Planar lighting device

Abstract

To provide a planar lighting device capable of appropriately switching an angle of field.SOLUTION: A planar lighting device comprises a plurality of light sources, a reflector, and a light distribution control film. The reflector has a plurality of reflective surfaces surrounding each of the plurality of light sources. The light distribution control film controls the spread of the light distribution on an emission side of the reflector. Two of the plurality of reflective surfaces that face each other in a first direction have different inclination angles.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a planar lighting device.

Background Art

[0002] Conventionally, as one of in-vehicle displays, a passenger seat display that mainly presents information to a passenger in the passenger seat is known. In the passenger seat display, it is displayed so that the driver cannot view it while the vehicle is running, and it is displayed so that the driver can also view it while the vehicle is stopped.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In order to switch the display form as described above, it is required to appropriately switch the viewing angle in the passenger seat display.

[0005] The present invention has been made in view of the above, and an object thereof is to provide a planar lighting device capable of appropriately switching a viewing angle.

Means for Solving the Problems

[0006] In order to solve the above-described problems and achieve the object, a planar lighting device according to an aspect of the present invention includes a plurality of light sources, a reflector having a plurality of reflecting surfaces surrounding each of the plurality of light sources, and a light distribution control film that controls the spread of light distribution on the emission side of the reflector, and two reflecting surfaces facing each other in a first direction among the plurality of reflecting surfaces have different inclination angles.

[0007] The planar lighting device according to one aspect of the present invention can appropriately switch the viewing angle.

Brief Description of Drawings

[0008]

Figure 1

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Figure 9

Modes for Carrying Out the Invention

[0009] Hereinafter, the planar lighting device according to the embodiment will be described with reference to the drawings. Note that the present invention is not limited by this embodiment. Also, the dimensional relationships of the elements in the drawings, the ratios of the elements, etc. may be different from the actual ones. There may also be parts where the dimensional relationships and ratios are different between the drawings. In addition, the content described in one embodiment or modification is generally applicable to other embodiments and modifications as well.

[0010] (First Embodiment) FIG. 1 is a diagram for explaining a usage example of the planar lighting device 1 according to the first embodiment. In FIG. 1, a case where the planar lighting device 1 is used as a direct-type backlight for a co-driver display (co-driver monitor) is explained. However, the present invention is not limited to this, and for example, when it is required to appropriately switch the viewing angle, the configuration of the planar lighting device 1 according to the present embodiment is applicable.

[0011] In FIG. 1, for convenience of explanation, the housing of the co-driver display is not shown, and the planar lighting device 1 attached to the co-driver display is shown. Further, the light-emitting surface of the planar lighting device 1 corresponds to the X-Y plane, and the light-emitting direction of the planar lighting device 1 corresponds to the Z direction. In the usage state visible to the user of the co-driver display, the X-axis direction corresponds to the horizontal direction (H), and the Y-axis direction corresponds to the vertical direction (V).

[0012] In FIG. 1, the planar lighting device 1 can switch between a privacy mode and a public mode. The privacy mode is a display state corresponding to when the vehicle is running, and the planar lighting device 1 emits light toward the co-driver seat. The public mode is a display state corresponding to when the vehicle is stopped, and the planar lighting device 1 emits light over a wide range including the co-driver seat and the driver seat. By this mode switching, the planar lighting device 1 controls the wide or narrow viewing angle of the co-driver display.

[0013] FIG. 2 is a diagram showing a configuration example of the planar lighting device 1 according to the first embodiment. In FIG. 2, the planar lighting device 1 includes an LED (Light Emitting Diode) substrate 2, a reflector 3, a liquid crystal dimming film 4, a brightness enhancement film 5, and a brightness enhancement film 6.

[0014] Hereinafter, in the description of FIG. 2, reference will be made to FIGS. 3 to 5 for explanation. FIG. 3 is a perspective view of the reflector 3. FIG. 4 is a plan view and a cross-sectional view of the reflector 3. FIG. 5 is a diagram for explaining the function of the liquid crystal dimming film 4.

[0015] The LED substrate 2 is formed of, for example, aluminum having excellent heat dissipation properties. On the LED substrate 2, a plurality of light sources 2a are two-dimensionally arranged in a lattice pattern after being appropriately insulated. The light source 2a is, for example, an LED. Each light source 2a is individually driven and can support so-called local dimming.

[0016] The reflector 3 is formed of resin or the like and has four reflecting surfaces 3a, 3b, 3c, 3d surrounding each of the plurality of light sources 2a. The reflecting surface 3a has an inclination angle substantially parallel to the optical axis (Z-axis). The inclination angle of the reflecting surface 3a (the angle with respect to the X-Y plane) is preferably, for example, 80 to 95 degrees, and more preferably 85 to 90 degrees. The reflecting surface 3b has a smaller inclination angle than the reflecting surface 3a. The inclination angle of the reflecting surface 3b is preferably, for example, 30 to 60 degrees, and more preferably 40 to 50 degrees. The reflecting surfaces 3c, 3d have an inclination angle of 60 to 70 degrees.

[0017] That is, the reflecting surface 3a and the reflecting surface 3b face each other in the horizontal direction (the X-axis direction, corresponding to the first direction in the present invention), and the inclination angles are different from each other. The reflecting surface 3a is arranged on the driver's seat side in the horizontal direction, and the reflecting surface 3b is arranged on the passenger seat side. Thereby, the reflector 3 distributes light toward the passenger seat by totally reflecting the light radiated radially from each light source 2a with respect to the optical axis (Z-axis) by the reflecting surfaces 3a, 3b. In FIGS. 3 and 4, one segment of the reflector 3 is illustrated, but actually, the reflector 3 has the same number of segments as the light sources 2a. Note that the reflector 3 may adjust the inclination angles of the reflecting surfaces 3a, 3b for each segment. Further, the reflecting surfaces 3a to 3d do not have to be planes with a constant inclination angle, and may be curved or may include a plurality of inclined surfaces. In that case, the average inclination angle can be used as a comparison target. Also, the reflecting surfaces 3c, 3d facing each other in the Y-axis direction (corresponding to the second direction in the present invention) orthogonal to the X-axis direction (the first direction) have the same absolute value of the inclination angle (symmetric) in the present embodiment, but similar to the reflecting surfaces 3a, 3b, the absolute values of the inclination angles may be different from each other.

[0018] The liquid crystal dimming film 4 is an optical element that is disposed on the light-emitting side of the reflector 3 and can change the light scattering state according to the supplied voltage. For example, the liquid crystal dimming film 4 has a structure in which a liquid crystal layer in which liquid crystal molecules 4b are encapsulated in a polymer medium 4a is sandwiched between two transparent electrode films, and the optical properties of the liquid crystal layer change by applying a voltage to both electrode films.

[0019] For example, as shown in FIG. 5, in the privacy mode, a voltage is applied, and the liquid crystal molecules 4b are oriented in equilibrium. As a result, since the refractive indices of the polymer medium 4a and the liquid crystal molecules 4b match, the liquid crystal dimming film 4 becomes in a "transparent state". On the other hand, in the public mode, no voltage is applied, and the liquid crystal molecules 4b are oriented unevenly. As a result, since the refractive indices of the polymer medium 4a and the liquid crystal molecules 4b do not match, the liquid crystal dimming film 4 becomes in a "scattering state" (opaque state).

[0020] That is, the liquid crystal dimming film 4 functions as a "light distribution control film (light distribution control optical element)" that controls the spread of light distribution by switching between the transparent state and the scattering state. Note that, contrary to the above-described voltage control, there is also known a film that becomes in a "scattering state" when a voltage is applied and becomes in a "transparent state" when no voltage is applied, and this is also applicable to the present embodiment.

[0021] The brightness enhancement film (first brightness enhancement film) 5 is an optical element (condensing film) that is disposed on the light-emitting side of the liquid crystal dimming film 4 and condenses light in the X-axis direction (horizontal direction). For example, the brightness enhancement film 5 has a plurality of triangular prisms protruding in the direction away from the light source 2a (that is, the positive Z-axis direction) on the light-emitting side surface. The triangular prisms of the brightness enhancement film 5 have linear ridges along the Y-axis direction and are arranged in a plurality along the X-axis direction.

[0022] The brightness enhancement film (second brightness enhancement film) 6 is an optical element (condensing film) that is disposed on the light-emitting side of the brightness enhancement film 5 and condenses light in the Y-axis direction (vertical direction). For example, the brightness enhancement film 6 has a plurality of triangular prisms protruding in a direction away from the light source 2a (i.e., the positive Z-axis direction) on the light-emitting side surface. The triangular prisms of the brightness enhancement film 6 have linear ridge lines along the X-axis direction and are arranged in a plurality along the Y-axis direction.

[0023] FIG. 6 is a diagram showing the light distribution of the emitted light of the liquid crystal dimming film 4, the brightness enhancement film 5, and the brightness enhancement film 6 in each mode. Note that the light distribution in FIG. 6 is a result obtained by simulation.

[0024] In FIG. 6, the peak of the light distribution in the privacy mode is located at approximately 20 degrees to the right in the horizontal direction (X = 20°, Y = 0°) in the emitted light of any of the liquid crystal dimming film 4, the brightness enhancement film 5, and the brightness enhancement film 6. As a result, it can be said that any of the emitted lights is emitted toward the passenger seat. On the other hand, the peak of the light distribution in the public mode is located at approximately the center (X = 0°, Y = 0°) in the emitted light of any of the liquid crystal dimming film 4, the brightness enhancement film 5, and the brightness enhancement film 6. As a result, it can be said that any of the emitted lights is emitted over a wide range including the passenger seat and the driver's seat.

[0025] As described above, in the planar lighting device 1 that is required to switch the width and / or direction of the viewing angle in the horizontal direction, the reflector 3 distributes the light of the light source 2a in a predetermined direction, and the liquid crystal dimming film 4 controls the spread of the light distribution by switching between the transparent state and the scattering state. Thereby, the planar lighting device 1 can appropriately switch the viewing angle of the display. When the reflector 3 according to the present invention is used to distribute the light of the light source 2a in a predetermined direction, there is an advantage that light loss can be reduced as compared with the case of using a louver film described later.

[0026] In addition, the planar lighting device 1 includes a brightness enhancement film 6 that condenses light in the vertical direction on the light-emitting side of the liquid crystal dimming film 4. Thereby, the planar lighting device 1 can improve the brightness. For example, in the public mode, the liquid crystal dimming film 4 diffuses light in all directions, resulting in a decrease in brightness (central brightness). However, the brightness enhancement film 6 can improve the brightness without affecting the visibility on the driver's seat side by condensing the light in the vertical direction.

[0027] (Second Embodiment) In the above embodiment, the case where the reflector 3 is used to distribute the light from the light source 2a toward the passenger seat has been described. However, the present invention is not limited to this. For example, it is also possible to use a louver film instead of the reflector 3.

[0028] FIG. 7 is a diagram showing a configuration example of the planar lighting device 1 according to the second embodiment. In FIG. 7, the planar lighting device 1 includes an LED substrate 2, a diffusion sheet 7, a brightness enhancement film 5, a louver film 8, a liquid crystal dimming film 4, and a brightness enhancement film 6. In FIG. 7, the description will be centered on the points different from FIG. 2, and the same components as those described in FIG. 2 will be denoted by the same reference numerals as in FIG. 2, and the description thereof will be omitted.

[0029] The diffusion sheet 7 is an optical sheet disposed on the light-emitting side of the LED substrate 2 and diffuses the light from the light source 2a.

[0030] The louver film 8 is an optical element (first light distribution control optical element) disposed on the light-emitting side of the brightness enhancement film 5 and emits light in a predetermined direction. For example, the louver film 8 has a plurality of louvers (vanes) along the YZ plane and condenses the light in the X-axis direction (horizontal direction). Note that the plurality of louvers (vanes) constituting the louver film 8 may be inclined with respect to the YZ plane in order to emit light in a direction inclined with respect to the Z-axis direction, or may not be inclined in order to emit light parallel to the Z-axis direction.

[0031] Thus, in the planar illumination device 1 according to the second embodiment, the louver film 8 distributes the light from the light source 2a in a predetermined direction, and the liquid crystal dimming film 4 (second light distribution control optical element) controls the spread of the light distribution by switching between the transparent state and the scattering state. As a result, the planar illumination device 1 can appropriately switch the viewing angle of the display. Further, by disposing the brightness enhancement film 6 that condenses light in a direction perpendicular to a direction different from the direction in which the louver film 8 distributes light on the light exit surface side of the liquid crystal dimming film 4, the brightness in the scattering state, which is lower than that in the transparent state, can be improved as compared with the case where the brightness enhancement film 6 is disposed on the side opposite to the light exit surface of the liquid crystal dimming film 4.

[0032] Using FIGS. 8 and 9, the brightness enhancement effect of the planar illumination device 1 according to the second embodiment will be described in comparison with the planar illumination device 1' according to the comparative example. FIG. 8 is a diagram showing a configuration example of the planar illumination device 1' according to the comparative example. FIG. 9 is a diagram showing the light distribution of the emitted light of each of the planar illumination devices 1 and 1' in each mode. The light distribution in FIG. 9 is a result obtained by simulation.

[0033] In FIG. 8, the planar illumination device 1' includes an LED substrate 2, a diffusion sheet 7, a brightness enhancement film 5, a brightness enhancement film 6, a louver film 8, and a liquid crystal dimming film 4 in the order shown in the figure. The configuration of the planar illumination device 1' is such that the liquid crystal dimming film 4 is disposed on the light exit side of an existing planar illumination device. Therefore, the difference between the planar illumination device 1 according to the second embodiment and the planar illumination device 1' according to the comparative example lies in the arrangement position of the brightness enhancement film 6 that condenses light in the Y-axis direction.

[0034] In FIG. 9, no significant difference was observed in the light distribution in the privacy mode between the planar illumination device 1 and the planar illumination device 1'. On the other hand, in the light distribution in the public mode, it was observed that the planar illumination device 1 condenses light in the vertical direction as compared with the planar illumination device 1'.

[0035] Table 1 shows the results of calculating the vertical and horizontal light distribution angles and relative luminance from the light distribution shown in FIG. 9. The vertical light distribution angle corresponds to the light distribution angle in the Y-axis direction, and the horizontal light distribution angle corresponds to the light distribution angle in the X-axis direction. The relative luminance is a relative luminance value calculated with the luminance (center) in the public mode of the planar lighting device 1' according to the comparative example set as 100%.

[0036]

Table 1

[0037] In Table 1, the planar lighting device 1 according to the second embodiment has a luminance increased by about 30% due to a smaller vertical light distribution angle (with the horizontal light distribution angle changing little) in the public mode compared to the planar lighting device 1' according to the comparative example. This is due to the difference in the arrangement position of the above-described luminance improvement film 6.

[0038] In the second embodiment, the case where the louver film 8 is applied as the first light distribution control optical element has been described, but the present invention is not limited thereto. Any optical element can be applied as the first light distribution control optical element as long as it can emit light in a predetermined direction. For example, the reflector 3 described in the first embodiment can also be applied as the first light distribution control optical element.

[0039] As described above, the embodiments and modifications of the present invention have been explained, but the present invention is not limited to the above embodiments, and various changes are possible without departing from the spirit thereof.

[0040] As described above, the planar lighting device according to the embodiment includes a plurality of light sources, a reflector having a plurality of reflecting surfaces surrounding each of the plurality of light sources, and a light distribution control film that controls the spread of light distribution on the emission side of the reflector. Of the plurality of reflecting surfaces, two reflecting surfaces facing each other in the first direction have different tilt angles. Thereby, the planar lighting device can appropriately switch the viewing angle (width and direction) in the first direction while suppressing light loss.

[0041] Further, on the light-emitting side of the light distribution control film, a condensing film that condenses light in a second direction perpendicular to the first direction on the light-emitting surface is further provided. Thereby, the planar lighting device can further improve the luminance.

[0042] Also, the light distribution control film controls the spread of the light distribution by switching between a transparent state and a scattered state. Thereby, the planar lighting device can appropriately switch the viewing angle.

[0043] The light distribution control film switches between the transparent state and the scattered state according to the presence or absence of power supply. Thereby, the planar lighting device can easily switch the viewing angle.

[0044] The two reflecting surfaces include a first reflecting surface having a predetermined inclination angle and a second reflecting surface having an inclination angle smaller than that of the first reflecting surface. Thereby, the planar lighting device can distribute light in a specific direction (for example, the direction of the passenger seat) in the transparent state.

[0045] The first reflecting surface has an inclination angle substantially parallel to the optical axis. Thereby, the planar lighting device can effectively suppress the light distribution to a wide viewing angle (the spread of light to the side opposite to the inclined side with respect to the optical axis of the light source) in the transparent state.

[0046] Also, the planar lighting device is used as a backlight for the passenger seat display. Thereby, the planar lighting device can appropriately switch the viewing angle in the privacy mode and the public mode of the passenger seat display.

[0047] The reflector emits light toward the passenger seat side. The light distribution control film emits the light emitted from the reflector without scattering during the running of the vehicle, and emits the light emitted from the reflector after scattering during the stop of the vehicle. Thereby, the planar lighting device can appropriately switch the viewing angles in the privacy mode and the public mode of the display for the passenger seat.

[0048] Of the two reflecting surfaces, the reflecting surface with the smaller tilt angle is arranged on the passenger seat side. Thereby, the planar lighting device can appropriately switch the viewing angles in the privacy mode and the public mode of the display for the passenger seat.

[0049] In addition, the planar lighting device according to the embodiment includes a plurality of light sources, a first light distribution control optical element that emits light in a predetermined direction on the emission side of the plurality of light sources, a second light distribution control optical element that controls the spread of light distribution on the emission side of the first light distribution control optical element, and a condensing film that condenses the light in a predetermined direction on the emission side of the second light distribution control optical element. Thereby, the planar lighting device can appropriately switch the viewing angle of the display and improve the luminance.

[0050] Further, the present invention is not limited by the above-described embodiment. The present invention also includes those configured by appropriately combining the above-described components. Further, additional effects and modifications can be easily derived by those skilled in the art. Therefore, a broader aspect of the present invention is not limited to the above-described embodiment, and various changes are possible.

Explanation of reference numerals

[0051] 1, 1’ Planar lighting device, 2 LED substrate, 2a Light source, 3 Reflector, 3a to 3d Reflecting surface, 4 Liquid crystal dimming film, 5 Luminance improvement film, 6 Luminance improvement film, 7 Diffusion sheet, 8 Louver film

Claims

1. A plurality of light sources, a reflector having a plurality of reflecting surfaces surrounding each of the plurality of light sources, and a light distribution control film for controlling the spread of light distribution on the emission side of the reflector, wherein, two reflecting surfaces facing each other in a first direction among the plurality of reflecting surfaces have different inclination angles from each other, a planar lighting device.

2. On the emission side of the light distribution control film, further comprising a condensing film for condensing light in a second direction perpendicular to the first direction on the emission surface, the planar lighting device according to Claim 1.

3. The light distribution control film controls the spread of the light distribution by switching between a transparent state and a scattered state, the planar lighting device according to Claim 1.

4. The light distribution control film switches between the scattered state and the transparent state depending on the presence or absence of power supply, the planar lighting device according to Claim 3.

5. The two reflecting surfaces include a first reflecting surface having a predetermined inclination angle and a second reflecting surface having an inclination angle smaller than that of the first reflecting surface, the planar lighting device according to Claim 1.

6. The first reflecting surface has an inclination angle substantially parallel to the optical axis, the planar lighting device according to Claim 5.

7. Used as a backlight for a co-driver's seat display, the planar lighting device according to Claim 1.

8. The reflector distributes light toward the co-driver's seat, the light distribution control film emits the light emitted from the reflector without scattering during the running of the vehicle, and emits the light emitted from the reflector after scattering during the stop of the vehicle, the planar lighting device according to Claim 7.

9. Among the two reflecting surfaces, the reflecting surface with the smaller inclination angle is arranged on the co-driver's seat side, the planar lighting device according to Claim 7.

10. A plurality of light sources, a first light distribution control optical element for emitting light in a predetermined direction on the emission side of the plurality of light sources, a second light distribution control optical element for controlling the spread of light distribution on the emission side of the first light distribution control optical element, and a condensing film for condensing light in a predetermined direction on the emission side of the second light distribution control optical element, a planar lighting device.

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