Display device using light-emitting elements, and driving method therefor

Abstract

The present disclosure is applicable to the technical field related to display devices, and relates to a display device using, for example, light-emitting diodes (LEDs), and a driving method therefor. The present disclosure comprises: a wiring board on which a plurality of unit pixel areas are defined; a pixel portion including at least two sets of light-emitting elements installed in each unit pixel area to form a unit sub-pixel; and a driver that drives the pixel portion, wherein one set of light-emitting elements includes a red light-emitting element, a green light-emitting element, and a blue light-emitting element, and the driver simultaneously operates the at least two sets of light-emitting elements under a first condition and independently drives the at least two sets of light-emitting elements under a second condition.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a display device that is applicable to the technical field related to display devices and uses, for example, a light emitting diode (LED), and a method of driving the same.BACKGROUND ART

[0002] Recently, display devices having advantageous characteristics such as a thin profile or flexibility have been developed in the field of display technologies. Currently, the main types of commercially available displays are represented by liquid crystal displays (LCDs) and organic light emitting diode (OLED) displays.

[0003] Meanwhile, a light emitting diode (LED) is a well-known semiconductor light-emitting element that converts electric current into light. Commercialization of red LEDs using GaAsP compound semiconductors began in 1962, and thereafter, GaP:N-based green LEDs have also been adopted as light sources for display images in electronic devices, including information and communication equipment.

[0004] Such light emitting diodes (LEDs) have been employed in various applications, such as pixels of display devices or planar lighting.

[0005] The target luminance of outdoor high-luminance display devices, which are installed outdoors, varies depending on the time of day (daytime / nighttime). The difference in the target luminance is approximately tenfold. For example, during the day, a minimum luminance of 3,000 nits is required. In some cases, a luminance of up to 8,000 nits is required. However, during the night, a luminance in the range of 300 to 500 nits is required.

[0006] Outdoor display devices are primarily used for advertising purposes, and a key aspect of such display devices is to attract the attention of nearby individuals. During the day, it may be advantageous for the display devices to be visibly presented to pedestrians, drivers, or passersby with a high luminance (at least 3,000 nits).

[0007] Accordingly, the gradation level representation of display devices has been evaluated based on the maximum luminance, and gradation level representation at low luminance levels has not been considered important and has therefore not been the subject of evaluation.

[0008] However, since 2010, rapid technological advancements have led to increase in the installation of display devices for outdoor signage, which has caused light pollution during the night. As a result, nighttime luminance has been legally regulated by individual countries or municipalities.

[0009] With the implementation of such nighttime luminance regulations, gradation level representation at nighttime luminance levels (300 to 500 nits) has become necessary.

[0010] In particular, display devices employing light emitting diodes (LEDs) are required to implement gradation level representation using individual light-emitting elements. Accordingly, improvements that take this situation into account are needed.DISCLOSURE TECHNICAL PROBLEM

[0011] An aspect of the present disclosure is to provide a display device using light-emitting elements and a method of driving the same, which allow for precise design of gradation level representation even at a minimum luminance level (corresponding to approximately one-tenth of the maximum luminance), so that an image may be represented precisely and smoothly in a low gradation level range.

[0012] In addition, the present disclosure provides a display device using light-emitting elements and a method of driving the same, which enable precise gradation level representation not only when external conditions of the display device require high luminance but also when low luminance is required.

[0013] In addition, the present disclosure provides a display device using light-emitting elements and a method of driving the same, which may extend the lifespan of the light-emitting elements by individually and selectively driving at least two sets of light-emitting elements forming each pixel.

[0014] In addition, the present disclosure provides a display device using light-emitting elements and a method of driving the same, which may improve the efficiency of the light-emitting elements by alleviating degradation in the efficiency of the light-emitting elements due to heat generation and reduction in the brightness of the light-emitting elements due to direct external light (sunlight) and heat resulting therefrom, so that heat generation in the display device may be reduced and the efficiency thereof may be improved.TECHNICAL SOLUTIONS

[0015] In accordance with a first aspect of the present disclosure for accomplishing the above objects, a display device using light-emitting elements includes a wiring substrate having a plurality of unit pixel areas defined therein, a pixel portion including at least two sets of light-emitting elements mounted in each of the unit pixel areas to form a unit subpixel, and a driver configured to drive the pixel portion, wherein one set of light-emitting elements includes a red light-emitting element, a green light-emitting element, and a blue light-emitting element, and the driver may be configured to simultaneously drive the at least two sets of light-emitting elements under a first condition and independently drive the at least two sets of light-emitting elements under a second condition.

[0016] In an exemplary embodiment, independently driving the at least two sets of light-emitting elements may include driving the at least two sets of light-emitting elements at the same time or different times.

[0017] In an exemplary embodiment, the first condition and the second condition may include conditions based on an external luminance level.

[0018] In an exemplary embodiment, the first condition may include a condition based on an external luminance level corresponding to daytime, and the second condition may include a condition based on an external luminance level corresponding to a time other than daytime.

[0019] In an exemplary embodiment, the first condition may correspond to the external luminance level in a range of 100 lux to 10,000 lux, and the second condition may correspond to the external luminance level equal to or less than 100 lux.

[0020] In an exemplary embodiment, the display device may further include an illuminance sensor configured to measure brightness of an external environment, and the first condition and the second condition may be distinguished based on an output value of the illuminance sensor.

[0021] In an exemplary embodiment, the at least two sets of light-emitting elements may be driven differently from each other according to the gradation level of the pixel portion under the second condition.

[0022] In an exemplary embodiment, under the second condition, a portion of the at least two sets of light-emitting elements may be driven according to the gradation level of the pixel portion.

[0023] In an exemplary embodiment, the driver may be configured to input the same driving signal (PWM) to the at least two sets of light-emitting elements under the first condition, and the driver may be configured to input the same or different driving signals (PWM) to the at least two sets of light-emitting elements under the second condition.

[0024] In an exemplary embodiment, the driver may be configured to input the same driving signal (PWM) to the at least two sets of light-emitting elements under the first condition, and the driver may be configured to input different driving signals (PWM) to the at least two sets of light-emitting elements according to the gradation level of the pixel portion under the second condition.

[0025] In an exemplary embodiment, for minimum gradation level representation, the driver may be configured to drive one set of light-emitting elements among the at least two sets of light-emitting elements or may be configured to drive the at least two sets of light-emitting elements in a divided manner.

[0026] In an exemplary embodiment, the driver may include an illuminance sensor configured to measure brightness of an external environment, a gate driver configured to apply a lighting signal to the pixel portion, a data driver configured to apply a brightness signal to the pixel portion, a current source configured to supply current to the data driver, and a controller configured to control at least one of the illuminance sensor, the gate driver, or the data driver.

[0027] In accordance with a second aspect of the present disclosure for accomplishing the above objects, a method of driving a display device, which includes a pixel portion including at least two sets of light-emitting elements mounted in each of unit pixel areas to form a unit subpixel, includes detecting ambient brightness, determining a luminance range based on the ambient brightness, simultaneously driving the at least two sets of light-emitting elements in a first luminance range, and independently driving the at least two sets of light-emitting elements in a second luminance range.

[0028] In an exemplary embodiment, the independently driving the at least two sets of light-emitting elements may include driving the at least two sets of light-emitting elements at the same time or different times.

[0029] In an exemplary embodiment, the first luminance range may include a condition based on an external luminance level corresponding to daytime, and the second luminance range may include a condition based on an external luminance level corresponding to a time other than daytime.

[0030] In an exemplary embodiment, the first luminance range may range from 100 lux to 10,000 lux, and the second luminance range may be equal to or less than 100 lux.

[0031] In an exemplary embodiment, the method may further comprise differently driving the at least two sets of light-emitting elements from each other according to the gradation level of the pixel portion in the second luminance range.

[0032] In an exemplary embodiment, the method may further comprise driving a portion of the at least two sets of light-emitting elements according to the gradation level of the pixel portion in the second luminance range.

[0033] In an exemplary embodiment, the method may further comprise inputting the same driving signal (PWM) to the at least two sets of light-emitting elements in the first luminance range, and inputting the same or different driving signals (PWM) to the at least two sets of light-emitting elements in the second luminance range.

[0034] In an exemplary embodiment, the method may further comprise inputting the same driving signal (PWM) to the at least two sets of light-emitting elements in the first luminance range, and inputting different driving signals (PWM) to the at least two sets of light-emitting elements according to the gradation level of the pixel portion in the second luminance range.ADVANTAGEOUS EFFECTS

[0035] According to an embodiment of the present disclosure, the following effects may be achieved.

[0036] First, according to an embodiment of the present disclosure, gradation level representation may be precisely designed even at a minimum luminance level (corresponding to approximately one-tenth of the maximum luminance). Accordingly, an image may be represented precisely and smoothly in a low gradation level range.

[0037] In addition, according to the structure and driving method of the pixel portion of the embodiment of the present disclosure, precise gradation level representation may be achieved not only when external conditions of the display device require high luminance but also when low luminance is required.

[0038] In addition, according to an embodiment of the present disclosure, the lifespan of the light-emitting elements may be extended by individually and selectively driving at least two sets of light-emitting elements forming each pixel. For example, depending on the driving conditions, only one light-emitting element in each pixel may be turned on, while the remaining light-emitting elements may be turned off, thereby improving the lifespan of the light-emitting elements.

[0039] In addition, according to an embodiment of the present disclosure, it may be possible to improve the efficiency of the light-emitting elements by alleviating degradation in the efficiency of the light-emitting elements due to heat generation and reduction in the brightness of the light-emitting elements due to direct external light (sunlight) and heat resulting therefrom. Accordingly, heat generation in the display device may be reduced and the efficiency thereof may be improved.

[0040] Furthermore, according to another embodiment of the present disclosure, additional technical effects not mentioned herein may also be exhibited. This will be understood by those skilled in the art from the entirety of the specification and the drawings.DESCRIPTION OF DRAWINGS

[0041] FIG. 1 is a block diagram showing the configuration of a display device using light-emitting elements according to an embodiment of the present disclosure. FIG. 2 is a schematic cross-sectional view showing the display device using light-emitting elements according to an embodiment of the present disclosure. FIG. 3 is a conceptual diagram showing a unit pixel of the display device using light-emitting elements according to an embodiment of the present disclosure. FIG. 4 is a circuit diagram of FIG. 3. FIG. 5 is a conceptual diagram showing a unit pixel of the display device using light-emitting elements according to another embodiment of the present disclosure. FIG. 6 is a circuit diagram of FIG. 5. FIG. 7 is a circuit diagram showing two pixels of the display device using light-emitting elements according to another embodiment of the present disclosure. FIG. 8 is a plan view showing a pixel structure of the display device using light-emitting elements according to an embodiment of the present disclosure. FIGs. 9 and 10 are graphs showing gradation level representation during driving of a general display device using light-emitting elements according to a comparative example. FIG. 11 is a graph showing gradation level representation based on driving of the display device using light-emitting elements according to an embodiment of the present disclosure. FIGs. 12 to 14 are conceptual diagrams showing a PWM driving state of the display device using light-emitting elements according to an embodiment of the present disclosure. FIGs. 15 and 16 are conceptual diagrams showing a PWM driving state of the display device using light-emitting elements according to another embodiment of the present disclosure. FIG. 17 is a flowchart showing a method of driving the display device using light-emitting elements according to another embodiment of the present disclosure. BEST MODE FOR DISCLOSURE

[0042] Reference will now be made in detail to embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts, and redundant description thereof will be omitted. As used herein, the suffixes "module" and "unit" are added or used interchangeably to facilitate preparation of this specification and are not intended to suggest distinct meanings or functions.

[0043] In describing embodiments disclosed in this specification, relevant well-known technologies may not be described in detail in order not to obscure the subject matter of the embodiments disclosed in this specification. In addition, it should be noted that the accompanying drawings are only for easy understanding of the embodiments disclosed in the present specification, and should not be construed as limiting the technical spirit disclosed in the present specification.

[0044] Furthermore, although the drawings are separately described for simplicity, embodiments implemented by combining at least two or more drawings are also within the scope of the present disclosure.

[0045] In addition, when an element such as a layer, region or module is described as being "on" another element, it is to be understood that the element may be directly on the other element or there may be an intermediate element between them.

[0046] In addition, the semiconductor light emitting device mentioned in this specification is a concept including an LED, a micro LED, and the like, which may be used in a mixed manner.

[0047] FIG. 1 is a block diagram showing the configuration of a display device using light-emitting elements according to an embodiment of the present disclosure. In addition, FIG. 2 is a schematic cross-sectional view showing the display device using light-emitting elements according to an embodiment of the present disclosure.

[0048] Referring to FIG. 1, the entire configuration of a display device 100 including a pixel portion 110 and a driver 200 configured to drive the pixel portion 110 is shown.

[0049] For example, the pixel portion 110 may include at least two sets of light-emitting elements forming a unit subpixel. In addition, one set of light-emitting elements may include a red light-emitting element R1(1), a green light-emitting element G1(1), and a blue light-emitting element B 1(1).

[0050] FIG. 1 shows an example in which three sets of light-emitting elements are included in each pixel in the pixel portion 110. That is, one pixel may include three red light-emitting elements R1(1), R1(2), and R1(3), three green light-emitting elements G1(1), G1(2), and G1(3), and three blue light-emitting elements B1(1), B1(2), and B1(3). Meanwhile, in other examples, one pixel may include two sets of light-emitting elements or may include more than three sets of light-emitting elements.

[0051] Pixels, each including three sets of light-emitting elements, may be connected to each other via scan lines Scan line 1, Scan line 2, ..., and Scan line n, respectively. As such, a predetermined number of pixels may be provided on each of the scan lines Scan line 1, Scan line 2, ..., and Scan line n. FIG. 1 shows a state in which m pixels are provided on one scan line. The m pixels may include 3m subpixels, and a total of 3*3m data lines Data line 1, Data line 2, ..., and Data line 3*3m may be provided by the three sets of light-emitting elements.

[0052] The data lines Data line 1, Data line 2, ..., and Data line 3*3m may be driven by a data driver 210. The data lines may be respectively connected to the light-emitting elements forming the subpixels. In addition, a current source 240 for supplying current to the data driver 210 may be disposed at the other end of each of the data lines. Accordingly, a total of 3*3m current sources 240 may be provided.

[0053] In addition, each of the scan lines Scan line 1, Scan line 2, ..., and Scan line n may be connected to a gate driver 220.

[0054] At least one of the data driver 210 or the gate driver 220 may be controlled by a controller 230.

[0055] At least two sets of light-emitting elements may be driven simultaneously or independently depending on conditions. Even when the at least two sets of light-emitting elements are driven independently, the two sets of light-emitting elements may be driven together. That is, the case in which the at least two sets of light-emitting elements are driven independently may include a case in which the two sets of light-emitting elements are driven together, a case in which the two sets of light-emitting elements are driven alternately, and a case in which only a portion of the two sets of light-emitting elements is driven. For example, the two sets of light-emitting elements may be driven at the same time or different times.

[0056] For example, the at least two sets of light-emitting elements may be driven simultaneously under a first condition, and may be driven independently under a second condition. As one example, the first condition and the second condition may be external light conditions of a place in which the display device 100 is located. That is, the first condition and the second condition may be luminance conditions of a place in which the display device 100 is located. That is, the first condition and the second condition may be conditions based on an external luminance level.

[0057] According to an exemplary embodiment, the first condition may be a condition in which the external luminance level corresponds to daytime, and the second condition may be a condition in which the external luminance level corresponds to a time other than daytime (e.g., at sunrise, sunset, or nighttime).

[0058] For example, under a high luminance condition (3,000 to 8,000 nits) during daytime (the first condition), the at least two sets of light-emitting elements constituting each pixel may be driven simultaneously. Meanwhile, under a low luminance condition (300 to 500 nits) during nighttime (the second condition), the at least two sets of light-emitting elements constituting each pixel may be driven separately.

[0059] According to an exemplary embodiment, the first condition may correspond to a case in which the external luminance level is in a range of 100 lux to 10,000 lux, and the second condition may correspond to a case in which the external luminance level is 100 lux or less.

[0060] According to an exemplary embodiment, the driver 200 may include an illuminance sensor 250 configured to detect the external light condition or the luminance condition.

[0061] Accordingly, the first condition and the second condition may be distinguished based on an output value of the illuminance sensor 250.

[0062] According to an exemplary embodiment, under the second condition, the at least two sets of light-emitting elements may be driven differently according to the gradation level of the pixel portion 110. For example, under the second condition, a portion of the at least two sets of light-emitting elements may be driven according to the gradation level of the pixel portion 110.

[0063] According to an exemplary embodiment, under the first condition, the driver 200 may input the same driving signal (pulse width modulation (PWM) signal) to the at least two sets of light-emitting elements, and under the second condition, the driver 200 may input the same or different driving signals (PWM signals) to the at least two sets of light-emitting elements.

[0064] According to an exemplary embodiment, under the first condition, the driver 200 may input the same driving signal (PWM) to the at least two sets of light-emitting elements, and under the second condition, the driver 200 may input different driving signals (PWM) to the at least two sets of light-emitting elements according to the gradation level of the pixel portion 110.

[0065] According to an exemplary embodiment, for minimum gradation level representation, the driver 200 may drive only one set of light-emitting elements among the at least two sets of light-emitting elements or may drive the at least two sets of light-emitting elements in a divided manner.

[0066] Driving of the display device 100 according to such external light conditions will be described later in detail with reference to the drawings.

[0067] As such, the driver 200 may include an illuminance sensor 250 configured to measure the brightness of the external environment in which the display device 100 is located, a gate driver 220 configured to apply a lighting signal to the pixel portion 110, a data driver 210 configured to apply a brightness signal to the pixel portion 110, and a current source 240 configured to supply current to the data driver 210. In addition, the driver 200 may include a controller 230 configured to control at least one of the illuminance sensor 250, the gate driver 220, or the data driver 210.

[0068] Referring to FIG. 2, the display device 100 may include a wiring substrate 120 in which a plurality of unit pixel areas P11 and P13 is defined.

[0069] The pixel portion 110 described above may include at least two sets of light-emitting elements mounted in each of the unit pixel areas P11 and P13 to form a unit subpixel.

[0070] One set of light-emitting elements P11 may include a red light-emitting element R1(1), a green light-emitting element G1(1), and a blue light-emitting element B1(1). In this case, the driving 200 may simultaneously drive the at least two sets of light-emitting elements under the first condition, and may independently drive the at least two sets of light-emitting elements under the second condition.

[0071] For example, individual light-emitting elements R1(1), G1(1), B1(1), R3(1), G3(1), and B3(1) mounted in the unit pixel areas P11 and P13 may substantially correspond to subpixels. For example, at least two sets of subpixels may constitute one pixel.

[0072] Each of the light-emitting elements R1(1), G1(1), B1(1), R3(1), G3(1), and B3(1) may be electrically connected to a pair of electrode pads 141 and 142. In this case, for example, an electrode pad 141 (hereinafter referred to as a first electrode pad) disposed in one direction in FIG. 2 may be connected to the scan line (or common electrode) described above. In this case, an electrode pad 142 (hereinafter referred to as a second electrode pad) disposed in the opposite direction may be connected to the data line (or signal electrode) described above. However, an opposite configuration may also be possible. In FIG. 2, for clarity of the electrode pad layout, illustration of the scan lines and the data lines is omitted.

[0073] Hereinafter, the same reference numerals will be used interchangeably for the electrode pads and the wiring electrodes. That is, the electrode pads and the wiring electrodes may be denoted using the same reference numerals.

[0074] As such, a unit subpixel may be defined at an intersection of the scan line and the data line.

[0075] Meanwhile, for example, the data line may be connected to a TFT layer 121 including a thin film transistor (TFT). Accordingly, each of the light-emitting elements R1(1), G1(1), B1(1), R3(1), G3(1), and B3(1) may be driven by switching operation through the TFT layer 121.

[0076] In FIG. 2, the TFT layer 121 is schematically shown as a single layer. However, the TFT layer 121 may include a plurality of TFT regions capable of performing switching operations. For example, each TFT region may include a gate electrode, a source electrode, a drain electrode, an insulating layer disposed between the electrodes, and a via electrode connectable to the data line or the second electrode pad 142. A detailed description thereof will be omitted. Each of the TFT regions may be connected to a respective one of the light-emitting elements R1(1), G1(1), B1(1), R3(1), G3(1), and B3(1).

[0077] As described above, at least two sets of light-emitting elements may form individual subpixels and may be repeatedly arranged on the wiring substrate 120. The light-emitting elements may include at least one of an organic light-emitting element or an inorganic light-emitting element. For example, the light-emitting elements may be inorganic semiconductor light emitting diodes (LEDs).

[0078] Such a semiconductor light emitting diode (LED) may have a size on the order of micrometers (µm). The size on the order of micrometers (µm) may mean that at least one surface of the light emitting diode has a width ranging from several micrometers (µm) to several hundred micrometers (µm).

[0079] The TFT layer 121 may be disposed on the substrate 120, and an insulating layer 130 may be coated on the TFT layer 121. The insulating layer 130 may cover a connection portion between the electrode pads 141 and 142 and the light-emitting element.

[0080] FIG. 3 is a conceptual diagram showing a unit pixel of the display device using light-emitting elements according to an embodiment of the present disclosure. FIG. 4 is a circuit diagram of FIG. 3.

[0081] Referring to FIGs. 3 and 4, an example in which a unit pixel includes two sets of light-emitting elements is illustrated. For example, the first pixel P11 on the wiring substrate 120 of the pixel portion 110 may include two sets of light-emitting elements R1(1), G1(1), B1(1), R1(2), G1(2), and B1(2).

[0082] For example, R1(1), G1(1), and B1(1) may refer to a first set of light-emitting elements of the first pixel P11, and R1(2), G1(2), and B1(2) may refer to a second set of light-emitting elements of the first pixel P11. As such, the first pixel P11 may include a total of six light-emitting elements. However, this is merely an example, and one set of light-emitting elements may include more light-emitting elements in addition to R1(1), G1(1), and B1(1). For example, one set of light-emitting elements may further include a red light-emitting element or a green light-emitting element in addition to R1(1), G1(1), and B1(1). As another example, one set of light-emitting elements may further include a white light-emitting element in addition to R1(1), G1(1), and B1(1). Hereinafter, an example in which one set of light-emitting elements includes R1(1), G1(1), and B1(1), that is, red, green, and blue light-emitting elements, will be mainly described.

[0083] FIG. 4 is a circuit diagram showing an example in which the first pixel P11 includes two sets of light-emitting elements R1(1), G1(1), B1(1), R1(2), G1(2), and B1(2).

[0084] A single pixel (e.g., P11) may include two red light-emitting elements R1(1) and R1(2), two green light-emitting elements G1(1) and G1(2), and two blue light-emitting elements B1(1) and B1(2).

[0085] One side of each of the two sets of light-emitting elements R1(1), G1(1), B1(1), R1(2), G1(2), and B1(2) may be commonly connected, and the other side thereof may be connected to the current source 240.

[0086] FIG. 5 is a conceptual diagram showing a unit pixel of the display device using light-emitting elements according to another embodiment of the present disclosure. FIG. 6 is a circuit diagram of FIG. 5.

[0087] Referring to FIGs. 5 and 6, an example in which a unit pixel includes three sets of light-emitting elements is illustrated. For example, the first pixel P11 on the wiring substrate 120 of the pixel portion 110 may include three sets of light-emitting elements R1(1), G1(1), B1(1), R1(2), G1(2), B1(2), R1(3), G1(3), and B1(3).

[0088] FIG. 6 is a circuit diagram showing an example in which the first pixel P11 includes three sets of light-emitting elements R1(1), G1(1), B1(1), R1(2), G1(2), B1(2), R1(3), G1(3), and B1(3).

[0089] A single pixel (e.g., P11) may include three red light-emitting elements R1(1), R1(2), and R1(3), three green light-emitting elements G1(1), G1(2), and G1(3), and three blue light-emitting elements B1(1), B1(2), and B1(3).

[0090] One side of each of the three sets of light-emitting elements R1(1), G1(1), B1(1), R1(2), G1(2), B1(2), R1(3), G1(3), and B1(3) may be commonly connected, and the other side thereof may be connected to the current source 240.

[0091] FIG. 7 is a circuit diagram showing two pixels of the display device using light-emitting elements according to another embodiment of the present disclosure.

[0092] Referring to FIG. 7, in the pixel portion 1100, a first pixel P11 includes three sets of light-emitting elements R1(1), G1(1), B1(1), R1(2), G1(2), B1(2), R1(3), G1(3), and B1(3), and a second pixel P12 includes three sets of light-emitting elements R2(1), G2(1), B2(1), R2(2), G2(2), B2(2), R2(3), G2(3), and B2(3).

[0093] As such, the plurality of pixels P11 and P12 may be structured to include the same number of light-emitting elements.

[0094] FIG. 8 is a plan view showing a pixel structure of the display device using light-emitting elements according to an embodiment of the present disclosure.

[0095] Referring to FIG. 8, the display device 100 using light-emitting elements includes a pixel portion 110 provided on a wiring substrate 120, and the pixel portion 110 includes six pixels in a horizontal direction and four pixels in a vertical direction. The display device 100 shown in FIG. 8 may correspond to a portion of the entire display device 100, and, for example, may correspond to one module of the entire display device 100.

[0096] The pixel portion 110 of the display device 100 may include six pixels P11 to P16 arranged in the horizontal direction. Each pixel may include three sets of light-emitting elements, as described above with reference to FIGs. 5 to 7.

[0097] In addition, the pixel portion 110 may include four pixels P11 to P41 arranged in the vertical direction. Accordingly, a pixel indicated by P46 may be located at the lower right corner.

[0098] Typically, the target luminance of outdoor high-luminance display devices, which are installed outdoors, varies depending on the time of day (daytime / nighttime). The difference in the target luminance is approximately tenfold. For example, during the day, a minimum luminance of 3,000 nits is required. In some cases, a luminance of up to 8,000 nits is required. However, during the night, a luminance in the range of 300 to 500 nits is required.

[0099] The reason is as follows. Outdoor display devices are primarily used for advertising purposes, and a key aspect of such display devices is to attract the attention of nearby individuals. During the day, it may be advantageous for the display devices to be visibly presented to pedestrians, drivers, or passersby with a high luminance (at least 3,000 nits).

[0100] Accordingly, the gradation level representation of display devices has been evaluated based on the maximum luminance, and gradation level representation at low luminance levels has not been considered important and has therefore not been the subject of evaluation.

[0101] However, since 2010, rapid technological advancements have led to increase in the installation of display devices for outdoor signage, which has caused light pollution during the night. As a result, nighttime luminance has been legally regulated by individual countries or municipalities.

[0102] With the implementation of such nighttime luminance regulations, gradation level representation at nighttime luminance levels (300 to 500 nits) has become necessary.

[0103] In particular, display devices employing light emitting diodes (LEDs) are required to implement gradation level representation using individual light-emitting elements. Accordingly, improvements that take this situation into account are needed.

[0104] Therefore, according to the display device 100 of an embodiment of the present disclosure having the above-described structure and driving conditions, gradation level representation may be precisely designed even at the lowest luminance level (corresponding to approximately one-tenth of the maximum luminance). Accordingly, an image may be represented precisely and smoothly at a low gradation level.

[0105] In particular, in the case of display devices installed outdoors, under high-luminance conditions due to, for example, sunlight, an image is represented with high luminance. However, under low-luminance conditions, for example, during nighttime, it may be difficult to achieve precise gradation level representation using the same pixel structure.

[0106] In contrast, according to the structure and driving method of the pixel portion of the embodiment of the present disclosure, precise gradation level representation may be achieved not only when external conditions of the display device require high luminance but also when low luminance is required. This will be described later in detail.

[0107] In addition, the lifespan of the light-emitting elements may be extended by individually and selectively driving at least two sets of light-emitting elements forming each pixel. For example, depending on the driving conditions, only one light-emitting element in each pixel may be turned on, while the remaining light-emitting elements may be turned off, thereby improving the lifespan of the light-emitting elements.

[0108] However, when one set of light-emitting elements is driven with high current, the efficiency of the light-emitting elements may be degraded due to heat generation, and the brightness of the light-emitting elements may be reduced due to direct external light (sunlight) and heat resulting therefrom.

[0109] In contrast, according to the embodiment of the present disclosure, the above issues may be addressed, and the efficiency of the light-emitting elements may be improved. Accordingly, heat generation in the display device may be reduced, and the efficiency of the display device may be increased.

[0110] FIGs. 9 and 10 are graphs showing gradation level representation during driving of a general display device using light-emitting elements according to a comparative example.

[0111] FIG. 9 shows an example of low-luminance driving in a general display device including one red LED, one green LED, and one blue LED in each unit pixel.

[0112] For example, referring to FIG. 9(a), when the external light condition is 500 nits (nighttime condition) and the target luminance is 1,000 nits, each LED may be driven with current of, for example, 10 mA.

[0113] In this case, referring to FIG. 9(b), it can be seen that, when a total of 256 gradation levels is represented, the gradation levels are distinctly represented in discrete steps even in the low gradation level range.

[0114] FIG. 10 shows examples of low-luminance and high-luminance driving in the display device identical to that shown in FIG. 9.

[0115] For example, referring to FIG. 10(a), when the external light condition is 3,000 nits (daytime condition) and the target luminance is 3,000 nits, each LED may be driven with current of, for example, 30 mA. In this case, it can be seen that, when a total of 256 gradation levels is represented, the gradation levels are distinctly represented in discrete steps even in the low gradation level range.

[0116] In another example, when the external light condition is 500 nits (nighttime condition) and the target luminance is 1,000 nits, each LED may be driven with current of, for example, 10 mA.

[0117] However, in this case, referring to FIG. 10(b), it can be seen that precise gradation level representation is not achieved in the low gradation level range (e.g., 60 th< gradation level or lower). That is, changes in luminance may not be represented in discrete steps in the low gradation level range. In addition, in the high gradation level range (e.g., 200 th< gradation level or higher), saturation may occur, resulting in failure to represent changes in luminance corresponding to gradation levels between 200 and 256.

[0118] Accordingly, referring to FIG. 10(b), when the target luminance is 1,000 nits, representation of gamma 2.2 may not be satisfied. As a result, the gradation level representation may not be smooth, resulting in the occurrence of a banding phenomenon.

[0119] FIG. 11 is a graph showing gradation level representation based on driving of the display device using light-emitting elements according to an embodiment of the present disclosure.

[0120] FIG. 11 shows examples of low-luminance and high-luminance driving in the display device according to the embodiment of the present disclosure including three sets of red, green, and blue LEDs in a unit pixel.

[0121] For example, referring to FIG. 11(a), when the external light condition is 3,000 nits (daytime condition) and the target luminance is 3,000 nits, the gradation levels may be represented by driving all three sets of light-emitting elements. In this case, it can be seen that, when a total of 256 gradation levels is represented, the gradation levels are distinctly represented in discrete steps even in the low gradation level range.

[0122] In another example, when the external light condition is 500 nits (nighttime condition) and the target luminance is 1,000 nits, the gradation levels may be represented by driving one set of light-emitting elements among the three sets of light-emitting elements.

[0123] In this case, it can be seen that, when a total of 256 gradation levels is represented, the gradation levels are also distinctly represented in discrete steps in the low gradation level range.

[0124] FIGs. 12 to 14 are conceptual diagrams showing a PWM driving state of the display device using light-emitting elements according to an embodiment of the present disclosure.

[0125] Driving of the display device 100 using light-emitting elements, that is, the on / off operation of the light-emitting elements, may employ a pulse width modulation (PWM) scheme. However, the present disclosure is not limited thereto, and a pulse amplitude modulation (PAM) scheme or other driving schemes may also be employed. Hereinafter, an example in which the display device using light-emitting elements according to an embodiment of the present disclosure is driven using the PWM scheme will be described.

[0126] FIGs. 12 to 14 show a gradation level representation process according to driving in a case in which the pixel portion 110 has the structure described above with reference to FIGs. 3 and 4. That is, a driving process in a case in which each pixel includes two sets of light-emitting elements #1 LED and #2 LED will be described.

[0127] Referring first to FIG. 12, for example, when the target luminance is 3,000 nits, that is, under daytime conditions, the gradation levels may be represented by driving both sets of light-emitting elements #1 LED and #2 LED.

[0128] That is, when a total of 256 gradation levels is represented, the 256 th< gradation level may be represented using a PWM waveform that turns on both sets of light-emitting elements #1 LED and #2 LED throughout the entire period. In addition, the 128 th< gradation level may be represented using a PWM waveform that turns on both sets of light-emitting elements #1 LED and #2 LED for half of the entire period. In addition, the minimum gradation level (1 st< gradation level) may be represented using a PWM waveform that turns on both sets of light-emitting elements #1 LED and #2 LED for a minimum duration within the entire period.

[0129] Through this process, the gradation level representation shown in FIG. 11 may be achieved.

[0130] Meanwhile, referring to FIG. 13, for example, when the target luminance is 1,000 nits, the gradation levels may be represented by driving two sets of light-emitting elements #1 LED and #2 LED using two methods Case 1 and Case 2.

[0131] First, according to the first method Case 1, the gradation levels may be represented through the same process as that shown in FIG. 12, using only one set of light-emitting elements (e.g., #1 LED) among the two sets of light-emitting elements #1 LED and #2 LED. That is, the gradation levels may be normally represented without turning on #2 LED.

[0132] Meanwhile, according to the second method Case 2, in the high gradation level range, the gradation levels are represented by simultaneously driving the two sets of light-emitting elements #1 LED and #2 LED. In this case, however, because the two sets of light-emitting elements #1 LED and #2 LED are driven simultaneously, each pulse width may correspond to half of that in the first method Case 1.

[0133] In addition, according to the second method Case 2, in the low gradation level range, the gradation levels are represented by selectively or alternately driving the two sets of light-emitting elements #1 LED and #2 LED. Referring to FIG. 13, an example in which a PWM signal is input to alternately drive the two sets of light-emitting elements #1 LED and #2 LED at the minimum gradation level (1 / 256 gradation level) is shown.

[0134] Referring to FIG. 14, for example, when the target luminance is 500 nits (external light condition other than daytime condition), the gradation levels may be represented by driving the two sets of light-emitting elements #1 LED and #2 LED using two methods Case 1 and Case 2.

[0135] First, according to the first method Case 1, the gradation levels may be represented using only one set of light-emitting elements (e.g., #1 LED) among the two sets of light-emitting elements #1 LED and #2 LED. That is, the gradation levels may be normally represented without turning on #2 LED.

[0136] In this case, because the target luminance is 500 nits, which is half of 1,000 nits in the case of FIG. 13, the pixel portion 110 may be driven using a waveform corresponding to half of that in FIG. 13 for high gradation level representation (e.g., 256 / 256 gradation level) and intermediate gradation level representation (e.g., 128 / 256 gradation level).

[0137] However, in the low gradation level range (e.g., 1 / 256), the pixel portion 110 may be driven using a minimum-sized waveform. In addition, the pixel portion 110 may be driven using a portion of the minimum-sized waveform.

[0138] Meanwhile, according to the second method Case 2, the gradation levels are represented by simultaneously driving the two sets of light-emitting elements #1 LED and #2 LED for high gradation level representation (e.g., 256 / 256 gradation level) and intermediate gradation level representation (e.g., 128 / 256 gradation level). In this case, however, because the two sets of light-emitting elements #1 LED and #2 LED are driven simultaneously, each pulse width may correspond to half of that in the first method Case 1.

[0139] In addition, according to the second method Case 2, in the low gradation level range (1 / 256 gradation level), the gradation levels are represented by selectively or alternately driving the two sets of light-emitting elements #1 LED and #2 LED. Referring to FIG. 14, an example in which a PWM signal is input to alternately drive the two sets of light-emitting elements #1 LED and #2 LED at the minimum gradation level (1 / 256 gradation level) is shown.

[0140] As such, in order to represent the gradation levels under dark external light conditions, for example, during nighttime, at least two sets of light-emitting elements #1 LED and #2 LED may be driven differently from each other.

[0141] That is, according to an exemplary embodiment, under the second condition corresponding to non-daytime, a portion of the at least two sets of light-emitting elements #1 LED and #2 LED may be driven according to the gradation level of the pixel portion 110.

[0142] In the embodiment in which the pixel portion 110 of the display device 100 is driven by PWM driving, under the first condition corresponding to daytime, the driver 200 may input the same driving signal PWM to the at least two sets of light-emitting elements #1 LED and #2 LED, and under the second condition corresponding to non-daytime (e.g., at sunrise, sunset, or nighttime), the driver 200 may input the same or different driving signals PWM to the at least two sets of light-emitting elements #1 LED and #2 LED.

[0143] According to an exemplary embodiment, under the first condition, the driver 200 may input the same driving signal PWM to the at least two sets of light-emitting elements #1 LED and #2 LED, and under the second condition, the driver 200 may input different driving signals PWM to the at least two sets of light-emitting elements #1 LED and #2 LED according to the gradation level of the pixel portion 110.

[0144] In addition, for minimum gradation level representation (e.g., 1 / 256 gradation level), the driver 200 may drive only one set of light-emitting elements among the at least two sets of light-emitting elements #1 LED and #2 LED or may drive the at least two sets of light-emitting elements #1 LED and #2 LED in a divided manner.

[0145] FIGs. 15 and 16 are conceptual diagrams showing a PWM driving state of the display device using light-emitting elements according to another embodiment of the present disclosure.

[0146] As described above, driving of the display device 100 using light-emitting elements, that is, the on / off operation of the light-emitting elements, may employ a pulse width modulation (PWM) scheme. However, the present disclosure is not limited thereto, and a pulse amplitude modulation (PAM) scheme or other driving schemes may also be employed.

[0147] FIGs. 15 and 16 show a gradation level representation process according to driving in a case in which the pixel portion 110 has the structure described above with reference to FIGs. 5 and 6. That is, a driving process in a case in which each pixel includes three sets of light-emitting elements #1 LED, #2 LED, and #3 LED will be described.

[0148] Referring first to FIG. 15, for example, when the target luminance is 3,000 nits, that is, under daytime conditions, the gradation levels may be represented by driving all three sets of light-emitting elements #1 LED, #2 LED, and #3 LED.

[0149] That is, when a total of 256 gradation levels is represented, the 256 th< gradation level may be represented using a PWM waveform that turns on all three sets of light-emitting elements #1 LED, #2 LED, and #3 LED. In this case, one set of light-emitting elements (e.g., #3 LED) may be driven to achieve a luminance of 1,000 nits, which corresponds to one-third of the target luminance of 3,000 nits.

[0150] In addition, the 128 th< gradation level may be represented using a PWM waveform that turns on all three sets of light-emitting elements #1 LED, #2 LED, and #3 LED for half of the period used to represent the 256 th< gradation level. In addition, the minimum gradation level (1 / 256 gradation level) may be represented using a PWM waveform that turns on all three sets of light-emitting elements #1 LED, #2 LED, and #3 LED for a minimum duration within the entire period.

[0151] Meanwhile, referring to FIG. 16, for example, when the target luminance is 500 nits (external light condition other than daytime condition), the gradation levels may be represented by driving the three sets of light-emitting elements #1 LED, #2 LED, and #3 LED using two methods Case 1 and Case 2.

[0152] First, according to the first method Case 1, the gradation levels may be represented using only one set of light-emitting elements (e.g., #1 LED) among the three sets of light-emitting elements #1 LED, #2 LED, and #3 LED. That is, the gradation levels may be normally represented without turning on #2 LED and #3 LED.

[0153] In this case, because the target luminance is 500 nits, which is one-sixth of 3,000 nits in the case of FIG. 15, one set of light-emitting elements (e.g., #1 LED) may be driven using an individual waveform corresponding to half of that in the case of FIG. 16 for high gradation level representation (e.g., 256 / 256 gradation level) and intermediate gradation level representation (e.g., 128 / 256 gradation level).

[0154] However, in the low gradation level range (e.g., 1 / 256), the pixel portion 110 may be driven using a minimum-sized waveform. In addition, one set of light-emitting elements (e.g., #1 LED) may be driven using a portion of the minimum-sized waveform.

[0155] Meanwhile, according to the second method Case 2, the gradation levels are represented by simultaneously driving the three sets of light-emitting elements #1 LED, #2 LED, and #3 LED for high gradation level representation (e.g., 256 / 256 gradation level) and intermediate gradation level representation (e.g., 128 / 256 gradation level). In this case, however, because the three sets of light-emitting elements #1 LED, #2 LED, and #3 LED are driven simultaneously, each pulse width may correspond to one-third of that in the first method Case 1 (the pulse width is schematically shown in FIG. 16).

[0156] In addition, according to the second method Case 2, in the low gradation level range (1 / 256 gradation level), the gradation levels are represented by selectively or alternately driving the three sets of light-emitting elements #1 LED, #2 LED, and #3 LED. Referring to FIG. 16, an example in which a PWM signal is input to alternately drive two sets of light-emitting elements #1 LED and #2 LED among the three sets of light-emitting elements #1 LED, #2 LED, and #3 LED at the minimum gradation level (1 / 256 gradation level) is shown.

[0157] As such, in order to represent the gradation levels under dark external light conditions, for example, during nighttime, the three sets of light-emitting elements #1 LED, #2 LED, and #3 LED may be driven differently from each other.

[0158] That is, according to an exemplary embodiment, under the second condition corresponding to non-daytime, a portion of the three sets of light-emitting elements #1 LED, #2 LED, and #3 LED may be driven according to the gradation level of the pixel portion 110.

[0159] In the embodiment in which the pixel portion 110 of the display device 100 is driven by PWM driving, under the first condition corresponding to daytime, the driver 200 may input the same driving signal PWM to the three sets of light-emitting elements #1 LED, #2 LED, and #3 LED, and under the second condition corresponding to non-daytime (e.g., at sunrise, sunset, or nighttime), the driver 200 may input the same or different driving signals PWM to the three sets of light-emitting elements #1 LED, #2 LED, and #3 LED.

[0160] According to an exemplary embodiment, under the first condition, the driver 200 may input the same driving signal PWM to the three sets of light-emitting elements #1 LED, #2 LED, and #3 LED, and under the second condition, the driver 200 may input different driving signals PWM to the three sets of light-emitting elements #1 LED, #2 LED, and #3 LED according to the gradation level of the pixel portion 110.

[0161] In addition, for minimum gradation level representation (e.g., 1 / 256 gradation level), the driver 200 may drive only one set of light-emitting elements among the three sets of light-emitting elements #1 LED, #2 LED, and #3 LED or may drive two sets of light-emitting elements #1 LED and #2 LED in a divided manner.

[0162] FIG. 17 is a flowchart showing a method of driving the display device using light-emitting elements according to another embodiment of the present disclosure.

[0163] Referring to FIG. 17, the above-described method of driving the display device 100 is illustrated using a flowchart. Hereinafter, an example in which each pixel of the display device 100 described above with reference to FIGs. 15 and 16 includes three sets of light-emitting elements #1 LED, #2 LED, and #3 LED will be described. Driving signals for driving the three sets of light-emitting elements #1 LED, #2 LED, and #3 LED may be referred to as pixel data data 1, data 2, and data 3.

[0164] First, ambient brightness may be detected (S10). The process of detecting ambient brightness may be a step of distinguishing between the daytime condition and the nighttime condition.

[0165] Accordingly, ambient brightness of the environment in which the display device 100 is located may be determined (S20), and a luminance range of the display device 100 (LED Display) may be determined (S30 and S40).

[0166] For example, if the ambient brightness of the environment in which the display device 100 is located is higher than that under the nighttime condition (Yes in S20), that is, if it corresponds to the daytime condition, the driving luminance range of the display device 100 (LED Display) may be determined to be a first luminance range (S30).

[0167] As such, if the driving luminance range of the display device 100 (LED display) is determined to be the first luminance range, the driver 200 may input the same PWM signal to the pixel portion 110 as pixel data (S31). That is, the driver 200 may input the same PWM signal to the three sets of light-emitting elements #1 LED, #2 LED, and #3 LED (S31).

[0168] Meanwhile, for example, if the ambient brightness of the environment in which the display device 100 is located is not higher than that under the nighttime condition (No in S20), that is, if it corresponds to sunset, sunrise, or nighttime, the driving luminance range of the display device 100 (LED display) may be determined to be a second luminance range (S40).

[0169] As such, if the driving luminance range of the display device 100 (LED display) is determined to be the second luminance range, the three sets of light-emitting elements #1 LED, #2 LED, and #3 LED may be driven independently.

[0170] For example, the driver 200 may input at least partially different PWM signals to the pixel portion 110 as pixel data (S41). That is, the driver 200 may input at least partially different PWM signals to the three sets of light-emitting elements #1 LED, #2 LED, and #3 LED (S41).

[0171] As described above, independently driving at least two sets of light-emitting elements (in this example, three sets of light-emitting elements #1 LED, #2 LED, and #3 LED) may correspond to driving at least two sets of light-emitting elements at the same time or different times.

[0172] In addition, the first luminance range may be a condition in which the external luminance level corresponds to daytime, and the second luminance range may be a condition in which the external luminance level corresponds to non-daytime.

[0173] As described above, according to an exemplary embodiment, the first luminance range may be from 100 lux to 10,000 lux, and the second luminance range may be equal to or less than 100 lux.

[0174] For details not described above, the driving process of the first embodiment described with reference to FIGs. 12 to 14 and the driving process of the second embodiment described with reference to FIGs. 15 and 16 may be equally applied.

[0175] The above description is provided merely by way of example to illustrate the present invention, and it will be understood by those of ordinary skill in the art that various modifications and changes may be made without departing from the essential features of the invention.

[0176] Accordingly, the embodiments disclosed herein are intended to describe, not to limit, the scope of the invention, and the scope of the invention should not be construed as being limited by these embodiments.

[0177] The scope of protection of the present invention shall be defined by the following claims, and all modifications or equivalents falling within the scope of the claims shall be construed as being included within the scope of the invention.INDUSTRIAL APPLICABILITY

[0178] According to the present disclosure, a display device using semiconductor light-emitting elements such as LEDs and a method of driving the same are provided.

Claims

1. A display device using light-emitting elements, the display device comprising: a wiring substrate having a plurality of unit pixel areas defined therein; a pixel portion comprising at least two sets of light-emitting elements mounted in each of the unit pixel areas to form a unit subpixel; and a driver configured to drive the pixel portion, wherein the one set of light-emitting elements comprises a red light-emitting element, a green light-emitting element, and a blue light-emitting element, and wherein the driver is configured to: simultaneously drive the at least two sets of light-emitting elements under a first condition, and independently drive the at least two sets of light-emitting elements under a second condition.

2. The display device of claim 1, wherein the independently driving the at least two sets of light-emitting elements comprises driving the at least two sets of light-emitting elements at the same time or different times.

3. The display device of claim 1, wherein the first condition and the second condition includes conditions based on an external luminance level.

4. The display device of claim 3, wherein the first condition includes a condition based on an external luminance level corresponding to daytime, and wherein the second condition includes a condition based on an external luminance level corresponding to a time other than daytime.

5. The display device of claim 3, wherein the first condition corresponds to the external luminance level in a range of 100 lux to 10,000 lux, and wherein the second condition corresponds to the external luminance level equal to or less than 100 lux.

6. The display device of claim 1, further comprising an illuminance sensor configured to measure brightness of an external environment, wherein the first condition and the second condition are distinguished based on an output value of the illuminance sensor.

7. The display device of claim 1, wherein the at least two sets of light-emitting elements are driven differently from each other according to a gradation level of the pixel portion under the second condition.

8. The display device of claim 7, wherein a portion of the at least two sets of light-emitting elements is driven according to a gradation level of the pixel portion under the second condition.

9. The display device of claim 1, wherein the driver is configured to input the same driving signal (PWM) to the at least two sets of light-emitting elements under the first condition, and wherein the driver is configured to input the same or different driving signals (PWM) to the at least two sets of light-emitting elements under the second condition.

10. The display device of claim 1, wherein the driver is configured to input the same driving signal (PWM) to the at least two sets of light-emitting elements under the first condition, and wherein the driver is configured to input different driving signals (PWM) to the at least two sets of light-emitting elements according to a gradation level of the pixel portion under the second condition.

11. The display device of claim 10, wherein, for minimum gradation level representation, the driver is configured to drive one set of light-emitting elements among the at least two sets of light-emitting elements or drive the at least two sets of light-emitting elements in a divided manner.

12. The display device of claim 1, wherein the driver comprises: an illuminance sensor configured to measure brightness of an external environment; a gate driver configured to apply a lighting signal to the pixel portion; a data driver configured to apply a brightness signal to the pixel portion; a current source configured to supply current to the data driver; and a controller configured to control at least one of the illuminance sensor, the gate driver, or the data driver.

13. A method of driving a display device comprising a pixel portion comprising at least two sets of light-emitting elements mounted in each of unit pixel areas to form a unit subpixel, the method comprising: detecting ambient brightness; determining a luminance range based on the ambient brightness; simultaneously driving the at least two sets of light-emitting elements in a first luminance range; and independently driving the at least two sets of light-emitting elements in a second luminance range.

14. The method of claim 13, wherein the independently driving the at least two sets of light-emitting elements comprises driving the at least two sets of light-emitting elements at the same time or different times.

15. The method of claim 13, wherein the first luminance range includes a condition based on an external luminance level corresponding to daytime, and wherein the second luminance range includes a condition based on an external luminance level corresponding to a time other than daytime.

16. The method of claim 13, wherein the first luminance range ranges from 100 lux to 10,000 lux, and wherein the second luminance range is equal to or less than 100 lux.

17. The method of claim 13, further comprising: differently driving the at least two sets of light-emitting elements from each other according to a gradation level of the pixel portion in the second luminance range.

18. The method of claim 17, further comprising: driving a portion of the at least two sets of light-emitting elements according to a gradation level of the pixel portion in the second luminance range.

19. The method of claim 13, further comprising: inputting a same driving signal (PWM) to the at least two sets of light-emitting elements in the first luminance range, and inputting the same or different driving signals (PWM) to the at least two sets of light-emitting elements in the second luminance range.

20. The method of claim 13, further comprising: inputting the same driving signal (PWM) to the at least two sets of light-emitting elements in the first luminance range, and inputting different driving signals (PWM) to the at least two sets of light-emitting elements according to a gradation level of the pixel portion in the second luminance range.

Images