JP2013089302A - Light emitting device and method for driving organic el element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting device capable of performing a highly-stable variable control of colors, and a method for driving an organic EL element.SOLUTION: A light emitting device comprises: an organic EL element 10A varying luminescent color according to the current value applied thereto; a driving circuit 20 supplying a drive waveform to the organic EL element 10A; and control means 30 having a correction function for varying at least one of the current value and the lighting rate of the drive waveform in the driving circuit 20 according to a desired luminescent color and correcting at least one of the current value and the lighting rate of the drive waveform applied thereto according to a drift of the luminescent color with a temperature change of the organic EL element 10A.

Description

  The present invention relates to a light emitting device using an organic EL (Electro Luminescence) element and a method for driving the organic EL element.

  Conventionally, an organic EL element known as a self-luminous element formed of an organic material is, for example, a first electrode made of ITO (Indium Tin Oxide) or the like serving as an anode, an organic layer having at least a light emitting layer, and a cathode. A non-translucent second electrode made of aluminum (Al) or the like is sequentially laminated (see Patent Document 1).

  Such an organic EL element emits light by injecting holes from the first electrode and injecting electrons from the second electrode, and the holes and electrons recombine in the light emitting layer. In addition to the use of organic EL elements in displays, lighting devices using organic EL elements as light sources have been developed in recent years.

JP 59-194393 A Japanese Patent Laid-Open No. 5-94875

  In addition, as an organic EL element, one that changes the emission color by changing an applied voltage is known (for example, see Patent Document 2). If such an organic EL element is applied to a light source, an illumination device capable of arbitrarily changing the illumination color can be obtained.

  However, the organic EL element has a characteristic that the light emission characteristic fluctuates due to a temperature change, deterioration with time due to continuous driving, and the like, and can be obtained by the above-described change in situation even when a similar driving current and driving voltage are applied. The luminescent color may be different, and there is still room for improvement in terms of the stability of the luminescent color when a color-variable organic EL element is used in a lighting device or the like. In particular, in an illuminating device in which a plurality of organic EL panels including organic EL elements are arranged adjacent to each other to form a light emitting cluster, color unevenness occurs when the light emission color of each organic EL element varies due to a change time or a manufacturing lot difference. Since it is recognized, there has been room for improvement as a light emitting device including a plurality of organic EL elements.

  Therefore, the present invention has been made in view of this problem, and an object of the present invention is to provide a light-emitting device and an organic EL element driving method capable of performing highly stable color variable control.

In order to solve the above problems, the light-emitting device of the present invention includes a plurality of organic EL elements whose emission colors change according to the applied current value;
A drive circuit for supplying a drive waveform to each organic EL element;
Depending on the desired emission color, at least one of the current value and lighting rate of the drive waveform in the drive circuit is varied for each organic EL element, and the emission color associated with the temperature change of each organic EL element Control means having a correction function of correcting at least one of the current value and the lighting rate of the driving waveform applied in accordance with the drift of each of the organic EL elements.

  The system includes an association information acquisition unit that acquires association information that is associated with a drift of a light emission color associated with a temperature change of each organic EL element, and the control unit is configured based on the association information from the association information acquisition unit. It is characterized in that at least one of the drive waveform current value and the lighting rate is corrected.

  The association information acquisition means includes at least one of a driving voltage of each organic EL element, a light amount of each organic EL element or another organic EL element having the same structure as each organic EL element, or an ambient temperature as the association information. It is characterized by acquiring.

  Each of the organic EL elements has a plurality of light emitting layers having different emission colors.

In order to solve the above problems, the light-emitting device of the present invention includes a plurality of organic EL elements whose emission colors change according to the applied current value;
A drive circuit for supplying a drive waveform to each organic EL element;
Depending on the desired emission color, at least one of the current value and the lighting rate of the drive waveform in the drive circuit is varied for each organic EL element, and the emission color associated with the deterioration of each organic EL element over time Control means having a correction function of correcting at least one of the current value and the lighting rate of the driving waveform applied in accordance with the drift of each of the organic EL elements.

  And an association information acquisition unit that acquires association information that is associated with a drift in emission color associated with the deterioration of each organic EL element over time, and the control unit drives the drive based on association information from the association information acquisition unit. It is characterized in that at least one of the waveform current value and the lighting rate is corrected.

  The association information acquisition means includes, as the association information, at least a driving voltage of each organic EL element, a light amount of each organic EL element or another organic EL element having the same structure as each organic EL element, or a light emission integration time. Get one.

  Each of the organic EL elements has a plurality of light emitting layers having different emission colors.

In order to solve the above-mentioned problem, the present invention is a method for driving a plurality of organic EL elements in which the emission color changes according to the applied current value,
Depending on the desired emission color, at least one of the current value and the lighting rate of the drive waveform applied to each organic EL element is varied for each organic EL element, and the temperature change of each organic EL element It is characterized in that at least one of the current value and the lighting rate of the drive waveform applied in accordance with the accompanying emission color drift is corrected for each organic EL element.

  Acquiring association information associated with a drift in emission color associated with a temperature change of each organic EL element, and correcting at least one of a current value and a lighting rate of the drive waveform based on the association information. And

  As the association information, at least one of a driving voltage of each organic EL element, a light amount of each organic EL element or another organic EL element having the same structure as each organic EL element, or an ambient temperature is acquired. And

In order to solve the above-mentioned problem, the present invention is a method for driving a plurality of organic EL elements in which the emission color changes according to the applied current value,
Depending on the desired emission color, at least one of the current value and the lighting rate of the drive waveform applied to each organic EL element is varied for each organic EL element, and the deterioration of each organic EL element over time It is characterized in that at least one of the current value and the lighting rate of the drive waveform applied in accordance with the accompanying emission color drift is corrected for each organic EL element.

  Acquiring association information associated with a drift in emission color associated with deterioration of each organic EL element with time, and correcting at least one of a current value and a lighting rate of the drive waveform based on the association information. And

  As the association information, obtaining at least one of a driving voltage of each organic EL element, a light amount of each organic EL element or another organic EL element having the same structure as each organic EL element, or a light emission integration time. Features.

In order to solve the above problems, the light-emitting device of the present invention includes a plurality of organic EL elements whose emission colors change according to the applied current value;
A drive circuit for supplying a drive waveform to each organic EL element;
And control means for varying at least one of the current value and the lighting rate of the drive waveform in the drive circuit for each organic EL element according to a desired emission color.

In order to solve the above-mentioned problem, the present invention is a method for driving a plurality of organic EL elements in which the emission color changes according to the applied current value,
It is characterized in that at least one of the current value and the lighting rate of the drive waveform applied to each organic EL element is varied according to the desired emission color.

  The present invention enables highly stable color variable control.

The figure which shows the electrical constitution of the illuminating device which is embodiment of this invention. The schematic diagram which shows the organic EL element used for an illuminating device same as the above. The figure which shows the drive waveform applied to an organic EL element same as the above. FIG. 3 is a diagram illustrating a relationship between a color temperature and a driving voltage in Embodiment 1. FIG. 3 is a diagram illustrating a relationship between a color temperature and a current value in Example 1. FIG. 4 is a diagram illustrating a relationship between a change amount of a light beam and a change amount of a drive voltage in the first embodiment. The figure which shows the relationship between the light beam in Example 1, and the electric current value at the time of lighting rate 100%. The figure which shows the relationship between the electric current value used as the initial light beam value in Example 1, and a lighting rate. FIG. 6 is a graph showing deterioration with time of color temperature in Example 2. FIG. 6 is a diagram showing deterioration of light flux with time in Example 2. The figure which shows the relationship between the color temperature of an organic EL element used for an illuminating device same as the above, and element junction temperature. FIG. 10 is a diagram illustrating a relationship between a change amount of a driving voltage and an element junction temperature in Example 5. The figure which shows the relationship between the light beam and element junction temperature in Example 6. FIG.

  Hereinafter, an embodiment in which a light emitting device and an organic EL element driving method of the present invention are applied to a lighting device will be described with reference to the accompanying drawings.

  FIG. 1 is a diagram showing an electrical configuration of a lighting apparatus 100 according to an embodiment of the present invention. The illuminating device 100 includes a plurality of organic EL panels 10 each having an organic EL element, which will be described later, as a light emitting unit, and a drive circuit 20 for applying a drive waveform to the organic EL panel 10. The lighting device 100 also acquires a control unit 30 that controls the drive circuit 20, an operation unit 40 that performs an input operation to the control unit 30, and association information acquisition that acquires association information described later and inputs the association information to the control unit 30. Means 50.

  FIG. 2 is a diagram illustrating an organic EL element 10 </ b> A provided in the organic EL panel 10. The organic EL element 10A is formed by laminating a first electrode 12 serving as an anode, an organic layer 13, and a second electrode 14 serving as a cathode on a support substrate 11. The organic EL element 10A is sealed by disposing a sealing substrate to which a hygroscopic agent is applied on the support substrate 11, but this sealing substrate is omitted in FIG.

  The support substrate 11 is a rectangular substrate made of translucent non-alkali glass, for example. Other glass substrates such as alkali glass may be used, and the glass thickness is not particularly limited. On the support substrate 11, the 1st electrode 12, the organic layer 13, and the 2nd electrode 14 are laminated | stacked in order.

The first electrode 12 serves as an anode for injecting holes, and a transparent conductive material such as ITO or AZO is formed on the support substrate 11 with a film thickness of 50 to 500 nm by means such as sputtering or vacuum deposition. And patterned into a predetermined shape by means such as photoetching. The surface of the first electrode 12 is subjected to a surface treatment such as UV / O ₃ treatment or plasma treatment. Note that the peripheral region of the support substrate 11 including the edge of the first electrode 12 is covered with an insulating film (not shown) made of, for example, a polyimide-based insulating material to define the shape of the light emitting portion and prevent a short circuit or the like.

  The organic layer 13 is a multilayer including at least a light emitting layer made of an organic material, and is formed on the first electrode 12. In the present embodiment, the hole injection layer 13a, the hole transport layer 13b, the first light emitting layer 13c, the second light emitting layer 13d, and the electron transport layer 13e are sequentially stacked from the first electrode 12 side. .

  The hole injection layer 13a has a function of taking holes from the first electrode 12, and for example, a hole transporting organic material such as an amine-based compound is formed in a layer shape having a film thickness of about 20 to 120 nm by means such as vapor deposition. Do it.

  The hole transport layer 13b has a function of transmitting holes to the first light-emitting layer 13c. For example, a hole transporting organic material such as an amine compound is about 20 to 40 nm thick by means such as vapor deposition. It is formed in layers.

The first light-emitting layer 13c is a mixed layer having a film thickness of 20 to 60 nm in which a first host material having electron transport property, a hole-transport material, and a first light-emitting dopant exhibiting light emission are mixed by means such as co-evaporation. Consists of.
The first host material can transport holes and electrons, and has a function of causing the first light-emitting dopant to emit light by recombination of holes and electrons in the molecule. Here, the electron transporting host material is an organic material having a relatively high electron transport capability, and specifically refers to a material having a high electron mobility μe and a low hole mobility μh. Specifically, for example, an anthracene derivative is used. As the hole transporting material, for example, the same material as the hole transporting layer 13b is used, but a different material may be used.
The first light-emitting dopant is made of an organic material having a function of emitting light in response to recombination of holes and electrons and exhibiting a predetermined emission color. In this embodiment, for example, a fluorescent material made of styrylamine or an amine-substituted styrylamine compound that emits blue-green light is used in a doping amount that does not cause concentration quenching.

The second light-emitting layer 13d is a mixed layer having a film thickness of 20 to 60 nm obtained by mixing an electron-transporting second host material, a hole-transporting material, and a second light-emitting dopant exhibiting light emission by means such as co-evaporation. Consists of.
The second host material can transport holes and electrons, and has a function of causing the second light-emitting dopant to emit light by recombination of holes and electrons in the molecule. Here, the electron transporting host material is an organic material having a relatively high electron transport capability, and specifically refers to a material having a high electron mobility μe and a low hole mobility μh. Specifically, it consists of an anthracene derivative, for example. As the hole transporting material, for example, the same material as the hole transporting layer 13b is used, but a different material may be used.
The second light-emitting dopant has a function of emitting light in response to recombination of holes and electrons, and is made of an organic material that exhibits a predetermined emission color different from the first light-emitting dopant. In this embodiment, for example, a fluorescent material having a fluoranthene skeleton or a pentacene skeleton that emits orange light is used at a doping amount that does not cause concentration quenching. As the first and second light-emitting dopants, a phosphorescent material or a thermally delayed fluorescent material may be used in addition to the fluorescent material. Moreover, you may reverse the luminescent color of the 1st light emitting layer 13c and the 2nd light emitting layer 13d.

  The electron transport layer 13e has a function of transmitting electrons to the second light-emitting layer 13d, and is composed of a mixed layer having a thickness of 20 to 60 nm in which a triazine derivative and an alkali metal complex are mixed by means such as co-evaporation.

  The second electrode 14 serves as a cathode for injecting electrons. On the electron transport layer 13e, for example, Al, magnesium (Mg), cobalt (Co), Li, gold (Au), copper (Cu), zinc ( It is made of a conductive film in which a low-resistance conductive material such as Zn) is formed into a layer having a thickness of 20 to 300 nm by means such as sputtering or vacuum deposition.

  As described above, the organic EL element 10A that emits light in a predetermined emission color when a voltage is applied between the first electrode 12 and the second electrode 14 is configured. It should be noted that well-known contents such as routing wires and terminals connected to the first electrode 12 or the second electrode 14 are omitted as appropriate in order to simplify the description.

  The drive circuit 20 is disposed between the variable current circuit 21 and the organic EL element 10A, which is connected to the power source Vcc and varies the current peak value I of the drive waveform P supplied to the organic EL element 10A. It has a switch circuit 22 having a plurality of switch elements for switching on / off of current supply to the organic EL element 10A, and a drive circuit 23 for controlling on / off of each switch element of the switch circuit 22. Further, the drive circuit 20 generates a rectangular wave shown in FIG. In FIG. 1, the drive circuit 20 is shown as a single circuit, but a separate drive circuit may be provided for each of the organic EL panels 10.

The control means 30 is mainly composed of a microcomputer, and controls the light emission of the organic EL element 10A by switching the switch circuit 22 on and off in accordance with the operation means 40 and other external inputs. . Further, the control unit 30 acquires correction data of the current peak value I from the storage unit 31 including a storage element such as an E ² PROM or a flash memory in accordance with the association information input from the association information acquisition unit 50, and the organic EL It has a correction function to be described later for correcting the current peak value I supplied to the element 10A for each organic EL element 10A.

  The operation means 40 includes a push button switch and a volume switch, and is a means for arbitrarily selecting ON / OFF of light emission of the organic EL element 10A, light emission luminance, and light emission color.

  The association information acquisition means 50 is associated with the drift (deviation) of the emission color accompanying the temperature change of each organic EL element 10A, that is, the color deviation with respect to the desired emission color when varied, or each organic EL This is means for acquiring association information associated with the drift of the emission color associated with the deterioration of the element 10A with time. In the present embodiment, it is associated with the drift of the emission color associated with the temperature change of each organic EL element 10A. The association information includes the drive voltage of each organic EL element 10A, the light flux (light quantity) of each organic EL element 10A or another organic EL element having the same structure as each organic EL element 10A, or the ambient temperature of each organic EL element 10A. At least one of them is obtained, and as the association information associated with the drift of the emission color associated with the deterioration with time of the organic EL element 10A, the driving power of each organic EL element 10A is obtained. , Obtaining at least one of the light emitting accumulation time of each organic EL element 10A or the light beam (light quantity) or the organic EL element 10A other organic EL elements each organic EL element 10A and the structure is similar.

  The illuminating device 100 is comprised by the above each part. The lighting device 100 is an aggregate of organic EL panels in which a plurality of organic EL panels 10 are arranged adjacent to each other, that is, a light emitting cluster.

  Next, a color variable control method in the driving method of the organic EL element 10A will be described.

  The organic EL element 10A in the present embodiment mainly includes the concentration of the hole transporting material in the first light emitting layer 13c on the first electrode 12 side and the hole in the second light emitting layer 13d on the second electrode 14 side. By making the concentration of the transporting material equal, the device structure is such that the recombination region of holes and electrons, that is, the light emitting region is easily moved by the carrier balance of hole injection transport and electron injection transport. , 14 moves between the light emitting regions according to the current density injected between them, so that the balance of the color mixture changes and the light emission color can be changed intentionally. In the organic EL element 10A of the present embodiment having the first light emitting layer 13c exhibiting blue-green light emission and the second light emitting layer 13d exhibiting orange light emission, when the current density is relatively low, holes and The recombination region of electrons moves to the hole transport layer 13b side, and a bluish cold-colored white light emission having a color temperature of about 6000 K is obtained. When the current density is increased, the recombination region of holes and electrons becomes an electron. It moves to the transport layer 13e side and becomes an orangeish warm white with a color temperature of about 3500K. Light with a color temperature of about 6000K is suitable for concentrating on work such as work and study, and light with a color temperature of about 3500K is a calm light with a sense of comfort compared to cold-colored light. It is. Note that this color temperature is merely an example, and the change range of the color temperature obtained by the color-variable organic EL element 10A in this embodiment is a color temperature from blue green to orange depending on the element structure and current density. The feeling can be selected arbitrarily widely.

  Therefore, the emission color is varied by varying the current peak value I of the drive waveform P applied to the organic EL element 10A shown in FIG. 3 in accordance with the operation input of the operation means 40. In this embodiment, since the drive waveform P is variable for each organic EL element 10A, if the operation means 40 is provided with a volume switch or the like corresponding to each organic EL element 10A, the organic EL panel 10 is respectively set. It is also possible to control the emission with different emission colors. Note that if only the current peak value I is varied, the luminous flux (brightness) also changes accordingly. Therefore, in order to make the luminous flux constant, the lighting rate (the light emission time in a predetermined frame time, that is, the current wave) is determined according to the current peak value I. It is necessary to adjust the ratio of the application time of the high value I) T.

  Next, among the correction methods in the present embodiment, a correction method for correcting the drift of the emission color accompanying the deterioration with time will be described.

In general, the organic EL element is continuously driven to deteriorate the constituent material. Therefore, in the color-variable organic EL element 10A, the color temperature of the emitted color drifts with the deterioration with time due to the continuous driving. Similarly, in the organic EL element 10A, the luminous flux decreases with time deterioration, and the drive voltage rises in inverse proportion (that is, a voltage drop occurs). Further, in the light emitting cluster in which a plurality of organic EL panels 10 are arranged as in the present embodiment, one organic EL panel 10 is replaced due to a failure or the like, or the organic EL panels 10 having different production lots are in one light emitting cluster. Therefore, a difference occurs between the organic EL panels 10 in the above-described drift of the emission color and the progress of the decrease of the luminous flux, which may be recognized as color unevenness. As a result of intensive studies, the inventors of the present application have focused attention on the association information correlated with the drift of the emission color accompanying the deterioration with time, and based on this association information, the current peak value I of the drive waveform P supplied to the organic EL element 10A and The present inventors have found a method of appropriately correcting the lighting rate T for each organic EL element 10A.

Example 1
(Correction method to obtain drive voltage as association information)
Hereinafter, a method for correcting the color temperature by monitoring the drive voltage of each organic EL element 10A will be described.
In this embodiment, separate drive circuits 20 for each organic EL panel 10 were prepared. A single drive circuit 20 may be used as long as the drive voltage of each organic EL element 10A can be monitored.
In correcting the color temperature and the luminous flux by the driving method, a current correction value that compensates for deterioration characteristics associated with the continuous driving of the organic EL element 10A is written in the storage unit 31 in advance, and each driving voltage is monitored to Trial calculation and correction of temperature drift were made possible. In addition, when there is a variation in characteristics caused by the manufacturing lot among the plurality of organic EL elements 10A, it is desirable to individually write correction values according to their own deterioration characteristics.
In this embodiment, the drive voltage monitor is provided in the control means 30 as a part of the protection function for stopping the operation when the organic EL panel 10 is short-circuited or poorly connected, and immediately after the drive circuit 20 is turned on. Therefore, it is created so that a current necessary for light emission is applied after monitoring every frame frequency and confirming that it is in a normal state. Therefore, it has been easily achieved to correct the color temperature by monitoring the drive voltage as in this embodiment.

The control means 30 calculates the difference from the initial voltage value, that is, the drive voltage value at the desired color temperature, from the result of measuring each drive voltage after power-on.
Next, a current correction value necessary for correcting the color temperature change amount derived from the difference is calculated.
Here, the luminous flux is determined from the current value and the output setting lighting rate, but when the current value is changed, the amount of change in luminous flux that rises or falls due to the difference in luminous efficiency with respect to the current value is estimated, The lighting rate difference is estimated from the change.
The color temperature is corrected by correcting the current peak value I based on the current correction value, and the light flux drift (deviation) can also be corrected by correcting the lighting rate T by applying the lighting rate difference. did. Therefore, by applying the present embodiment, it is possible to correct the color temperature drifted by continuous driving by lighting, and the color temperature drift is not visually recognized. Further, the correction of the current peak value I and the lighting rate T is performed for each organic EL element 10A. Therefore, even when there is a difference in the drift of the emission color between the organic EL panels 10, it is possible to suppress the occurrence of color unevenness.

In this embodiment, 5 × 5 organic EL panels 10 of variable color temperature type in which the outer size is 150 mm × 25 mm, the light emission area is 31 cm ² , the initial luminous flux is 30 lm, and the variable width of the color temperature is changed from 3500K to 6000K are arranged. The luminescent cluster was made.
FIG. 4 shows the relationship between the color temperature and the drive voltage when the change range of the color temperature is changed from 3700K to 6300K in the initial state and continuous driving. FIG. 5 shows the relationship between the color temperature and the current value when the change range of the color temperature is changed from 3700K to 6300K in the initial state and continuous driving. As shown in FIG. 4, for example, the driving voltage at a color temperature of 4000 K in the initial state is shifted from 8.2 V to 8.5 V by continuous driving. In association with this, light emission at a color temperature of 4000 K is obtained as shown in FIG. Current value changes from 1.9 A to 2.7 A. This indicates that the obtained color temperature drifts when the current value is kept at the initial value. Therefore, in the setting for obtaining the color temperature of 4000 K, the color temperature drift is corrected by changing the current peak value I of the drive waveform P to 2.7 A by the correction method of this embodiment.
In addition, from the relationship between the change amount of the light beam and the change amount of the drive voltage shown in FIG. 6, the change amount of the light beam expected from the shift of the drive voltage is known in advance as shown in FIG. The luminous flux at the lighting rate of 100% obtained when the change is made is known, and the relationship between the current peak value I and the lighting rate T, which is the initial luminous flux value (30 lm) calculated from the figure, is shown in consideration of the drift of the luminous flux. By making a trial calculation as shown in FIG. 8, the light flux value drift was also corrected by correcting the lighting rate T. In this embodiment, when the luminous flux is reduced to 75% with respect to the initial lighting ratio of 21% at the color temperature of 4000K, the lighting ratio T is corrected to 16% to obtain the initial luminous flux value.
As a confirmation, when the relationship between the luminous flux value and the color temperature at the lighting rate of 100% is obtained from FIGS. 5 and 7, the luminous flux value at the lighting rate of 100% at the color temperature of 4000K is from 148 lm in the initial state. After the correction of the current peak value I, it becomes 162 lm, and it can be seen that the initial luminous flux value of 30 lm can be obtained by changing the lighting rate from 21% to 16%.
Such correction is easily performed by registering the relationship between the luminous flux value and the lighting rate in the storage unit 31. FIG. 6 shows the relationship between the amount of change in luminous flux and the amount of change in drive voltage. FIG. 7 shows the relationship between the initial state, the state in which the light beam has deteriorated to 90% of the initial state, and the state in which the light beam has deteriorated to 75% of the initial state, and the current value at a lighting rate of 100%. FIG. 8 shows the relationship between the lighting value and the current value that is the initial light flux value in the initial state, the state where the light flux is degraded to 90% of the initial state, and the state where the light flux is degraded to 75% of the initial state.
By performing the same correction for each organic EL panel 10, color unevenness was not recognized in this example having a total of 25 organic EL panels 10.
In the above description, light emission driving at a color temperature of 4000 K is taken as an example, but it is clear that the drift of the color temperature can be corrected by performing the same correction at any position in the variable range of the color temperature. .

In this embodiment, the driving voltage associated with light emission is high on the high current density side where the color temperature is warm, and the driving voltage is low on the low current density side where the color temperature is cold. When the voltage difference in the correction area is large, depending on the resolution at which the color temperature drift is corrected, a high resolution of the drive voltage difference is required, and the amount of data to be stored increases. ,Caution must be taken.
Further, the present embodiment only shows correction for one color temperature setting value of the color temperature variable width, but when changing another color temperature, for example, the color temperature, the color temperature is changed by a switching volume or the like. The lighting device 100 is formed and the setting of the color temperature is determined to be, for example, 10 steps or 128 steps. However, it is necessary to store and calculate the correction data according to the number of change steps of the color temperature. Therefore, when the number of stages is large, it is necessary to provide the drive circuit 20 and the control means 30 that can hold a large amount of data.
Further, these trial calculations can be easily made with a microcomputer as the control means 30. In the present invention, since these are calculated for each frame frequency immediately after the drive circuit 20 is turned on, the lighting device 100 always receives the color temperature feedback. .
The above correction is premised on the specification that the plurality of organic EL panels 10 always emit light at the same color temperature. In the specification in which the color temperature of each organic EL panel 10 is individually changed, correction is made for the set current value at the color temperature selected for each organic EL panel 10.
In addition, the trial calculation method and procedure of the change amount of the color temperature and the current correction value are not limited to the present embodiment. In particular, the characteristic data of the organic EL element 10A with variable color temperature, the performance of the drive circuit 20 and the control means 30, the trial resolution, and the like should be changed as appropriate.

Example 2
(Correction method to acquire luminous flux as association information)
Next, as a second embodiment, a method for correcting color temperature drift by monitoring a light beam will be described.
Using the light-emitting clusters created by the same method as in Example 1, each organic EL panel is composed of a 1 mm × 1 mm test element (other organic EL elements) created by the same method as the organic EL element 10A. Are arranged on each circuit board constituting the drive circuit 20 corresponding to the above, and photodiodes are arranged so that light beams emitted from the respective test elements can be directly monitored. In this embodiment, the means for monitoring the luminous flux is arranged on the circuit board. However, a test element and a photodiode serving as the means may be arranged outside the circuit board, or the display frame of each organic EL panel 10 may be arranged. A further organic EL element may be formed on the outside as a test element with a size of, for example, about 1 mm × 1 mm, and a photodiode may be installed so that light from the element can be directly monitored. In that case, it is desirable that the organic EL panel 10 takes the form of a module, has a shape that hides the frame of the organic EL panel 10, and further has a structure in which the photodiode and the test element for detecting the light beam cannot be seen. In the present embodiment, the test element provided separately is configured to measure the luminous flux with a photodiode. However, a photodiode may be installed so as to monitor a part of the organic EL element 10A constituting the light emitting unit. You may install so that the light which is not the light emission part radiate | emitted from the edge part of the cut surface of the support substrate 11 may be monitored. Furthermore, another color temperature variable type organic EL panel having the same characteristics is installed on the back surface of each organic EL panel 10, or another color temperature variable type organic EL panel made smaller than that, and each panel is installed. May be monitored.

Next, a method for correcting the color temperature based on the light flux monitored as described above will be described.
As in the first embodiment, a current correction value associated with the deterioration characteristics of the organic EL element 10A is written in the storage unit 31, and each light flux from the start of light emission is monitored and input to the control means 30.
Next, the control means 30 calculates or writes in advance the light flux value before the drift occurs from the set current value output to each organic EL panel 10 and the lighting rate, or writes it in the storage unit 31 in advance. Each difference is estimated.
Next, the amount of change in the drive voltage is calculated from each difference. As shown in FIG. 6, the organic EL element generally has a linear relationship between the deterioration characteristic of the luminous flux and the amount of change in the drive voltage, and the same tendency is shown in the color variable organic EL element 10A of the present invention.
When the amount of change in each drive voltage is calculated, the amount of change in color temperature is calculated in the same manner as in the first embodiment.
Next, a correction current value for correcting the change amount of each color temperature is calculated. When each correction current value is estimated, a lighting rate T for correcting a difference in luminous flux value from the set lighting rate is calculated on the assumption that the correction current value is applied.
By applying the current peak value I calculated for each organic EL element 10A and the lighting rate T to the corresponding organic EL element 10A, the drifted color temperature is corrected in the same manner as in Example 1, and the color temperature changes. Is not visible.
It should be noted that feedback may be applied by measuring each luminous flux after color temperature correction and re-correcting the lighting rate T when each luminous flux value deviates from a desired value.
In this embodiment, a photodiode is used for measuring each light beam. However, a CCD, CMOS, photomultiplier, or the like may be used. Also, spectroscopy is performed using this, the amount of change in color temperature is measured from the emission spectrum, and the current peak value I and the lighting rate T applied to each organic EL element 10A are corrected by the same method as described above. It doesn't matter. In this case, however, a burden is imposed on the microcomputer as the control means 30, so that a trial calculation is delayed or a delay for feedback occurs, and a change in color temperature due to correction may be visually recognized. In addition, since the size is increased, this method is suitable when the large organic EL panel 10 is used. However, the frame is too large in the small organic EL panel 10, so that it is separated from the organic EL panel 10. The lighting device 100 is configured to prepare a test element or another different color temperature variable organic EL panel at a location, measure the amount of change in color temperature, transfer it to the control means 30, and correct the drive. Is desirable.
It is obvious that the color temperature drifting with continuous driving of the color temperature variable type organic EL panel 10 can be similarly corrected also in this embodiment. Further, the correction of the current peak value I and the lighting rate T is performed for each organic EL element 10A. Therefore, even when there is a difference in the emission color drift between the organic EL panels 10, color unevenness was not recognized.
As another correction example, each light beam is measured, and the amount of change of each light beam due to continuous driving is estimated. Next, the amount of change in color temperature is calculated from the relationship between the amount of change in each luminous flux and the color temperature, the current correction value for correcting the amount of change in each color temperature is calculated, and the lighting rate when each current value is corrected The lighting rate may be calculated from the calculation of the luminous flux value at 100%, and the color temperature and the luminous flux value may be corrected.
Further, when the color temperature drift and the light flux drift have a linear relationship due to the characteristics of the organic EL element 10A, each current value for making the light flux the same value as the initial value is estimated from the measurement of each light flux, Correction of the color temperature may be compensated by correcting each lighting rate, and there are other methods for calculating the color temperature change amount and the current correction value, but the calculation method and procedure are limited to this embodiment. It is not a thing. In particular, it should be changed according to the characteristics of the organic EL element 10A with variable color temperature, experimental data, the performance of the drive circuit 20 and the control means 30, the trial resolution, and the like.
Although it is the same as in the first embodiment, it is desirable that these are estimated and data are stored according to the number of steps of the color temperature change in the color temperature variable width.

Example 3
(Correction method to obtain the accumulated light emission time as association information)
Next, as Example 3, an example in which the color temperature drift is corrected by monitoring the accumulated light emission time of each organic EL element 10A will be described. In this example, the same light emission cluster as in Example 1 was used.
First, a current correction value associated with the deterioration characteristics of the organic EL element 10A due to continuous driving is written in the storage unit 31 in advance.
The accumulated light emission time can be estimated by integrating with the lighting rate set within a frame frequency that is a constant period, and the accumulated light emission time calculated by this method is stored in the storage unit 31. It is also possible to prepare an analog counter or the like outside and record the accumulated light emission time using them.
The control means 30 first calculates each light emission integration time, and calculates the amount of change in the color temperature that drifts in each light emission integration time. Similarly, the amount of change in the luminous flux drifting in each light emission integration time is estimated. This is obtained from the relationship between the color temperature and the continuous driving time obtained from the life test conducted in advance as shown in FIGS. 9 and 10, and from the relationship between the luminous flux and the continuous driving time. The amount of change and the current correction value corresponding to the change amount are recorded in the storage unit 31 and are derived based on each light emission integration time. FIG. 9 shows the color temperature when the initial emission color temperature is 3500 K and the drive current value is 4.7 A, and when the initial emission color temperature is 6000 K and the drive current value is 0.5 A. The relationship between the amount of change and the continuous drive time is shown. FIG. 10 shows the relationship between the amount of change in luminous flux and the continuous drive time.
Next, the current peak value I for correcting the change amount of each color temperature is derived, and the difference between the luminous flux obtained from each current peak value I and the change amount of the luminous flux is corrected by changing the lighting rate T. .
In this embodiment, it is obvious that the color temperature drifting with continuous driving can be corrected as in the other embodiments. Further, the correction of the current peak value I and the lighting rate T is performed for each organic EL element 10A. Therefore, even when there is a difference in the emission color drift between the organic EL panels 10, color unevenness was not recognized.
In this embodiment, the correction current value is taken in the storage unit 31 in advance, but the initial value of each drive voltage is read when the power is turned on. For example, the method shown in Embodiment 1 is used in combination, A current value for correcting the color temperature may be estimated from a change in the driving voltage. As can be seen from FIGS. 6 and 10, the light emission integration time and the amount of change in the drive voltage show a substantially straight line result, which is easy to derive.
Furthermore, the luminous flux shown in the second embodiment is measured, and the light emission integration time shown in this embodiment is monitored, and the amount of change in color temperature is predicted from the relationship between the light flux reduction rate and the light emission integration time, and the current to be corrected is corrected. The value may be determined.
In particular, depending on the characteristics of the organic EL element 10A having a variable color temperature, the trial calculation method is not limited to this method, and the change amount of the color temperature shown in the first, second, and third embodiments is detected and corrected. This method may be used in combination.

Example 4
(Addition of a light emitting layer that emits green light)
Next, an example will be described in which a green third light-emitting layer is further provided on each organic EL element 10A shown in the above embodiment. In Examples 1 to 3, the first and second light emitting layers 13c and 13d that emit blue-green and orange light were stacked, and the organic EL element 10A having a variable color temperature that changed from 3500K to 6000K was created. As a light source in lighting applications, it is desirable that the color rendering index be 80 or more, and it is desirable to emit light having an emission spectrum over the entire visible light region. Therefore, in this embodiment, by adding a third light emitting layer that emits green light in a wavelength range of about 500 to 600 nm between the second light emitting layer 13d and the electron transport layer 13e, light emission over the entire visible light range is achieved. An organic EL element 10A having a variable color temperature and having a spectrum was formed.
The third light-emitting layer is formed in a layer shape having a film thickness of 10 to 40 nm by doping a third host material having electron transport property, a hole transport material, and a third light-emitting dopant by a method such as a co-evaporation method. It becomes.
In the third host material, holes and electrons are transported and recombined to form excitons, and energy is transferred to the light emitting dopant to cause the light emitting dopant to emit light. The third host material is made of an anthracene derivative, for example. As the hole transporting material, for example, the same material as the hole transporting layer 13b is used, but a different material may be used.
The third light-emitting dopant is a fluorescent material made of, for example, a coumarin derivative and emits green light. The doping amount of the third light emitting dopant is set so as not to cause concentration quenching. The third light-emitting dopant may be a phosphorescent material or a thermally delayed fluorescent material.
In this example, the blue first light emitting layer 13c, the orange second light emitting layer 13d, and the green third light emitting layer were formed in this order, but the orange light emitting layer, the blue light emitting layer, and the green light emitting layer It may be formed by changing the arrangement position.
Also in the organic EL element 10A having a variable color temperature of this example, the color temperature could be changed from about 3000K to about 5000K by changing the current peak value I applied during driving. Furthermore, the color rendering index was 82.
In addition, if the color temperature correction method according to the first to third embodiments is applied to a light emitting cluster in which a plurality of organic EL panels having the organic EL elements 10A of the present embodiment are arranged, the color temperature is corrected and the lighting rate is corrected. Obviously, the luminous flux can be similarly corrected.

  Next, among the correction methods in the present embodiment, a correction method for correcting the drift of the emission color accompanying the temperature change will be described.

In general, an organic EL element has temperature characteristics, and it is known that, for example, light emission efficiency and color temperature change as the temperature rises. Also in the organic EL element 10A with variable color temperature of this embodiment, as shown in FIG. 11, the luminous efficiency and the color temperature are changed by changing the environmental temperature and the junction temperature (junction temperature) Tj of the organic EL element 10A due to self-heating. The color temperature decreases and the luminous flux increases as the temperature rises. FIG. 11 shows the relationship between the color temperature and the junction temperature Tj when the junction temperature Tj is 25 ° C. and the color temperature of the emitted color is 6000K. Therefore, for example, when there is a temperature difference between the organic EL panels 10 in the light emitting cluster, for example, when the environmental temperature is low at the entrance / exit side of the light emitting cluster arranged on the ceiling and the environmental temperature is high in the center of the room, the organic EL panel 10 Each time the color temperature changes, there is a risk of being recognized as color unevenness. As a result of intensive studies, the inventors of the present application pay attention to the association information correlated with the drift of the emission color accompanying this temperature change, and based on this association information, the current wave height I of the drive waveform P applied to each organic EL element 10A. And a method of appropriately correcting the lighting rate T.

Example 5
(Correction method to obtain drive voltage as association information)
Hereinafter, a method for correcting the color temperature by monitoring the driving voltage of each organic EL element 10A will be described. In this example, the same light emission cluster as in Example 1 was used.
Next, the temperature measurement used in this example will be described.
In general, as a characteristic of the organic EL element, the driving voltage of the element tends to decrease as the junction temperature Tj of the element increases without being saturated below the glass transition temperature which is the heat resistant limit temperature of the element. The same applies to the organic EL element 10A with variable color temperature according to the present embodiment, and the drive voltage changes according to the increase or decrease of the junction temperature Tj as shown in FIG. FIG. 12 shows the relationship between the change amount of the drive voltage and the junction temperature Tj.
In this example, the same method as that described in Example 1 was used, and the environmental temperature and the junction temperature Tj accompanying self-heating were increased and decreased by monitoring the driving voltage of each organic EL element 10A.
The control means 30 monitors the amount of change associated with the temperature change of each drive voltage, and estimates the amount of change in the junction temperature Tj associated therewith from the relationship shown in FIG. Next, from the relationship shown in FIG. 11, the amount of change in color temperature accompanying the amount of change in each junction temperature Tj is estimated.
After that, as shown in the first embodiment, the current correction value for correcting the change amount of each color temperature is calculated, and the change amount of the light flux associated therewith is calculated. At this time, if the light emission efficiency of each organic EL element 10A changes, a light flux trial value obtained by multiplying it may be prepared.
As can be seen from this example, it is clear that the color temperature drift can be easily corrected by the driving method by using this correction method for the color temperature drift due to the environmental temperature and the temperature change caused by self-heating. It is. Further, the correction of the current peak value I and the lighting rate T is performed for each organic EL element 10A. Therefore, even when a temperature difference occurs between the organic EL panels 10, color unevenness was not visually recognized.

Example 6
(Correction method to acquire luminous flux as association information)
Next, as a sixth embodiment, a method for correcting color temperature drift by monitoring a light beam will be described. In this example, the same light emission cluster as in Example 1 was used.
As described in Example 2, the detection of the luminous flux was monitored by creating a test element of 1 mm × 1 mm on the outermost periphery of each organic EL panel 10 and installing a photodiode on each test element. .
In addition, each test element and each photodiode are modularized so as to be hidden from the light emitting part, and light is not allowed to enter from the outside. Since each organic EL panel 10 for detecting a light beam created in the present embodiment directly monitors a light beam due to a temperature change of the panel, it can respond more sensitively to changes in the environmental temperature than a method of installing on a circuit board. is there.
Further, when the change in the environmental temperature does not change greatly, or when the drive circuit 20 is disposed near the organic EL panel 10, it is preferable to provide the test element and the photodiode on the circuit board. Further, as described in the second embodiment, a test element for detecting a light beam and a photodiode may be connected to the back surface of each organic EL panel 10.
As shown in FIG. 13, in the organic EL element 10 </ b> A in which the light emission efficiency changes due to the temperature change, the temperature change amount can be calculated from the light flux change amount. FIG. 13 shows the relationship between the luminous flux and the junction temperature Tj when the junction temperature Tj is 25 ° C. and the color temperature of the emitted color is 6000K.
As in the fifth embodiment, the control means 30 calculates the change amount of the color temperature accompanying each temperature change from the relationship shown in FIG. 11, and similarly calculates the current peak value I and the lighting rate T to be applied. By correcting each of them, it is possible to correct a color temperature drift accompanying a temperature change. Further, the correction of the current peak value I and the lighting rate T is performed for each organic EL element. Therefore, even when a temperature difference occurs between the organic EL panels, color unevenness was not visually recognized.
In addition, depending on the organic EL element 10A, there may be a reverse U-shaped characteristic in which the change in luminous efficiency has a peak value depending on the temperature. In that case, in order to determine which side, each drive voltage may be monitored to determine which side. As shown in FIG. 12, since the drive voltage does not exhibit an inverted U-shaped characteristic with respect to the temperature change, it is easy to determine the temperature and to estimate the amount of change in the color temperature due to the temperature change.
Further, after the color temperature is corrected, each light beam is measured again, and when each light beam value deviates from a desired value, the lighting rate T may be corrected again to provide further feedback.
Although a photodiode is used in this embodiment, a CCD, CMOS, photomultiplier, or the like may be used. In addition, if this is used to perform spectroscopy, and the emission spectrum of a specific wavelength has temperature characteristics, each emission spectrum is measured, and the amount of change in color temperature is directly measured. Thus, the current peak value I and the lighting rate T applied to each organic EL element 10A may be corrected. However, in this case, since a load is applied to the microcomputer as the control means 30, there is a case where a trial calculation is slow or a delay for feedback occurs, and a change in the color temperature due to the correction is visually recognized. In addition, since the size is increased, this method is suitable when using a large organic EL panel 10, but the frame size becomes too large for the small organic EL panel 10, so Prepare a test element and another different color temperature variable type organic EL panel at a remote location, measure the amount of change in color temperature with CCD, CMOS, photomal, etc., transfer to the control means 30, and correct the drive It is desirable to configure the lighting device 100 as described above.

-Example 7
(Correction method to obtain ambient temperature as related information)
Next, as Example 7, an example in which the color temperature drift is corrected by monitoring the ambient temperature of each organic EL element 10A (including the temperature of the organic EL element 10A itself, hereinafter the same) will be described. In this example, the same light emission cluster as in Example 1 was used.
The detection of the ambient temperature includes a method of measuring with the driving voltage described in the first and fifth embodiments, and a method of measuring the light beam described in the second and sixth embodiments. In that case, it is apparent from the above description that the color temperature is corrected.
In addition, thermistors and thermocouples can be monitored, for example, thermocouples are attached to each organic EL panel 10 and the temperature is measured to estimate the amount of change in temperature. Each amount of change in temperature is estimated, and then a current correction value for correcting the amount of change in each color temperature is calculated. When the correction of the current peak value I by each current correction value is determined, the color temperature can be corrected by a temperature change by correcting the lighting rate T in order to make the luminous flux a desired value. Further, the correction of the current peak value I and the lighting rate T is performed for each organic EL element. Therefore, even when a temperature difference occurs between the organic EL panels, color unevenness was not visually recognized.
When the temperature is measured by a thermistor or a thermocouple, the ambient temperature may be monitored by installing it inside or outside the circuit board of the drive circuit 20, for example, or the installation position of each organic EL panel 10 is determined from the circuit board. When installed in a place where the ambient temperature is likely to change, the junction temperature Tj of each organic EL element 10A may be connected to the back surface of each organic EL panel 10 and monitored for direct measurement.
Further, a material whose resistance is changed by heat, such as resistance heat measurement, may be provided in each organic EL panel 10 to monitor the temperature. In this case, if there is a margin in the drive voltage, the drive circuit 20 is driven from the organic EL panel 10 by mounting in parallel on the cathode (second electrode 14) line and the anode (first electrode 12) line of the organic EL element 10A. Temperature changes can be monitored without adding additional wiring.

  The above description exemplifies the present invention, and it goes without saying that various changes and modifications can be made without departing from the spirit of the present invention. In addition, the correction method of the emission color drift accompanying the deterioration over time and the correction method of the emission color drift accompanying the temperature change have been described separately.For example, the first correction is the correction of the emission color drift accompanying the deterioration over time, The correction of the emission color drift accompanying the temperature change may be executed in combination as the second correction. Further, the organic EL element used in the light emitting device of the present invention is not limited to the structure having a plurality of light emitting layers, and any single light emitting layer may be doped with two or more kinds of light emitting dopants as long as the color variable control can be performed by the current value. It may be what you did. Moreover, although the illuminating device 100 was mentioned as a light-emitting device in this embodiment, a display apparatus may be sufficient as others.

  The present invention is suitable for a light emitting device using a color variable organic EL element and a driving method of the color variable organic EL element.

DESCRIPTION OF SYMBOLS 100 Illuminating device 10 Organic EL panel 10A Organic EL element 11 Support substrate 12 1st electrode 13 Organic layer 13a Hole injection layer 13b Hole transport layer 13c 1st light emitting layer 13d 2nd light emitting layer 13e Electron transport layer 14 2nd Electrode 20 Drive circuit 21 Variable current circuit 22 Switch circuit 23 Drive circuit 30 Control means 31 Storage unit 40 Operation means 50 Association information acquisition means

Claims (16)

A plurality of organic EL elements whose emission color changes according to the applied current value;
A drive circuit for supplying a drive waveform to each organic EL element;
Depending on the desired emission color, at least one of the current value and lighting rate of the drive waveform in the drive circuit is varied for each organic EL element, and the emission color associated with the temperature change of each organic EL element And a control unit having a correction function for correcting at least one of the current value and the lighting rate of the drive waveform applied in accordance with the drift of each of the organic EL elements. . The system includes an association information acquisition unit that acquires association information that is associated with a drift of a light emission color associated with a temperature change of each organic EL element, and the control unit is configured based on the association information from the association information acquisition unit. The light emitting device according to claim 1, wherein at least one of a current value of a driving waveform and a lighting rate is corrected. The association information acquisition means includes at least one of a driving voltage of each organic EL element, a light amount of each organic EL element or another organic EL element having the same structure as each organic EL element, or an ambient temperature as the association information. The light emitting device according to claim 1, wherein the light emitting device is obtained. The light-emitting device according to claim 1, wherein each organic EL element has a plurality of light-emitting layers having different emission colors. A plurality of organic EL elements whose emission color changes according to the applied current value;
A drive circuit for supplying a drive waveform to each organic EL element;
Depending on the desired emission color, at least one of the current value and the lighting rate of the drive waveform in the drive circuit is varied for each organic EL element, and the emission color associated with the deterioration of each organic EL element over time And a control unit having a correction function for correcting at least one of the current value and the lighting rate of the drive waveform applied in accordance with the drift of each of the organic EL elements. . And an association information acquisition unit that acquires association information that is associated with a drift in emission color associated with the deterioration of each organic EL element over time, and the control unit drives the drive based on association information from the association information acquisition unit. 6. The light emitting device according to claim 5, wherein at least one of the waveform current value and the lighting rate is corrected. The association information acquisition means includes, as the association information, at least a driving voltage of each organic EL element, a light amount of each organic EL element or another organic EL element having the same structure as each organic EL element, or a light emission integration time. The light-emitting device according to claim 5, wherein either one is acquired. 6. The light emitting device according to claim 5, wherein each organic EL element has a plurality of light emitting layers having different emission colors. A driving method of a plurality of organic EL elements whose emission color changes according to a current value to be applied,
Depending on the desired emission color, at least one of the current value and the lighting rate of the drive waveform applied to each organic EL element is varied for each organic EL element, and the temperature change of each organic EL element A driving method of an organic EL element, wherein at least one of a current value and a lighting rate of the driving waveform applied according to the accompanying emission color drift is corrected for each of the organic EL elements. Acquiring association information associated with a drift in emission color associated with a temperature change of each organic EL element, and correcting at least one of a current value and a lighting rate of the drive waveform based on the association information. The method for driving an organic EL element according to claim 9. As the association information, at least one of a driving voltage of each organic EL element, a light amount of each organic EL element or another organic EL element having the same structure as each organic EL element, or an ambient temperature is acquired. The method for driving an organic EL element according to claim 9. A driving method of a plurality of organic EL elements whose emission color changes according to a current value to be applied,
Depending on the desired emission color, at least one of the current value and the lighting rate of the drive waveform applied to each organic EL element is varied for each organic EL element, and the deterioration of each organic EL element over time A driving method of an organic EL element, wherein at least one of a current value and a lighting rate of the driving waveform applied according to the accompanying emission color drift is corrected for each of the organic EL elements. Acquiring association information associated with a drift in emission color associated with deterioration of each organic EL element with time, and correcting at least one of a current value and a lighting rate of the drive waveform based on the association information. The method for driving an organic EL element according to claim 12. As the association information, obtaining at least one of a driving voltage of each organic EL element, a light amount of each organic EL element or another organic EL element having the same structure as each organic EL element, or a light emission integration time. The method of driving an organic EL element according to claim 12, wherein A plurality of organic EL elements whose emission color changes according to the applied current value;
A drive circuit for supplying a drive waveform to each organic EL element;
And a control means for varying at least one of the current value and the lighting rate of the drive waveform in the drive circuit in accordance with a desired light emission color for each of the organic EL elements. . A driving method of a plurality of organic EL elements whose emission color changes according to a current value to be applied,
A driving method of an organic EL element, wherein at least one of a current value of a driving waveform applied to each organic EL element and a lighting rate is varied according to a desired emission color.

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