Display apparatus and control method thereof

Provided is a display apparatus including: a light emitting unit having a light source; a display unit configured to display an image by controlling a transmittance of light from the light emitting unit; first and second sensors provided in the light emitting unit to detect a brightness of the light source; and a control unit configured to control a transmittance of the display unit on the basis of detection values from the first and second sensors. A distance from the light source to the second sensor is longer than a distance from the light source to the first sensor. The control unit controls the transmittance of the display unit on the basis of a change degree of the detection value from the first sensor during a given period and a change degree of the detection value from the second sensor during the period.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a display apparatus and a control method thereof.

Description of the Related Art

Some examples of color image display apparatuses include a color liquid crystal panel having a color filter, and a light source device (backlight device) which illuminates the back surface of the color liquid crystal panel with white light. Conventionally, as the light source of a light source device, a fluorescent lamp such as Cold Cathode Fluorescent Lamp (CCFL) has been used mainly. However, recent years have seen an increased use of a light emitting diode (LED), which is excellent in terms of power consumption, lifetime, color reproducibility, and environmental load, as the light source of a light source device.

In general, a light source device (LED backlight device) using an LED as a light source has a large number of LEDs. Japanese Patent Application Laid-open No. 2001-142409 discloses an LED backlight device including a plurality of light emitting units each having one or more LEDs. Japanese Patent Application Laid-open No. 2001-142409 also discloses individual control of the brightness of each of the light emitting units. By reducing the emission brightness of the light emitting unit which illuminates with light the region of the screen of a color image display apparatus where a dark image is displayed, power consumption is reduced and the contrast of the image is improved. Such brightness control performed individually for each of the light emitting units in accordance with the characteristic feature of the image is referred to as local dimming control.

On the other hand, when a bright image and a dark image are adjacent to each other in the local dimming control, unevenness referred to as a halo presents a problem. Since the light emitting unit which illuminates with light the region where the bright image is displayed has a high emission brightness, the light from the light emitting unit leaks out into the adjacent region where the dark image is displayed to be visually recognized as unevenness.

To reduce such unevenness, the following method is used. In the method, an emission brightness distribution when each of the light emitting units is individually turned on is obtained in advance. The respective brightnesses of the individual light emitting units that have been determined by local dimming control are subjected to multiplication to be summed up on each other. Thus, the brightness distribution of the light incident on a color liquid crystal panel is determined and, in accordance therewith, the light transmittance of the color liquid crystal panel is adjusted. Japanese Patent Application Laid-open No. 2009-139470 shows an example thereof.

SUMMARY OF THE INVENTION

However, when discoloration, contamination, blur, or the like has occurred in the optical member forming a backlight device due to aging, an emission brightness distribution (hereinafter referred to as individual brightness distribution) and an emission color distribution (hereinafter referred to as individual color distribution) when each of the emitting units is individually turned on change. As a result, the brightness distribution of light incident on the color liquid crystal panel and the color distribution thereof, which are obtained by sum of the individual brightness distributions on each other and sum of the individual color distributions on each other, also change. This causes a problem in that the conventional method cannot sufficiently reduce the unevenness.

To solve the problem, the present invention reduces the unevenness of brightness and chromaticity in a display apparatus including a backlight when discoloration, contamination, blur, or the like has occurred in the optical member forming the backlight due to aging.

A first aspect of the present invention is a display apparatus, comprising:

a light emitting unit having a light source;

a display unit configured to display an image by controlling a transmittance of light from the light emitting unit;

first and second sensors provided in the light emitting unit to detect a brightness of the light source; and

a control unit configured to control a transmittance of the display unit on the basis of detection values from the first and second sensors, wherein

a distance from the light source to the second sensor is longer than a distance from the light source to the first sensor, and

the control unit controls the transmittance of the display unit on the basis of a change degree of the detection value from the first sensor during a given period and a change degree of the detection value from the second sensor during the period.

A second aspect of the present invention is a method of controlling a display apparatus including: a light emitting unit having a light source; a display unit configured to display an image by controlling a transmittance of light from the light emitting unit; and first and second sensors provided in the light emitting unit to detect a brightness of the light source, a distance from the light source to the second sensor being longer than a distance from the light source to the first sensor,

the method comprising:

acquiring detection values from the first and second sensors; and

controlling a transmittance of the display unit on the basis of the detection values from the first and second sensors, wherein

in the controlling, the transmittance of the display unit is controlled on the basis of a change degree of the detection value from the first sensor during a given period and a change degree of the detection value from the second sensor during the period.

According to the present invention, in a display apparatus including a backlight, unevenness in brightness and chromaticity can be reduced when discoloration, contamination, blur, or the like has occurred in the optical member forming the backlight due to aging.

DESCRIPTION OF THE EMBODIMENTS

A description will be given below of a light source device according to Embodiment 1 of the present invention. In Embodiment 1, an example of the case where the light source device is a backlight device used in a color image display apparatus will be described. However, the light source device is not limited to the backlight device used in a display apparatus. For example, the light source device may also be an illuminating device such as a street lamp or a room lamp.

FIG. 1is a schematic diagram showing an example of a configuration of the color image display apparatus according to Embodiment 1. The color image display apparatus has a backlight device, and a color liquid crystal panel105. The backlight device has a light source board101, a diffusion plate102, a light focusing sheet103, a reflection-type polarization film104, and the like.

The light source board101emits light (white light) which illuminates the back surface of the color liquid crystal panel105. The light source board101is provided with a plurality of light sources. As the light sources, cold cathode-ray tubes, organic EL elements, or the like can also be used besides the light emitting diodes (LEDs).

The diffusion plate102, the light focusing sheet103, and the reflection-type polarization film104which are shown inFIG. 1are placed in parallel with the light source board to cause an optical change in the light from the light source board101.

Specifically, the diffusion plate102reflects/diffuses the light from the foregoing plurality of light sources (LED chips in Embodiment 1) to cause the light source board101to function as a surface light source.

The light focusing sheet103focuses the light, which has been reflected/diffused by the diffusion plate102and incident at various angles of incidence, in a front direction (toward the color liquid crystal panel105) to improve front brightness (brightness in the front direction).

The reflection-type polarization film104efficiently reflects/polarizes the incident white light to improve the front brightness.

To the top surface of the light source board101, a reflection sheet (not shown) with a high reflectance has been stuck to return reflected light from the diffusion plate102, the light focusing sheet103, and the reflection-type polarization film104toward the light source board101back to the color liquid crystal panel105.

Note that the display apparatus may also include a member other than the optical members described above and need not include at least any one of the optical members described above.

The color liquid crystal panel105has a plurality of pixels each including an R factice-pixel which transmits red light, a G factice-pixel which transmits green light, and a B factice-pixel which transmits blue light. The color liquid crystal panel105controls the transmittance of the emitted white light on a per-factice-pixel basis to display a color image. Note that, in the display apparatus of the present invention, display unit for displaying an image by controlling the transmittance of the light from the backlight is not limited to the liquid crystal panel. For example, the display unit may also be an MEMS-shutter display using a micro electromechanical system (MEMS) shutter instead of a liquid crystal element.

A backlight device having a configuration as described above (configuration as shown inFIG. 1) is generally referred to as a direct-lit backlight device.

FIG. 2is a schematic diagram showing an example of a configuration of the light source board101.

The light source board101has five light emitting units111in a vertical direction and seven light emitting units111in a lateral direction. That is, the light source board101has the total of thirty-five light emitting units111in five rows and seven columns.

The respective emission brightnesses (amounts of emission) of the light emitting units111can individually be controlled. Each of the light emitting units111is provided with four light sources (LED chips112). As each of the LED chips112, a white LED which emits white light can be used. As each of the LED chips112, a chip configured to be able to provide white light using a plurality of LEDs which emit light beams in different colors (such as, e.g., a red LED which emits red light, a green LED which emits green light, and a blue LED which emits blue light) may also be used.

The light source board101is provided with optical sensors113which detect light and output detection values. The light from each of the light emitting units111is partly reflected by the diffusion plate, the reflection-type polarization film, and the like and returned toward the light emitting unit. Each of the optical sensors113detects the light reflected by the diffusion plate, the reflection-type polarization film, and the like and returned toward the light emitting unit in addition to the light directly incident thereon from the light emitting unit111. In Embodiment 1, a microcomputer125described later detects a brightness change due to the degradation and temperature characteristics of the LEDs in each of the light emitting unit111from detection value from the optical sensor113. The microcomputer125further detects the change of each of an individual brightness distribution and an individual color distribution due to the occurrence of discoloration, contamination, blur, or the like in the optical member forming the backlight device due to aging using the detection value from the optical sensor113(the details thereof will be described later). The individual brightness distribution is a brightness distribution in the color liquid crystal panel105due to light from each of the light emitting units. The individual color distribution is a color distribution in the color liquid crystal panel105due to the light from each of the light emitting units.

In Embodiment 1, each of the light emitting units111is provided with the optical sensor113on a one-by-one basis. As the optical sensor113, a sensor which outputs a brightness as a detection value, such as a photodiode or phototransistor, can be used. A color sensor which outputs a brightness on a per-color basis may also be used as the optical sensor113. Note that the number and locations of the optical sensors113are not limited to those in the example described in Embodiment 1. As will be described later, it is sufficient as long as at least two optical sensors are provided in the backlight device. The at least two optical sensors are a first sensor at a shorter distance from the light emitting unit111and a second sensor at a longer distance therefrom which are caused to emit light when a sensor value is acquired.

FIG. 3is a schematic diagram showing an example of the arrangement of the light emitting units111in the light source board101when the light source board101is viewed from the front direction (from the color liquid crystal panel105).

Among the light emitting units111(X,Y) (Vertical Direction X=1 to 5, Lateral direction Y=1 to 7), the light emitting unit111(1,1) is placed at the upper left end. On the right side of the light emitting unit111(1,1), the light emitting units111(1,2),111(1,3),111(1,4),111(1,5),111(1,6), and111(1,7) are successively arranged. Under the light emitting unit111(1,1), the light emitting units111(2,1),111(3,1),111(4,1), and111(5,1) are successively arranged.

FIG. 4is a block diagram showing the relations among individual portions in the process performed by the microcomputer125in Embodiment 1, i.e., the process in which the microcomputer125causes the light emitting units111to emit light, acquires detection values from the optical sensors113, and performs unevenness correction.

The microcomputer125may also perform the process of sensor value detection and correction during a vacant time during which a user does not use the color image display apparatus or during a short time during which the user uses the color image display apparatus but the process performed by the microcomputer125is visually unrecognized by the user. The microcomputer125periodically performs the process of sensor value detection and correction at given intervals.

The microcomputer125causes the light emitting unit111(3,4) as a detection target to emit light, while forcibly turning off the other light emitting units111. The major part of light121(3,4) emitted from the light emitting unit111(3,4) is incident on the color liquid crystal panel105(not shown inFIG. 4). However, the light121(3,4) is partly returned as reflected light from the diffusion plate, the reflection-type polarization film (not shown), and the like toward the light emitting unit. A close optical sensor113(3,4) provided in the light emitting unit111(3,4) additionally detects the reflected light as well as the light directly incident thereon from the light emitting unit111(3,4). The major part of the reflected light is reflected again by the reflection sheet (not shown) stuck onto the light source board101(not shown) toward the color liquid crystal panel105(not shown). The light121(3,4) repeatedly reflected by each of the optical members several times is incident also on the optical sensor113distant from the light emitting unit111(3,4). Each of the optical sensors113outputs an analog value122(detection value) representing the brightness of detected light in accordance with the brightness.

The subsequent processes include the process of detecting a brightness change due to the degradation and temperature characteristics of the LEDs in each of the light emitting units111and the process of detecting the change of each of the individual brightness distribution and the individual color distribution due to the occurrence of discoloration, contamination, blur, or the like in the optical member due to aging. First, a description will be given of the former process.

An A/D converter123selects, among the analog values122output from the individual sensors113, an analog value122(3,4) output from the close optical sensor113(3,4) provided in the light emitting unit111(3,4). Then, the A/D converter123converts the selected analog value to a digital value through analog-digital conversion and outputs a digital value124to the microcomputer125. The microcomputer125adjusts the emission brightness of the light emitting unit111(3,4) on the basis of the detection value (specifically, a digital value124(3,4)) from the optical sensor113(3,4).

The description has been given heretofore of the case where the light emitting unit111(3,4) is turned on as a representative and detection is performed. However, the same process is performed for each of the other light emitting units111. That is, in the state where only the light emitting unit111for which the process is to be performed is caused to emit light, the brightness thereof is detected by the close optical sensor113provided in each of the light emitting units. In the A/D converter123, the analog value122of the optical sensor113provided in the light emitting unit111the emission brightness of which is to be adjusted is converted to the digital value124, and the digital value124is output to the microcomputer125. As a result, from the A/D converter123, the total of thirty-five detection values (detection values from the optical sensors, i.e., the digital values124) is output to the microcomputer125.

The microcomputer125adjusts the emission brightness of each of the light emitting units111on the basis of the detection value (specifically, the digital value124) from each of the optical sensors113. Specifically, the microcomputer125has stored, in a nonvolatile memory126, a reference brightness value (reference value for the detection value) for each of the light emitting units111, which was determined during the manufacturing/inspection of the color image display apparatus. The microcomputer125compares, for each of the light emitting units111, the detection value from the optical sensor113provided in the light emitting unit111to the foregoing reference value. Then, the microcomputer125individually adjusts the emission brightness of each of the light emitting units111in accordance with the result of the foregoing comparison so as to bring the detection value closer to the reference value. The microcomputer125adjusts the emission brightness by, e.g., adjusting an LED driver control signal127to be output from the microcomputer125to an LED driver120. The LED driver120drives the light emitting unit111in accordance with the LED driver control signal127. The LED driver control signal127represents, e.g., the pulse width of the pulse signal (current or voltage pulse signal) applied to the light emitting unit111. In that case, the microcomputer125adjusts the LED driver control signal127to subject the emission brightness of the light emitting unit111to PWM control. Note that the LED driver control signal127is not limited thereto. For example, the LED driver control signal127may represent the wave height value of the pulse signal applied to the light emitting unit111or may represent each of the pulse width and the wave height value thereof. By adjusting the emission brightness of each of the light emitting units111so as to bring the detection value closer to the reference value, even when a brightness change has occurred due to the degradation and temperature characteristic of the light emitting unit111, the brightness unevenness of the entire backlight device can be suppressed.

Next, a description will be given of the process of detecting the change of each of the individual brightness distribution and the individual color distribution due to the occurrence of discoloration, contamination, blur, or the like in the optical member forming the backlight device due to aging and adjusting the transmittance of the color liquid crystal panel so as to compensate for the change. However, only the outline of the process is described herein usingFIG. 4, and the details thereof will be described later.

It is assumed that the detection of the change of each of the individual brightness distribution and the individual color distribution is performed using a representative one of the light emitting units111. A description is given herein of an example using the light emitting unit111(3,4) located at the center of the backlight device. This is conceivably because, in the same backlight device, the state of discoloration, contamination, blur, or the like in the optical member due to aging could not differ from region to region. However, in a structure in which the temperature considerably differs from region to region and aging tends to differ from region to region, the same detection and correction may also be performed individually for each of the regions.

The A/D converter123first selects, among the analog values122output from the individual optical sensors113, the analog value122(3,4) output from the close optical sensor113(3,4) (first sensor) provided in the light emitting unit111(3,4). Then, the A/D converter123converts the selected analog value to a digital value through analog-digital conversion and outputs the digital value124to the microcomputer125. Then, the A/D converter123selects the analog value122(3,7) output from the optical sensor distant from the light emitting unit111(3,4), which is the optical sensor113(3,7) (second sensor) herein. Then, the A/D converter123similarly converts the selected analog value to a digital value through analog-digital conversion and outputs the digital value124to the microcomputer125. During the manufacturing/inspection of the color image display apparatus also, the microcomputer125acquired the detection values from the close and distant optical sensors113(3,4) and113(3,7) that detected the light121(3,4) from the light emitting unit111(3,4) by the same procedure. These detection values have been stored as reference values in the nonvolatile memory126.

From the respective detection values from the close and distant optical sensor113(3,4) and113(3,7) thus acquired and the respective reference values therefor, the microcomputer125determines a fractional decrease rate RYELdue to the degradation of the optical member in a decrease rate R of the detection value from the distant optical sensor113(3,7). The decrease rate may be decrease degree. An accelerated deterioration test is performed in advance using an equivalent color image display apparatus as a sample to evaluate the correspondence relationship between the fractional decrease rate RYELdue to the degradation of an optical member that has been determined by a similar detection method and each of the individual brightness distribution and the individual color distribution. In the color image display apparatus used by a user, information on the foregoing correspondence relationship is stored in advance in the nonvolatile memory126during manufacturing. When the user starts to use the color image display apparatus, the microcomputer125determines the fractional decrease rate RYELdue to the degradation of the optical member by regular detection. The microcomputer125obtains the individual brightness distribution and the individual color distribution which correspond to the fractional decrease rate RYELdue to the degradation of the optical member from the magnitude of the fractional decrease rate RYELand the information on the foregoing correspondence relationship stored in the nonvolatile memory126. The details of this process will be described later.

First, a description will be given of a method of determining the fractional decrease rate RYELdue to the degradation of the optical member in the decrease rate R of the detection value from the distant optical sensor.

FIG. 5is a schematic diagram showing the locations of a light emitting unit200used to detect the change of each of the individual brightness distribution and the individual color distribution, a close optical sensor S1, and a distant optical sensor S2when viewed from the front direction (from the color liquid crystal panel105).

As the light emitting unit200used to detect the change of each of the individual brightness distribution and the individual color distribution, the light emitting unit111(3,4) located at the center of the light source board101is used. As the close optical sensor S1(first sensor), the optical sensor113(3,4) provided in the light emitting unit111(3,4) is used. As the distant optical sensor (second sensor), the optical sensor113(3,7) is used herein.

On the close optical sensor S1, not only light is directly incident from the light emitting unit111(3,4), but also the light reflected by the diffusion plate and the reflection-type polarization film is incident. However, the number of times the light is reflected is small. Consequently, a detection value from the close optical sensor S1is barely affected by discoloration, contamination, blur, or the like in the optical member due to aging.

On the other hand, on the distant optical sensor S2, the light from the light emitting unit111(3,4) is seldom directly incident, but the light that has been reflected a considerable number of times is incident. Consequently, the influence of discoloration, contamination, blur, or the like in the optical member due to aging increases, which will be described usingFIGS. 6 and 7.

FIG. 6is a schematic diagram of reflection of light in the backlight device when viewed in a cross section.

From the LED chip112, light121is emitted in the direction of the color liquid crystal panel105. The light121gradually travels in the backlight device, while subjected to repeated transmission and reflection including transmission (210) by the diffusion plate102(210), reflection (211) by the reflection-type polarization film104, and reflection (212) by the reflection sheet over the light source board101.

FIG. 7is a graph showing an example of the change of a spectral transmittance (reflectance) when discoloration, contamination, and blur has occurred in the optical member due to aging.

In general, an optical member is formed of a resin. For example, polycarbonate is used for the diffusion plate102, while polyethylene naphthalate is used for the reflection-type polarization film104and the reflection sheet. A resin material is likely to be modified by heat or light. Since heat and light is emitted from the LEDs of the backlight device, modification cannot be avoided. When a power supply time exceeds ten thousand hours, the influence of such discoloration, contamination, and blur becomes prominent, though the degree thereof differs depending on temperature and humidity conditions in an installation environment.

It is assumed that a spectral transmittance (reflectance)220in an initial state (immediately after manufacturing) has a flat characteristic at each wavelength in a visible light band (400 to 700 nm). By contrast, a spectral transmittance (reflectance)221after a lapse of time decreases particularly in the blue color (short wavelength) range so that transmitted (reflected) light is discolored into yellow. The transmittance (reflectance) considerably decreases at all the wavelengths including the red color (long wavelength) range so that the optical member is recognized to be rather blurred. In addition, gas may be emitted from another member due to aging and deposited to result in contamination.

Every time the transmission or reflection of the light121emitted from each of the LED chips112by the optical member is repeated, the light121undergoes a reduction in spectral transmittance (reflectance), as shown inFIG. 7. That is, the light that has reached a place distant from the LED chip112of the light emitting unit111and is detected by the distant optical sensor S2is significantly affected by discoloration, contamination, and blur due to aging.

In Embodiment 1, it is assumed that the optical sensor113(3,7) used as the distant optical sensor S2is sufficiently distant from the light emitting unit111(3,4) and the distance therebetween is about six times the diffusion distance (distance between each of the LED chips112mounted on the light source board101and the diffusion plate102) of the backlight device in the present embodiment. It follows that, when the diffusion distance is 30 mm, the optical sensor113(3,7) is 180 mm distant from the light emitting unit111(3,4). In general, when the distance therebetween is not less than several times the diffusion distance, the light reflected by the optical member a considerable number of times is incident. Accordingly, it is possible to detect the influence of discoloration, contamination, and blur due to aging.

FIG. 8is a graph showing the change of the individual color distribution due to lapse of time.

The x-axis represents the distance from each of the LED chips112, and the LED chip112is placed at DISTANCE x=0. The y-axis shows a color difference Δu′v′ based on the chromaticity of light immediately over the LED chip112(over the diffusion plate102) used as a reference (y=0). The color difference was measured from outside the backlight device using a surface brightness meter.

In a curve230obtained in an initial state (immediately after manufacturing), even though light has been emitted away from the LED chip112and reflected by the optical member a considerable number of times, the color difference scarcely increases.

In a curve231obtained after a lapse of time, as light has been emitted farther away from the LED chip112and reflected by the optical member a larger number of times, the color difference increases.

A detection value from the close optical sensor S1corresponds to a value around DISTANCE x=0 in the distribution shown inFIG. 8. Since the number of times light has been reflected by the optical member is zero or small, the detection value is immune to the influence of discoloration, contamination, blur, or the like in the optical member due to aging.

A detection value from the distant sensor S2corresponds to a value at a sufficiently increased distance x in the distribution shown inFIG. 8. Since the light has been reflected by the optical member a considerable number of times, the detection value is significantly affected by aging. More specifically, the light in which a component in the blue color (short wavelength) range has decreased due to the reflection by the optical member is detected so that the detection value decreases.

FIG. 9is a graph showing the change of the individual brightness distribution due to lapse of time.

The x-axis represents the distance from each of the LED chips112. The LED chip112is placed at DISTANCE x=0. The y-axis represents a brightness Y which has the apex immediately over the LED chip112(over the diffusion plate102). The brightness Y was measured from outside the backlight device using a surface brightness meter. Each of the curves has been normalized with the brightness (apex) at DISTANCE x=0.

In a curve240obtained in the initial state (immediately after manufacturing), the brightness decreases with distance from the LED chip112. This is a typical characteristic feature of an individual brightness distribution in a direct-lit backlight device.

In a curve231obtained after a lapse of time, an amount of brightness decrease with distance from the LED chip112is larger than in the curve240obtained in the initial state (immediately after manufacturing).

The detection value from the close optical sensor S1corresponds to a value around DISTANCE x=0 in the distribution shown inFIG. 9. Since the number of times light has been reflected by the optical member is zero or small, the detection value is immune to the influence of discoloration, contamination, blur, or the like in the optical member due to aging. Accordingly, the close optical sensor S1mainly detects a brightness decrease due to the aging degradation of the LED chip112.

The detection value from the distant optical sensor S2corresponds to a value at a sufficiently increased distance x in the distribution shown inFIG. 9. Since the light has been reflected by the optical member a considerable number of times, the detection value is affected by aging. More specifically, the distant optical sensor S2detects the light in which the brightness has been reduced by the reflection by the optical member so that the detection value therefrom decreases.

FIG. 10is a graph showing the details of the decrease rate R in each of the detection values from the close and distant optical sensors S1and S2.

First, the decrease rate R in each of the detection values is defined as in Expression 1:
[Math 1]
R=1−V(T)/V(T0)  Expression 1

In Expression 1, V(T) represents the detection value from each of the optical sensors113at a time T and V(T0) represents the detection value in the initial state (during the manufacturing/inspection of the color image display apparatus). Expression 1 shows how much the detection value V(T) has decreased relative to the detection value V(T0). In the initial state, the decrease rate R is 0, which shows that the detect value has not decreased. The decrease rate R at the given time T has a value larger than 0 and smaller than 1, which shows that the detection value has decreased with approach to 1.

InFIG. 10, in the initial state (T=T0), the decrease rate R is 0 in either of the close and distant optical sensors S1and S2.

At the time T when a sufficient power supply time has elapsed, the decrease rate R of the detection value is larger than 0. The number of times the light detected by the close optical sensor S1has been reflected by the optical member is zero or small. Consequently, the detection value is immune to the influence of discoloration, contamination, blur, or the like in the optical member due to aging. Accordingly, the decrease rate R includes only the fractional decrease rate RLEDdue to the degradation of the LED chip. On the other hand, the light detected by the distant optical sensor S2has been reflected by the optical member a considerable number of times and affected by discoloration, contamination, blur, or the like in the optical member due to aging. Consequently, the decrease rate R includes the fractional decrease rate RYELdue to the degradation of the optical member. In addition, the decrease rate R also includes the fractional decrease rate RLEDdue to the degradation of the LED chip equal to the factional decrease rate RLEDin the close optical sensor S1.

Accordingly, by subtracting the decrease rate R=RLEDin the close optical sensor S1from the decrease rate R of the detection value from the distant optical sensor S2, the fractional decrease rate RYELdue to the degradation of the optical member in the decrease rate R of the detection value from the distant optical sensor S2can be determined.

Next, a description will be given of the process of preliminarily performing an accelerated deterioration test using an equivalent color image display apparatus as a sample and evaluating the correspondence relationship between the fractional decrease rate RYELdue to the degradation of the optical member and each of the individual brightness distribution and the individual color distribution.

The degradation of the optical member is conspicuous when ten thousand hours is exceeded, but it is difficult to preliminarily evaluate the degradation of the optical member in actual time. Accordingly, a test is performed herein under several tens of times accelerated conditions and the degradation of the optical member up to the assumed maximum lifetime of the color image display apparatus is fully evaluated. For example, when the maximum lifetime is assumed to be hundred thousand hours, the test is completed in about 100 days under the accelerated conditions.

First, by assuming that the test is started (initial state) at a time T0, the decrease rate R of the detection value from the close optical sensor S1and the decrease rate R of the detection value from the distant optical sensor S2are periodically acquired. For example, acquiring the decrease rates R every 24 hours corresponds to acquiring the decrease rates R every 1000 hours in actual time.

FIG. 11is a graph showing the relationship between the decrease rate R in each of the close and distant optical sensors S1and S2and the time T.

The decrease rate R in the close optical sensor S1includes only the fractional decrease rate RLEDdue to the degradation of the LED chip. The fractional decrease rate RLEDgradually increases with lapse of the time T. The decrease rate R in the distant optical sensor S2includes the fractional decrease rate RYELdue to the degradation of the optical member in addition to the fractional decrease rate RLEDdue to the degradation of the LED chip. As a result, at any time T, the decrease rate R in the distant optical sensor S2is higher.

FIG. 12shows an example of data showing the relationship between the detection vales at each of the times T and the fractional decrease rate RYELdue to the degradation of the optical member that has been determined from the detection values in the accelerated deterioration test.

At the time T0when the test is started (in the initial state), a detection value VS1from the close optical sensor S1is 1000. At this time, a detection value VS2from the distant optical sensor S2is 100. The amount of light incident on the distant optical sensor S2is smaller than the amount of light incident on the close optical sensor S1so that the detection value is also small. Using these detection values as a reference, the decrease rate R is determined at each of the subsequent times T. For example, at a time T3, the detection value VS1is 850 and the detection value VS2is 70, while a decrease rate RS1of the detection value in the close optical sensor S1is determined to be 0.15 and a decrease rate RS2of the detection value in the distant optical sensor S2is determined to be 0.30. The fractional decrease rate RYELdue to the degradation of the optical member in the decrease rate RS2is determined to be 0.15 by subtracting the decrease rate RS1from the decrease rate RS2.

Thus, the fractional decrease rate RYELdue to the degradation of the optical member at each of the times T is determined. At the same time, at each of the times T, an individual color distribution and an individual brightness distribution as shown inFIGS. 8 and 9are measured from outside the backlight device using a surface brightness meter. In this manner, the correspondence relationship between the fractional decrease rate RYELand each of the individual brightness distribution and the individual color distribution is determined.

In the evaluation based on the accelerated deterioration test, an average result may also be obtained from sample data from several backlight devices.

Next, a description will be given of the process of periodically detecting, in the color image display apparatus used by the user, the change of each of the individual brightness distribution and the individual color distribution due to lapse of time using the result of the evaluation based on the accelerated deterioration test and performing correction.

In the accelerated deterioration test, the correspondence relationship between the fractional decrease rate RYELdue to the degradation of the optical member and each of the individual brightness distribution and the individual color distribution is determined. In the color image display apparatus used by the user, information on the correspondence relationship is stored in advance in the nonvolatile memory126during manufacturing.

When the user starts to use the color image display apparatus, the microcomputer125periodically detects sensor values from the optical sensors S1and S2to determine the fractional decrease rate RYELdue to the degradation of the optical member in the detection value from the distant optical sensor S2. When the factional decrease rate RYELdue to the degradation of the optical member increases with time, the microcomputer125detects the change of each of the individual brightness distribution and the individual color distribution.

The microcomputer125performs the process of obtaining the brightness distribution and color distribution of light incident on the color liquid crystal panel by sum of the individual brightness distributions on each other and sum of the individual color distributions on each other in each of the light emitting units111and adjusting the light transmittance of the color liquid crystal panel105in accordance with the brightness distribution and the color distribution to reduce unevenness. On detecting the change of each of the individual brightness distribution and the individual color distribution from a change in the fractional decrease rate RYEL, the microcomputer125newly reads the individual brightness distribution and the individual color distribution which correspond to the current fractional decrease rate RYELfrom the nonvolatile memory. Then, the microcomputer125corrects the image signal to be input to the color liquid crystal panel105to perform an unevenness reducing process. A description will be given of the process usingFIGS. 13 and 14.

FIG. 13Ais a graph showing the change of the individual color distribution due to lapse of time in an LED chip112a.FIG. 13Ais equivalent toFIG. 8and shows a curve230aobtained in the initial state (immediately after manufacturing) and a curve231aobtained after a lapse of time.

FIG. 13Bis a graph showing the change of the individual color distribution due to lapse of time in an LED chip112b.FIG. 13Bis also equivalent toFIG. 8, but the position of the LED chip112bis away at a given distance from x=0 serving as a reference point.230bshows a curve obtained in the initial state (immediately after manufacturing) and231bshows a curve after a lapse of time.

The microcomputer125calculates to obtain a curve resulting from the superimposition of the individual brightness distributions and a curve resulting from the superimposition of the individual color distributions in each of the light emitting units111and obtain the color distribution of the light incident on the color liquid crystal panel105. Here, for the sake of simplicity, the case is shown where the color distribution of the light incident on the color liquid crystal panel105is obtained by sum of the individual color distribution in the LED chip112ainFIG. 13Aand the individual color distribution in the LED chip112binFIG. 13Bon each other.

FIG. 13Cis a graph showing the color distribution of the light incident on the color liquid crystal panel, which has been obtained by sum of the individual color distributions in the LED chips112aand112bon each other.

A curve260shows the color distribution of the light incident on the color liquid crystal panel in an initial state (immediately after manufacturing), which has been obtained by sum of the curves230aand230binFIG. 13AandFIG. 13Bon each other. In the initial state, even in the light emitted away from the LED chip112and reflected by the optical member a considerable number of times, the color difference scarcely increases. Accordingly, the curve260resulting from the superimposition thereof also scarcely increases irrespective of the distance x.

A curve261shows the color distribution of the light incident on the color liquid crystal panel after a lapse of time, which has been obtained by sum of the curves231aand231binFIGS. 13A and 13Bon each other. In the individual color distribution after a lapse of time, as the light has been emitted further away from the LED chip112and reflected by the optical member a larger number of times, the color difference increases. However, the curve261obtained by sum of the curves231aand231bon each other has the large color difference at each position irrespective of the distance X. In addition, in the curve261, the color difference varies toward the middle point between the LED chips112aand112b. In the curve261, the color difference is largest at the middle point between the LED chips112aand112b.

The microcomputer125performs the process of adjusting the light transmittance of the color liquid crystal panel105in accordance with the color distribution of the light incident on the color liquid crystal panel105to reduce unevenness. The microcomputer125adjusts the transmittance of the color liquid crystal panel105on the basis of the color difference curve shown inFIG. 13Cso as to reduce (to zero) the color difference against the power source position (x=0) at each of the distances x in the color distribution of the light after transmitted by the color liquid crystal panel.

The curve260obtained in the initial state (immediately after manufacturing) scarcely needs to be adjusted in the color liquid crystal panel. The curve261after a lapse of time needs to be adjusted such that, in the color distribution of the light after transmitted by the color liquid crystal panel, the color difference against the light source position (x=0) is zero at each of the distances x. For example, when the blue color of the light incident on the color liquid crystal panel decreases as a result of the discoloration of the optical member due to aging and the light is changed into yellow, the microcomputer125performs adjustment such that the transmittance of the color liquid crystal panel with respect to the blue color is increased to compensate for the color change.

FIG. 14Ais a graph showing the change of the individual brightness distribution in the LED chip112adue to lapse of time.FIG. 14Ais equivalent toFIG. 9and shows a curve240aobtained in the initial state (immediately after manufacturing) and a curve241aobtained after a lapse of time.

FIG. 14Bis a graph showing the change of the individual brightness distribution in the LED chip112bdue to lapse of time.FIG. 14Bis also equivalent toFIG. 9, but the position of the LED chip112bis away at a given distance from x=0 serving as the reference point.FIG. 14Bshows a curve240bobtained in the initial state (immediately after manufacturing) and a curve241bobtained after a lapse of time.

The microcomputer125obtains the brightness distribution of the light incident on the color liquid crystal panel by sum of the individual brightness distributions in all the light emitting units111on each other. Here, for the sake of simplicity, the case is shown where the brightness distribution of the light incident on the color liquid crystal panel is obtained by sum of the individual brightness distribution in the LED chip112ainFIG. 14Aand the individual brightness distribution in the LED chip112binFIG. 14Bon each other.

FIG. 14Cis a graph showing the brightness distribution of the light incident on the color liquid crystal panel obtained by sum of the individual color distributions in the LED chips112aand112bon each other.

A curve270shows the brightness distribution of the light incident on the color liquid crystal panel in the initial state (immediately after manufacturing), which has been obtained by sum of the curves240aand240binFIGS. 14A and 14Bon each other. In each of the curves240aand240b, the brightness decreases with distance from the LED chip112. However, it is assumed that, in a curve obtained by sum of the curves240aand240bon each other, the brightness scarcely changes irrespective of the distance x to provide a state free from unevenness, as in the curve270.

A curve271shows the brightness distribution of the light incident on the color liquid crystal panel after a lapse of time, which has been obtained by sum of the curves241aand241binFIGS. 14A and 14Bon each other. In the individual brightness distribution after a lapse of time, the amount of decrease in brightness with the distance from the LED chip112is larger than in the curve obtained in the initial state (immediately after manufacturing). In the curve271obtained by sum of the curves241aand241bon each other, the brightness decreases with approach to the LED chips112aand112b, while having a peak at the middle point between the LED chips112aand112b.

The microcomputer125performs the process of adjusting the light transmittance of the color liquid crystal panel105in accordance with the brightness distribution of the light incident on the color liquid crystal panel105to reduce unevenness. The microcomputer125performs the process of correcting (adjusting) the transmittance of the liquid crystal panel so as to compensate for the difference between the curve271obtained after a lapse of time and the curve270inFIG. 14Cobtained in the initial state.

The curve270obtained in the initial state need not be adjusted so that the microcomputer125does not particularly correct the image signal to be input to the color liquid crystal panel105. On the other hand, to adjust the difference between the curve271obtained after a lapse of time and the curve270, the microcomputer125performs adjustment on the color liquid crystal panel105such that the transmittance increases with approach to the LED chips112aand112b. As a result, in the brightness distribution (unevenness) of the light after transmitted by the color liquid crystal panel, the change due to lapse of time is reduced.

UsingFIGS. 13 and 14, the unevenness reducing process performed using the liquid crystal panel has been described. However, the process in the liquid crystal panel and the process in the backlight device can also be performed in combination.

FIG. 15is a graph showing task assignment when the unevenness reducing process in accordance with the color distribution of the light incident on the color liquid crystal panel is performed by combining the process in the backlight device with the process in the liquid crystal panel.

A curve261shows the color distribution of the light incident on the color liquid crystal panel105after a lapse of time. As has been described above usingFIG. 13, the microcomputer125adjusts the transmittance of the color liquid crystal panel105on the basis of the curve261such that, in the color distribution of the light after transmitted by the color liquid crystal panel, the color difference against the light source position (x=0) becomes zero at each of the distances x. Of the graph, the portion corresponding to an amount of adjustment280can uniformly be adjusted irrespective of the distance x. Accordingly, the microcomputer125performs the adjustment of the portion corresponding to the amount of adjustment280by adjusting the amount of emission from each of the light emitting units of the backlight. For example, in a backlight having a configuration including LED chips formed of RGB three-color LEDs, the brightness ratio among the RGB three-color LEDs is changed to allow the colors of the light emitted from the light emitting units to be adjusted. On the other hand, the portion of the graph corresponding to an amount of adjustment281needs to be adjusted in accordance with the distance x. Accordingly, the microcomputer125performs the adjustment of the portion corresponding to the amount of adjustment281by adjusting the transmittance of the color liquid crystal panel105on a per-pixel basis.

By thus applying Embodiment 1, even when discoloration, contamination, blur, or the like has occurred in the optical member forming the backlight device due to aging, the change of each of the individual brightness distribution and the individual color distribution can be detected and unevenness is sufficiently reduced.

A description will be given below of a light source device according to Embodiment 2 of the present invention. In Embodiment 1, one close optical sensor and one distant optical sensor are used. In Embodiment 2, a description will be given of an example of the case where a plurality of distant optical sensors is used. Note that the same members as used in Embodiment 1 are designated by the same reference numerals and a description thereof is omitted.

FIG. 16is a schematic diagram showing the locations of a light emitting unit300used to detect the change of each of an individual brightness distribution and an individual color distribution, a close optical sensor S3, and distant optical sensors S4when viewed in the front direction (from the color liquid crystal panel105).

The microcomputer125uses, as the light emitting unit300used to detect the change of each of the individual brightness distribution and the individual color distribution, the light emitting unit111(3,4) located at the center portion of the screen. The microcomputer125uses, as the close optical sensor S1, the optical sensor113(3,4) provided in the light emitting unit111(3,4).

The microcomputer125uses, as the distant optical sensor S4, the total four optical sensors which are the optical sensors113(1,1),113(1,7),113(5,1) and113(5,7). The four optical sensors113are at approximately equal distances301,302,303, and304to the light emitting unit300.

When the distances to the light emitting unit300are equal, the light detected by each of the distant optical sensors S4has been reflected by the optical member an equal number of times. Accordingly, the fractional decrease rate RYELdue to the degradation of the optical member in the decrease rate R of the detection value after a lapse of time is also equal in each of the distant optical sensors S4.

The microcomputer125uses the sum of detection values from the total of four optical sensors113as a detection value from the distant optical sensor S4and determines the fractional decrease rate RYELfrom the difference between the decrease rate of the sum of the four detection values and the decrease rate of the detection value from the close optical sensor S1. Since the amount of light incident on the distant optical sensor is small, the detection value decreases to reduce an S/N ratio, which may result in a detection error. However, by using the sum of the plurality of detection values as in Embodiment 2, the situation is improved.

Next, a description will be given of another example of the case where the plurality of distant optical sensors is used.

FIG. 17shows the locations of a light emitting unit310used to detect the change of each the individual brightness distribution and the individual color distribution, a closest optical sensor S5, a third-most-distant optical sensor S6, a second-most-distant optical sensor S7, and a most distant optical sensor S8when viewed from the front direction (from the color liquid crystal panel105).

The microcomputer125uses, as the light emitting unit310used to detect the change of each of the individual brightness distribution and the individual color distribution, the light emitting unit111(3,1) located at the left end of the light source board101. The microcomputer125uses, as the closest optical sensor S5, the optical sensor113(3,1) provided in the light emitting unit111(3,1).

The microcomputer125uses, as the distant optical sensor, the three optical sensors113at different distances to the light emitting unit310. The microcomputer125uses the optical sensor113(3,3) as the third-most-distant optical sensor S6, uses the optical sensor113(3,5) as the second-most-distant optical sensor S7, and uses the optical sensor113(3,7) as the most distant optical sensor S8.

Since the distances to the light emitting unit310are different, the number of times the light detected by each of the optical sensors113has been reflected by the optical member is also different. Accordingly, the fractional decrease rate RYELdue to the degradation of the optical member in the decrease rate R of the detection value after a lapse of time is also different in each of the optical sensors113. By using this, the microcomputer125performs correction using the detection values from the third-most-distant optical sensor S6and the second-most-distant optical sensor S7to finally determine the fractional decrease rate RYELin the most distant optical sensor S8.

FIG. 18is a graph showing the decrease rates R in the closest optical sensor S5, the third-most-distant optical sensor S6, the second-most-distant optical sensor S7, and the most distant optical sensor S8. The detection value from the closest optical sensor S5is immune to the influence of discoloration, contamination, blur, or the like in the optical member due to aging since the number of times the light has been reflected by the optical member is zero or small. Accordingly, the closest optical sensor S5mainly detects a brightness decrease due to the aging degradation of the LED chip112.

The detection value from the most distant sensor S8is affected by aging since the light has been reflected by the optical member a considerable number of times. The detection value from the second-most-distant-sensor S7is less affected by aging than the detection value from the most distant optical sensor S8. The detection value from the third-most-distant optical sensor S6is less affected by aging than the detection value from the second-most-distant optical sensor S7.

In the accelerated deterioration test performed in advance, the ratio among the fractional decrease rates RYELdue to the degradation of the optical member in the most distant optical sensor S8, the second-most-distant optical sensor S7, and the third-most-distant optical sensor S6is preliminarily evaluated. For example, it is assumed that, in the accelerated deterioration test, the ratio thereamong is RYEL/S8:RYEL/S7:RYEL/S6=3:2:1. Information on the fractional decrease rates in the individual optical sensors obtained in the test is stored in the nonvolatile memory126.

In the color image display apparatus used by the user, to determine the fractional decrease rate RYEL/S8in the most distant optical sensor S8, the microcomputer125acquires, from the nonvolatile memory126, the information obtained in the foregoing accelerated deterioration test. Then, the microcomputer125determines the ratio among the fractional decrease rates in the individual optical sensors and corrects the fractional decrease rate RYEL/S8in the most distant optical sensor S8. This improves the accuracy of detection of the change of each of the individual brightness distribution and the individual color distribution. For example, it is assumed that, in the color image display apparatus used by the user, the microcomputer125has detected the fractional decrease rates at the ratio of RYEL/S8:RYEL/S7:RYEL/S6=3.1:2:1. Since the detected fractional decrease rate RYEL/S8is slightly higher than in the data stored in the nonvolatile memory126, the microcomputer125performs correction which slightly reduces the factional decrease rate RYEL/S8.

Thus, even when the plurality of distant optical sensors are used as in Embodiment 2 and discoloration, contamination, blur, or the like has occurred in the optical member forming the backlight device due to aging, the change of each of the individual brightness distribution and the individual color distribution is detected and unevenness is sufficiently reduced.

Other Embodiments

This application claims the benefit of Japanese Patent Application No. 2014-075651, filed on Apr. 1, 2014, which is hereby incorporated by reference herein in its entirety.