JP4417784B2 - Light emitting device and display device - Google Patents

Description

  The present invention relates to a light emitting device suitable for general illumination or a direct-view display and a projection display, and a display device using the same, and more particularly to a light emitting device used as a white light source.

  A white light source is used as a light source in lighting used indoors, a direct-view display using a backlight transmissive liquid crystal, a front light reflective liquid crystal, and a projection display such as a liquid crystal projector.

  As a white light source, a fluorescent tube is used for illumination, and a cold cathode fluorescent tube is generally used for a direct-view display for monitoring. In a small direct-view display used for a mobile phone device, a light emitting diode (LED) is also used. In the projection display, a high-pressure mercury lamp or the like is used.

  A commonly used white light source such as a cold-cathode tube has a problem that the red color purity is low and the color reproduction range is narrow because there are few red wavelength components. In addition, when white balance is achieved, the intensity of other green and blue wavelength components is suppressed in accordance with the intensity of the red wavelength component, so that the light use efficiency is low as a whole.

  The “projection display device” described in Japanese Patent Application Laid-Open No. 2000-305040 aims to improve the light use efficiency and expand the color reproduction range. In the example described in this document, a dichroic mirror is used to obtain green and blue wavelength components from light from a high-pressure mercury lamp, and red wavelength components from light from a light emitting diode. As the red wavelength component, light from a light-emitting diode that can easily obtain a single color and has high color purity is used. In another example described in this document, a high-pressure mercury lamp and a red light emitting diode are similarly used, and the light of the high-pressure mercury lamp is used as the green and blue wavelength components, but the red wavelength component is mercury. Utilizes the light from both the lamp and the red light emitting diode.

  The light of the high-pressure mercury lamp has a problem that red color reproducibility is poor because there are few red wavelength components. Furthermore, in order to achieve white balance, it is necessary to suppress the light amounts of the blue and green wavelength components in order to match the red light intensity. However, in this example, by using the light of the light emitting diode, it is possible to realize a projection display device that has a wide color reproduction range, can efficiently use light, and has a good white balance.

  The “light source” described in Japanese Patent Application Laid-Open No. 2000-182404 aims to expand the color reproduction range. In the fluorescent lamp, a part of the phosphor in the glass container coated with the phosphor is removed, an opening of the phosphor is provided, and light from a plurality of light emitting diodes is arranged to enter the inside of the glass container from there. Thus, the color purity is increased by using the light emitting diode, and the light source having a uniform light distribution characteristic is realized by making the light of the light emitting diode enter the inside of the glass container.

JP 2000-305040 A JP 2000-182404 A

  Both the projection type display device described in Japanese Patent Laid-Open No. 2000-305040 and the light source described in Japanese Patent Laid-Open No. 2000-182404 use a plurality of different light sources. These light sources are different in temperature characteristics, deterioration characteristics, and the like, and light emission characteristics change with time. Therefore, the white balance, which was good at the time of manufacture, collapses over time.

  An object of the present invention is to provide a light emitting device that always has a good white balance even when time elapses.

  According to the present invention, a light emitting device includes a first light source having a dominant wavelength in a red wavelength region and a second light source having an emission peak in at least a blue wavelength region, and the red light intensity of the first light source is The light intensity of at least one of the first light source and the second light source is controlled so that the ratio of the blue light intensity of the second light source is constant.

  Furthermore, according to the present invention, the light intensity of the first light source is controlled in accordance with the light intensity of the second light source in the blue wavelength region.

  Further, according to the present invention, the first photosensor having a peak sensitivity in red for monitoring the light intensity of the first light source, and the second having a peak sensitivity in blue for monitoring the light intensity of the second light source. And an optical sensor.

  According to the present invention, the light intensity of the first light source is controlled according to the light intensity in the blue wavelength region of the second light source monitored by the second light sensor.

  According to the present invention, there is provided a photosensor having peak sensitivity in a blue wavelength range and a red wavelength range for monitoring light intensities of the first light source and the second light source, and the first light source is in an OFF period. A monitor value of the light intensity in the blue wavelength range of the second light source is obtained from a monitor value by the optical sensor, and the light intensity of the first light source is controlled based on the monitor value of the blue light intensity.

  According to the present invention, by subtracting the monitor value obtained by the photosensor during the period when the first light source is OFF from the monitor value obtained by the photosensor during the period when the first light source is ON, A monitor value of the light intensity of the first light source is obtained.

  According to the present invention, based on the temperature of the light source monitored by a temperature sensor, the light intensity of the light source is obtained from the relationship between the temperature characteristics of the light source and the light intensity.

According to the invention, the first light source is a light emitting diode.
According to the present invention, the second light source is a white fluorescent lamp.

  According to the present invention, the second light source is a fluorescent tube having emission peaks in the blue wavelength range and the green wavelength range and exhibiting a cyan color.

According to the invention, the light source is pulse width controlled.
According to the present invention, the display device uses the light emitting device described above.

  According to the present invention, it is possible to realize a light emitting device with a simple configuration and good white balance.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. A first example of a light emitting device according to the present invention will be described with reference to FIG. The light emitting device of this example includes a red light emitting diode 101 and a cold cathode fluorescent tube 102 that form a light source, a light guide plate 103 that mixes light from the light source, and photosensors 104 and 105 provided on an end surface of the light guide plate 103. Have

  The red light emitting diode 101 has a dominant wavelength in the red wavelength region, and the cold cathode fluorescent tube 102 has emission peaks in the blue and green wavelength regions and emits cyan. The main wavelength of the light source will be described later with reference to FIG. Light from the red light emitting diode 101 and the cold cathode fluorescent tube 102 is mixed by the light guide plate 103 to generate white light. The light guide plate 103 functions as a surface light source that generates white light.

  In this example, a plurality of different types of light sources 101 and 102 are used. These light sources have different light emission characteristics, temperature characteristics, etc., and their temporal changes are also different from each other. Therefore, even if the white balance is initially maintained, it will collapse with the passage of time. In this example, as described below, white balance is always maintained by feedback control of the light intensity of the light source.

  The first optical sensor 104 has a peak sensitivity in the red wavelength region and monitors the emission intensity of the red light emitting diode 101. The second photosensor 105 has peak sensitivity in the blue and green wavelength ranges, and monitors the emission intensity of the cold cathode fluorescent tube 102. The red light emitting diode 101 is always constant so that the ratio of the light emission intensity of the red light emitting diode 101 monitored by the first light sensor 104 and the light emission intensity of the cold cathode fluorescent tube 102 monitored by the second light sensor 105 is always constant. The emission intensity of at least one of the cold cathode fluorescent tubes 102 is controlled.

  Preferably, the light emission intensity of the red light emitting diode 101 is controlled by the blue and green light emission intensities of the cold cathode fluorescent tube 102 monitored by the second photosensor 105. For example, when the light emission intensity of the cold cathode fluorescent tube 102 decreases, the light intensity of the red light emitting diode 101 is decreased accordingly. Conversely, when the emission intensity of the cold cathode fluorescent tube 102 increases, the emission intensity of the light emitting diode 101 is increased. Thereby, the ratio of the emission intensity of the red light emitting diode 101 and the emission intensity of the cold cathode fluorescent tube 102 is kept constant, and the white balance of the white light generated by the light guide plate 103 can always be kept.

  The reason why the light emission intensity of the cold cathode fluorescent tube 102 is monitored and the light emission intensity of the red light emitting diode 101 is controlled accordingly is that the light emitting diode has a faster response speed and is easy to control, and thousands of hours and tens of thousands of hours. This is because the cold cathode fluorescent tube deteriorates more quickly than the red light emitting diode when considering a change over time such as time.

  When the light emitting device of this example is used as white illumination or a white light source, illumination having a uniform white balance with little color change can be obtained. In this example, the light from the cold cathode fluorescent tube 102 and the light from the red light emitting diode 101 are mixed by the light guide plate 103 to obtain white light. That is, almost all the light emitted from the light source is used. Compared with the case where the red wavelength component is removed by the dichroic mirror as in the projection display device of Patent Document 1, the light use efficiency is high and the color reproduction range is wide.

  In FIG. 1, the size relationship of each component is exaggerated for easy understanding, and the size ratio of each component is different from the actual size. In FIG. 1, one cold cathode fluorescent tube 102 and one red light emitting diode 101 are provided, but a plurality of them may be provided. The second photosensor 105 has peak sensitivity in blue and green, but two photosensors may be used instead, that is, a photosensor having peak sensitivity in blue and a photosensor having peak sensitivity in green.

  Further, although the first optical sensor 104 and the second optical sensor 105 are illustrated as separate objects, they may be formed as a single chip, and light having a peak sensitivity in the red wavelength region. A sensor, three photosensors for blue, and one for green may be integrated into one chip. Instead of the red light emitting diode that forms the light source, a red cold cathode fluorescent tube or electroluminescence may be used. The light sensor may be disposed at a different end face instead of the end face of the light guide plate shown in the drawing.

  The main wavelength of the light source will be described with reference to FIG. The horizontal axis in the figure represents the x coordinate in the XYZ color system, the vertical axis represents the y coordinate, and the bold curve represents the spectrum locus on the xy chromaticity diagram. The point on the spectrum locus indicates the wavelength of the monochromatic light stimulus. The dominant wavelength is a straight line connecting the white point W having x and y coordinates (x, y) = (1/3, 1/3) and the chromaticity point F of light from the light source on the xy chromaticity diagram. Is the wavelength of the monochromatic light stimulus at point D where it intersects the spectral trajectory. The white point W of (x, y) = (1/3, 1/3) is used when determining the dominant wavelength for the light source.

  FIG. 3 shows an emission spectrum of a commonly used white cold cathode fluorescent tube. The horizontal axis is the wavelength, and the vertical axis is the light intensity. It has peaks at wavelengths of 437 to 490 nm (blue), 550 nm (green), 590 nm (yellow), and 608 nm (red). The region having a wavelength of 650 to 670 nm (red) has almost no emission wavelength component. Note that this emission spectrum is merely an example, and the peak positions and component amounts do not always match.

  The solid line in FIG. 4 shows the emission spectrum of the cold cathode fluorescent tube 102 used in FIG. 1, and the broken line shows the emission spectrum of the red light emitting diode 101 having the dominant wavelength in the red wavelength region. The emission spectrum of the cold cathode fluorescent tube 102 has peaks near wavelengths of 437 to 490 nm (blue), 550 nm (green), and 590 nm (yellow). There is no peak in the wavelength region of 650 to 670 nm (red). Since the cold cathode fluorescent tube 102 has emission peaks in the blue and green wavelength regions, it emits cyan.

  The emission spectrum of the red light emitting diode 101 has a peak in the vicinity of 645 nm (red). Since the emission spectrum of the white cold cathode fluorescent tube in FIG. 3 has a peak near 608 nm (red), the peak of the emission spectrum of the red light emitting diode 101 is longer in wavelength than the red peak of the emission spectrum of the white cold cathode fluorescent tube. .

  In the example of FIG. 1, white light is obtained by adding the red component from the red light emitting diode 101 to the blue and green components from the cold cathode fluorescent tube 102. Therefore, deep red light can be obtained as compared with the case where a white cold cathode fluorescent tube is used.

  FIG. 5 shows the chromaticity when a 4.5R4 / 13 color substance having a Munsell hue of 4.5R, lightness of 4, and saturation of 13 in the Munsell color system is irradiated with light from a light source. The horizontal axis in the figure represents the x coordinate in the XYZ color system, the vertical axis represents the y coordinate, and the bold curve represents the spectrum locus on the xy chromaticity diagram.

  A square point 501 represents chromaticity when a white cold cathode fluorescent tube (CCFL) is used as a light source, and a triangular point 502 represents a light emitting diode 101 having a main wavelength in the red wavelength region as a light source and cold cathode fluorescence. The chromaticity in the case of using light (GB + R) obtained by mixing light from the tube 102 is shown. The chromaticity point 502 when the light source (GB + R) comprising the red light emitting diode 101 and the cold cathode fluorescent tube 102 is used is lower right on the chromaticity diagram than the chromaticity point 501 when the cold cathode fluorescent tube (CCFL) is used. This indicates that the color purity is higher.

  FIG. 6 shows the light receiving sensitivity of the first and second photosensors. In the figure, the horizontal axis represents wavelength and the vertical axis represents sensitivity. As indicated by a broken line, the first photosensor 104 has a peak sensitivity in the red wavelength range, and as indicated by a solid line, the second photosensor 105 has a peak sensitivity in the blue and green wavelength ranges.

  A display device using a second example of the light emitting device according to the present invention will be described with reference to FIG. In FIG. 7, the same members in FIG. The display device of this example includes a red light emitting diode 101 and a white cold cathode fluorescent tube 201 that form a light source, a light guide plate 103 that mixes light from the light source, a photosensor 202 provided on an end surface of the light guide plate 103, 203 and a liquid crystal panel 204. The liquid crystal panel 204 uses the light from the light guide plate 103 and controls incident light by a color filter and liquid crystal to perform color display of an image.

  The red light emitting diode 101 has a dominant wavelength in the red wavelength region, and the white cold cathode fluorescent tube 201 has emission peaks in the blue, green, and red wavelength regions. Light from the red light emitting diode 101 and the white cold cathode fluorescent tube 201 is mixed by the light guide plate 103 to generate white light. The light guide plate 103 functions as a surface light source that generates white light. An image is displayed by modulating light from the light guide plate 103 by the liquid crystal panel 204.

  In FIG. 7, the size relationship of each component is exaggerated for easy understanding, and the size ratio of each component is different from the actual size. In FIG. 7, one white cold cathode fluorescent tube 201 and one red light emitting diode 101 are provided, but a plurality of them may be provided. In this example, an inexpensive cold cathode fluorescent tube is generally used as a white light source, but a white light emitting diode or electroluminescence may be used instead. Although the white cold cathode fluorescent tube 201 having emission peaks in the blue, green, and red wavelength regions is used, a cold cathode fluorescent tube having a dominant wavelength in the blue and green wavelength regions may be used instead. Instead of the red light emitting diode, a red cold cathode fluorescent tube or electroluminescence may be used. The light sensor may be disposed at a different end face instead of the end face of the light guide plate shown in the drawing.

  In addition, although the first optical sensor 202 and the second optical sensor 203 are illustrated as separate objects, the two may be integrated into one chip, and light having a peak sensitivity in the red wavelength region. A sensor, three photosensors for blue, and one for green may be integrated into one chip. Instead of the red light emitting diode that forms the light source, a red cold cathode fluorescent tube or electroluminescence may be used.

  In this example, a plurality of different types of light sources are used. These light sources have different light emission characteristics, temperature characteristics, etc., and their temporal changes are also different from each other. Therefore, even if the white balance is initially maintained, it will collapse with the passage of time. In this example, as described below, white balance is always maintained by feedback control of the light intensity of the light source.

  The first optical sensor 202 has a peak sensitivity in the red wavelength region, and monitors the emission intensity of the red light emitting diode 101. The second photosensor 203 has a peak sensitivity in the blue wavelength region, and monitors the blue emission intensity of the cold cathode fluorescent tube 201.

  The red light emission so that the ratio of the light emission intensity of the red light emitting diode 101 monitored by the first light sensor 202 and the blue light emission intensity of the cold cathode fluorescent tube 201 monitored by the second light sensor 203 is always constant. The emission intensity of at least one of the diode 101 and the cold cathode fluorescent tube 201 is controlled.

  Preferably, the light emission intensity of the red light emitting diode 101 is controlled by the blue light emission intensity of the cold cathode fluorescent tube 201 monitored by the second photosensor 203. For example, when the blue light emission intensity of the cold cathode fluorescent tube 201 decreases, the light intensity of the red light emitting diode 101 is decreased accordingly. Conversely, when the blue emission intensity of the cold cathode fluorescent tube 201 increases, the emission intensity of the red light emitting diode 101 is increased accordingly. As a result, the ratio of the light emission intensity of the red light emitting diode 101 and the blue light emission intensity of the cold cathode fluorescent tube 201 is kept constant, and the white balance of white light generated by the light guide plate 103 can always be kept.

  The reason for monitoring the blue emission intensity of the white cold cathode fluorescent tube 201 will be described. In general, in a phosphor used for a fluorescent tube such as the cold cathode fluorescent tube 201, a phosphor emitting blue light is most easily deteriorated and has a short lifetime.

  FIG. 8 shows the relationship between the luminous efficiency of each color phosphor in the fluorescent tube and the elapsed time. The horizontal axis is time, and the vertical axis is luminous efficiency. The luminous efficiency of the blue phosphor indicated by the solid line is larger with time and the lifetime is shorter than that of the red and green phosphors indicated by the broken line.

  Usually, when monitoring the emission intensity of white light, a photosensitivity light sensor is used. Since the visibility light sensor has a sensitivity close to human visibility, it has a peak sensitivity in green. Therefore, when the white light of the cold cathode fluorescent tube 201 is monitored by the visibility light sensor, it is impossible to accurately detect the deterioration of the blue light emission characteristic.

  That is, it is better to monitor the blue light emission intensity of the cold cathode fluorescent tube 201 with the photosensor 203 having the peak sensitivity in the blue wavelength range than to monitor the light emission intensity of the white light of the cold cathode fluorescent tube 201 with the visibility light sensor. Therefore, it is possible to more accurately detect the deterioration of the light emission performance of the cold cathode fluorescent tube 201. Therefore, in this example, the blue emission intensity of the cold cathode fluorescent tube 201 is monitored.

  With reference to FIG. 9 and FIG. 10, changes in color temperature when using a luminous sensitivity sensor and when using an optical sensor having peak sensitivity in the blue wavelength region will be described. The color temperature is used to express the color of light. When the light color of the light source is equal to the standard black body light color, the temperature of the black body is called the color temperature, and the light color is black body. The case where it deviates from the locus is called correlated color temperature. The correlated color temperature is a black body temperature that does not completely match the temperature of the black body but is a good approximation, and the fact that the correlated color temperatures are equal indicates that there is little change in hue.

  FIG. 9 shows an example in which the chromaticity at correlated color temperatures of 5500K, 6500K, and 7500K is displayed on the chromaticity diagram. The horizontal axis represents the x coordinate in the XYZ color system, and the vertical axis represents the y coordinate. The broken-line triangle graph sRGB is an international standard color space. As shown in the figure, each correlated color temperature is represented by a substantially vertical curve.

  FIG. 10 shows the change with time of the color temperature when white is displayed on the liquid crystal panel 204. The horizontal axis is the x coordinate, and the vertical axis is the y coordinate. The solid triangle graph is the color reproduction range of the light emitting device, and the dashed triangle graph sRGB is an international standard color space. The V-shaped curve in the center of the figure shows the change over time of the chromaticity coordinates of white light obtained by mixing the light emission of the cold cathode fluorescent tube 201 and the red light emitting diode 101. In the V-shaped curve, the intersection portion where the solid line and the dotted line collide shows the initial balanced state.

  A V-shaped solid line portion shows a case where the blue light emission intensity of the cold cathode fluorescent tube 201 is monitored by the second photosensor 203 and the light emission intensity of the red light emitting diode 101 is controlled based on the monitored value. A substantially vertical curve is drawn, indicating that the correlated color temperature is constant.

  A V-shaped broken line portion indicates a case where the white light emission intensity of the cold cathode fluorescent tube 201 is monitored by a luminous sensitivity sensor, and the light emission intensity of the red light emitting diode 101 is controlled based on the monitored value. A substantially horizontal curve is drawn, and it can be seen that the correlated color temperature changes. The correlated color temperature is greatly affected by the balance between blue and red. However, when a luminous sensitivity sensor is used, the intensity change of blue cannot be accurately monitored, and thus the correlated color temperature changes.

  FIG. 11 shows a flowchart of the feedback control of the light source of the second example of the light emitting device according to the present invention. When the control starts, first, in step S101, the second light sensor 203 monitors the blue emission intensity of the white cold cathode fluorescent tube 201. Next, in step S102, the first light sensor 202 monitors the light emission intensity of the red light emitting diode 101. In step S103, the target value of the emission intensity of the red light emitting diode 101 is determined from the monitor value obtained by the second optical sensor 203. The target of the light emission intensity of the red light emitting diode 101 is obtained by referring to a table having a correspondence relationship between the blue light emission intensity of the white cold cathode fluorescent tube 201 and the light emission intensity of the red light emitting diode 101 so as to obtain the set correlated color temperature. Determine the value. In step S104, the monitor value by the first optical sensor 202 is compared with the target value. If both are the same, this process ends. If they are not the same, the process proceeds to step S105, and it is determined whether or not the target value is larger than the monitor value. If the target value is larger than the monitor value, the process proceeds to step S106, and the light emission intensity of the red light emitting diode 101 is increased. If the target value is smaller than the monitor value, the process proceeds to step S107, and the light emission intensity of the red light emitting diode 101 is decreased. Note that the order of steps S101 and S123 may be reversed.

  When performing feedback control of the light source, a method of using a light sensor of R (red), G (green), and B (blue) and controlling the light source while monitoring the emission intensity of the three colors is also conceivable. However, in this example, focusing on only blue and red, the target value is determined using a table having a correspondence relationship between the blue light emission intensity of the white cold cathode fluorescent tube 201 and the light emission intensity of the red light emitting diode 101. Therefore, there is no need to calculate the color temperature, and feedback control can be performed with a simple configuration. Furthermore, since only the intensity of two colors needs to be monitored, the number of photosensors can be reduced. Even when the light emitting device is made into one chip, since the light receiving area of the photosensor is small, the size can be reduced as compared with the case where the RGB photosensor is used.

  A display device using a third example of the light emitting device according to the present invention will be described with reference to FIG. In FIG. 12, the same members as those in FIGS. 1 and 7 are denoted by the same reference numerals. The display device of this example includes a red light emitting diode 101 and a cold cathode fluorescent tube 102 that form a light source, a light guide plate 103 that mixes light from the light source, a photosensor 301 provided on an end surface of the light guide plate 103, and a liquid crystal. And a display panel 204. The red light emitting diode 101 has a dominant wavelength in the red wavelength region, and the cold cathode fluorescent tube 102 has emission peaks in the blue and green wavelength regions. Light from the red light emitting diode 101 and the cold cathode fluorescent tube 102 is mixed by the light guide plate 103 to generate white light. The light guide plate 103 functions as a surface light source that generates white light. Light from the light guide plate 103 is applied to the liquid crystal display panel 204. The liquid crystal panel 204 controls incident light by a color filter and liquid crystal, and performs color display of an image.

  In this example, a plurality of different types of light sources are used. These light sources have different light emission characteristics, temperature characteristics, etc., and their temporal changes are also different from each other. Therefore, even if the white balance is initially maintained, it will collapse with the passage of time. In this example, as described below, white balance is always maintained by feedback control of the light intensity of the light source.

  The optical sensor 301 has peak sensitivity in the blue wavelength range and the red wavelength range, and monitors the emission intensity of the red light emitting diode 101 and the emission intensity of the cold cathode fluorescent tube 102 in the blue wavelength range. That is, the light intensity of both the cold cathode fluorescent tube 102 and the red light emitting diode 101 is monitored by one photosensor 301.

  Light emission of at least one of the red light emitting diode 101 and the cold cathode fluorescent tube 102 so that the ratio of the light emission intensity of the red light emitting diode 101 monitored by the optical sensor 301 and the blue light emission intensity of the cold cathode fluorescent tube 102 is always constant. Control strength.

  Preferably, the light emission intensity of the red light emitting diode 101 is controlled by the blue light emission intensity of the cold cathode fluorescent tube 102 monitored by the optical sensor 301. That is, the light emission intensity of the cold cathode fluorescent tube 102 is fed back to the red light emitting diode 101 via a control unit (not shown). For example, when the blue light emission intensity of the cold cathode fluorescent tube 102 decreases, the light intensity of the red light emitting diode 101 is decreased accordingly. Conversely, when the blue emission intensity of the cold cathode fluorescent tube 102 increases, the emission intensity of the red light emitting diode 101 is increased accordingly. Thereby, the ratio of the light emission intensity of the red light emitting diode 101 and the blue light emission intensity of the cold cathode fluorescent tube 102 is kept constant, and the white balance of the white light generated by the light guide plate 103 can always be kept.

  In FIG. 12, the size relationship of each component is exaggerated for easy understanding, and the size of each component is different from the actual size. The reason for monitoring the blue emission intensity of the white cold cathode fluorescent tube 102 has already been described with reference to the example of FIG.

  In this example, the light emission intensity of the red light-emitting diode 101 is controlled by pulse width modulation (PWM). In the control by pulse width modulation, the light emission intensity is changed by changing the ratio (duty ratio) between the pulse width when ON and the pulse width when OFF. By controlling the light emitting diode by PWM control, it is possible to adjust the light in a wide range. Accordingly, there are periodic periods in which the red light emitting diode 101 is lit and periods in which the red light emitting diode 101 is not lit.

  The light emitting diode has a high response speed and is suitable for PWM control. However, since the cold cathode fluorescent tube has a slow response speed, it is not suitable for PWM control.

  With reference to FIG. 13, a method for obtaining the light emission intensity of the red light emitting diode 101 and the cold cathode fluorescent tube 102 with one optical sensor 301 will be described. FIG. 13 shows the time change of the light emission intensity from the light source in the display apparatus of this example. The horizontal axis represents time, and the vertical axis represents emission intensity.

  As described above, since the response speed of the cold cathode fluorescent tube is slow, it is not possible to quickly control lighting and extinguishing of the cold cathode fluorescent tube. Therefore, the cold cathode fluorescent tube is always turned on. Times t1 to t2 are periods in which the red light emitting diode 101 is not lit, and the light emission intensity a of the light source represents the light emission intensity of the cold cathode fluorescent tube 102. The emission intensity a is monitored by the optical sensor 301.

  Times t2 to t3 are periods in which both the cold cathode fluorescent tube 102 and the red light emitting diode 101 are lit, and the light emission intensity b of the light source is an emission intensity by both the cold cathode fluorescent tube 102 and the red light emitting diode 101. . The light emission intensity b is monitored by the optical sensor 301. Two such periods are repeated.

  Therefore, the emission intensity of the red light emitting diode 101 can be obtained by subtracting the emission intensity b from the emission intensity a. Note that the emission intensity of the cold cathode fluorescent tube 102 is obtained from the output of the optical sensor 301 at times t1 to t2, as described above.

  In this way, in this example, the light intensity of the cold cathode fluorescent tube 102 and the light intensity of the red light emitting diode 101 can be obtained separately by one photosensor 301.

  FIG. 14 is a diagram showing a color reproduction range in the display device of this example. The horizontal axis represents the x coordinate in the XYZ color system, and the vertical axis represents the y coordinate. A triangle indicated by a dotted line in the figure indicates a color reproduction range of sRGB, which is an international standard color space, and indicates that a color represented by chromaticity coordinates inside the triangle can be displayed. Triangles indicated by solid lines in the figure indicate the color reproduction range of the display device of this example, and RGB indicates chromaticity coordinates when red, green, and blue are displayed, respectively. It can be seen that the red color reproduction is outside sRGB and the color reproduction range is wide and very excellent.

  FIG. 15 is a comparison of the color reproduction range in the display device of this example and the color reproduction range when a white cold cathode tube and a red light emitting diode are used as a light source. As in FIG. 14, the horizontal axis represents the x coordinate in the XYZ color system, and the vertical axis represents the y coordinate. A solid triangle R-LED + GB-CCFL is a color reproduction range in the case of using the display device of this example, that is, the cold cathode tube 102 and the red light emitting diode 101 having emission peaks in the blue and green wavelength regions. A broken triangle R-LED + W-CCFL is a color reproduction range when a white cold-cathode tube and a red light-emitting diode are used as a light source. It can be seen that the color reproduction range of the display device of this example is greatly expanded centering on the red portion.

  A display device using the fourth example of the light emitting device according to the present invention will be described with reference to FIG. In FIG. 16, the same members as those in the above-described embodiment are denoted by the same reference numerals. The display device of this example includes a light-emitting diode array 401 composed of light-emitting diodes of a plurality of colors, a light guide plate 103, a liquid crystal display panel 204, and temperature sensors 402 and 403.

  The light from the light emitting diode array 401 is mixed by the light guide plate 103 to generate white light. The light guide plate 103 functions as a surface light source that generates white light. Light from the light guide plate 103 is applied to the liquid crystal display panel 204. The liquid crystal panel 204 controls incident light by a color filter and liquid crystal, and performs color display of an image.

  As shown in FIG. 17, the light emitting diode array 401 includes a red light emitting diode 4011, a green light emitting diode 4012, and a blue light emitting diode 4013.

  In this example, a plurality of light emitting diodes are used as the light source. These light emitting diodes have different temperature characteristics and the like, and their temporal changes are also different. Therefore, even if the white balance is initially maintained, it will collapse with the passage of time. In this example, as described below, white balance is always maintained by feedback control of the light intensity of the light source.

  The first temperature sensor 402 monitors the temperature of the red light emitting diode 4011, and the second temperature sensor 403 monitors the temperature of the blue light emitting diode 4013. The light source control unit (not shown) includes a table indicating the relationship between the light source temperature and the light emission intensity of the red light emitting diode 4011 and the blue light emitting diode, and the actual light emission based on the monitor value of the light source temperature obtained by the temperature sensors 402 and 403. Calculate the intensity. A method for calculating the actual light emission intensity and an example of the table will be described later.

  The light emission intensity of at least one of the red light emitting diode 4011, the green light emitting diode 4012, and the blue light emitting diode 4013 is set so that the ratio between the light emission intensity of the red light emitting diode 4011 and the light emission intensity of the blue light emitting diode 4013 thus calculated is always constant. Control.

  Preferably, the light emission intensity of the blue light emitting diode 4013 is controlled by the light emission intensity of the red light emitting diode 4011. For example, when the emission intensity of the red light emitting diode 4011 decreases, the emission intensity of the green light emitting diode 4012 and the blue light emitting diode 4013 is lowered accordingly. Conversely, when the emission intensity of the red light emitting diode 4011 increases, the emission intensity of the green light emitting diode 4012 and the blue light emitting diode 4013 is increased accordingly. Thereby, the ratio of the emission intensity of the three light emitting diodes is kept constant, and the white balance of the white light generated by the light guide plate 103 can always be kept.

  In this example, the light emission intensity of the light emitting diodes 4011, 4012, and 4013 is controlled by pulse width modulation (PWM).

  The reason why the emission intensity of the red light emitting diode 4011 is monitored will be described with reference to FIG. FIG. 18 shows a table showing the relationship between the light source temperature and the emission intensity. The horizontal axis indicates the light source temperature, the vertical axis indicates the light emission output from the light emitting diode, and the light emission intensity at room temperature of 25 ° C. is 100%. The dashed curve R-LED indicates the light output characteristic of the red light emitting diode 4011, and the solid curve B-LED indicates the light output characteristic of the blue light emitting diode 4013.

  Comparing the two curves, it can be seen that the light output characteristics of the red light-emitting diode largely change with temperature. That is, in the case of a red light emitting diode, the light emission intensity greatly decreases as time elapses and the temperature rises.

  Therefore, when a light emitting diode is used as the light source, the light emission intensity of the other light emitting diodes may be controlled based on the light emission intensity of the red light emitting diode 4011 having a large change with time.

  FIG. 19 shows a flowchart of the feedback control of the light source in the light emitting device of FIG. First, in step S201, the temperature of the red light emitting diode 4011 is monitored by the first temperature sensor 402, and the light output is referred to from the table in FIG. In step S202, the temperature of the blue light emitting diode 4013 is monitored by the second temperature sensor 403, and the light output is referred to from the table in FIG. In step S203, the present actual light emission intensity of each light emitting diode is calculated by multiplying this light output by the duty ratio of the pulse width modulation of each light emitting diode. This is because in the pulse width modulation, when the light emitting diode is actually ON, it is only a period corresponding to the value of the duty ratio in one cycle.

  In step S204, the target value of the light emission intensity of the blue light emitting diode 405 at the target color temperature is referred to from the calculated actual light emission intensity of the red light emitting diode 101.

  In step S205, the target value is compared with the calculated actual light emission intensity of the blue light emitting diode 405. If both are the same, this process ends. If they are not the same, the process proceeds to step S206. In step S206, it is determined whether or not the target value is greater than the current emission intensity of the blue light emitting diode 405. If the target value is greater than the actual light emission intensity of the blue light emitting diode 405, the light emission intensity of the blue light emitting diode 405 is increased in step S207. If the target value is smaller than the current actual light emission intensity of the blue light emitting diode 405, the light emission intensity of the blue light emitting diode 405 is decreased in step S208.

  By periodically repeating such light source feedback control, it is possible to suppress changes in the hue of light emitted from the light source. Since the balance between the emission intensity of blue and red greatly affects the color temperature of white light, the change in hue of white light can be suppressed by balancing blue and red. The light emission intensity of the red light emitting diode 4011 and the blue light emitting diode 4013 may be monitored, and the light emission intensity of the green light emitting diode 4012 need not be monitored. Since only two colors are controlled, a simple configuration is possible.

  In FIGS. 16 and 17, the size relationship of each component is exaggerated for easy understanding, and the size of each component is different from the actual size. Here, the blue light emitting diode is controlled from the red light emission intensity, but the red light emitting diode may be controlled from the blue light emission intensity. Further, any combination of the various members shown in Examples 1 to 4, the control of emission intensity, the monitoring method, and the like may be used. These light emitting devices can be used as a light source such as a liquid crystal display or as an illumination.

  Although the examples of the present invention have been described above, the present invention is not limited to the above-described examples, and it can be understood by those skilled in the art that various modifications can be made within the scope of the invention described in the claims. I will.

It is explanatory drawing which shows schematic structure of the 1st example of the light-emitting device of this invention. It is explanatory drawing about the dominant wavelength of a light source. It is explanatory drawing which shows the emission spectrum of a white cold cathode fluorescent tube. It is a figure which shows the emission spectrum of the cold cathode fluorescent tube and red light emitting diode of the 1st example of the light-emitting device of this invention. It is a figure which shows a chromaticity coordinate when light is irradiated to a to-be-photographed object by the 1st example of the light-emitting device of this invention. It is a figure which shows the relationship between the wavelength of a photosensor of the 1st example of the light-emitting device of this invention, and a sensitivity. It is a figure which shows schematic structure of the 2nd example of the light-emitting device of this invention, and a display apparatus using the same. It is a figure which shows the time-dependent change of the light source in the 2nd example of the light-emitting device of this invention. It is explanatory drawing of the correlation color temperature in a white light source. It is a figure which shows the change of the white point by the time-dependent change of the 2nd example of the light-emitting device of this invention. It is a figure which shows the flowchart of the feedback control in the 2nd example of the light-emitting device of this invention. It is a figure which shows schematic structure in the 3rd example of the light-emitting device of this invention, and a display apparatus using the same. It is a figure which shows the waveform of the emitted light intensity in the 3rd example of the light-emitting device of this invention. It is a figure shown about the color reproduction range in the 3rd example of the light-emitting device of this invention. It is a figure which shows the difference in the color reproduction range by the difference in the light source in the 3rd example of the light-emitting device of this invention. It is explanatory drawing which shows schematic structure in the 4th example of the light-emitting device of this invention, and a display apparatus using the same. It is a figure which shows the structural example of the light emitting diode array in the 4th example of the light-emitting device of this invention. It is a figure which shows the relationship between the temperature of a light source, and light output in the 4th example of the light-emitting device of this invention. It is a figure which shows the flowchart of the feedback control in the 4th example of the light-emitting device of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Red light emitting diode, 102 ... Cold cathode fluorescent tube, 103 ... Light guide plate, 104, 105 ... Optical sensor, 201 ... Cold cathode fluorescent tube, 202, 203 ... Optical sensor, 204 ... Liquid crystal panel, 301 ... Optical sensor, 401 ... light emitting diode array, 402, 403 ... temperature sensor, 4011 ... red light emitting diode, 4012 ... green light emitting diode, 4013 ... blue light emitting diode

Claims (11)

A first light source having a dominant wavelength in the red wavelength region;
A second light source having an emission peak in at least a blue wavelength region and also having a wavelength region of another color ;
With
When the light intensity in the blue wavelength range of the second light source changes, the light intensity of the first light source is controlled to control the red light intensity of the first light source and the blue light intensity of the second light source. A light-emitting device configured to keep the ratio of the above constant .   2. The light emitting device according to claim 1, wherein the first photosensor having a peak sensitivity in red for monitoring the light intensity of the first light source and the peak sensitivity in blue for monitoring the light intensity of the second light source. And a second light sensor. 3. The light emitting device according to claim 2 , wherein the light intensity of the first light source is controlled in accordance with the light intensity in the blue wavelength range of the second light source monitored by the second light sensor. Light-emitting device. The light-emitting device according to claim 1 , further comprising: an optical sensor having peak sensitivity in a blue wavelength range and a red wavelength range for monitoring light intensities of the first light source and the second light source, wherein the first light source The monitor value of the blue light wavelength range of the second light source is obtained by the monitor value of the light sensor during the OFF period, and the light intensity of the first light source is determined based on the monitor value of the blue light intensity. A light-emitting device that is controlled. 5. The light emitting device according to claim 4 , wherein a monitor value obtained by the optical sensor during a period when the first light source is OFF is obtained from a monitor value obtained by the optical sensor during a period when the first light source is ON. A light-emitting device characterized by obtaining a monitor value of the light intensity of the first light source by subtraction.   2. The light emitting device according to claim 1, wherein the light intensity of the light source is obtained from the relationship between the temperature characteristic of the light source and the light intensity based on the temperature of the light source monitored by a temperature sensor. The light emitting device according to any one of claims 1 6, the light emitting device, wherein said first light source is a light emitting diode. The light emitting device according to any one of claims 1 7, said second light source is a light emitting device which is a fluorescent lamp white. The light emitting device according to any one of claims 1 to 8 , wherein the second light source is a fluorescent tube having emission peaks in a blue wavelength region and a green wavelength region and exhibiting a cyan color. Light-emitting device. The light emitting device according to any one of claims 1 9, the light emitting device which is characterized in that a pulse width controlling the light source. Display device using the light-emitting device according to any one of claims 1 to 10.

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