JP2009123581A - Surface light source device and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface light source device capable of controlling luminance of a display device according to light volume of the outside without using a dedicated photosensor, and a display device. <P>SOLUTION: A backlight 2 includes a plurality of light-emitting diodes 14, a light guide plate 12 which guides light from the light-emitting diodes 14 and emits light in surface shape, and a driver 16 which detects the light volume of the outside and adjusts the emission volume of the light source based on the light volume. Detection of the light volume of the outside is carried out by the light-emitting diodes 14 at the time of non-lighting. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a planar light source device and a display device.

  2. Description of the Related Art Conventionally, as a planar light source device using a light emitting diode (LED) as a point light source, a planar light source device of a liquid crystal display device used for a personal computer monitor or the like is well known. This planar light source device includes a light guide plate that emits light in a planar shape and a light source unit. And the light-guide plate is formed with resin with a large refractive index by permeation | transmission, such as polycarbonate resin and an acrylic resin. The light source unit has a plurality of LEDs mounted on a substrate, and is disposed to face the side surface of the light guide plate.

  However, in conventional display devices, the illumination relies on a light source with the same brightness in both bright and dark places, regardless of outside light. There was a problem that it was difficult to see because it felt too much light emission.

  In order to solve the above-described problem, the planar light source device disclosed in Patent Document 1 includes an optical sensor that measures the amount of external light incident on the display device, and the planar light source device according to the measurement result of the optical sensor. There was provided a means for controlling the amount of emitted light. Therefore, in the conventional planar light source device, a dedicated optical sensor has to be provided separately.

Japanese Patent Laid-Open No. 6-18880

  However, when a special light sensor is provided in the surface light source device, the number of parts of the surface light source device is increased, and the number of assembly steps is increased. Moreover, since the optical sensor itself is expensive, the addition of the optical sensor has a problem of increasing the cost of the planar light source device itself. In addition, there is a problem in that a space for arranging the optical sensor is required, which is an obstacle to obtaining a thin and narrow frame display device.

  The present invention has been made to solve the above-described problem, and provides a planar light source device and a display device that can control the luminance of the display device according to the amount of external light without using a dedicated optical sensor. With the goal.

  The planar light source device of the present invention includes a plurality of light sources, a light guide that guides light from the light sources to emit light in a planar shape, a light emission amount adjustment unit that detects an external light amount and adjusts the light emission amount of the light source based on the light amount. In addition, the external light quantity is detected by a light source when not lit.

  In the planar light source device according to the present invention, since the light source when not lit detects the amount of external light, the increase in cost is suppressed and a thin and narrow frame is maintained as compared with the case where a dedicated optical sensor is used. It is possible to obtain the light emission amount of the light source according to the external light amount.

  Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.

<Embodiment 1>
(Constitution)
In the present embodiment, a description will be given based on a form in which a planar light source device is used as a backlight of a liquid crystal display device. However, the planar light source device of the present invention is not limited to the above form. First, FIG. 1 is an exploded perspective view showing a configuration of a liquid crystal display device 30 (display device) according to the present embodiment. A liquid crystal display device 30 shown in FIG. 1 includes a liquid crystal display panel (liquid crystal display element) 1 that is a display element that writes and displays a desired image on a pixel, and a backlight that emits light from the back surface of the liquid crystal display panel 1 ( A planar light source device) 2 is provided. The liquid crystal display panel 1 has glass substrates 3a and 3b bonded with two glass substrates facing each other, and liquid crystal is held between the opposing substrates. Further, TFTs (Thin Film Transistors) are formed in a matrix (not shown) on one glass substrate to drive the liquid crystal, and pixels connected to the TFTs are also formed in a matrix ( Not shown). The liquid crystal display panel 1 according to the present embodiment is a transmissive type.

  The liquid crystal display panel 1 includes a plurality of gate wiring driving drivers 4 for turning on / off TFTs provided for each pixel and a plurality of source wiring driving for supplying image data to each pixel via the TFTs. A driver 5 is provided. The gate wiring driving driver 4 and the source wiring driving driver 5 are configured to mount, for example, separately formed semiconductor chips on the glass substrate 3b. The gate line driver 4 and the source line driver 5 are controlled by a controller (not shown) and write image data to each pixel. Note that image data is written to each pixel based on an image signal input to the controller. Then, a gate wiring (not shown) provided on the glass substrate 3b is supplied with a signal for turning on the TFT at a predetermined scanning cycle, and at the timing of the signal, a source wiring (shown in the figure) provided on the glass substrate 3b. (Not shown) is supplied with image data, and the image data is written to the pixels.

  Next, the backlight 2 is a planar light source device that emits uniform light from the opening 6 formed in the housing 10, and is disposed on the back side of the liquid crystal display panel 1 as can be seen from FIG. 1. Yes.

  FIG. 2 is a plan view showing the configuration of the backlight 2. Light source units 17 in which a plurality of light emitting diodes (light sources) 14 are arranged on a circuit board 15 are arranged at both ends inside the housing 10. Each light source unit 17 is connected to a driver (light emission amount adjusting unit) 16 that controls driving of the plurality of light emitting diodes 14.

  FIG. 3 is a cross-sectional view of the backlight 2 shown in FIG. 2 on the II-II ′ plane in the state where the liquid crystal display panel 1 is mounted. As described above, the backlight 2 has the housing 10, and the light source units 17 are arranged at both ends inside the housing 10. A reflector 13 is installed above the light emitting diode 14, and a light guide plate (light guide unit) 12 is disposed between the reflectors 13 at both ends. An opening 6 is provided above the light guide plate 12 in the housing 10 so that light from the light emitting diode 14 can be emitted, and the liquid crystal display panel 1 is disposed above the opening 6. Here, a direction in which the liquid crystal display panel 1 is installed with respect to the light guide plate 12 is a front surface. A reflection sheet 18 is disposed on the back side of the light guide plate 12, and the optical sheet 11 is disposed between the light guide plate 12 and the liquid crystal display panel 1.

  Here, the housing 10 is a frame for storing and holding the constituent members of the backlight 2, and a synthetic resin or metal having excellent strength and workability is used. In particular, the housing 10 is preferably made of aluminum or copper having excellent thermal conductivity from the viewpoint of heat dissipation against heat generated by light emission of the light emitting diode 14.

  The optical sheet 11 is a sheet-like optical member having transparency such as a diffusion sheet for diffusing light and a prism sheet on which prism rows are formed. Here, the diffusion sheet is a sheet obtained by roughening the surface of a transparent member such as synthetic resin or glass. The optical sheet 11 described above is used to adjust the luminance value of the emitted light, and thus is used in combination of a plurality of types as necessary.

  The light guide plate 12 is an optical member that guides light from the light source unit 17 arranged on the short side and emits light in a planar shape on the front side where the liquid crystal display panel 1 is provided. The light guide plate 12 is a plate-like member having translucency such as an organic resin material (such as an acrylic resin or a polycarbonate resin) or glass. A diffusion pattern (not shown) is formed on the back side of the light guide plate 12. This diffusion pattern is an optical means that diffuses light propagating through the light guide plate 12 and emits uniform light to the front side.

  Specifically, a method for forming a diffusion pattern on the back side of the light guide plate 12 includes a method of screen printing a white pigment containing titanium oxide or the like on the back side of the light guide plate 12, or a circular shape when the light guide plate 12 is formed. Alternatively, a method of forming a fine pattern such as a conical shape or a rectangular shape at the time of molding may be considered. By adjusting the diffusion pattern, the luminance distribution in the direction parallel to the long side of the light guide plate 12 can be made a desired distribution. That is, the density, shape, size, depth, etc. of the diffusion pattern are determined so that the luminance distribution of the light emitted from the light source unit 17 is optimized.

  In addition, although the light source in the light source unit 17 was the light emitting diode 14, a laser diode (LD: Laser Diode) may be used. These light sources are capable of high-speed response of several nanoseconds (ns) or less. In the light source unit 17 according to the present embodiment, a plurality of light emitting diodes 14 emitting a single color are combined and arranged in a line.

  FIG. 4 is a diagram illustrating an example of a light source unit in which the light emitting diodes 14 as a plurality of light sources are arranged in a line. In the light source unit 17, light emitting diodes 14 that emit single colors of red (R), green (G), and blue (B) are arranged in a row on a rectangular circuit board 15. However, the numbers of R, G, and B of the light-emitting diodes 14 are not necessarily equal, and the numbers may be determined so that the light passing through the liquid crystal display panel 1 has a desired white chromaticity. Thus, the chromaticity of the light emitted from the backlight 2 can be easily changed by combining a plurality of single-color light emitting diodes 14 and adjusting the amount of light emitted from each.

  The RGB single color light emitting diode 14 has higher luminous efficiency than the light emitting diode that emits white light, and the transmission characteristics of each color (RGB) of the color filter used in the liquid crystal display panel 1 and the emission spectrum of the light emitting diode 14 are obtained. By matching, the color reproducibility of the liquid crystal display device 30 can be improved. Furthermore, since the RGB single color light emitting diode 14 can control each color independently, the color of the emitted light can be easily changed as compared with the light emitting diode that emits white light. In addition, in the circle which shows the light emitting diode 14 of FIG. 4, each color of RGB is specified.

  FIG. 5 is a wiring diagram schematically showing the wiring of the light source section. The RGB light emitting diodes 14 are connected in series for each color. This is because the light emission amount between the light emitting diodes 14 of the same color can be made uniform by driving the light emitting diodes 14 with a constant current. The wiring 19 connected to the light emitting diode 14 is formed on the circuit board 15 with a copper pattern. Further, the light emitting diode 14 is connected to the driver 16 via the wiring 19 on the circuit board 15 and is driven and controlled. The driver 16 is driven in units of light emitting diodes of the same color.

  Next, the reflector 13 shown in FIG. 3 includes a plurality of light emitting diodes 14 except for the end face side of the light guide plate 12, and efficiently reflects light from the light emitting diodes 14 to the end face side of the light guide plate 12. The reflector 13 is made of a material such as a metal plate having a reflective layer formed of silver or aluminum, a resin sheet on which silver or aluminum is vapor-deposited, a white resin sheet, or the like. The reflectance of the reflector 13 is desirably 90% or more in order to suppress loss on the reflecting surface. Moreover, a reflector is unnecessary in the planar light source device having a configuration in which the light emitting surface of the light emitting diode and the light guide plate light incident surface (end surface) are in close contact with each other.

  In addition, a reflection sheet 18 that reflects light from the light guide plate 12 to the front side is provided on the back side of the light guide plate 12. The reflection sheet 18 is a sheet-like optical member made of a flat plate on which silver or aluminum is vapor-deposited or a white resin plate. The reflectance of the reflection sheet 18 is desirably 90% or more in order to effectively emit light from the light source unit to the liquid crystal display panel 1.

(Operation)
Next, with reference to a cross-sectional view of the backlight 2 shown in FIG. 3, light emission and light propagation of the backlight 2 according to the present embodiment, and light reception (light amount detection) of the external light amount will be described. First, light emission of the backlight 2 according to the present embodiment occurs when the light emitting diode 14 of the light source unit 17 driven by the driver 16 emits light. The light emitted from the light source unit 17 is directly incident on the light guide plate 12 or incident after being reflected by the reflector 13. The light incident on the light guide plate 12 propagates in the light guide plate 12 by being repeatedly reflected on the front surface and the back surface of the light guide plate 12. A large amount of light propagating in the light guide plate 12 is diffused by a diffusion pattern formed on the back side of the light guide plate 12. The diffused light is reflected directly or by the reflection sheet 18 and is emitted from the front surface of the light guide plate 12 and is incident on the back surface of the liquid crystal display panel 1.

  External light passes through the liquid crystal display panel 1 and the optical sheet 11 and enters the light guide plate 12. The light diffused by the diffusion pattern of the light guide plate 12 propagates through the light guide plate 12. The light emitted from the end face of the light guide plate 12 enters the light source unit 17 directly or after being reflected by the reflector 13. The incident light enters the light emitting diodes 14 of RGB colors when the light emitting diode 14 is not lit, and the amount of light is detected. As shown in FIG. 4, the light source unit 17 according to the present embodiment has a feature that the amount of light that can be detected can be increased and the detection sensitivity can be increased because a plurality of light emitting diodes 14 for each color of RGB are provided. Further, since the light emitting diodes 14 are linearly arranged on the end face of the light guide plate 12, it is possible to average and detect the light of the entire surface of the light guide plate 12, and the influence of partial luminance unevenness and color unevenness. It becomes difficult to receive.

  As described above, in the backlight 2 according to the present embodiment, the light emitting diode 14 is used as a light emitting element and also as a light receiving element when not lit. Hereinafter, an operation principle when the light emitting diode 14 is used as a light emitting element or a light receiving element will be described.

  First, when the light-emitting diode 14 is used as a light-emitting element, when the light-emitting diode 14 is in a thermal equilibrium state as shown in FIG. 6, electrons biased toward the n-type semiconductor are difficult to move to the p-type semiconductor because the energy barrier is high. . However, when a forward bias voltage is applied to the light-emitting diode 14 as shown in FIG. 7, the energy barrier is lowered, so that electrons biased toward the n-type semiconductor are likely to move to the p-type semiconductor. Therefore, the electrons of the n-type semiconductor move from a conductor with a high energy level to a valence band with a low energy level, and recombine with holes near the valence band. The energy lost during the recombination is emitted as light, and the light emitting diode 14 emits light.

  Although not shown, conversely, when light is applied to the light emitting diode 14 from the outside and the light energy is larger than the energy difference between the conduction band and the valence band (that is, the band gap energy), electrons in the valence band are conducted. Excited to the body, holes remain in the valence band. This electron-hole pair is generated everywhere in the n-type semiconductor, the p-type semiconductor, and the depletion layer. In the depletion layer, the electric field accelerates electrons to the n-type semiconductor and holes to the p-type semiconductor. Of the electron-hole pairs generated in the n-type semiconductor, the electrons remain in the conduction band of the n-type semiconductor together with the electrons transferred from the p-type semiconductor, and are positive among the electron-hole pairs generated in the n-type semiconductor. The holes diffuse to the depletion layer, are accelerated, and move to the valence band of the p-type semiconductor.

  Thus, the light-emitting diode 14 generates electron-hole pairs in proportion to the amount of incident light, and these electron-hole pairs are accumulated in the n-type semiconductor and the p-type semiconductor, respectively. As a result, the p-type semiconductor is positively charged and the n-type semiconductor is negatively charged, so that electrons flow from the n-type semiconductor and holes from the p-type semiconductor to the opposite electrodes, thereby generating currents. The light emitting diode 14 can detect the amount of light received by measuring this current. When a voltage in the reverse bias direction is applied to the light emitting diode 14, the upper limit of the range in which the relationship between the incident light quantity and the output current is linear is improved, so that the range of illuminance that can be measured is increased.

  From the above, it can be seen that the light emitting diode 14 functions as a light emitting element when a forward bias voltage is applied, and functions as a light receiving element when a non-lighting or reverse bias voltage is applied.

  The light-emitting diode 14 as the light-emitting element has a larger energy difference (band gap energy) between the conduction band and the valence band of the p-type semiconductor, and the energy of light emitted when electrons fall from the conduction band to the valence band. Will grow. In addition, since the color of light changes depending on the wavelength, the shorter the wavelength, the more the light energy is emitted. Therefore, when using the RGB light emitting diodes 14 as in the present embodiment, the main wavelength increases in the order of B, G, and R, and the band gap energy increases in the order of R, G, and B.

  The light emitting diode 14 as the light receiving element does not generate a photovoltaic power unless the absorbed light energy is larger than the band gap energy Eg of the light receiving element. Regarding this, it is generally known that the relationship between the limit wavelength λh (nm) of the light receiving sensitivity characteristic and the band gap energy Eg (eV) is λh = 1240 / Eg.

  As in the present embodiment, when the RGB light emitting diodes 14 are used, the band gap energy Eg increases in the order of R, G, B, so that the limit wavelength λh increases in the order of B, G, R. . In addition, since the ratio in which the incident light of a short wavelength is absorbed in the diffusion layer on the surface of the light emitting diode 14 increases rapidly, the sensitivity of the light emitting diode 14 is higher as the diffusion layer is thinner and the pn junction is closer to the surface. Become. As described above, since the light receiving diode 14 has different light receiving sensitivity characteristics for each color of RGB, when light of a certain wavelength enters the light source unit 17, not only the luminance of the incident light but also the chromaticity can be obtained. However, in order to obtain the chromaticity, it is necessary to apply a voltage in the reverse bias direction to the RGB light emitting diodes 14 and calculate the voltage fluctuation.

  Next, the driver 16 connected to the light source unit 17 adjusts the light emission amount of the light emitting diode 14 functioning as the light emitting element based on the light amount detected by the light emitting diode 14 functioning as the light receiving element. Yes. FIG. 8 shows the relationship between the external light amount and the light emission amount of the light emitting diode 14. The driver 16 adjusts the light emission amount of the light emitting diode 14 to increase when the external light amount, that is, the ambient brightness becomes bright, and to decrease the light emission amount of the light emitting diode 14 when the ambient brightness becomes dark.

  The amount of light emission can be adjusted by increasing or decreasing the current or voltage input to the light emitting diode 14 and the duty ratio. For example, as shown in FIG. 8, when the outside is dark, the light emission amount of the light emitting diode 14 is decreased. Conversely, when the outside is bright, the amount of light emitted from the light emitting diode 14 is increased. Further, from the detection result of the external light, when the amount of red (R) light is high, the external light is reflected on the liquid crystal display panel 1 and the red component of the display increases, so that the color reproducibility on the display is adjusted. Therefore, the light emission amount of the R light emitting diode 14 among the light emitting diodes 14 functioning as the light emitting element is reduced. That is, the light emitting diode 14 when not lit detects the external light amount for each wavelength, and the driver 16 adjusts the light emission amount of the light emitting diode 14 for each wavelength based on the light amount. By performing such feedback control, the liquid crystal display device 30 according to the present embodiment can keep the luminance and color reproducibility range of the emitted light constant.

  FIG. 9 shows the lighting timing of the backlight 2 according to the present embodiment. The timing shown in FIG. 9 is an example of lighting timing. In FIG. 9, the RGB light emitting diodes 14 are illustrated separately.

  Hereinafter, the operation of the backlight 2 according to the present embodiment will be described with reference to FIG. First, as shown in FIG. 9, the light source unit 17 is turned on for the period T1. That is, the lighting period of the light source unit 17 is provided for the period T1. Thereafter, a non-lighting period of the light source unit 17 is provided for the period T2. The driver 16 according to the present embodiment is driven by repeating the T1 period and the T2 period at a predetermined timing. Here, the lighting frequency f of the light source unit 17 is f = 1 / (T1 + T2), but a frequency of 60 Hz or more is necessary to eliminate flickering by visual observation, and preferably 120 Hz or more.

  The distribution of the T1 period and the T2 period described above can be arbitrarily changed. That is, when it is desired to increase the luminance, the T1 period is made longer than the T2 period, and when it is desired to decrease the luminance, the T1 period is made shorter than the T2 period.

  In the T1 period, the light emitting diode 14 of the light source unit 17 functions as a light emitting element. During the period T2, the light emitting diode 14 of the light source unit 17 functions as a light receiving element. That is, the light emitting diode 14 is provided with a non-lighting period, and a voltage in the reverse bias direction is applied to the light emitting diode 14 of the light source unit 17 during the period, so that the light emitting diode 14 functions as a light receiving element.

  Note that when the light source unit 17 is driven as shown in FIG. 9, the output is lower during the time that the light emitting diode 14 is lit than when the light emitting diode 14 is always lit. For this reason, in the present embodiment, the luminance of the emitted light from the backlight 2 is made the same as the luminance when the light emitting diode 14 is always lit by passing a larger current than usual through the light emitting diode 14. By doing in this way, it can drive with the power consumption equivalent to the case where the light emitting diode 14 is always lighted, without increasing the number of the light emitting diodes 14.

  Furthermore, in the present invention, a configuration in which the light-emitting diode 14 that detects light quantity and does not emit light is mounted is also conceivable. In this case, the dedicated light emitting diode 14 for detecting the amount of light does not generate heat due to light emission, and thus has an advantage that the light receiving sensitivity characteristic is not affected by the heat. Moreover, mounting the light emitting diode 14 responsible for light emission and the light emitting diode 14 responsible for light reception on the same circuit board 15 means that the light emitting diode 14 responsible for light emission on a separate circuit board 15 and a separate optical sensor As compared with the case of mounting separately, the assembling work can be simplified and the manufacturing cost can be reduced.

  Note that the backlight 2 according to the present embodiment forms a white light source by combining the light emitting diodes 14 of RGB colors, but the present invention is not limited to this, and a white light emitting diode 14 may be used.

  In the present invention, a light emitting diode 14 that emits light having a long wavelength may be mounted on the circuit board 15 in addition to the RGB light emitting diodes 14. In particular, the IR (infrared) light-emitting diode 14 having a wavelength of infrared light (780 nm or more) as a main wavelength has a light-receiving sensitivity characteristic limit wavelength of 1000 nm. Therefore, when only the R, G, and B light-emitting diodes 14 are provided. In comparison with the above, since the detection sensitivity of the R component is improved, a more stable luminance and color reproducibility range can be obtained.

  In the present invention, an optical sensor may be separately provided in addition to the light-emitting diode 14 that receives light. By providing a separate optical sensor, it becomes possible to control the light emission state of the light emitting diode 14 more accurately by combining the information obtained from the light emitting diode 14 responsible for light reception with the information obtained by the optical sensor. A more stable luminance and color reproducibility range can be obtained.

  Since the liquid crystal display panel 1 displays by transmitting light as described above, when the external light is guided to the light emitting diode 14 through the liquid crystal display panel 1, the average transmission of the liquid crystal display panel 1 is determined according to the display content at that time. Because the rates are different, the external light cannot be measured accurately. In order to avoid this problem, the liquid crystal display panel is corrected by correcting the amount of light detected by the light emitting diode 14 with a light amount correction unit (not shown) based on the panel average transmittance during light reception (when the light emitting diode is not lit). The external light quantity can be received regardless of the display content of 1.

  When the measured value at the time of light reception is α and the transmittance of the liquid crystal display panel 1 at that time is β, when the coefficient is k, the ambient brightness A can be derived by A = k · α / β. . In addition, when the light emitting diode 14 receives light (when the light emitting diode 14 is not lit), the liquid crystal display panel 1 is provided with a full transmission mode (all white mode) period, thereby measuring the external light amount independent of the panel display content. Can do. (Since the panel transmittance is 1, the external light quantity can be derived with A = k · α). Further, since the liquid crystal display panel 1 is set to the full transmission mode during the non-lighting period of the light emitting diode 14, the display content is not affected.

(effect)
As described above, in the backlight 2 according to the present embodiment, the light emitting diode 14 when not lit can detect the amount of light from the outside and adjust the light amount of the light emitting diode 14 based on the current. Therefore, it is possible to realize the backlight 2 that can suppress the increase in cost, and can obtain a stable luminance according to the external light quantity while maintaining a thin and narrow frame.

<Embodiment 2>
(Constitution)
FIG. 10 is a diagram showing a cross section of the liquid crystal display device 30 according to the present embodiment.

  The light emitting diode 14 in the backlight 2 includes a white light emitting diode, and the housing 10 and the reflector 13 are provided with holes formed so that the light emitting diode 14 is exposed to the outside. Moreover, in this Embodiment, it has the frame frame 21 holding the liquid crystal display panel 1 and the backlight 2, and the hole 20 is provided also in the frame frame 21 so that it may connect with the above-mentioned hole. Further, an ultraviolet transmission-visible absorption filter (ultraviolet transmission-visible light non-transmission member) 22 is provided between the hole 20 and the backlight 2.

  The frame frame 21 is a frame for storing and holding the respective constituent members in the same manner as the housing 10, and a synthetic resin or metal having excellent strength and workability is used.

  FIG. 11 shows the transmission characteristics of the ultraviolet transmission-visible absorption filter 22 and the emission spectrum of the white light-emitting diode. The ultraviolet transmission-visible absorption filter 22 is a dark color filter that transmits the ultraviolet region and absorbs the visible light region without transmitting it. In particular, a filter that does not transmit the emission spectrum region of the white light emitting diode is used.

  The ultraviolet transmission-visible absorption filter 22 is produced by mixing a material that absorbs light into the material (generally glass) itself as a base material or by forming an optical thin film on the surface of the base material. Light absorption has wavelength selectivity. For example, semiconductor fine particles such as Cds are dispersed in glass, and light transmitted through the absorption is selected. Optical thin films formed on the substrate surface are roughly classified into metal thin films and dielectric thin films. Dielectric thin films use the fact that the light transmission characteristics change due to interference between reflections generated at the interface between air and dielectric, dielectric and substrate, and different dielectric thin films, and are sometimes called interference filters. . In many cases, the dielectric thin film is not a single layer but a multi-layered film (dielectric multilayer film).

  Since the other structure in the liquid crystal display device 30 is the same as that of Embodiment 1, detailed description here is abbreviate | omitted.

(Operation)
Next, the path of light until external light reaches the light emitting diode 14 will be described. External light enters through a hole 20 formed in the frame frame 21 as indicated by an arrow 23. Among the external light, components in the visible light region are absorbed or reflected by the ultraviolet transmission-visible absorption filter 22, and only the light in the ultraviolet region is guided from the hole of the housing 10. Further, the light incident on the hole of the housing 10 is guided to the light emitting diode 14 from the hole formed in the reflector 13. The light incident from the hole of the reflector 13 is received by the white light emitting diode 14 when the light emitting diode 14 is not lit, and the amount of light is detected. The blue light-emitting diode used in the white light-emitting diode 14 is better because it is suitable for ultraviolet light detection.

  Further, regarding the light path of the light emitting diode 14 at the time of lighting, the light enters the ultraviolet transmission-visible absorption filter 22 from the hole of the reflector 13 through the hole of the housing 10. However, the light from the light emitting diode 14 is not transmitted through the ultraviolet transmission-visible absorption filter 22 as described above, but is absorbed or reflected. Thereby, it can prevent that the light of the light emitting diode 14 leaks outside, and can prevent light leakage.

  Since the light detection mechanism of the light emitting diode 14 other than the light path, the timing of lighting and non-lighting of the light emitting diode 14 and the like are the same as those in the first embodiment, detailed description thereof is omitted here.

  The backlight 2 according to the present embodiment uses the white light emitting diodes 14, but may use light emitting diodes 14 of R, G, and B colors. In this case, external light is detected mainly by a blue diode.

(effect)
As described above, in the backlight 2 according to the present embodiment, external light is not introduced through the liquid crystal display panel 1, so that the external light is not affected by the transmittance of the liquid crystal display panel 1. It is possible to detect the amount of light, and it is possible to realize the backlight 2 that can obtain stable luminance according to the amount of external light.

1 is a perspective view of a liquid crystal display device according to Embodiment 1 of the present invention. It is a top view of the backlight which concerns on Embodiment 1 of this invention. It is sectional drawing of the backlight which concerns on Embodiment 1 of this invention. It is a top view of the light source unit which concerns on Embodiment 1 of this invention. It is a wiring diagram of the light source unit which concerns on Embodiment 1 of this invention. It is a figure explaining operation | movement of the light emitting diode which concerns on Embodiment 1 of this invention. It is a figure explaining operation | movement of the light emitting diode which concerns on Embodiment 1 of this invention. It is a figure which shows the relationship between the ambient brightness which concerns on Embodiment 1 of this invention, and the light emission amount of a light emitting diode. It is a figure which shows the lighting timing of the light source unit which concerns on Embodiment 1 of this invention. It is sectional drawing of the liquid crystal display device which concerns on Embodiment 2 of this invention. It is a figure which shows the permeation | transmission characteristic of the ultraviolet transmission-visible absorption filter which concerns on Embodiment 2 of this invention, and the emission spectrum of a white light emitting diode.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Liquid crystal display panel, 2 Backlight, 3a, 3b Glass substrate, 4 Gate wiring drive driver, 5 Source wiring drive driver, 6 Opening part, 10 Housing | casing, 11 Optical sheet, 12 Light guide plate, 13 Reflector, 14 Light emission Diode, 15 Circuit board, 16 Driver, 17 Light source unit, 18 Reflection sheet, 19 Wiring, 20 Hole, 21 Frame frame, 22 Ultraviolet transmission-visible absorption filter, 23 Arrow, 30 Liquid crystal display device.

Claims (15)

Multiple light sources;
A light guide that guides light from the light source and emits light in a planar shape;
A light emission amount adjustment unit that detects an external light amount and adjusts the light emission amount of the light source based on the light amount;
The planar light source device, wherein the external light quantity is detected by the light source when not lit. The planar light source device according to claim 1, wherein the light source repeats a lighting period and a non-lighting period at a predetermined timing. The plurality of light sources include light sources having different wavelengths of emitted light,
The light source at the time of non-lighting detects an external light amount for each wavelength, and the light emission amount adjustment unit adjusts the light emission amount of the light source for each wavelength based on the light amount. The planar light source device according to claim 2. The planar light source device according to claim 3, wherein the plurality of light sources include light sources that emit red, blue, and green wavelengths. The planar light source device according to claim 4, wherein the plurality of light sources further include a light source that emits light having a wavelength longer than a wavelength of the red monochromatic light. The planar light source device according to claim 5, wherein the long wavelength light is infrared light. The planar light source device according to claim 1, wherein the light source is a light emitting diode or a laser diode. The light source is a light emitting diode;
The planar shape according to any one of claims 1 to 6, wherein a voltage in a forward bias direction is applied to the light emitting diode when it is lit, and a voltage in a reverse bias direction is applied when it is not lit. Light source device. Multiple light sources;
A light guide that guides light from the light source and emits light in a planar shape;
A light emission amount adjustment unit that detects an external light amount and adjusts the light emission amount of the light source based on the light amount;
The planar light source device is characterized in that the external light amount is detected by a dedicated light source for detecting the light amount among the plurality of light sources. A planar light source device according to any one of claims 1 to 9,
A display device comprising: a display element disposed on an emission surface side of the planar light source device and displaying an image. The display device according to claim 10, wherein the display element is a liquid crystal display element. The display device according to claim 11, wherein external light passes through the liquid crystal display element and enters the light source. The display device according to claim 12, further comprising a light amount correction unit that corrects a light amount detected by the light source based on a transmittance of the liquid crystal display element. The display device according to claim 12, wherein the transmittance of the liquid crystal display element is set to a total transmission mode during a period in which the amount of light detected by the light source is detected. A frame provided with a hole for introducing an external light quantity into the light source;
The ultraviolet light transmitting / visible light non-transmitting member which is provided between the hole and the light source and transmits the ultraviolet region and does not transmit the visible light region is further provided. The display device described.

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