Driving method of light-emitting device, light-emitting device, and display device

Abstract

To provide a driving method of a light-emitting device having high stability of chromaticity, a light-emitting device, and a display device.SOLUTION: The method for driving a light-emitting device is a method for pulse-width-modulation controlling a light-emitting device including first light-emitting elements that emit light having peak wavelengths in a range from 490nm to 680nm. In an energization period in which the first light emitting element is continuously energized, a value of a current flowing through the first light emitting element at the end of the energization period is made larger than a value of a current flowing through the first light emitting element at the beginning of the energization period.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to a method for driving a light-emitting device, a light-emitting device, and a display device. [Background technology]

[0002] In recent years, light-emitting devices using light-emitting diodes that emit red, green, and blue light have been used as light sources for display devices. Such light-emitting devices are required to have stable chromaticity because the chromaticity of the emitted light directly affects the image quality of the display device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-111507 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide a method for driving a light emitting device, a light emitting device, and a display device that have high chromaticity stability. [Means for solving the problem]

[0005] A method for driving a light emitting device according to an embodiment of the present disclosure is a method for pulse-width modulation control of a light emitting device including a first light emitting element having a peak wavelength of emitted light in the range of 490 nm to 680 nm, wherein, during a current-carrying period in which the first light emitting element is continuously energized, a current value passed through the first light emitting element at the end of the current-carrying period is made larger than a current value passed through the first light emitting element at the beginning of the current-carrying period.

[0006] A light emitting device according to an embodiment of the present disclosure includes a first light emitting element having a peak wavelength of emitted light in a range of 490 nm to 680 nm, and a controller configured to pulse width modulate the first light emitting element, wherein the controller controls a current value flowing through the first light emitting element at the end of a continuous current flow period to be greater than a current value flowing through the first light emitting element at the beginning of the current flow period.

[0007] A display device according to an embodiment of the present disclosure includes a mounting substrate, the light-emitting devices disposed on the mounting substrate, and temperature measurement units disposed on the mounting substrate, the number of the temperature measurement units being less than the number of the light-emitting devices. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to realize a method for driving a light emitting device, a light emitting device, and a display device with high chromaticity stability. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a plan view showing a light emitting device according to a first embodiment. [Figure 2] FIG. 2 is an end view taken along line II-II shown in FIG. [Figure 3] 1 is a block diagram showing a light emitting device according to a first embodiment. [Figure 4] 1 is a graph showing a first relationship, with the horizontal axis representing the temperature of the first light-emitting element and the vertical axis representing the peak wavelength of light emitted by the first light-emitting element. [Figure 5] 10 is a graph showing the second relationship, with the horizontal axis representing the value of the current flowing through the first light emitting element and the vertical axis representing the peak wavelength of the light emitted by the first light emitting element. [Figure 6] 5 is a flowchart showing a method for driving the light emitting device according to the first embodiment. [Figure 7] 1 is a graph showing a method for driving a light-emitting device according to a first embodiment, with the horizontal axis representing time and the vertical axis representing the current value flowing through the light-emitting element, the measurement results of the temperature measurement unit, and the peak wavelength of the light emitted by the light-emitting element. [Figure 8]1 is a graph showing a method of driving the light emitting device according to the first embodiment, with the horizontal axis representing time and the vertical axis representing the current values ​​flowing through the first light emitting element, the second light emitting element, and the third light emitting element. [Figure 9] 1 is a graph showing a method of driving a light emitting device according to a first modified example of the first embodiment, with time taken on the horizontal axis and current values ​​flowing through light emitting elements taken on the vertical axis. [Figure 10] 10 is a graph showing a method of driving a light emitting device according to a second modified example of the first embodiment, with time taken on the horizontal axis and current values ​​flowing through light emitting elements taken on the vertical axis. [Figure 11] 10 is a graph showing a method of driving a light emitting device according to a third modified example of the first embodiment, with time taken on the horizontal axis and current values ​​flowing through light emitting elements taken on the vertical axis. [Figure 12] 10 is a graph showing a method of driving a light-emitting device according to a fourth variant of the first embodiment, with the horizontal axis representing time and the vertical axis representing the current value flowing through the light-emitting element, the measurement results of the temperature measurement unit, and the peak wavelength of the light emitted by the light-emitting element. [Figure 13] 10 is a graph showing a method of driving a light-emitting device according to a fifth variant of the first embodiment, with time on the horizontal axis and the current values ​​flowing through the first light-emitting element, the second light-emitting element, and the third light-emitting element on the vertical axis. [Figure 14] FIG. 4 is an end view showing a light emitting device according to a second embodiment. [Figure 15] FIG. 10 is a block diagram showing a light emitting device according to a third embodiment. [Figure 16] 10 is a graph showing the third relationship, with the horizontal axis representing the temperature of the light-emitting element and the vertical axis representing the voltage between the anode electrode and the cathode electrode of the light-emitting element. [Figure 17] 10 is a graph showing a method of driving a light emitting device according to a fourth embodiment, with the horizontal axis representing time and the vertical axis representing the value of current flowing through a light emitting element. [Figure 18] FIG. 10 is a block diagram showing a light emitting device according to a fifth embodiment. [Figure 19] 10 is a flowchart showing a method for driving a light emitting device according to a fifth embodiment. [Figure 20] FIG. 10 is a plan view showing a light emitting device according to a sixth embodiment. [Figure 21] FIG. 21 is an end view taken along line XXI-XXI shown in FIG. 20. [Figure 22] 10 is a graph showing a method of driving a light emitting device according to a seventh embodiment, with time taken on the horizontal axis and current values ​​passed through the first light emitting element, the second light emitting element, and the third light emitting element taken on the vertical axis. [Figure 23] 13 is a graph showing a method of driving a light emitting device according to the eighth embodiment, with time taken on the horizontal axis and current values ​​passed through the first light emitting element, the second light emitting element, and the third light emitting element taken on the vertical axis. [Figure 24] FIG. 13 is a plan view showing a display device according to a ninth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] First Embodiment The light emitting device according to this embodiment is a light emitting device used, for example, as a light source for a display device, and emits red light, green light, and blue light to emit white light overall. Note that the configuration of the light emitting device described below is one example for realizing the present disclosure, and the configuration of the light emitting device is not limited to this.

[0011] (Light-emitting device) FIG. 1 is a plan view showing a light emitting device according to this embodiment. FIG. 2 is an end view taken along line II-II shown in FIG. FIG. 3 is a block diagram showing the light emitting device according to this embodiment. FIG. 4 is a graph showing the first relationship, with the horizontal axis representing the temperature of the first light-emitting element and the vertical axis representing the peak wavelength of light emitted by the first light-emitting element. FIG. 5 is a graph showing the second relationship, with the horizontal axis representing the value of the current flowing through the first light-emitting element and the vertical axis representing the peak wavelength of the light emitted by the first light-emitting element.

[0012] As shown in FIGS. 1 to 3, the light emitting device 1 according to this embodiment includes a first light emitting element 11 that emits light with a peak wavelength in the range of 490 nm to 680 nm, and a control unit 20 that performs pulse width modulation control on the first light emitting element 11. The light emitting device 1 further includes a second light emitting element 12 and a third light emitting element 13. The first light emitting element 11, the second light emitting element 12, and the third light emitting element 13 are light emitting diodes (LEDs). Hereinafter, the first light emitting element 11, the second light emitting element 12, and the third light emitting element 13 will be collectively referred to simply as "light emitting elements."

[0013] The first light emitting element 11 emits, for example, green light whose peak wavelength is in the range of 490 nm or more and less than 540 nm. x Al y Ga 1-x-y The first light emitting element 11 includes a compound semiconductor in which the composition ratios x and y are changed within the respective ranges in a chemical formula of N (0≦x, 0≦y, x+y≦1). The first light emitting element 11 includes, for example, an InGaN compound semiconductor.

[0014] The second light emitting element 12 emits red light with a peak wavelength in the range of 540 nm to 680 nm. The second light emitting element 12 includes, for example, one or more compound semiconductors selected from the group consisting of InAlGaP, GaInP, GaAs, and AlGaAs. In another embodiment, the second light emitting element 12 includes, for example, In x Al y Ga 1-x-y The second light emitting element 12 includes a compound semiconductor in which the composition ratios x and y are varied within the respective ranges in a chemical formula of N (0≦x, 0≦y, x+y≦1). The second light emitting element 12 includes, for example, an InGaN compound semiconductor.

[0015] The third light emitting element 13 emits blue light, the peak wavelength of which is in the range of 360 nm or more and less than 490 nm. x Al y Ga 1-x-yThe third light-emitting element 13 includes a compound semiconductor in which the composition ratios x and y are varied within the respective ranges in a chemical formula of N(0≦x, 0≦y, x+y≦1). The third light-emitting element 13 includes, for example, one or more compound semiconductors selected from the group consisting of GaN and InGaN.

[0016] The control unit 20 performs pulse width modulation (PWM) control on the first light emitting element 11. The control unit 20 can also perform pulse width modulation control on the second light emitting element 12 and the third light emitting element 13. The control unit 20 determines the duty ratio based on the luminance. The duty ratio is determined by the energization period T on That is, the control unit 20 determines the ratio of the energization period T on and the non-energized period T off and are set independently for each light-emitting element, and the duty ratio in each frame F is adjusted, thereby making it possible to control the luminance of each light-emitting element in that frame F. The control unit 20 outputs a control signal including information regarding the duty ratio and current value of each light-emitting element.

[0017] The light emitting device 1 may further include a substrate 30, a light reflecting member 40, a light-transmitting member 50, a memory unit 60, a driving unit 70, and a temperature measuring unit 80. In the first embodiment, the substrate 30 is, for example, an ASIC (Application Specific Integrated Circuit) substrate, and includes a control unit 20, a memory unit 60, and a driving unit 70. The first light emitting element 11, the second light emitting element 12, and the third light emitting element 13 are disposed on the substrate 30 and connected to wiring of the substrate 30. The temperature measuring unit 80 is disposed on the upper surface of the substrate 30 together with the light emitting elements.

[0018] The light reflecting member 40 is arranged on the substrate 30 in a frame shape along the outer edge of the substrate 30 in a top view. The light reflecting member 40 is arranged in a position surrounding all of the light emitting elements in a top view. The outer surface of the light reflecting member 40 forms a flat surface that is continuous with the outer surface of the substrate 30. The inner surface of the light reflecting member 40 is inclined so that the further away from the substrate 30 it is, the closer it is to the outer surface of the light reflecting member 40. The light reflecting member 40 reflects light emitted from the light emitting elements. The light reflecting member 40 is formed, for example, from a resin material containing a light reflecting material. Note that a light absorbing member containing a light absorbing material such as carbon black may be used instead of the light reflecting member 40.

[0019] The light-transmitting member 50 is disposed on the substrate 30 at a position surrounded by the light-reflecting member 40. The light-transmitting member 50 covers all the light-emitting elements and the temperature measuring unit 80. The light-transmitting member 50 transmits light emitted from the light-emitting elements. The light-transmitting member 50 is formed of, for example, a transparent resin material.

[0020] The storage unit 60 is provided within the substrate 30. The storage unit 60 stores, for each of the first light-emitting element 11, the second light-emitting element 12, and the third light-emitting element 13, a first relationship between the temperature of the light-emitting element and the peak wavelength of light emitted by the light-emitting element, and a second relationship between the value of a current flowing through the light-emitting element and the peak wavelength of light emitted by the light-emitting element.

[0021] As shown in Fig. 4, in the first relationship, as the temperature of the light-emitting element rises, the peak wavelength of the light emitted by the light-emitting element increases. Fig. 4 shows an example of the first relationship for the first light-emitting element 11. In the example shown in Fig. 4, the peak wavelength of the first light-emitting element 11 increases by about 5 nm as the temperature rises from -20°C to +100°C. The second light-emitting element 12 and the third light-emitting element 13 also include light-emitting elements that exhibit the above-mentioned first relationship. For example, an InGaN compound semiconductor light-emitting element exhibits the above-mentioned first relationship.

[0022] As shown in Fig. 5, in the second relationship, as the value of the current flowing through the light-emitting element increases, the peak wavelength of the light emitted by the light-emitting element shortens. Fig. 5 shows an example of the second relationship for the first light-emitting element 11. In the example shown in Fig. 5, the peak wavelength of the first light-emitting element 11 shortens by about 20 nm as the current value increases from 1 mA to 150 mA. The second light-emitting element 12 and the third light-emitting element 13 also have the above-mentioned second relationship. For example, an InGaN compound semiconductor light-emitting element exhibits the above-mentioned second relationship.

[0023] The driving unit 70 is provided inside the substrate 30. The driving unit 70 is connected to the control unit 20 and an external power supply. The driving unit 70 supplies current from the external power supply to each light-emitting element based on a control signal output from the control unit 20.

[0024] The temperature measurement unit 80 is disposed on the substrate 30. The temperature measurement unit 80 measures the temperature of the light-emitting element and outputs the measurement result to the control unit 20. The physical distance between the first light-emitting element 11 and the temperature measurement unit 80 is shorter than the physical distance between the third light-emitting element 13 and the temperature measurement unit 80. In an InGaN compound semiconductor light-emitting element, the shift in peak wavelength with increasing temperature is most pronounced in, for example, the first light-emitting element 11. By positioning the temperature measurement unit 80 close to the first light-emitting element 11, temperature changes in the first light-emitting element 11 can be detected with high accuracy, resulting in a light-emitting device with high chromaticity stability. Furthermore, the physical distance between the first light-emitting element 11 and the temperature measurement unit 80 may be shorter than the physical distance between the second light-emitting element 12 and the temperature measurement unit 80. Note that the temperature measurement unit 80 may be disposed so that the physical distance between the light-emitting element with the most pronounced shift in peak wavelength with increasing temperature is closer than the physical distance between the other light-emitting elements and the temperature measurement unit 80.

[0025] (Method of driving a light-emitting device) Next, the operation of the light emitting device according to this embodiment, that is, the method of driving the light emitting device according to this embodiment, will be described. FIG. 6 is a flowchart showing a method for driving the light emitting device according to this embodiment. Figure 7 is a graph showing a method for driving a light-emitting device according to this embodiment, with the horizontal axis representing time and the vertical axis representing the current value flowing through the light-emitting element, the measurement results of the temperature measurement unit, and the peak wavelength of the light emitted by the light-emitting element. FIG. 8 is a graph showing a method for driving the light emitting device according to this embodiment, with the horizontal axis representing time and the vertical axis representing the current values ​​flowing through the first light emitting element, the second light emitting element, and the third light emitting element.

[0026] 6 and 7 show the operation of only one light-emitting element. As an example, only the operation of the first light-emitting element 11 is shown. In reality, the control unit 20 controls the first light-emitting element 11, the second light-emitting element 12, and the third light-emitting element 13 independently. In addition, in FIG. 7, the solid line indicates this embodiment in which temperature-based current value control is performed, and the dashed line indicates a comparative example in which temperature-based current value control is not performed.

[0027] First, as shown in step S11 of FIG. 6 and in FIG. 7, the control unit 20 generates a current waveform for the light-emitting element based on a control signal input from an external device. A "current waveform" is a diagram showing the change over time in the value of the current supplied to the light-emitting element. The control signal input from an external device contains information about the luminance that the light-emitting element should achieve. The control unit 20 determines the duty ratio based on the luminance.

[0028] In addition, the power-on period T on The current value to be applied initially is a predetermined value I0. on In each current application period T on The current value initially flowing through the light-emitting element is the same predetermined value I0. Note that "same" means that the set value of the current value is the same, and the current value actually flowing through the light-emitting element may include unavoidable errors. For example, if it is within ±5% of the predetermined value I0, it is considered to be the same as the predetermined value I0. Note that the predetermined value I0 of the current value may be the same or different among the first light-emitting element 11, the second light-emitting element 12, and the third light-emitting element 13.

[0029] The current waveform generated by the control unit 20 at this point is shown by the dashed line in Fig. 7A. For convenience of explanation, in Fig. 7, the current conduction period T on and non-energized period T off In this example, the energization period T is set once for each frame F. on and non-energized period T off may be set.

[0030] 3 and step S12 in FIG. 6, the driving unit 70 starts supplying current to the light-emitting element based on the control signal output from the control unit 20. This causes the light-emitting element to start emitting light. In addition, as shown in FIG. 7B, the temperature of the light-emitting element starts to rise. The temperature change of the light-emitting element is detected by the temperature measurement unit 80.

[0031] Next, as shown in step S13 of FIG. 6, the control unit 20 acquires the measurement result of the temperature measurement unit 80.

[0032] Next, as shown in step S14 of Fig. 6, the temperature of the light-emitting element detected by the temperature measurement unit 80 is compared with a threshold value. If the temperature does not exceed the threshold value, the process proceeds to step S15, and the predetermined current application period T on If it has not reached, the process returns to step S13.

[0033] On the other hand, if the temperature of the light-emitting element exceeds the threshold value, the process proceeds from step S14 to step S16, and the control unit 20 acquires the first relationship and the second relationship from the storage unit 60.

[0034] Then, as shown in step S17, the peak wavelength of the light-emitting element is predicted based on the temperature measurement results and the first relationship, and the current value for returning the peak wavelength of the light-emitting element to the set value is determined based on the second relationship, and the current value is changed.

[0035] As shown in FIG. 4, the peak wavelength becomes longer as the temperature of the light-emitting element increases. Furthermore, as shown in FIG. 5, in order to shorten the peak wavelength, it is necessary to increase the current value. In this embodiment, the increase in the peak wavelength due to an increase in temperature is offset by the increase in the current value due to a decrease in the peak wavelength. Therefore, as shown in FIG. 7A, the new current value after the change is on The current value I0 that flows initially is larger than the current value I0.

[0036] Next, as shown in step S18 of FIG. 6, the remaining current-carrying period is set based on the new current value after the change. The remaining current-carrying period is set so that the integral value of the current value with respect to time is equal to the integral value of the original current waveform shown by the dashed line in FIG. 7A. Then, proceeding to step S15, the predetermined current-carrying period T on If it has not reached, the process returns to step S13.

[0037] In this way, the control unit 20 determines the current application period T on The current value flowing through the light emitting element during the current application period T on In this case, the rate of change of the current value with respect to time is always positive. When the integral of the current value with respect to time reaches a predetermined value, the power supply to the light emitting element is stopped.

[0038] As a result, as shown in FIG. 7A, the current-carrying period T on is the initially set energization period T on The time-adjacent energization periods T on The interval between the two periods, i.e., one non-energized period T off The length of one current-carrying period T on It is preferable that the non-energized period T off The length of the current-carrying period T on By making it longer than the current-carrying period T onThis makes it easier to reduce the temperature of the light-emitting element that has risen during this period, making it easier to keep the temperature of the light-emitting element constant at the start of each frame F. This makes it easier to keep the peak wavelength of the light-emitting element constant, and stabilizes the chromaticity of the light-emitting device 1.

[0039] In this way, the control unit 20 makes the current value flowing through the light emitting element at the end of the current-carrying period greater than the current value flowing through the light emitting element at the beginning of the current-carrying period during the current-carrying period. In this embodiment, the current value flowing through the light emitting element increases linearly with time. That is, during the current-carrying period T on In this case, the rate of change of the current value with respect to time is always positive and constant. In other words, the first derivative of the current value with respect to time is positive, and the second derivative is zero.

[0040] As a result, even if the temperature of the light-emitting element rises as shown by the solid line in FIG. 7B, the peak wavelength of the light emitted by the light-emitting element is prevented from becoming longer as shown by the solid line in FIG. 7C. As a result, the chromaticity of the light-emitting device 1 is stabilized. Furthermore, by changing the power-on period in accordance with changes in the current value, it is possible to reduce the increase in luminance that accompanies an increase in the current value. As a result, the luminance of the light-emitting device 1 is stabilized.

[0041] In light-emitting elements made of InGaN compound semiconductor, the shift in peak wavelength to longer wavelength with increasing temperature is most pronounced in the first light-emitting element 11. Therefore, in one embodiment, the above-described current value control is performed for the first light-emitting element 11, and the current values ​​of the second light-emitting element 12 and the third light-emitting element 13 may remain the same as the current waveform generated in step S11. The above-described current value control may also be performed for the second light-emitting element 12 and the third light-emitting element 13, as in the first light-emitting element 11.

[0042] When performing the above-described current value control for the first light-emitting element 11 and the second light-emitting element 12, it is preferable that the control unit 20 make the rate of change with time of the current value flowing to the second light-emitting element 12 during the current-carrying period when current is passed through the second light-emitting element 12 smaller than the rate of change with time of the current value flowing to the first light-emitting element 11 during the current-carrying period when current is passed through the first light-emitting element 11. For the third light-emitting element 13, the current value may remain the current waveform generated in step S11.

[0043] 8, when the above-described current value control is performed for the first light-emitting element 11, the second light-emitting element 12, and the third light-emitting element 13, it is preferable that the control unit 20 set the rate of change with time of the current value flowing through the first light-emitting element 11 during the energization period when the first light-emitting element 11 is energized to be greater than the rate of change with time of the current value flowing through the second light-emitting element 12 during the energization period when the second light-emitting element 12 is energized, and the rate of change with time of the current value flowing through the third light-emitting element 13 during the energization period when the third light-emitting element 13 is energized. This makes it possible to efficiently reduce the shift in peak wavelength due to an increase in temperature in each light-emitting element.

[0044] (effect) According to this embodiment, the shift of the peak wavelength to a longer wavelength due to an increase in the temperature of the light-emitting element is offset by increasing the current value to shift the peak wavelength to a shorter wavelength, thereby stabilizing the chromaticity of the light-emitting device 1.

[0045] Furthermore, according to this embodiment, the current-carrying period T on Within the LED, a temperature measurement unit 80 measures the temperature of the light-emitting elements, and a control unit 20 successively corrects the current flowing through each light-emitting element. This enables highly accurate control that reflects the actual temperature, and makes it possible to stabilize the chromaticity of the light-emitting device 1 with even greater accuracy.

[0046] Furthermore, according to this embodiment, when the integral of the current value over time reaches a predetermined value, the power supply to the light-emitting element is stopped, thereby suppressing the increase in luminance even when the current value is increased, and making it possible to stabilize the luminance of the light-emitting device 1.

[0047] Furthermore, according to this embodiment, two adjacent current-carrying periods T on In each current application period T on The current value that flows through the light emitting element at the beginning is the same, which simplifies the configuration of the control unit 20.

[0048] Furthermore, according to this embodiment, the non-energized period T off The energization period T on This makes the energization period T on The light emitting element is heated during the non-energizing period T off As a result, the current can be sufficiently cooled during the energization period T on At the beginning, the peak wavelength of the light emitting element tends to be constant, and the chromaticity of the light emitting device 1 becomes stable.

[0049] Furthermore, in this embodiment, the physical distance between the first light-emitting element 11 and the temperature measurement unit 80 is shorter than the physical distance between the third light-emitting element 13 and the temperature measurement unit 80. This allows the temperature measurement unit 80 to be located near the first light-emitting element 11, which experiences a large change in chromaticity due to temperature changes, and therefore allows the temperature measurement results to be used effectively.

[0050] According to the xy chromaticity diagram, when the wavelength of the green light emitted from the first light-emitting element 11 increases by 5 nm from 520 nm to 525 nm, the x value increases by approximately 0.06 and the y value decreases by approximately 0.01. In contrast, when the wavelength of the red light emitted from the second light-emitting element 12 increases by 5 nm from 600 nm to 605 nm, the x value increases by approximately 0.01 and the y value decreases by approximately 0.01. Similarly, when the wavelength of the blue light emitted from the third light-emitting element 13 increases by 5 nm from 460 nm to 465 nm, the x value decreases by approximately 0.01 and the y value increases by approximately 0.01. Thus, the amount of change in chromaticity when the wavelength of the light emitted from the first light-emitting element 11 changes is greater than the amount of change in chromaticity when the wavelength of the light emitted from the second light-emitting element 12 and the third light-emitting element 13 changes. Therefore, the chromaticity of the light emitted from the first light-emitting element 11 is more sensitive to temperature than the second light-emitting element 12 and the third light-emitting element 13.

[0051] <First Modification of the First Embodiment> FIG. 9 is a graph showing a method for driving a light emitting device according to this modification, with the horizontal axis representing time and the vertical axis representing the value of current flowing through a light emitting element.

[0052] 9, in this modification, the current value flowing through the light emitting element increases with time in a downwardly convex curve. on In this example, the rate of change of the current value with respect to time is always positive, and the rate of change increases with time. In other words, the first derivative of the current value with respect to time is positive, and the second derivative is also positive. The current value may change in this manner depending on the behavior of the temperature rise of the light-emitting element over time, the first relationship, and the second relationship. Other than the above, the configuration, operation, and effects of this modified example are the same as those of the first embodiment.

[0053] <Second Modification of the First Embodiment> FIG. 10 is a graph showing a method for driving a light emitting device according to this modification, with the horizontal axis representing time and the vertical axis representing the value of current flowing through a light emitting element.

[0054] 10, in this modification, the current value flowing through the light emitting element increases with time in the form of an upwardly convex curve. on In this example, the rate of change of the current value with respect to time is always positive and decreases with time. In other words, the first derivative of the current value with respect to time is positive and the second derivative is negative. The current value may change in this manner depending on the behavior of the temperature rise of the light-emitting element over time, the first relationship, and the second relationship. Other than the above, the configuration, operation, and effects of this modified example are the same as those of the first embodiment.

[0055] <Third Modification of the First Embodiment> FIG. 11 is a graph showing a method for driving a light emitting device according to this modification, with the horizontal axis representing time and the vertical axis representing the value of current flowing through a light emitting element.

[0056] 11, in this modification, the value of the current flowing through the light emitting element changes discontinuously with time. on In this example, the waveform showing the change in current value increases in a step-like manner. This type of current waveform may occur if the control unit 20 only rarely corrects the current value and the resistance and inductance of the circuit including the light-emitting element are sufficiently small relative to the current driving capacity of the driving unit 70. However, even in this case, the current waveform is not necessarily composed of only straight lines, and curved portions may be interposed between the straight line portions. Other than the above, the configuration, operation, and effects of this modified example are the same as those of the first embodiment.

[0057] <Fourth Modification of the First Embodiment> Figure 12 is a graph showing a method for driving a light-emitting device according to this modified example, with the horizontal axis representing time and the vertical axis representing the current value flowing through the light-emitting element, the measurement results of the temperature measurement unit, and the peak wavelength of the light emitted by the light-emitting element.

[0058] In the first embodiment described above, as shown in FIG. 7A, two adjacent current-carrying periods T on In each current application period T on The current value that is initially passed through the light emitting element is the same predetermined value I0.

[0059] In contrast to this, in this modification, as shown in FIG. 12A, two adjacent current-carrying periods T on Of these, the latter energization period T on The current value I2 that flows through the light emitting element at the beginning of the current application period T on is smaller than the current value I1 flowing through the light emitting element at the end of the previous energization period T on The current value I0 that flows through the light emitting element at the beginning is different from I2. <I1である。

[0060] Note that "different" is an antonym of the above-mentioned "same" and means that the set values ​​generated by the control unit 20 are different. For example, if the current value I2 is greater than or less than the predetermined value I0 by more than 5%, the current value I2 is considered to be different from the predetermined value I0. For example, in the subsequent current application period T onThe current value I2 that flows through the light emitting element at the beginning of the current application period T on is larger than the current I0 initially applied to the light emitting element. <I2<I1である。

[0061] As a result, as shown in FIG. 12B, the subsequent energization period T on At the beginning of the current application period T on When the temperature is not cooled to the initial temperature, the peak wavelength of the light-emitting element can be appropriately controlled as shown in Fig. 12C. Other configurations, operations, and effects of this modification are the same as those of the first embodiment.

[0062] <Fifth Modification of the First Embodiment> FIG. 13 is a graph showing a method for driving a light emitting device according to this modification, with the horizontal axis representing time and the vertical axis representing the current values ​​flowing through the first light emitting element, the second light emitting element, and the third light emitting element.

[0063] As shown in FIG. 13, in this modification, the second light emitting element 12 is energized for a period T on The maximum length of the energization period T on This makes it possible to compensate for the phenomenon in which visibility decreases as the peak wavelength of red light becomes longer. Other than the above, the configuration, operation, and effects of this modified example are the same as those of the first embodiment.

[0064] <Second embodiment> FIG. 14 is an end view showing the light emitting device according to this embodiment. 14, the light emitting device 2 according to this embodiment differs from the light emitting device 1 according to the first embodiment in that a temperature measuring unit 80 is arranged within the substrate 30 in addition to the control unit 20. For example, three temperature measuring units 80 are provided, and are arranged directly below the first light emitting element 11, the second light emitting element 12, and the third light emitting element 13, respectively.

[0065] It is noted that only one temperature measuring unit 80 may be provided. In this case, the temperature measuring unit 80 may be disposed directly below the first light-emitting element 11. In this case, it is preferable that the physical distance between the first light-emitting element 11 and the temperature measuring unit 80 is shorter than the physical distance between the third light-emitting element 13 and the temperature measuring unit 80. Other configurations, operations, and effects of this embodiment are the same as those of the first embodiment.

[0066] <Third embodiment> FIG. 15 is a block diagram showing a light emitting device according to this embodiment. FIG. 16 is a graph showing the third relationship, with the horizontal axis representing the temperature of the light-emitting element and the vertical axis representing the voltage between the anode electrode and the cathode electrode of the light-emitting element.

[0067] As shown in FIG. 15, the light emitting device 3 according to this embodiment differs from the light emitting device 1 according to the first embodiment in that it does not include a temperature measurement unit 80 and the control unit 20 estimates the temperature of the light emitting element based on the voltage between the anode electrode and cathode electrode of the light emitting element. In addition to the first and second relationships described above, the storage unit 60 also stores a third relationship. The third relationship is the relationship between the voltage applied to the anode electrode and cathode electrode of the light emitting element (hereinafter referred to as the "anode-cathode voltage") and the temperature of the light emitting element.

[0068] 16, as the temperature of the light-emitting element increases, the anode-cathode voltage decreases. Therefore, the temperature of the light-emitting element can be estimated by measuring the anode-cathode voltage. The anode-cathode voltage may be measured for only the first light-emitting element 11, only the second light-emitting element 12, or all the light-emitting elements.

[0069] According to this embodiment, there is no need to provide a dedicated temperature measuring unit 80, which simplifies the configuration of the light emitting device 3. Other configurations, operations, and effects of this embodiment are the same as those of the first embodiment.

[0070] <Fourth embodiment> FIG. 15 shows a block diagram of the light emitting device according to this embodiment. FIG. 17 is a graph showing a method for driving the light emitting device according to this embodiment, with the horizontal axis representing time and the vertical axis representing the value of the current flowing through the light emitting element.

[0071] 17, in the method for driving the light emitting device according to this embodiment, a preliminary light emitting step S0 is performed before a main light emitting step S1. In the main light emitting step S1, a plurality of energizing periods T on The driving method in the light emitting step S1 is the same as that in the third embodiment.

[0072] In the preliminary light-emitting step S0, a voltage is applied to the anode and cathode electrodes of the light-emitting element, and the temperature of the light-emitting element is estimated from the anode-cathode voltage of the light-emitting element based on the third relationship described above. Then, in the main light-emitting step S1, the current-carrying period T on The current value I0 to be applied to the light emitting element at the beginning of the main light emission step S1 is determined. on It may be applied only to the entire energization period T on may be applied to.

[0073] According to this embodiment, the preliminary light emission step S0 is performed before the main light emission step S1, so that the current application period T on The current value I0 to be applied to the light emitting element at the beginning of the current application period T on The chromaticity of the light emitting device can be stabilized from the very beginning. The configuration, operation, and effects of this embodiment other than those described above are the same as those of the third embodiment. In the fourth embodiment, the temperature of the light emitting element in the preliminary light emission step S0 is estimated based on the third relation, but a temperature measurement unit 80 may be provided and the temperature of the light emitting element may be measured by the temperature measurement unit 80.

[0074] <Fifth embodiment> FIG. 18 is a block diagram showing a light emitting device according to this embodiment. FIG. 19 is a flowchart showing a method for driving the light emitting device according to this embodiment.

[0075] 18, the light emitting device 5 according to this embodiment differs from the light emitting device 1 according to the first embodiment in that it does not include a temperature measuring unit 80 and that it includes a memory unit 61 instead of the memory unit 60. The memory unit 61 stores a predetermined current waveform instead of the first and second relationships.

[0076] In this embodiment, the current waveform to be applied to the light-emitting element is determined in advance by a preliminary experiment or a simulation, and is stored in the storage unit 61. The storage unit 61 stores a current waveform corresponding to the luminance for each light-emitting element. In these current waveforms, on The current value flowing through the light emitting element at the end of the current conduction period T on The current value is larger than the current value that flows through the light emitting element at the beginning of the current application period T on In this case, the current waveform is set so that when the integral value of the current value over time reaches a predetermined value, the supply of current to the light emitting element is stopped.

[0077] 18 and 19, when the driving of the light emitting device 5 starts, the control unit 20 acquires a current waveform from the storage unit 61 based on a control signal input from outside. Then, the control unit 20 generates a control signal based on the acquired current waveform and outputs it to the drive unit 70.

[0078] As shown in step S22, the driving unit 70 starts supplying current to the light emitting element based on the control signal output from the control unit 20. As a result, the light emitting element starts emitting light. At this time, the temperature of the light emitting element rises, but the control unit 20 does not measure the temperature or sequentially correct the current value. Then, the process proceeds to step S23, where the predetermined current application period T on If it has reached this value, the drive is terminated.

[0079] In this embodiment, by knowing the degree of temperature rise of the light-emitting element in advance, fluctuations in peak wavelength can be effectively reduced and chromaticity and brightness can be stabilized even when the operation is based on a predetermined current waveform.

[0080] Furthermore, according to this embodiment, there is no need to correct the current value while the light emitting device is being driven, which simplifies the configuration of the light emitting device 5. Furthermore, since the light emitting device 5 can be driven at high speed, it becomes easier to support local dimming, for example. Other configurations, operations, and effects of this embodiment are the same as those of the first embodiment.

[0081] Sixth Embodiment FIG. 20 is a plan view showing the light emitting device according to this embodiment. FIG. 21 is an end view taken along line XXI-XXI shown in FIG.

[0082] As shown in FIGS. 20 and 21 , the light emitting device 6 according to this embodiment does not include a second light emitting element 12 that emits red light. A first light emitting element 11 that emits green light and a third light emitting element 13 that emits blue light are disposed on a substrate 30. A wavelength conversion member 90 is also disposed on the substrate 30 to cover the first light emitting element 11 and the third light emitting element 13. The wavelength conversion member 90 includes, for example, a transparent base material in which a phosphor that absorbs blue light and emits red light is disposed. A light-transmitting member 50 is disposed inside the light reflecting member 40 and on the wavelength conversion member 90. The control unit 20, the driving unit 70, and the temperature measurement unit 80 are disposed within the substrate 30. The wavelength conversion member 90 does not need to be disposed within the light emitting device 6. For example, the wavelength conversion member 90 may be disposed outside the light emitting device 6, spaced apart from the light emitting device 6.

[0083] According to this embodiment, by omitting the second light-emitting element 12 that emits red light, it is possible to simplify the configuration and driving of the light-emitting device 6. Other configurations, operations, and effects of this embodiment are the same as those of the first embodiment.

[0084] Seventh Embodiment FIG. 22 is a graph showing a method of driving the light emitting device according to this embodiment, with the horizontal axis representing time and the vertical axis representing the current values ​​flowing through the first light emitting element, the second light emitting element, and the third light emitting element.

[0085] As shown in FIG. 22, in this embodiment, among the first light emitting element 11, the second light emitting element 12, and the third light emitting element 13, two light emitting elements are turned on for a current-carrying period T on The current value at the end of the current flow period T on The current value is set to be larger than the current value initially applied to the other light-emitting element during the current application period T on The current value at the end of the current flow period T on For example, for the first light emitting element 11 and the third light emitting element 13, the current value is set to be equal to the value of the current that is initially applied during the energization period T on The current value is increased during the energization period T on The current value is kept constant.

[0086] According to this embodiment, the light emitting elements that exhibit the above-described first and second relationships are controlled in the same manner as in the first embodiment, and the light emitting elements that do not exhibit at least one of the first and second relationships are controlled in the same manner as in the first embodiment. on The current value is kept constant in this state. This allows the display device as a whole to be appropriately controlled. For example, when a quaternary light-emitting element is used as the second light-emitting element 12, the second relationship described above may not be observed. Other configurations, operations, and effects of this embodiment are the same as those of the first embodiment.

[0087] Eighth Embodiment FIG. 23 is a graph showing a method of driving the light emitting device according to this embodiment, with the horizontal axis representing time and the vertical axis representing the current values ​​flowing through the first light emitting element, the second light emitting element, and the third light emitting element.

[0088] As shown in FIG. 23, in this embodiment, one of the first light emitting element 11, the second light emitting element 12, and the third light emitting element 13 is turned on for a period T on The current value at the end of the current flow period T onThe current value is set to be larger than the value initially applied to the other two light-emitting elements during the current application period T on The current value at the end of the current flow period T on For example, for the first light emitting element 11, the current value is set to be equal to the value of the current that is initially applied during the energization period T on The current value is increased during the energization period T on The current value is kept constant.

[0089] According to this embodiment, the first light-emitting element 11 that emits green light, which is subject to a large influence of wavelength changes on chromaticity, can be controlled in the same manner as in the first embodiment, thereby reducing changes in chromaticity. Other configurations, operations, and effects of this embodiment are the same as those of the first embodiment.

[0090] <Ninth embodiment> This embodiment is an embodiment of a display device. FIG. 24 is a plan view showing the display device according to this embodiment.

[0091] As shown in Figure 24, the display device 101 of this embodiment has a mounting substrate 110, a plurality of light-emitting devices 9 arranged on the mounting substrate 110, and a plurality of temperature measurement units 180 arranged on the mounting substrate 110.

[0092] The light emitting device 9 has a configuration similar to that of the light emitting device 1 according to the first embodiment, except that it does not have a temperature measuring unit 80. A plurality of light emitting devices 9 are arranged, for example, in a matrix on the surface of the mounting substrate 110. A plurality of temperature measuring units 180 are arranged along a pair of long sides of the mounting substrate 110. The number of temperature measuring units 180 is less than the number of light emitting devices 9. Only one temperature measuring unit 180 may be provided. Alternatively, the temperature measuring unit 180 may be provided inside the mounting substrate 110.

[0093] In this embodiment, the temperature measurement units 180 are arranged along the sides of the mounting substrate 110, and the number of temperature measurement units 180 is made smaller than the number of light emitting devices 9, thereby enabling the light emitting devices 9 to be arranged at a high density. The display device 101 may be used as an LED display device in which each light emitting device 9 serves as a pixel, or may be overlapped with a liquid crystal panel and used as a light source for the liquid crystal panel. Other configurations, operations, and effects of this embodiment are the same as those of the first embodiment.

[0094] The above-described embodiments and their modifications are examples of realizing the present disclosure, and the present disclosure is not limited to these embodiments and modifications. For example, the present disclosure also includes the addition, deletion, or modification of some components or steps in the above-described embodiments and modifications. Furthermore, the above-described embodiments and modifications can be implemented in combination with each other.

[0095] The present disclosure includes the following aspects.

[0096] (Appendix 1) A method for driving a light emitting device that performs pulse width modulation control on a light emitting device including a first light emitting element whose peak wavelength of emitted light is in the range of 490 nm to 680 nm, A method for driving a light-emitting device, in which, during a current-carrying period in which current is continuously passed through the first light-emitting element, the current value passed through the first light-emitting element at the end of the current-carrying period is made larger than the current value passed through the first light-emitting element at the beginning of the current-carrying period.

[0097] (Appendix 2) A method for driving a light-emitting device as described in Appendix 1, in which the value of the current flowing to the first light-emitting element during the power-on period is sequentially corrected based on a first relationship between the temperature of the first light-emitting element and the peak wavelength of the light emitted by the first light-emitting element, and a second relationship between the value of the current flowing to the first light-emitting element and the peak wavelength of the light emitted by the first light-emitting element.

[0098] (Appendix 3) In the first relationship, as the temperature increases, the peak wavelength increases, and 3. The method for driving a light emitting device according to claim 2, wherein, in the second relationship, the peak wavelength becomes shorter as the current value increases.

[0099] (Appendix 4) 4. The method for driving a light emitting device according to claim 1, wherein during the energization period, the rate of change of the current value with respect to time is always positive and increases with time.

[0100] (Appendix 5) 4. The method for driving a light emitting device according to claim 1, wherein during the energization period, the rate of change of the current value with respect to time is always positive and decreases with time.

[0101] (Appendix 6) 4. The method for driving a light emitting device according to claim 1, wherein the current value changes discontinuously with respect to time during the energization period.

[0102] (Appendix 7) 7. The method for driving a light emitting device according to any one of claims 1 to 6, wherein the interval between adjacent power-on periods is longer than one power-on period.

[0103] (Appendix 8) 8. The method for driving a light emitting device according to claim 1, wherein the current value flowing through the first light emitting element at the start of each of two adjacent current conduction periods is the same.

[0104] (Appendix 9) A method for driving a light-emitting device described in any one of Appendices 1 to 7, wherein the current value flowing through the first light-emitting element at the beginning of a later current-flow period between two adjacent current-flow periods is smaller than the current value flowing through the first light-emitting element at the end of a previous current-flow period and different from the current value flowing through the first light-emitting element at the beginning of the previous current-flow period.

[0105] (Appendix 10) a main light emission step of executing the plurality of energization periods by pulse width modulation control; a preliminary light-emitting step of applying a voltage to the first light-emitting element before the main light-emitting period; Equipped with In the preliminary light emission step, a temperature of the first light emitting element is estimated based on a third relationship between a voltage applied to an anode electrode and a cathode electrode of the first light emitting element and a temperature of the first light emitting element; 4. The method for driving a light emitting device according to claim 2, further comprising determining a current value to be passed through the first light emitting element at the beginning of the current application period in the main light emitting step based on the estimated temperature.

[0106] (Appendix 11) 11. The method for driving a light emitting device according to any one of claims 1 to 10, wherein the current supply to the first light emitting element is stopped when the integral value of the current value over time reaches a predetermined value during the current supply period.

[0107] (Appendix 12) a first light-emitting element having a peak wavelength of light emitted in the range of 490 nm to 680 nm; a control unit that performs pulse width modulation control on the first light emitting element; Equipped with The control unit is a light-emitting device that, during a power-on period in which power is continuously applied to the first light-emitting element, makes the current value flowing through the first light-emitting element at the end of the power-on period greater than the current value flowing through the first light-emitting element at the beginning of the power-on period.

[0108] (Appendix 13) a storage unit configured to store a first relationship between a temperature of the first light-emitting element and a peak wavelength of light emitted by the first light-emitting element, and a second relationship between a current value flowing through the first light-emitting element and a peak wavelength of light emitted by the first light-emitting element, 13. The light-emitting device according to claim 12, wherein the control unit sequentially corrects the current value flowing through the first light-emitting element during the power-on period based on the temperature of the first light-emitting element, the first relationship, and the second relationship.

[0109] (Appendix 14) In the first relationship, as the temperature increases, the peak wavelength increases, and 14. The light emitting device according to claim 13, wherein, in the second relationship, the peak wavelength shortens as the current value increases.

[0110] (Appendix 15) The light-emitting device according to any one of claims 12 to 14, wherein the control unit stops the supply of current to the first light-emitting element when the integral value of the current value over time during the power-on period reaches a predetermined value.

[0111] (Appendix 16) the light emitting device further comprises a second light emitting element; the first light-emitting element emits light having a peak wavelength in the range of 490 nm or more and less than 540 nm; the second light emitting element emits light with a peak wavelength in the range of 540 nm to 680 nm, the control unit sets a current-carrying period for energizing the second light-emitting element independently from the current-carrying period for energizing the first light-emitting element; The light-emitting device according to any one of claims 12 to 15, wherein the control unit makes the rate of change with time of the current value flowing through the second light-emitting element during the energization period when the second light-emitting element is energized smaller than the rate of change with time of the current value flowing through the first light-emitting element during the energization period when the first light-emitting element is energized.

[0112] (Appendix 17) 17. The light emitting device according to claim 16, wherein the first light emitting element and the second light emitting element include an InGaN compound semiconductor.

[0113] (Appendix 18) the light emitting device further includes a third light emitting element having a peak wavelength of emitted light in the range of 360 nm or more and less than 490 nm; the control unit sets a current-carrying period for energizing the third light-emitting element independently from a current-carrying period for energizing the first light-emitting element and a current-carrying period for energizing the second light-emitting element; The light-emitting device described in Appendix 16 or 17, wherein the control unit makes the rate of change over time of the current value flowing through the third light-emitting element during the power-on period when power is applied to the third light-emitting element smaller than the rate of change over time of the current value flowing through the first light-emitting element.

[0114] (Appendix 19) Further, a temperature measurement unit is provided which outputs a measurement result to the control unit, 19. The light emitting device according to claim 18, wherein a distance between the first light emitting element and the temperature measuring unit is shorter than a distance between the third light emitting element and the temperature measuring unit.

[0115] (Appendix 20) 20. The light emitting device according to any one of claims 16 to 19, wherein the maximum length of a power-on period during which current is applied to the second light emitting element is longer than the maximum length of a power-on period during which current is applied to the first light emitting element.

[0116] (Appendix 21) a substrate on which the first light emitting element is arranged; a temperature measurement unit disposed within the substrate, which measures the temperature of the first light-emitting element and outputs the measurement result to the control unit; 14. The light-emitting device of claim 13, further comprising:

[0117] (Appendix 22) a mounting board; a light emitting device according to any one of appendices 12 to 20, which is disposed on the mounting substrate; a temperature measuring unit disposed on the mounting board; Equipped with A display device in which the number of the temperature measurement units is smaller than the number of the light emitting devices. [Industrial Applicability]

[0118] The present disclosure can be used, for example, as a light source for a display device. [Explanation of symbols]

[0119] 1, 2, 3, 5, 6, 9 Light-emitting device 11 First light-emitting element 12 Second light-emitting element 13 Third light-emitting element 20 Control Unit 30 boards 40 Light reflecting member 50 Translucent material 60, 61 Storage section 70 Drive unit 80 Temperature measurement section 90 Wavelength conversion material 101 Display device 110 Mounting board 180 Temperature measurement section

Claims

1. A method for driving a light emitting device, which performs pulse width modulation control on a light emitting device including a first light emitting element whose peak wavelength of emitted light is in the range of 490 nm to 680 nm, A method for driving a light-emitting device, wherein during a current-carrying period in which current is continuously passed through the first light-emitting element, the current value passed through the first light-emitting element at the end of the current-carrying period is made larger than the current value passed through the first light-emitting element at the beginning of the current-carrying period.

2. 2. A method for driving a light-emitting device according to claim 1, wherein the value of the current flowing through the first light-emitting element during the power-on period is sequentially corrected based on a first relationship between the temperature of the first light-emitting element and the peak wavelength of the light emitted by the first light-emitting element, and a second relationship between the value of the current flowing through the first light-emitting element and the peak wavelength of the light emitted by the first light-emitting element.

3. In the first relationship, as the temperature increases, the peak wavelength increases; The method for driving a light emitting device according to claim 2 , wherein in the second relationship, the peak wavelength becomes shorter as the current value increases.

4. 2. The method for driving a light emitting device according to claim 1, wherein during the energization period, the rate of change of the current value with respect to time is always positive, and the rate of change increases with time.

5. 2. The method for driving a light emitting device according to claim 1, wherein during the energization period, the rate of change of the current value with respect to time is always positive, and the rate of change decreases with time.

6. 2. The method for driving a light emitting device according to claim 1, wherein the current value changes discontinuously with time during the energization period.

7. The method for driving a light emitting device according to claim 1 , wherein an interval between adjacent energization periods is longer than one energization period.

8. 2. The method for driving a light emitting device according to claim 1, wherein the current values ​​flowing through the first light emitting element at the beginning of each of the two adjacent current conduction periods are the same.

9. 2. The method for driving a light-emitting device according to claim 1, wherein, of two adjacent current-carrying periods, the current value flowing through the first light-emitting element at the beginning of the later current-carrying period is smaller than the current value flowing through the first light-emitting element at the end of the earlier current-carrying period and is different from the current value flowing through the first light-emitting element at the beginning of the earlier current-carrying period.

10. a main light emission step of executing the plurality of energization periods by pulse width modulation control; a preliminary light-emitting step of applying a voltage to the first light-emitting element before the main light-emitting period; Equipped with In the preliminary light emission step, a temperature of the first light emitting element is estimated based on a third relationship between a voltage applied to an anode electrode and a cathode electrode of the first light emitting element and a temperature of the first light emitting element; The method for driving a light emitting device according to claim 2 , wherein a value of a current to be passed through the first light emitting element at the beginning of the current application period in the main light emitting step is determined based on the estimated temperature.

11. 2. The method for driving a light emitting device according to claim 1, wherein the current supply to the first light emitting element is stopped when an integral value of the current value with respect to time reaches a predetermined value during the current supply period.

12. a first light-emitting element having a peak wavelength of emitted light in the range of 490 nm to 680 nm; a control unit that performs pulse width modulation control on the first light emitting element; Equipped with The control unit, during a power-on period in which current is continuously applied to the first light-emitting element, makes the current value flowing through the first light-emitting element at the end of the power-on period greater than the current value flowing through the first light-emitting element at the beginning of the power-on period.

13. a storage unit configured to store a first relationship between a temperature of the first light-emitting element and a peak wavelength of light emitted by the first light-emitting element, and a second relationship between a current value flowing through the first light-emitting element and a peak wavelength of light emitted by the first light-emitting element, The light emitting device according to claim 12 , wherein the control unit sequentially corrects a value of the current flowing through the first light emitting element during the energization period based on the temperature of the first light emitting element, the first relationship, and the second relationship.

14. In the first relationship, as the temperature increases, the peak wavelength increases; The light emitting device according to claim 13 , wherein in the second relationship, the peak wavelength shortens as the current value increases.

15. The light emitting device according to claim 12 , wherein the control unit stops the current supply to the first light emitting element when an integral value of the current value with respect to time during the current supply period reaches a predetermined value.

16. the light emitting device further includes a second light emitting element, the first light-emitting element emits light having a peak wavelength in the range of 490 nm or more and less than 540 nm; the second light-emitting element emits light having a peak wavelength in the range of 540 nm to 680 nm, the control unit sets a current-carrying period during which current is applied to the second light-emitting element independently from the current-carrying period during which current is applied to the first light-emitting element; 13. The light-emitting device of claim 12, wherein the control unit makes the rate of change over time of the current value flowing through the second light-emitting element during the energization period when the second light-emitting element is energized smaller than the rate of change over time of the current value flowing through the first light-emitting element during the energization period when the first light-emitting element is energized.

17. The light emitting device according to claim 16 , wherein the first light emitting element and the second light emitting element include an InGaN compound semiconductor.

18. the light emitting device further includes a third light emitting element having a peak wavelength of emitted light in the range of 360 nm or more and less than 490 nm; the control unit sets a current-carrying period for energizing the third light-emitting element independently from a current-carrying period for energizing the first light-emitting element and a current-carrying period for energizing the second light-emitting element; The light-emitting device according to claim 16, wherein the control unit makes the rate of change of the current value flowing through the third light-emitting element with respect to time smaller than the rate of change of the current value flowing through the first light-emitting element with respect to time during the energization period in which the third light-emitting element is energized.

19. Further, a temperature measurement unit is provided which outputs a measurement result to the control unit, The light emitting device according to claim 18 , wherein a distance between the first light emitting element and the temperature measuring unit is shorter than a distance between the third light emitting element and the temperature measuring unit.

20. The light emitting device according to claim 16 , wherein a maximum length of a current-carrying period during which the second light emitting element is energized is longer than a maximum length of a current-carrying period during which the first light emitting element is energized.

21. a substrate on which the first light-emitting element is arranged; a temperature measurement unit disposed within the substrate, measuring the temperature of the first light-emitting element and outputting the measurement result to the control unit; The light emitting device of claim 13 further comprising:

22. a mounting board; the light emitting device according to any one of claims 12 to 20, which is disposed on the mounting substrate; a temperature measuring unit disposed on the mounting board; Equipped with A display device in which the number of the temperature measurement units is smaller than the number of the light emitting devices.

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