The following disclosure relates to backlight devices and display devices. The present application claims the benefit of priority to Japanese Patent Application, Tokugan, No. 2018-206368 filed Nov. 1, 2018, the entire contents of which are incorporated herein by reference.
White-shining area light source units are known that include blue light-emitting elements and a fluorescent sheet that emits yellow or orange light when hit by the light emitted by the light-emitting elements (see, for example, Patent Literature 1).
Liquid crystal display devices that perform area active drive are also known (see, for example, Patent Literature 2). In area active drive, the screen of a liquid crystal display device is divided into areas, and the luminance of the backlight light source is controlled for each area on the basis of the input image for that area. Area active drive is sometimes referred to as local dimming drive.
Patent Literature 1: Japanese Unexamined Patent Application Publication, Tokukai, No. 2017-33927
Patent Literature 2: PCT International Application Publication No. WO2011/013402
The conventional area light source unit includes a fluorescent sheet that has the same area as the light-emitting face thereof and for this reason requires a large amount of fluorescent material, which adds to the manufacturing cost of the area light source unit. The following disclosure has an object to provide low cost manufacturing technology for backlight devices.
To address the problems described above, the present disclosure, in an aspect thereof, is directed to a backlight device including: a plurality of light-emitting bodies arranged in a planar manner, the light-emitting bodies being configured to emit first light upwards; and a transparent plate above the light-emitting bodies, wherein the plate includes a plurality of wavelength conversion sections arranged next to each other in a lateral direction, the wavelength conversion sections being configured to convert the first light to second light, and each of the wavelength conversion sections at least partially overlaps at least one of the light-emitting bodies when viewed from above.
The present disclosure, in an aspect thereof, can provide a backlight device that can be manufactured at low cost.
The following will describe embodiments with reference to attached drawings.
The control unit 200 feeds image data from the outside of the display device 100. The display device 100 may be fed with image data in any specific manner, for example, via an HDMI® cable or by television broadcasting waves from an external video output device. The control unit 200 controls the backlight device 400 and the display panel 300 based on image data sets each specific to one of the areas into which the display region 310 of the display panel 300 is divided, to implement local dimming drive in order to produce a display on the display region 310 based on the image data.
The display panel 300 produces a display based on the image data by using the light emitted from the backlight device 400. The display panel 300 in accordance with the first embodiment is a liquid crystal display panel. The display panel 300 includes a plurality of pixels. Each pixel is individually controlled to alter the transmittance thereof.
The backlight device 400 includes a plurality of light-emitting bodies to emit light in the direction of the display panel 300. The backlight device 400 will be described later in more detail.
A description is given next of a configuration of the control unit 200 in accordance with the first embodiment. The control unit 200 in accordance with the first embodiment includes a local dimming unit 210, a display panel control unit 220, and a backlight control unit 230. The local dimming unit 210 generates display panel control data and backlight device control data for implementing local dimming drive based on the incoming mage data. The local dimming unit 210 then sends the display panel control data to the display panel control unit 220 and sends the backlight device control data to the backlight control unit 230.
The display panel control unit 220 generates a control signal for controlling the transmittance of each pixel in the display panel 300 based on the display panel control data supplied from the local dimming unit 210, to drive the display panel 300. The backlight control unit 230 generates a control signal for controlling the light emission intensity of each light-emitting body in the backlight device 400 based on the backlight device control data supplied from the local dimming unit 210, to drive the backlight device 400.
The housing 41 supports, for example, the substrate 42. The substrate 42 is made for example, metal and carries thereon the light-emitting bodies 43. A reflective sheet may be attached to the surface of the substrate 42 to enhance the use efficiency of the light emitted from the light-emitting bodies 43. In
The light-emitting bodies 43 emit light upwards and are arranged in a planar manner on the substrate 42. The light-emitting body 43 is a chip LED fabricated by, for example, sealing an LED element with a resin or like material and attaching wires to the sealed LED element for external contacts. Each light-emitting body 43 may include a single LED element or a plurality of LED elements. In the first embodiment, the light-emitting body 43 is a blue chip LED and emits blue light.
The plate 44 is a transparent platelike member and provided above the light-emitting bodies 43. The dents 49 are provided at prescribed intervals in the top face of the plate 44. Each dent 49 contains therein a different one of the wavelength conversion sections 45. The light-emitting bodies 43 are separated by a gap from the plate 44. In other words, the light-emitting bodies 43 are separated by a gap from the wavelength conversion sections 45 in the plate 44. This particular structure can slow down the degradation of the wavelength conversion sections 45 under the heat discharged by the light-emitting bodies 43.
The wavelength conversion section 45 absorbs and converts part of the light emitted by the light-emitting body 43 to light of a wavelength that is different from the wavelength of the absorbed light before emitting the resultant light. The reset of the light from the light-emitting body 43 passes through the wavelength conversion section 45 without being absorbed by the wavelength conversion section 45. Hence, both the non-absorbed light and the absorbed and wavelength-converted light comes out of the wavelength conversion section 45. The wavelength conversion section 45 contains a wavelength conversion material and is encased in, for example, a resin. In the first embodiment, the wavelength conversion section 45 contains quantum dots as the wavelength conversion material. More specifically, the wavelength conversion section 45 contains quantum dots for converting blue light to green light and quantum dots for converting blue light to red light. Because green light and red light mix to produce yellow light, the wavelength conversion section 45 converts first light (blue light) emitted by the light-emitting body 43 to second light (yellow light). The wavelength conversion section 45 alternatively converts the first light (blue light) emitted by the light-emitting body 43 to second light (either of green and red light) and third light (the other of green and red light). The part of the first light emitted by the light-emitting body 43 that is passed through the wavelength conversion section. 45, the part of the first light emitted by the light-emitting body 43 that is passed not through the wavelength conversion section 45, and the second light emitted by the wavelength conversion section 45 mix to produce white light. The light obtained by the conversion by the quantum dots exhibits so small a full width at half maximum that the light is highly pure. The inclusion of quantum dots in the wavelength conversion section 45 can therefore expand the color reproduction range of the display device 100.
The wavelength conversion sections 45 in accordance with the first embodiment are arranged next to each other in a lateral direction in the plate 44. The “lateral direction” is perpendicular to the thickness direction of the plate 44 and matches either the X-axis or Y-axis direction shown in
The plate 44 is made of a transparent white material in the first embodiment. The plate 44 hence scatters incident light. This property enables the plate 44 to well mix the light coming from the light-emitting body 43 and the light coming from the wavelength conversion section 45, which in turn better restrains irregular color mixing in white light.
The diffusion plate 46 is provided above the plate 44. The diffusion plate 46 diffuses the light emitted by the light-emitting bodies 43 and the wavelength conversion sections 45 so that the backlight emission can be uniform across the plane.
The optical sheets 47 are provided above the diffusion plate 46. Each optical sheet 47 is responsible for a different function such as diffusion, converging, or light use efficiency enhancement.
The wavelength conversion section 45 needs only to be at least partially overlapping the light-emitting body 43 when viewed from above. In the first embodiment, the wavelength conversion section 45 is positioned overlapping the entire light-emitting body 43 when viewed from above as shown in
The wavelength conversion section 45 in accordance with the first embodiment is circular as shown in
The wavelength conversion section 45 in accordance with the first embodiment has a larger diameter than the dimensions of the light-exiting portion 48 as shown in
The plate 44 is formed, for example, by injection molding in a metal die that has convexities for the dents 49. This particular technique can readily provide the plate 44 with the dents 49 of prescribed dimensions in prescribed locations. The wavelength conversion sections 45 may be formed, for example, by pouring a photocuring or thermosetting resin containing quantum dots into the dents 49 and curing the resin under light or heat. Alternatively, the wavelength conversion sections 45 may be formed, for example, by preparing disc-shaped resin pellets encasing quantum dots in advance and placing the pellets in the dents 49. The use of the plate 44 having the dents 49 fabricated in this manner allows for the provision of the wavelength conversion sections 45 in the dents 49. The wavelength conversion sections 45 are thus readily provided in prescribed locations.
Since the dents 49 reside in the top face of the plate 44, and the wavelength conversion sections 45 sit in the dents 49 as described above, the plate 44 is sandwiched between the wavelength conversion sections 45 and the light-emitting bodies 43. The wavelength conversion sections 45 are therefore not directly exposed to heat discharged by the light-emitting bodies 43. That in turn restrains the wavelength conversion sections 45 from being degraded by the heat discharged by the light-emitting bodies 43.
The top face of the wavelength conversion section 45 resides below the top face of the plate 44 as shown in
The light-emitting body 43 in accordance with the first embodiment has 2.5 mm×2.5 mm dimensions when viewed from above. The light-emitting body 43 has a height of 0.58 mm. The plate 44 is made of a transparent white polycarbonate resin. The plate 44 has a thickness of 2.0 mm. The plate 44 exhibits a total optical transmittance of 45.0% in portions where there exist no wavelength conversion sections 45. The top faces of the light-emitting bodies 43 and the bottom face of the plate 44 are separated by a distance of 1.42 mm. In other words, the light-emitting bodies 43 and the plate 44 are separated by a gap of 1.42 mm. The bottom faces of the light-emitting bodies 43 and the bottom face of the plate 44 are separated by a distance of 2.0 mm. The dents 49 are depressed by 1.5 mm from the top face of the plate 44. The bottom faces of the dents 49 and the bottom face of the plate 44 are therefore separated by a distance of 0.5 mm. The wavelength conversion sections 45 each have a diameter of 6.0 mm and a thickness of 1.0 mm. The top faces of the wavelength conversion sections 45 therefore reside 0.5 mm below the top face of the plate 44. This set of dimensions, as an example, can further reduce irregular color mixing.
When a display device including a display panel and a backlight device is subjected to local dimming drive as described above, the backlight device lights up partially where some light-emitting bodies emit light while the others do not emit light (“partial lighting”). If the backlight device includes a fluorescent sheet that has the same area as the entire light-emitting face of the backlight device as described in, for example, Patent Literature 1, irregular color mixing can occur. This phenomenon is discussed with reference to
In contrast, in the backlight device 400 in accordance with the first embodiment, the wavelength conversion sections 45 at least partially overlap the respective light-emitting bodies 43 when viewed from above. In other words, a light-emitting body 43 and a wavelength conversion section 45 positioned over the light-emitting body 43 are paired up producing white light emission that is free from irregular color mixing. The display device 100 including the backlight device 400 in accordance with the first embodiment thus causes no irregular color mixing in local dimming drive, thereby preventing image quality degradation.
A description is given next of a backlight device 400A in accordance with a second embodiment. The description will focus on distinctions between the backlight device 400A and the first embodiment and may not mention similarities between the backlight device 400A and the first embodiment.
The frame member 50 may be integrated to the plate 44A.
In each region enclosed by the frame member 50, the frame member 50 reflects the light emitted from the light-emitting bodies 43 in the region to prevent the light from leaking out of the region, thereby enhancing light use efficiency. When the light-emitting bodies 43 are turned on in some of the areas of the backlight device 400A in local dimming drive, the frame member 50 can enhance the use efficiency of the light emitted by the light-emitting bodies 43 inside those areas and also prevent, the light from leaking out of the areas, which can in turn improves the effects of the local dimming drive.
A description is given next of a backlight device 400B in accordance with a third embodiment. The description will focus on distinctions between the backlight device 400B and the first embodiment and may not mention similarities between the backlight device 400B and the first embodiment.
Taking a large-sized display device as an example, it becomes difficult to manufacture and assemble the backlight device if the plate has the same size as the display section. In contrast, since the plates 44B in accordance with the third embodiment are arranged in a planar manner as described above, the individual plates 44B are small and easy to manufacture. In addition, since the individual plates 44B are light and small, the individual plates 4413 are easy to handle, which makes it easy to assemble the backlight device 400B.
In the backlight device, the light-emitting bodies generate heat that in turn expands the plate. If the plate has the same size as the display section, the thermal expansion of the plate could cause large displacement of the wavelength conversion sections in the plate relative to the light-emitting bodies. However, since the plates 44B in accordance with the third embodiment are arranged in a planar manner, and the clearance 51 is provided between the adjacent plates 44B, the clearance 51 can prevent the displacement by making up for the effects of the expansion.
A description is given next of a backlight device 400C in accordance with a fourth embodiment. The description will focus on distinctions between the backlight device 400C and the first embodiment and may not mention similarities between the backlight device 400C and the first embodiment.
There are provided no projections 52 above and below the wavelength conversion sections 45 in the fourth embodiment as shown in
In the backlight device in accordance with the present disclosure, light is emitted downwards from the wavelength conversion sections 45, for example, as indicated by thick arrows in
The shape and layout of the projections 52 shown in
A description is given next of a backlight device 400D in accordance with a fifth embodiment. The description will focus on distinctions between the backlight device 400D and the first embodiment and may not mention similarities between the backlight device 400D and the first embodiment.
Each wavelength conversion section 45D needs only to at least partially overlap one or more of the light-emitting bodies 43 when viewed from above. In the fifth embodiment, each wavelength conversion section 45D overlaps all the four light-emitting bodies 43 when viewed from above as shown in
In the backlight device 400D in accordance with the fifth embodiment, each wavelength conversion section 45D at least partially overlaps one or more of the light-emitting bodies 43 when viewed from above. In other words, at least one light-emitting body 43 and a wavelength conversion section 45D positioned over the light-emitting body 43 are paired up producing white light emission that is free from irregular color mixing. The display device 100 including the backlight device 400D in accordance with the fifth embodiment thus causes no irregular color mixing in local dimming drive, thereby preventing image quality degradation.
In addition, since the four light-emitting bodies 43 are disposed next to each other and covered by the wavelength conversion section 45D, the backlight device 400D can emit more intense light.
The number of light-emitting bodies 43 disposed next to each other is not necessarily four and may be selected appropriately in accordance with, for example, the necessary amount of light.
A description is given next of a backlight device 400E in accordance with a sixth embodiment. The description will focus on distinctions between the backlight device 400E and the first embodiment and may not mention similarities between the backlight device 400E and the first embodiment.
Each wavelength conversion section 45E needs only to at least partially overlap one or more of the light-emitting bodies 43 when viewed from above as described above. In the sixth embodiment, each wavelength conversion section 45E overlaps all the four light-emitting bodies 43 when viewed from above as shown in
In the backlight device 400F in accordance with the fifth embodiment, each wavelength conversion section 45E at least partially overlaps one or more of the light-emitting bodies 43 when viewed from above. In other words, one or more light-emitting bodies 43 and a wavelength conversion section 45E positioned over the light-emitting body/bodies 43 are paired up producing white light emission that is free from irregular color mixing. The display device 100 including the backlight device 400E in accordance with the sixth embodiment thus causes no irregular color mixing in local dimming drive, thereby preventing image quality degradation.
When the number and layout of the light-emitting bodies 43 do not change, the plate 44E in accordance with the sixth embodiment includes fewer wavelength conversion section 45E than the plate 44 in accordance with the first embodiment includes wavelength conversion sections 45. The plate 44E can be hence more easily manufactured.
The number of light-emitting bodies 43 covered by the wavelength conversion section 45E is not necessarily limited to four.
The light-emitting bodies 43 are blue chip LEDs in the foregoing embodiments. Alternatively the light-emitting bodies 43 may be light-emitting elements other than LEDs.
The light-emitting bodies 43 emit Hue light in the foregoing embodiments. Additionally, the wavelength conversion sections 45 to 45E (hereinafter, collectively referred to as the wavelength conversion sections 45) contain a wavelength conversion material that converts blue light to green light and a wavelength conversion material that converts blue light to red light to produce yellow light. The light emitted by the light-emitting bodies 43 and the light emitted by the wavelength conversion sections 45 are not necessarily limited to these examples. Alternatively, as an example, the light-emitting bodies 43 may contain blue light-emitting elements and green light-emitting elements to produce cyan light. In such a case, the wavelength conversion sections 45 are made of a wavelength conversion material that converts blue and/or green light to red light. As another alternative, for example, the light-emitting bodies 43 may contain green light-emitting elements to produce green light. In such a case, the wavelength conversion sections 45 are made of a wavelength conversion material that converts green light to blue light and a wavelength conversion material that converts green light to red light. In such a case, the wavelength conversion sections 45 emit magenta light. There are various combinations available for the light emitted by the light-emitting bodies 43 and the wavelength conversion sections 45 as described here. In any of these cases, the wavelength conversion sections 45 convert the first light emitted by the light-emitting bodies 43 to the second light. As an additional note, research and studies are conducted on so-called “light upconversion” technology where light is converted from a relatively long wavelength to a relatively short wavelength, for example, from green to blue.
The wavelength conversion sections 45 contain quantum dots as a wavelength conversion material in the foregoing embodiments. Alternatively, the wavelength conversion sections 45 may contain a wavelength conversion material other than quantum dots.
The wavelength conversion sections 45 contain a wavelength conversion material that converts blue light to green light and a wavelength conversion material that converts blue light to red light in the foregoing embodiments. Alternatively, the wavelength conversion material may be such as to emit light over a relatively broad spectrum, for example, emit light with a spectrum centered at yellow wavelengths and spreading into red and green regions. A liquid crystal display device needs a backlight device capable of illuminating the liquid crystal panel with white light containing red, green, and blue components. Therefore, the backlight device include no wavelength conversion sections 45 that emit pure yellow light, but may include wavelength conversion sections 45 that emit light the spectrum of which includes red and green wavelengths. A similar discussion applies to other color combinations.
The plates 44 to 44E in the foregoing embodiments (hereinafter, collectively referred to as the plate 44) have the dents 49 to 49E (hereinafter, collectively referred to as the dents 49) formed in the top face thereof. Alternatively, the plate 44 may have the dents 49 formed in the bottom face thereof. In such a case, the wavelength conversion sections 45 are also provided in the bottom face of the plate 44. The bottom Ike of the wavelength conversion section 45 may reside above the bottom face of the plate 44.
The plate 44 is made of a transparent white polycarbonate resin in the foregoing embodiments. Alternatively, the plate 44 may not be white so long as it is transparent. The plate 44 may be, for example, colorless and transparent. In addition, the plate 44 is not necessarily made entirely of a transparent white material and may be, for example, partially made of a colorless transparent material. Additionally, the plate 44 may be made of any substance commonly used in the field that is chosen appropriately, other than polycarbonate resin.
The wavelength conversion sections 45 are circular when viewed from above in the foregoing embodiments. Alternatively, the wavelength conversion sections 45 may have any non-circular shape when viewed from above. The wavelength conversion sections 45 may have a shape that is, for example, modified in accordance with the light emission properties of the light-emitting bodies 43.
The plate 44 has the dents 49 formed therein, and the dents 49 contain the wavelength conversion sections 45 respectively, in the foregoing embodiments. Alternatively, the plate 44 may include the wavelength conversion sections 45 without being provided with the dents 49. The wavelength conversion sections 45 may be provided, for example, by preparing disc-shaped pellets encasing quantum dots in a resin in advance and placing the pellets in the prescribed location in the top or bottom face of a plate that has no dents.
The display panel 300 is a liquid crystal display panel in the foregoing embodiments. Alternatively, the display panel 300 may be, for example, a display panel with pixels formed of MEMSs (micro-electro-mechanical systems). The MEMS is an integrated device including mechanical elements, actuators, and electronic circuits on a single silicon or glass substrate. A panel including MEMS-based pixels includes thereon mechanical shutters serving as pixels. The mechanical shutters are opened and closed at high speed in accordance with an image signal. Similarly to the liquid crystal panel, the MEMS is thus capable of adjusting transmittance for the backlight emission to display an image. Alternatively, the display panel 300 may be a display panel including electrowetting-based pixels. Electrowetting is a phenomenon where turning on a switch provided between an electrode on an inner face of a thin tube and an external electrode changes the wettability of the liquid with respect to the inner face of the thin tube and reduces the contact angle of the liquid on the inner face of the thin tube, thereby causing the liquid to spread, and turning off the switch changes the wettability of the liquid with respect to the inner face of the thin tube and abruptly increases the contact angle, thereby causing the liquid to flow out of the thin tube. Similarly to the pixels in the liquid crystal panel, the electrowetting-based pixels can be opened/closed by turning on/off the switch and are thus capable of adjusting transmittance for the backlight emission to display an image. The backlight devices 400 and 400A to 400E of the foregoing embodiments may be applied to display devices that do not implement local dimming drive.
The present invention is not necessarily limited to the foregoing embodiments and examples. Embodiments based on a proper combination of technical means disclosed in different embodiments and those based on modifications of the foregoing embodiments are encompassed in the technical scope of the present invention.
The control unit 200 in the display device 100 may be implemented by logic circuits (hardware) fabricated, for example, in the form of an integrated circuit (IC chip) and may be implemented by software.
In the latter form of implementation, the display device 100 includes a computer that executes instructions from programs or software by which various functions are provided. This computer includes among others at least one processor (control device) and at least one storage medium containing the programs in a computer-readable format. The processor in the computer then retrieves and runs the programs contained in the storage medium, thereby achieving the object of an aspect of the present disclosure. The processor may be, for example, a CPU (central processing unit). The storage medium may be a “non-transitory, tangible medium” such as a ROM (read-only memory), a tape, a disc/disk, a card, a semiconductor memory, or programmable logic circuitry. The display device 100 may further include, for example, a RAM (random access memory) for loading the programs. The programs may be supplied to the computer via any transmission medium (e.g., over a communications network or by broadcasting waves) that can transmit the programs. The present disclosure, in an aspect thereof, encompasses data signals on a carrier wave that are generated during electronic transmission of the programs.
Number | Date | Country | Kind |
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2018-206368 | Nov 2018 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2019/039760 | 10/9/2019 | WO | 00 |