Patent ID: 12216278

DETAILED DESCRIPTION

In the following, embodiments of the present invention will be described in detail with reference to the drawings.

First Embodiment

FIG.1is an exploded perspective view illustrating an overview of a light source device according to a first embodiment of the present invention. As is also apparent from the drawing, a light source device (main body)10is formed of, for example, plastic or the like, and is constituted of a light source device case11formed by housing an LED, a collimator, a synthetic diffusion block (diffusion block), a light guide, and the like, which will also be described in detail below, inside the light source device. A liquid crystal display element50is attached to the upper surface of the light source device, an LED substrate12on which a light emitting diode (LED) element which is a semiconductor light source and a control circuit thereof are mounted is attached to one side surface of the light source device, and a heatsink13for cooling heat generated in the above-described LED element and control circuit is attached to the outer side surface of the LED substrate12.

Further, the liquid crystal display element50attached to the upper surface of the light source device case11is constituted of a liquid crystal display panel frame51, a liquid crystal display panel52attached to the frame, and a flexible printed circuit board (FPC)53electrically connected to the panel. In other words, as will also be described in detail below, the liquid crystal display panel52is controlled by a control signal from a control circuit (not illustrated) constituting the electronic device.

FIG.2illustrates a configuration of an optical system housed inside the light source device10described above, that is, in the light source device case11.

A plurality of (four in this example) LEDs14ato14d(only two LEDs14aand14bare illustrated in FIG.2) constituting the light sources are attached to a bottom of each of the LED collimators15having a conical convex outer shape obtained by rotating a substantially parabolic disconnection line, and a rectangular synthetic diffusion block16is provided on a light emission side of the LED collimators. In other words, the laser light emitted from the LED14aor14bis reflected by a boundary surface of the parabolic line of the LED collimator15, is converted into parallel light, and is incident on the synthetic diffusion block16.

Further, a rod-shaped light guide17having a substantially triangular cross section is provided on an emission surface side of the synthetic diffusion block16described above via a first diffusion plate18a, and a second diffusion plate18bis attached to the upper surface of the light guide. Thus, horizontal light of the LED collimator15described above is reflected upward in the drawing by an action of the light guide17, and is guided to an incidence surface of the liquid crystal display element50described above. Note that, at this point, intensity of the light is uniformized by the first and second diffusion plates18aand18bdescribed above.

Usability of High-Luminance LED Light Source

In the present embodiment, a high-output type LED light source is used as the LED light source, and a basic configuration thereof is a configuration in which a phosphor is excited by a blue LED, and a blue excitation light and fluorescent light (including a green component and a red component) are mixed and diverged.FIG.21is a characteristic diagram illustrating spectral radiant energy of a high-luminance LED for an HUD backlight, which is a Product X of Company A, as a relative value. A radiant light flux of 224 to 355 (lm) is output at an input current of 1000 (mA). The high-luminance blue LED for exciting a phosphor containing a green component and a red component as output light has a peak wavelength of 440 (nm), a wavelength of 420 (nm) on a short-wavelength side at which luminance is 10% of a peak luminance, and a cutoff wavelength of 360 (nm), and is such that light belonging to a blue short-wavelength region (indicated as a high-energy region in the drawing) from a high-energy ultraviolet region is diverged. Other high-luminance LEDs for backlight include, for example, a Product Y of Company B.FIG.23illustrates a characteristic in which spectral radiant energy is used as a relative value. A light flux of 168 (lm) is output at an input current of 650 (mA). The high-luminance blue LED for exciting a phosphor containing a green component and a red component as output light has a peak wavelength of 445 (nm), a wavelength of 423 (nm) on the short-wavelength side at which the luminance is 10% of the peak luminance, and the cutoff wavelength of 400 (nm). Divergence characteristics of a light source light from the high-luminance LED for the HUD backlight inFIG.21are as illustrated inFIG.22.

On the other hand, an LED as a representative example used as a backlight light source for a liquid crystal TV includes, for example, a Product Z of Company B.FIG.25illustrates a characteristic in which the spectral radiant energy is used as a relative value. A light flux of 168 (lm) is output at an input current of 650 (mA). The high-luminance blue LED for exciting a phosphor containing a green component and a red component as output light has a peak wavelength of 450 (nm), a wavelength of 430 (nm) on the short-wavelength side at which the luminance is 10% of the peak luminance, and the cutoff wavelength of 420 (nm), and has characteristics in which the peak wavelength and cutoff wavelength of the high-luminance LED are shifted to a long-wavelength side.

Therefore, in the light source device using the high-luminance LED, it is necessary to limit the amount of blue light (light in the blue region) having high energy which is incident on a liquid crystal panel and a polarizing plate. Therefore, in the present embodiment, for example, an optical filter FIL having transmission characteristics illustrated inFIG.27is disposed between the LED as the light source and an LCD and the polarizing plate as the image source. The filter having a characteristic A obtained by sputtering the metal multilayer film illustrated inFIG.27and the filter having a characteristic B obtained by vapor deposition may be provided on a light source light (parallel light) passing surface of an optical element. The filter having the characteristic A is provided at a location closer to an LED as a light source, and light in the high-energy region is completely shielded by the filter having the characteristic A. In addition, it is more preferable that the filter having the characteristic B is provided on a light source light passing surface of a different optical element. In order to obtain the filter characteristics described above, it is essential that the light source light is perpendicularly incident on a filter installation surface.

However, the divergence characteristics of the light source light from the LED are as illustrated inFIGS.22,24, and26. InFIGS.22,24, and26, relative luminance is illustrated with a direction perpendicular to an emission surface of the LED (divergence angle of 0 degrees) as 100%. At a divergence angle of 40 degrees, the relative luminance is 80%, and at a divergence angle of 60 degrees, the relative luminance is 55% to 50%, and when the LED described above is used as is, the light source light is obliquely incident on the filter installation surface described above. As a result, the cutoff wavelength is shifted to the short-wavelength side, and affects reliability of the polarizing plate and the LCD panel.

As a countermeasure against the above, in the present embodiment, as illustrated inFIGS.4,5A, and5B, divergent light from the LED is converted into substantially parallel light by the LED collimator15, and then the filter FIL having the characteristics illustrated inFIG.27is provided on an emission surface152of the LED collimator15or an incidence surface162of the synthetic diffusion block16, or on both of these surfaces. Thus, the high-energy, short-wavelength blue light and ultraviolet light can be cut off, and the resistance to the high-luminance light source light can be improved.

In a second embodiment to be described below, as illustrated inFIGS.16,17A, and17B, the divergent light from the LED is converted into substantially parallel light by the LED collimator15, and then the filter having the characteristics illustrated inFIG.27is provided on the emission surface152, or an incidence surface214of a polarization conversion element21, or on both of these surfaces. Thus, as in the first embodiment, the high-energy, short-wavelength blue light and ultraviolet light can be cut off, and resistance to the high-luminance light source light can be significantly improved.

By providing the filter having the characteristic A illustrated inFIG.27on the emission surface152of the LED collimator, light (e.g., blue light) in the high-energy region reflected by the filter having the characteristic A excites the phosphor of the high-luminance LED again, so that light output is increased. When the filter characteristic A illustrated inFIG.27is used as a reference (cutoff wavelength of 435 nm), the light output is improved by about 15%. When the cutoff wavelength of 430 (nm) is used, the light output is improved by 12%, and when the cutoff wavelength of 420 (nm) is used, the light output is improved by 4%, whereby the light output improvement effect can be confirmed.

Detailed Structure of Light Guide

Details of the light guide17constituting the light source device10described above will now be described with reference to the drawings. Note thatFIG.3Ais a perspective view illustrating the entire light guide17, the upper part ofFIG.3Bincludes a cross-sectional view of the light guide, and the lower part ofFIG.3Bincludes partially enlarged cross-sectional views illustrating the details of the cross sections of the light guide.

The light guide17is, for example, a rod-shaped member having a substantially triangular cross section (seeFIG.3B) and made of a translucent resin such as acrylic. As illustrated inFIG.3A, the light guide17includes a light guide light incidence portion (surface)171configured to face the emission surface of the synthetic diffusion block16described above with the first diffusion plate18ainterposed therebetween, a light guide light reflection portion (surface)172configured to form an inclined surface, and a light guide light emission portion (surface)173configured to face the liquid crystal display panel52of the liquid crystal display element50described above with the second diffusion plate18binterposed therebetween.

As illustrated in the lower part ofFIG.3Bwhich includes partially enlarged views thereof, a large number of reflection surfaces172aand connection surfaces172bare alternately formed in a saw-tooth shape on the light guide light reflection portion (surface)172of the light guide17. Each reflection surface172a(line segment rising to the right in the drawing) forms an angle αn (n: natural number, e.g., 1 to 130 in this example) with respect to a horizontal plane indicated by the dashed-and-dotted line in the drawing, and αn is here set to 52 degrees or less (but 44 degrees or more) as an example.

On the other hand, each connection surface172b(line segment falling to the right in the drawing) forms an angle of μn (n: natural number, e.g., 1 to 130 in this example) with respect to the reflection surface172a. In other words, the connection surface172bof the reflection portion is inclined with respect to incident light at an angle at which a shadow is formed within a range of a half-value angle of a scatterer to be described below. As will also be described in detail below, α1, α2, α3, α4. . . form a reflection surface elevation angle, and μ1, μ2, μ3, μ4. . . form a relative angle between the reflection surface and the connection surface, and is set to 90 degrees or more (but 180 degrees or less) as an example. Note that, in this example, β1=β2=β3=ξ4= . . . =β122= . . . μ130.

FIGS.4,5A, and5Billustrate, for explanatory purposes, schematic diagrams in which the reflection surface172aand the connection surface172bare made relatively larger than the light guide17. At the light guide incidence portion (surface)171of the light guide17, the main light beam is deflected by δ in a direction in which the incidence angle with respect to the reflection surface172aincreases (seeFIG.5B). In other words, the light guide incidence portion (surface)171is formed in a curved convex shape inclined toward the light source side. According to this, the parallel light from the emission surface of the synthetic diffusion block16is diffused through the first diffusion plate18ato be incident, and as is also apparent from the drawing, the incident light reaches the light guide light reflection portion (surface)172while being slightly bent (deflected) upward by the light guide incidence portion (surface)171(see comparative example ofFIG.6).

Note that a large number of reflection surfaces172aand connection surfaces172bare alternately formed in a saw-tooth shape on the light guide light reflection portion (surface)172, and the diffused light is totally reflected on each reflection surface172aand directed upward, and further is incident on the liquid crystal display panel52as a parallel diffused light via the light guide light emission portion (surface)173and the second diffusion plate18b. Therefore, the reflection surface elevation angles α1, α2, α3, α4. . . are set such that each reflection surface172ahas an angle larger than or equal to a critical angle with respect to the above-described diffused light, and on the other hand, the relative angles β1, β2, β3, β4. . . between the reflection surface172aand the connection surface172bare set to a certain angle as described above, and more preferably are set to an angle of 90 degrees or more (βn≥90°), the reason for which will also be described below.

According to the above-described configuration, since each of the reflection surfaces172ais always formed at an angle larger than or equal to the critical angle with respect to the diffused light, total reflection is possible even if a reflective film made of metal or the like is not formed on the reflection portion172, and thus, a low-cost light source device can be realized. On the other hand, as illustrated inFIG.6as a comparative example, when the main light beam is not bent (polarized) at the light guide incidence portion of the light guide17, a part31bof the diffused light becomes less than or equal to the critical angle with respect to the reflection surface172a, making it impossible to secure a sufficient reflectance and to realize light source device having good (bright) characteristics.

The reflection surface elevation angles α1, α2, α3, α4. . . slightly increase from the lower portion to the upper portion of the light guide light reflection portion (surface)172. Since the light transmitted through the liquid crystal display panel52of the liquid crystal display element50has a certain degree of divergence angle, in order to prevent the so-called peripheral darkening in which a part of the light transmitted through the peripheral portion of the liquid crystal display panel52is blocked by a peripheral edge of a mirror disposed on a downstream side, a configuration is realized such that a peripheral light beam is slightly deflected toward a central axis, as indicated by a light beam30inFIG.4.

As described above, β1=β2=β3=β4. . . βn≥90°. This is because, as illustrated inFIG.9, the reflection surface172aand the connection surface172bcan be simultaneously machined by an endmill35having a relative angle β between the bottom surface and the side surface in the machining of a mold40for manufacturing the light guide17by injection-molding. Since the reflection surface172aand the connection surface172bcan be machined by relatively thick tools, the machining time can be greatly shortened and the machining cost can be greatly reduced. In addition, a boundary edge between the reflection surface172aand the connection surface172bcan be machined accurately, and light guiding characteristics of the light guide17can be improved.

In addition, inFIG.4, Lr1, Lr2, Lr3, Lr4. . . represent projected lengths of the reflection surface172awith respect to the horizontal plane, Lc1, Lc2, Lc3, Lc4. . . represent projected lengths of the connection surface172bwith respect to the horizontal plane, and Lr/Lc, or the ratio between the reflection surface172aand the connection surface172b, can be changed depending on the location. The intensity distribution of the main light beam30incident on the light guide17does not necessarily coincide with the intensity distribution desired on the incidence surface of the liquid crystal display panel. Therefore, a configuration is adopted in which the intensity distribution is adjusted by the ratio Lr/Lc between the reflection surface172aand the connection surface172b. Note that, as this ratio is increased, an average intensity of the reflected light at the portion of the surfaces can be increased. In general, since the light beam30incident on the light guide tends to be strong at a center portion, the ratio Lr/Lc is set to be different depending on the location in order to correct the light beam, and in particular, the ratio Lr/Lc is set to be small at the center portion. Since the above-described ratio Lr/Lc and the above-described reflection surface elevation angles α1, α2, α3, α4. . . are depending on the location, an envelope172crepresenting a general shape of the reflection portion172has a curved shape as illustrated inFIG.4.

Further, Lr1+Lc1=Lr2+Lc2=Lr3+Lc3=Lr4+Lc4. . . =Lr+Lc≤0.6 mm. By adopting such a configuration, it is possible to make the repetition pitches of the reflection surfaces viewed from a light emission surface173of the light guide17the same. Since the pitch is 0.6 mm or less, in combination with the action and effect of the diffusion plates18aand18b, when viewed through the liquid crystal display panel52, the individual emission surfaces are not separated and are viewed as a continuous surface, so that the spatial luminance through the liquid crystal display panel52can be made uniform, thereby improving the display characteristics. In other words, with the present configuration, the intensity distribution of incident light on the liquid crystal display panel52can be made uniform. On the other hand, if the value of Lr+Lc is smaller than 0.2 mm, not only a long machining time is required, but also it becomes difficult to accurately machine each reflection surface172a, so that the value is desirably 0.2 mm or more.

Further, although not illustrated, the value of Lr+Lc described above (sum of the lengths) may be, in whole or in part, a configuration such that Lr1+Lc1>Lr2+Lc2>Lr3+Lc3>Lr4+Lc4. . . , Lr1+Lc1=Lr2+Lc2=Lr3+Lc3=Lr4+Lc4. . . =Lr90+Lc90>Lr91+Lc91=Lr92+Lc92>Lr93+Lc93. . . >Lr130+Lc130, or Lr1+Lc1≥Lr2+Lc2≥Lr3+Lc3≥Lr4+Lc4. . . Lr1+Lc1>Lr130+Lc130. By adopting such a configuration, the repetition pitch of the reflection surface172aviewed from the emission surface173of the light guide17becomes finer as the repetition pitch approaches the emission surface173. Thus, with the present configuration, the repetition pitch of the reflection surface172aof the light guide17as viewed from the diffusion plate18bbecomes finer as the repetition pitch approaches the diffusion plate18b. The repetitive structure of the reflection surface172arequires a certain degree of diffuseness of the diffusion plate18bbecause the visibility increases toward the diffusion plate18band the uniformity of the light intensity is impaired, but by adopting the present configuration, the repetitive pitch of the reflection surface disposed at a position close to the diffusion plate18bbecomes finer, so that the uniformity of the light intensity can be secured even if the diffuseness of the scattering plate is small, and thus the light utilization efficiency can be improved. Further, the value of Lr+Lc is desirably set within the range of 0.2 mm or more and 0.6 mm or less as described above.

According to the shape of the light guide light reflection portion (surface)172of the light guide17described above, the total reflection condition of the main light can be satisfied, a reflection film such as aluminum on the reflection portion172need not be provided, light can be reflected efficiently, an operation such as a vapor deposition operation of an aluminum thin film which causes an increase in manufacturing cost need not be performed, and a bright light source can be realized at lower cost. Each relative angle β is set to an angle at which the connection surface172bis shaded with respect to the light in which the main light beam30is diffused by the synthetic diffusion block16and the diffusion plate18a. Thus, by suppressing the incidence of unnecessary light on the connection surface172b, it is possible to reduce the reflection of unnecessary light, and it is possible to realize a light source device having favorable characteristics.

In general, it is desirable that the inclination of the main light beam incident on the liquid crystal display panel is close to vertical. However, depending on the characteristics of the liquid crystal display panel, as illustrated inFIG.5B, the main light beam can also be inclined by an angle η. In other words, some commercially available liquid crystal display panels have better characteristics when the incidence angle is inclined by about 5° to 10°, but in this case, it is desirable to set η described above to 5° to 10° according to the characteristics.

Instead of inclining the panel by η, it is also possible to incline the inclination of the main light beam to the liquid crystal display panel by adjusting the angle of the reflection surface172a. Further, if it is necessary to incline the light beam in a side surface direction of the light guide, it can be realized by making the inclination of the slopes of triangular textures161formed on the emission surface of the synthetic diffusion block16asymmetric, or by changing a formation direction of the textures formed by the reflection surfaces172aand172b.

The synthetic diffusion block16, which is another component of the light source device10, will now be described with reference toFIGS.7and8. Note thatFIG.7illustrates the synthetic diffusion block16integrated with the LED collimator15described above, andFIG.8illustrates a partially enlarged cross section of the synthetic diffusion block16.

As is also apparent fromFIG.8, a large number of textures161having a substantially triangular cross section are formed on the emission surface of the synthetic diffusion block16, and the light emitted from the LED collimator15is diffused in a direction vertical to the plane of the drawing of the incidence portion (surface)171of the light guide17described above by the action of the textures161. By the interactions between the above-described substantially triangular textures161and diffusion plates18aand18b, even when the LED collimators15are discretely disposed, the individual intensity distribution of the light emitted from the emission portion173of the light guide17can be made uniform. In particular, since a diffusion direction can be limited to the side surface direction of the light guide, and further, the diffuseness in the side surface direction can be controlled by the textures161, it is possible to weaken the isotropic diffuseness of the first and second diffusion plates18aand18bdescribed above, and as a result, the light utilization efficiency is improved, and it is possible to realize a light source device having good characteristics. Note that, in this example, as an example of the substantially triangular textures161, the angle γ=30 degrees and the formation pitch a of the textures=0.5 mm.

As described above in detail, according to the light source device10of the present invention, the light utilization efficiency of the laser light from the LED light source and the uniform illumination characteristics thereof can be further improved, and the light source device can be miniaturized and manufactured at low cost, so that in particular, it is possible to provide a light source device suitable as an illumination light source in a display device of an electronic device such as an HUD or an ultra-small projector.

Modification Example of Light Source Device

FIGS.10and11illustrate a modification example of the light source device according to the first embodiment of the present invention, and as the modification example, an exterior perspective view of an entire light source device10band the internal configuration of the light source device are illustrated. In this modification example, a plurality of LED collimators15each having a conical convex shape to which an LED is attached are attached at an inclined position below the device by using a synthetic diffusion block16bhaving a substantially trapezoidal cross section. Note that the reference numeral13bin the drawing denotes a heatsink for cooling heat that is generated in the LED elements and the control circuit.

Another Modification Example of Light Source Device

Further,FIG.12illustrates another modification example of the light source device according to the first embodiment of the present invention, and as another modification example, an exterior perspective view of an entire light source device10cis illustrated. In this another modification example, although not illustrated in detail, the light source device has a structure in which heat that is generated in an LED substrate12is cooled by a heatsink13cdisposed at the lower portion of the device through a heat transfer plate13d. With the present configuration, a light source device having a short overall length can be realized.

<Another Form of Collimator in Light Source Device>

Further,FIG.13illustrates another form of the collimator15bin the light source device according to the first embodiment of the present invention, and illustrates an example of a shape in which the above-described synthetic diffusion block16is combined. The collimator shapes illustrated inFIGS.7and8have external shapes having conical convex shapes obtained by rotating a substantially parabolic disconnection line, but the shapes are based on substantially quadrangular pyramid convex shapes corners thereof being chamfered or curved. In view of the efficiency of the light emitted from the LED and emitted from the light guide17, the paraboloid of revolution shapes illustrated in FIGS. and8are suitable, but the present configuration can realize a more uniform light intensity distribution because the boundaries of the substantially quadrangular pyramid convex shapes are smoothly connected.

Note that the light source devices10band10c, which are modification examples of the light source device of the present invention described above, also have the same action and effect as the light source device10illustrated inFIG.1described above. Note that, by appropriately selecting these light source devices10,10b, and10c, it is possible to reliably attach the light sources to electronic devices such as an HUD and ultra-small projector having various shapes and forms so as to be adapted to the internal storage spaces of the electronic devices.

Application Example of Light Source Device

In addition, an example in which the above-described light source device10of the present invention is mounted on an HUD and an ultra-small projector will be described below as a representative example of an electronic device using the light source device as a light source of the display device thereof.

FIG.14Aillustrates an example in which the light source device described above according to the first embodiment of the present invention is applied to an HUD. Note that, in this drawing, in a head-up display device100, an image displayed on an image display device300including a projector, a liquid crystal display (LCD), or the like is reflected by a mirror131or another mirror132(e.g., a free-curved surface mirror or a mirror having an optical axis asymmetric shape), and is projected onto a windshield3of a vehicle2. On the other hand, a driver105sees the image projected onto the windshield103, thereby visually recognizing the image described above as a virtual image in front of the transparent windshield103through the transparent windshield.

FIG.14Billustrates an example of the internal configuration of the head-up display device100described above, in particular, the image display device300thereof. As is also apparent from this drawing, a case where the image display device300is a projector is illustrated, and the image display device300includes, for example, a light source301, an illumination optical system302, and a display element303. Note that, by adopting the above-described light source device10of the present invention as the light source301, it is possible to generate favorable illumination light for projection.

Note that this example further includes the illumination optical system302which is an optical system for condensing illumination light generated by the light source301, making the illumination light more uniform, and irradiating the display element303with the illumination light, and further includes the display element303which is an element for generating an image to be projected. However, in the above-described embodiment, these elements are already included in the light source device10of the present invention as the synthetic diffusion block16, the first diffusion plate18a, the light guide17, and the second diffusion plate18b, and further as the liquid crystal display panel52. Therefore, the light source device10of the present invention itself can be used as the image display device300of the head-up display device100. According to this, in particular, it is possible to realize the head-up display device100which can be easily attached in a narrow space such as a dashboard in an automobile.

Note that it will be apparent to those skilled in the art that the light emitted from the image display device300described above is further projected onto the windshield103of a vehicle102via a display distance adjustment mechanism400and a mirror drive unit500.

As described above in detail, by using the light source device10of the present invention as an illumination light source of a display device, it is possible to realize an electronic device which can be easily attached even in a narrow space and which is more miniaturized and inexpensive.

Second Embodiment

Details of a second example (second embodiment) of the present invention will now be described. Note that, in the second embodiment, unlike the first embodiment described above, attention is paid to the transmittance with respect to the polarized wave of the liquid crystal display panel52constituting the liquid crystal display element50on which the illumination light from the light source device is incident, and further, a polarization conversion element for aligning a polarization direction of the light emitted from the collimating optical system in one direction is provided, thereby realizing a more miniaturized and highly efficient light source device.

FIGS.15to17Billustrate the configuration of a light source device according to the second embodiment of the present invention, in particular, the configuration of an optical system serving as a feature thereof. In other words, in the second embodiment, in the configuration of the first embodiment described above, the number of LEDs14aand14bconstituting the light sources is two, which is half that of the first embodiment, and the polarization conversion element21is provided between the LED collimator15for each of the LEDs and the synthetic diffusion block16. Note that other configurations in the drawings are the same as those of the first embodiment described above, and are denoted by the same reference numerals, and detailed description thereof will be omitted here to avoid duplication.

As is apparent from these drawings, particularly fromFIG.17A, the polarization conversion element21is configured by combining a columnar (hereinafter referred to as a parallelogram column) translucent member having a parallelogram cross section and a columnar (hereinafter referred to as a triangular column) translucent member having a triangular cross section, which extend along a direction perpendicular to the plane of the drawing, and arranging a plurality of combinations of the members in an array parallel to a plane orthogonal to the optical axis of the parallel light from the LED collimator15(in this example, the direction vertical to the plane of the drawing). Further, polarizing beam splitter (hereinafter abbreviated as “PBS”) films211and reflective films212are alternately provided at the interface between the adjacent translucent members arranged in an array, and a ½λ phase plate213is also provided on the emission surface from which light incident on the polarization conversion element21and transmitted through the PBS films211is emitted.

As described above, the above-described polarization conversion element21is configured symmetrically with respect to the plane (the vertical plane extending vertically on the plane of the drawing) formed by the optical axis of the parallel light from the LED collimator15and an extending direction of the translucent member of the parallelogram column, that is, the optical axis plane of the parallel light, and the inclination of the parallelogram column or the triangular column of the translucent member that is a component of the polarization conversion element is 45 degrees with respect to the optical axis plane. The polarization conversion elements21constitute each of the polarization conversion elements divided into two groups in the vertical direction of the drawing with respect to the parallel light beams from the two LED collimators15.

According to the polarization conversion element21configured as described above, as illustrated inFIG.17A, an S-polarized wave (see symbol “×” in the drawing), for example, of incident light emitted from the LED14aand converted into parallel light by the LED collimator15is reflected by the PBS film211, and then further reflected by the reflective film212to reach an incidence surface of the synthetic diffusion block16. On the other hand, a P-polarized wave (see the up and down arrows in the drawing) is transmitted through the PBS film211and then converted into an S-polarized wave by the ½λ phase plate213to reach the incidence surface of the synthetic diffusion block16.

As described above, according to the polarization conversion element21, all of the light emitted from the (plurality of) LEDs and converted into parallel light by the LED collimator15become S-polarized waves and are incident on the incidence surface of the synthetic diffusion block16. Then, the light emitted from the emission surface of the synthetic diffusion block16is made incident on the light guide17, which is already described above in detail, via the first diffusion plate18a, and is reflected upward in the drawing by the action of the light guide17to be guided to the incidence surface of the above-described liquid crystal display element50, as in the first embodiment. In other words, the action of the light guide17has already been described in detail above, and the description thereof will be omitted here to avoid duplication.

Note thatFIG.18is a perspective view illustrating a state in which the two LED collimators15described above are attached to the polarization conversion element21described above.FIG.19is a perspective view illustrating the exterior configuration of the synthetic diffusion block16attached to the emission surface side of the polarization conversion element, andFIG.20is a side view illustrating the detailed structure of the synthetic diffusion block16and a partially enlarged cross-sectional view thereof. As is also apparent from these drawings, also in the second embodiment, a large number of textures161having a substantially triangular cross section are formed on the emission surface of the synthetic diffusion block16. However, the details thereof have already been described above and will be omitted here.

In other words, according to the light source device described above of the second embodiment, since the light incident on the liquid crystal display panel52constituting the liquid crystal display element50is converted into the S-polarized wave by the polarization conversion element21described above, the transmittance of the light in the liquid crystal display panel can be improved, so that a more miniaturized and highly efficient light source device can be realized at a lower cost by a smaller number of light emission sources (LEDs). Note that, although in the above description, the polarization conversion element21is attached after the LED collimator15, the present invention is not limited thereto, and it will be apparent to those skilled in the art that the same action and effect can be obtained by providing the polarization conversion element in the optical path leading to the liquid crystal display element.

Further, although it has been described that the an excellent liquid crystal display panel has transmittance for S-polarized waves, it will be apparent to those skilled in the art that the same action and effect can be obtained by a polarization conversion element having the same configuration as that described above even when the liquid crystal display panel has an excellent transmittance for P-polarized waves. It will be apparent to those skilled in the art that the light source device described above according to the second embodiment can also be used as a light source device in an electronic device such as a head-up display device or a projector, as in the light source device described above according to the first embodiment.

A planar light source device suitable for use in an electronic device including an image display device according to various embodiments of the present invention has been described above. However, the present invention is not limited only to the above-described embodiments, and includes various modification examples. For example, in the above-described embodiments, the entire system has been described in detail in order to explain the present invention in an easy-to-understand manner, and the present invention is not necessarily limited to a system including all the configurations described above. A part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of a certain embodiment. A part of the configuration of each embodiment can be added, deleted, or replaced with another configuration.

REFERENCE SIGNS LIST

10LIGHT SOURCE DEVICE (MAIN BODY)11CASE50LIQUID CRYSTAL DISPLAY ELEMENT12LED SUBSTRATE13HEATSINK14a,14bLED15LED COLLIMATOR16SYNTHETIC DIFFUSION BLOCK17LIGHT GUIDE171LIGHT GUIDE LIGHT INCIDENCE PORTION (SURFACE)172LIGHT GUIDE LIGHT REFLECTION PORTION (SURFACE)172aREFLECTION SURFACE172bCONNECTION SURFACE173LIGHT GUIDE LIGHT EMISSION PORTION (SURFACE)21POLARIZATION CONVERSION ELEMENT211PBS FILM212REFLECTIVE FILM213½λ PHASE PLATE