wall 11c side.

  The light guide plate 12 is a flat plate whose one side surface is processed (hereinafter, this processed portion is referred to as an incident portion 12a). The incident portion 12a includes an incident surface 12g, an incident portion reflecting surface 12h, and a support portion 12i. The incident surface 12g is a rectangular plane extending in the longitudinal direction of the incident portion 12a. The incident part reflection surface 12h is a curved surface formed in a cross-sectional shape along the top and bottom of the incident surface 12g (the lower incidence part reflection surface 12h cannot be observed). The support portions 12i are provided on both sides of the incident surface 12g, have the same thickness as the other portions of the light guide plate 12, and extend from the other portions in a direction parallel to the emission surface 12f. The main surface of the light guide plate 12 is an emission surface 12f on the upper side and a reflection surface 12e on the lower side (the reflection surface 12e cannot be observed), and the side surfaces 12b, 12c and 12d (side surfaces 12c, 12c, 12d is hidden by the exit surface 12f and cannot be observed).

  A circuit board 13, a plurality of LEDs 14, and an elastomer 15 are arranged on the incident surface 12 g side of the light guide plate 12. The circuit board 13 is a flat plate extending in the longitudinal direction of the incident portion 12 a of the light guide plate 12. The LEDs 14 are arranged in a line along the longitudinal direction of the incident portion 12 a and are mounted on the circuit board 13. The elastomer 15 is a single rectangular column extending in the longitudinal direction of the incident portion 12a, and is interposed between the light exit surface of the LED 14 and the incident surface 12g of the light guide plate 12, and mechanically and optically adheres both.

  The reflection sheet 16 includes a bottom surface 16e and side walls 16b, 16c, and 16d that are bent along three sides of the bottom surface 16e. The bottom portion 16e is in contact with the reflecting surface 12e of the light guide plate 12 through an air layer. The side walls 16b, 16c, and 16d are in contact with the side surfaces 12b, 12c, and 12d of the light guide plate 12 through a double-sided tape (not shown).

  The back frame 17 includes a bottom surface 17e and side walls 17a, 17b, 17c, and 17d provided on four sides of the bottom surface 17e. The back frame 17 houses the light guide plate 12, the circuit board 13, the LED 14, the elastomer 15, and the reflection sheet 16. The back frame 17 is covered with the front frame 11 together with these members.

  The circuit board 13 is attached to the side wall 17 a of the back frame 17. The elastomer 15 is affixed to the incident surface 12g of the light guide plate 12 using weak adhesiveness. In this state, the light guide plate 12 is housed in the back frame 17, and the LED 14, the elastomer 15 and the light guide plate 12 are positioned so that the elastomer 15 is in light contact with the light exit surface of the LED 14. Finally, the back frame 17 is covered with the front frame 11. As a result, the spring mechanism 11 f pushes the side surface 12 c of the light guide plate 12, the support portion 12 i comes into strong contact with the side wall 17 a, and the light guide plate 12 is fixed to the back frame 17.

  FIG. 2 is a plan view of the planar light unit 10. As shown in FIG. 2, the optical sheet 19 is observed from the center of the frame-shaped front frame 11. The optical sheet 19 not shown in FIG. 1 is laminated on the light exit surface 12f (see FIG. 1) of the light guide plate 12 (see FIG. 1) (see FIG. 4). A cutting hole 11g for forming a spring mechanism 11f (see FIG. 1) is observed on the upper side of the front frame 11 (side wall 11c (see FIG. 1)). A bottom surface 17e of the back frame 17 (see FIG. 1) is observed from the cut and bent hole 11g.

FIG. 3 is a plan view of the planar light unit 10 with the front frame 11 and the optical sheet 19 removed. As shown in FIG. 3, the exit surface 12f, the incident portion reflecting surface 12h, and the support portion 12i of the light guide 12 are observed. On the side surface 12c side (see FIG. 1) of the light guide plate 12, a bottom surface 17e of the back frame 17 (see FIG. 1) is observed. In the incident part 12a (see FIG. 1) of the light guide plate 12, the circuit board 13, the LED 14 mounted on the circuit board 13, and the light exit surface of the LED 14 and the light guide plate 12 enter so as to be sandwiched between the support parts 12i. The elastomer 15 arranged between the faces 12g is observed. The bottom surface 17e of the back frame 17 is observed from the left and right gaps of the LED 14. Side walls 17a to 17d of the back frame 17 are not shown.

  4 is a cross-sectional view of the planar light unit 10 drawn along the line AA ′ of FIG. For the sake of explanation, the enlargement ratio in the thickness direction (vertical direction in the figure) is made larger than that in the light guide direction (horizontal direction in the figure). Therefore, the width of the cutting hole 11g is the same as that of the spring mechanism 11f even though the width of the cutting hole 11g of the front frame 11 (horizontal direction in the figure) and the length of the spring mechanism 11f (vertical direction in the figure) are substantially equal. It is illustrated so as to be smaller than the length (the same applies to FIGS. 5 to 7).

  As shown in FIG. 4, the reflection sheet 16, the light guide plate 12, and the optical sheet 19 are laminated on the bottom surface 17 e of the back frame 17. In the light guide plate 12, the incident surface 12g and the incident portion reflecting surface 12h are observed at the incident portion 12a on the left side of the drawing. The incident surface 12g is a flat surface. The incident part reflecting surface 12h is provided above and below the incident surface 12g, and has a curved surface with a cross-section (secondary curve). The right side surface of the elastomer 15 is in close contact with the incident surface 12g. The left surface of the elastomer 15 is in close contact with the light emitting surface of the LED 14 (the right surface of the LED 14). The elastomer 15 is deformed because of pressure, but this deformation is not shown. The LED 14 is mounted on the circuit board 13. The circuit board 13 is attached to the side wall 17a of the back frame 17 with a double-sided tape (not shown).

  As shown in FIG. 4, on the right side of the light guide plate 12, the side wall 16c of the reflection sheet 16 is attached to the side surface 12c with a double-sided tape (not shown). The top of the spring mechanism 11f is in contact with the side wall 16c. The spring mechanism 11f hangs downward from the upper surface 11e of the front frame 11 and has a cross-sectional shape in a dogleg shape. This spring mechanism 11f is obtained by processing a member obtained by opening a cut-and-bending hole 11g in the upper surface 11e of the front frame 11 into a U-shaped cross section, and an upper end is connected to the left end of the cut-and-bend hole 11g. .

  In FIG. 4, when the back frame 17 is covered with the front frame 11, the spring mechanism 11 f pushes the light guide plate 12 to the left in the drawing via the reflection sheet 16. As a result, pressure is applied to the elastomer 15, and the light exit surface of the LED 14 and the incident surface 12g of the light guide plate 12 are completely adhered. At this time, the support portion 12 i of the light guide plate 12 (not shown) strongly contacts the side wall 17 a of the back frame 17. Since the elastomer 15 is highly flexible, the force with which the elastomer 15 presses the light exit surface of the LED 14 is significantly smaller than the force with which the side wall 17a is pressed. However, the elastomer 15 itself is completely fixed to the light guide plate 12 and the like by this force. If there is a concern about the vertical movement of the elastomer 15 due to vibration or the like, a groove into which the elastomer 15 is fitted may be formed in the light guide plate 12 (in FIG. 4, the position of the incident surface 12g) (in this case, The bottom of the groove (when the groove is drawn in FIG. 4, it becomes the right surface) becomes the incident surface).

  The front frame 11 and the back frame 17 are made of an aluminum plate having a thickness of 0.2 to 0.6 mm. As shown in FIG. 4, when the top of the spring mechanism 11f, the center line of the light guide plate 12 (the center in the thickness direction), and the center axis of the LED 14 are aligned, an unnecessary moment is applied to the light guide plate 12, the elastomer 15, and the like. It won't hang. Further, a spring mechanism (rubber, leaf spring, spring, etc.) is inserted between the side wall 16c of the reflection sheet 16 and the side wall 17c of the back frame 17, or the light guide plate 12 is pushed with a screw from the side wall 17c side. 11f may be assisted.

The light guide plate 12 has a thickness of 2.0 to 3.0 mm and is made of polycarbonate, acrylic, or the like, and a dot (not shown) whose diameter is changed depending on the location so that the luminance on the emission surface 12f is uniform is formed on the reflection surface 12e. Is formed. This dot is a recess formed by laser processing and has a diameter of 50 to 500 μm. The circuit board 13 is an FPC (flexible printed circuit) based on polyimide.

  The LED 14 is a package product in which an LED die is mounted on a submount substrate serving as an interposer, and the periphery of the LED die is covered with a sealing resin. The LED 14 may be one in which one LED 14 emits white light by a combination of a fluorescent resin (a sealing resin containing a phosphor) and a blue light emitting diode, and a set of three LEDs 14 includes a red light emitting LED and a green light emitting diode. A light emitting LED and a blue light emitting LED may be used to emit white light. The electrodes of the LED 14 are connected to the electrodes formed on the circuit board 13 with solder or the like.

  The elastomer 15 is made of a highly flexible silicone resin, and compressively deforms to optically and mechanically connect the light exit surface of the LED 14 and the incident surface 12g of the light guide plate 12, and the shape error and temperature characteristics of the light guide plate 12 and the like. Absorbs thermal expansion deformation caused by For example, the elastomer 15 may have a Young's modulus of about 0.1 to 1 MPa. When the Young's modulus is this value, a pressure of about 10 MPa is generated on the LED 14 due to thermal expansion or the like. However, since the LED 14 does not break down to about 100 Mpa, there is no problem if the pressure is about 10 Mpa. The elastomer 15 preferably has the same refractive index as that of the light guide plate 12, that is, the refractive index thereof is 1.4 to 1.6.

  The reflection sheet 16 is made of white PET and has a thickness of 200 μm. A double-sided tape (not shown) has adhesive layers on both sides of a transparent PET sheet and has a thickness of 100 μm. The optical sheet 19 is a diffusion sheet or a prism sheet, and is laminated on the emission surface 12 f of the light guide plate 12.

  The light emitted from the LED 14 enters the elastomer 15 and then enters the light guide plate 12 from the elastomer 15 through the incident surface 12g. The light that has entered the incident surface 12g with a small incident angle propagates in the light guide plate 12 while being repeatedly reflected between the upper and lower main surfaces (the output surface 12f and the reflecting surface 12e). Light entering from the incident surface 12g at a large incident angle is totally reflected by the incident portion reflecting surface 12h, and then propagates through the light guide plate 12 while being repeatedly reflected between the upper and lower main surfaces. The light propagating in the light guide plate 12 has its traveling direction changed by the dots formed on the reflection surface 12e, and is emitted to the outside of the light guide plate 12 from the emission surface 12f.

As is well known, when light enters a medium having a refractive index n1 from a medium having a refractive index n1,
R = | n1-n2 | / (n1 + n2)
(R is the square root of reflectivity). In the planar light unit 10, the sealing resin of the LED 14, the light guide plate 12, and the refractive index of the elastomer 15 are all about 1.4 to 1.5, so that almost no loss due to reflection occurs. As a result, in the planar light unit 10, since the loss due to reflection is greatly reduced, the light emission efficiency is improved.

  As described above, in the planar light unit 10, first, the circuit board 13 on which the LEDs 14 are mounted is attached to the side wall 17 a of the back frame 17. At this time, as shown in FIG. 4, the optical axis of the LED 14 (axis passing through the center of the light emitting surface of the LED 14 and perpendicular to the light emitting surface) and the center line of the light guide plate 12 (center height in the thickness direction) are Make sure they match. Next, the light guide plate 12 to which the elastomer 15 and the reflection sheet 16 are attached is placed horizontally on the bottom surface 17 e of the back frame 17. Then, the back frame 17 is shifted horizontally so that the elastomer 15 is brought into light contact with the light emitting surface of the LED 14. As a result, the light guide plate 12, the LED 14, and the elastomer 15 are aligned. Thereafter, when the optical sheet 19 is laminated on the light guide plate 12, the front frame 11 is covered. At this time, the spring mechanism 11f pushes and moves the light guide plate 12 in the horizontal direction. However, since the moving distance of the light guide plate 12 is small, the aligned state is maintained.

  As described above, the planar light unit 10 is prevented from being displaced between the light guide plate 12, the LED 14, and the elastomer 15. That is, in the planar light unit 10, even if the elastomer 15 is interposed between the LED 14 and the incident surface 12 g of the light guide plate 12 for adhesion, no positional deviation occurs between the LED 14 and the light guide plate 12. As a result, it is possible to obtain the planar light unit 10 that is easy to assemble and has good luminous efficiency and uniformity.

(Second Embodiment)
In the planar light unit 10 shown in FIGS. 1 to 4, a cut / bend hole 11 g for forming the spring mechanism 11 f is provided in the upper surface 11 e of the front frame 11. However, the part where the cut hole is formed is not limited to the upper surface of the front frame. Therefore, referring to FIG. 5, a planar light unit 20 in which the cut and hole forming the spring mechanism extends from the upper surface of the front frame to the side wall will be described as a second embodiment of the present invention.

  5 is a cross-sectional view of the planar light unit 20 at a position corresponding to the line AA ′ of FIG. In addition, since the difference in structure between the planar light unit 20 and the planar light unit 10 is slight, an exploded perspective view and a plan view are not shown in the description of the planar light unit 20.

  As shown in FIG. 5, the planar light unit 20 is different from the front frame 11 of the planar light unit 10 shown in FIG. That is, the cut-and-bend hole 21g extends from the upper surface 21e of the front frame 21 to the side wall 21c. In this way, a portion for forming the spring mechanism 21f can be secured from the side wall 21c. This means that the distance between the side surface 12c of the light guide plate 12 and the side wall 17c of the back frame 17 can be reduced. As a result, the planar light unit 20 is reduced in size by extending the cut and bent hole 21g from the upper surface 21e to the side wall 21c.

(Third embodiment)
In the planar light unit 10 shown in FIGS. 1 to 4, the spring mechanism 11 f is connected to the upper surface 11 e on the LED 14 side of the cut and bent hole 11 g formed in the front frame 11. However, in the front frame, the connection position between the spring mechanism and the upper surface is not limited to the LED 14 side of the cutting hole. Therefore, referring to FIG. 6, as a third embodiment of the present invention, a planar light unit 30 in which the connection position between the spring mechanism and the upper surface of the front frame is provided on the side opposite to the LED 14 side of the cutting hole is provided. explain.

  FIG. 6 is a cross-sectional view of the planar light unit 30 at a position corresponding to the line AA ′ in FIG. In addition, since the difference in structure between the planar light unit 30 and the planar light unit 10 is slight, an exploded perspective view and a plan view are not shown in the description of the planar light unit 30.

  As shown in FIG. 6, the planar light unit 30 is different from the front frame 11 of the planar light unit 10 shown in FIG. 4 in the connection portion between the upper surface 31 e of the front frame 31 and the spring mechanism 31 f. That is, in the planar light unit 30, the spring mechanism 31 f is connected to the upper surface 31 e of the front frame 31 on the side wall 31 c side (the side opposite to the LED 14) of the cutting hole 31 g formed in the front frame 31. In this way, it is possible to observe how the spring mechanism 31f pushes the side surface 12c of the light guide plate 12 through the cut / bend hole 31g. In FIG. 6, the side surface 12c of the light guide plate 12 and the side wall 16c of the reflection sheet 16 are moved to the right by the width of the cutting hole 31g with respect to FIG.

(Fourth embodiment)
In the planar light units 10, 20, and 30 shown as the first to third embodiments, the front frames 11, 21, and 31 and the spring mechanisms 11f, 21f, and 31f are made of metal. However, the front frame and the spring mechanism are not limited to metal and may be resin. Accordingly, a planar light unit 40 in which the front frame and the spring mechanism are made of resin will be described with reference to FIG. 7 as a fourth embodiment of the present invention.

  7 is a cross-sectional view of the planar light unit 40 at a position corresponding to the line AA ′ of FIG. In addition, since the difference in structure between the planar light unit 40 and the planar light unit 10 is slight, an exploded perspective view and a plan view are not shown in the description of the planar light unit 40.

  As shown in FIG. 7, the planar light unit 40 is different from the front frame 11 of the planar light unit 10 shown in FIG. 4 in the structure around the spring mechanism 41 f of the front frame 41. That is, as shown in FIG. 7, the spring mechanism 41f is a plate-like portion having a first slope (upper slope) and a second slope (lower slope) on the LED 14 side, and a vertical surface on the side wall 41c side. And hangs downward from the upper surface 41e. The side surface 12c of the light guide plate 12 is a slope so that the side surface 12c of the light guide plate 12 and the first slope contact each other. The spring mechanism 41f may be divided into a plurality of parts in the paper surface direction.

  When the front frame 41 is put on the back frame 17, the spring mechanism 41f slides the first inclined surface of the spring mechanism 31 and the side surface 12c of the light guide plate 12 forming the inclined surface to push the light guide plate 12 to the LED 14 side. Move. As a result, the light guide plate 12 is fixed to the back frame 17.

  In the planar light units 10, 20, 30, and 40, the support portion 12 i supports the light guide plate 12 with respect to the back frame 17 and prevents the LED 14 from being pressed more than necessary. When the light guide plate 12 can be supported and fixed only by the repulsive force of the elastomer 15, the support portion 12i can be omitted.

  Further, the light guide plate 12 was provided with an incident portion reflecting surface 12h in the incident portion 12a. The incident part reflecting surface 12h totally reflects light that has entered the incident surface 12g at a large incident angle, reduces light that leaks out of the light guide plate 12, and improves light emission efficiency. When this loss can be ignored, the incident part reflecting surface 12h can be omitted.

10, 20, 30, 40 ... planar light unit,
11, 21, 31, 41 ... front frame,
11a-11c, 21c, 31c, 41c ... side wall,
11e, 21e, 31e, 41e ... upper surface,
11f, 21f, 31f, 41f ... spring mechanism,
11g, 21g, 31g ... cut and bent holes,
12 ... light guide plate,
12a: Incident part,
12b-12d ... side surface,
12e ... reflective surface,
12f ... emitting surface,
12g ... incident surface,
12h ... incident part reflecting surface,
12i ... support part,
13 ... Circuit board,
14 ... LED,
15 ... Elastomer (transparent flexible member),
16 ... reflective sheet,
16b-16d ... side wall,
16e ... bottom surface,
17 ... back frame,
17a-17d ... side wall,
17e ... bottom,
18 ... Case,
19: Optical sheet.

Claims (6)

In a planar light unit in which an LED and a light guide plate are housed in a case,
The case includes a back frame and a front frame covering the back frame,
The front frame includes a spring mechanism extending downward from the upper surface,
The light guide plate has an entrance surface and an exit surface orthogonal to the entrance surface,
A transparent flexible member is interposed between the LED and the incident surface,
The planar light unit, wherein the spring mechanism pushes a side surface of the light guide plate facing the incident surface toward the incident surface. The light guide plate includes a support portion that protrudes from both sides of the incident surface and extends parallel to the emission surface,
The planar light unit according to claim 1, wherein the spring mechanism causes the support portion to abut against a side wall of the back frame.   The planar light unit according to claim 1, wherein the light guide plate includes an incident portion reflecting surface having a cross-sectional shape between the incident surface and the exit surface.   The planar light unit according to any one of claims 1 to 3, wherein the spring mechanism is made of metal, includes a part of the front frame, and has a U-shaped cross section.   The planar light unit according to any one of claims 1 to 3, wherein the spring mechanism is made of resin and integrated with the front frame.   The spring mechanism has an inclined surface, the light guide plate has an inclined surface on the side surface facing the incident surface, and when the front frame is put on the back frame, the inclined surfaces slide to each other. The planar light unit according to claim 5, wherein a light guide plate is fixed to the back frame.