LED Lighting System

Abstract

The LED lighting system includes an LED light source including three or more (N) LED channels, each having one or more LEDs and configured to emit light having different color temperatures ranging from a relatively highest color temperature to a relatively lowest color temperature, a driver configured to electrically drive each of the LED channels, and a control unit configured to control the driver to adjust the brightness of the light emitted from each of the LED channels in response to an input dimming signal. The control unit controls the brightness and color temperature of the mixed light emitted from the LED light source to decrease in conjunction with an increase in a dimming level indicated by the dimming signal.

Description

[Technical field]

[0001] The present invention relates to an LED lighting system, and more particularly to an LED lighting system configured to change the correlated color temperature (CCT) of light in conjunction with light dimming. [Background technology]

[0002] LEDs (Light Emitting Diodes), which have a long life span and excellent energy efficiency, are used as the light source for various types of lighting systems, and various attempts are being made to improve the lighting quality by improving the optical characteristics of LEDs. One example of such attempts is a technology that gradually lowers the correlated color temperature as the brightness decreases in an LED lighting system with a dimming function that gradually reduces the brightness of the output light (so-called dim-to-warm technology).

[0003] As an example, US Patent US7,288,902 discloses a technique for controlling the driving current of LEDs having different color temperatures so as to mimic the color temperature change according to the brightness change of an incandescent lamp. As another example, US Patent US9,769,895 discloses a technique for independently controlling the driving current of a white LED and a red LED so as to mimic the dimming characteristics of an incandescent lamp. As another example, Korean Patent 10-2136773 discloses a technique for independently controlling the operating current of a cool LED and a warm LED so as to mimic the correlated color temperature of an incandescent lamp during dimming. As another example, US Patent US8,330,394 discloses a technique for controlling the operating voltage of an LED so that the color of light changes from white to red as the light is dimmed.

[0004] Although the existing technologies provide a means for changing the correlated color temperature in conjunction with the dimming of an LED lighting system, they only provide a method for making the correlated color temperature warmer as the brightness decreases to mimic the light characteristics of an incandescent bulb. Therefore, there is a need to optimize an LED lighting system while realizing desired light characteristics in consideration of the required correlation between brightness and correlated color temperature during dimming. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent No. 7,288,902 [Patent Document 2] U.S. Patent No. 9,769,895 [Patent Document 3] Korean Patent No. 10-2136773 [Patent Document 4] U.S. Patent No. 8,330,394 Summary of the Invention [Problem to be solved by the invention]

[0006] The problem to be solved by the present invention is to provide an LED lighting system having a dim-to-warm function that is optimized in terms of structure and manufacturing cost according to the brightness and correlated color temperature required during dimming by using a plurality of LEDs having different correlated color temperatures. [Means for solving the problem]

[0007] According to an embodiment of the present invention, an LED lighting system capable of implementing a dimming function for adjusting the brightness of output light to decrease includes an LED light source including three or more LED channels configured to emit light of different color temperatures, and an electric circuit configured to electrically drive the three or more LED channels, wherein the electric circuit is configured to drive the three or more LED channels such that the brightness and color temperature of the output light obtained by the LED light source decrease together in conjunction with each other during dimming to decrease the brightness of the output light.

[0008] The electric circuit may be operable to drive the remaining LED channels except for at least one of the three or more LED channels at all dimming levels according to the dimming function to generate output light according to the dimming levels.

[0009] The electric circuit may be configured to divide the three or more LED channels into dimming control sections, the number of which is one less than the number of the three or more LED channels, and to drive the three or more LED channels, and the electric circuit may be configured to selectively use any one of combinations of two LED channels selected from the three or more LED channels in each dimming control section to realize brightness and color temperature of the output light according to the dimming level.

[0010] The combination of two LED channels may be two LED channels having adjacent color temperatures among the three or more LED channels.

[0011] The electrical circuit may be configured to drive one or more of the two LED channels constituting the selected LED combination at each dimming level to realize brightness and color temperature of the output light according to the dimming level.

[0012] The light produced by the combination of the two LED channels may each be configured to produce light whose coordinates on the blackbody locus on a chromaticity diagram lie within a 10-step MacAdam ellipse.

[0013] Each of the LED channels can emit light that is located within a 10-step MacAdam ellipse in coordinates on the blackbody locus on a chromaticity diagram.

[0014] An LED channel emitting light having the highest color temperature among the three or more LED channels may have a light spectrum in which a maximum value of relative emission intensity is 60% or more in a 380 to 500 nm band, and an LED channel emitting light having the lowest color temperature among the three or more LED channels may have a light spectrum in which a maximum value of relative emission intensity is 30% or less in a 380 to 500 nm band.

[0015] The LED lighting system according to another embodiment of the present invention may further include a control interface configured to receive a desired dimming level from a user and output a dimming signal corresponding to the input dimming level to the electric circuit.

[0016] The electric circuit may be configured to implement a timer function, and when the timer function is activated, the electric circuit may control the light emitted from the LED channel having the lowest color temperature to be automatically dimmed for a predetermined time and then turned off, or may control the mixed light emitted from the LED channel having the lowest color temperature and the LED channel having the next lowest color temperature to be automatically dimmed while decreasing in color temperature for a predetermined time and then turned off.

[0017] The ratio of the maximum brightness of the k-th LED channel in descending order of color temperature among the three or more LED channels to the maximum brightness of the LED channel that emits light with the highest color temperature among the three or more LED channels may be smaller than the value calculated by (N - k + 1) 2 / (4 * (N - 1)) (where 1 < k <= N).

[0018] The three or more LED channels may include a first LED channel having at least one first LED that emits light with a first color temperature, a second LED channel having at least one second LED that emits light with a second color temperature lower than the first color temperature, and a third LED channel having at least one third LED that emits light with a third color temperature lower than the second color temperature. The electric circuit can be controlled to selectively use any one of the combinations of two LED channels selected from the first to third LED channels according to the magnitude of the brightness of the mixed light corresponding to the dimming level so that the desired brightness and color temperature are realized.

[0019] The first and second LED channels can emit white light, and the third LED channel can emit amber or red light.

[0020] The first color temperature can be 10,000K to 4,000K, the second color temperature can be 3,500K to 2,500K, and the third color temperature can be 2,500K to 1,000K.

[0021] The first to third LED channels can emit light located within a 10-step MacAdam ellipse at coordinates on the blackbody locus on the chromaticity diagram.

Advantages of the Invention

[0022] According to the present invention, by providing three or more LED channels each emitting light having a different color temperature and generating mixed light using two LED channels with adjacent color temperatures in each section during dimming, it is possible to achieve color expression over a wide range of color temperatures and color expression that can closely follow the blackbody locus on a chromaticity diagram.

[0023] Furthermore, when the brightness becomes darker due to an increase in the dimming level, the brightness and color temperature decrease together, so that the maximum brightness of the LED channel emitting warm light with a low color temperature can be reduced, and therefore the number of LEDs in the LED channel emitting light with a low color temperature can be reduced. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a block diagram of an LED lighting system according to one embodiment of the present invention. [Diagram 2] 2 shows a chromaticity diagram showing schematic coordinates of light from three LED channels having different color temperatures of an LED lighting system according to an embodiment of the present invention. [Diagram 3] 1 shows a chromaticity diagram showing a locus of mixed light that can be realized by combining two lights having relatively high color temperatures among the three lights shown in the chromaticity diagram of FIG. 2. [Figure 4] 3 shows a chromaticity diagram showing a locus of mixed light that can be realized by combining two lights having relatively low color temperatures among the three lights shown in the chromaticity diagram of FIG. 2. [Diagram 5] 3 shows an example of a graph showing target brightness and target color temperature according to dimming levels using the three lights shown in the chromaticity diagram of FIG. 2. [Figure 6] 6 shows an example of a graph showing the brightness of three lights according to dimming levels for realizing the target brightness and the target color temperature shown in FIG. 5. [Figure 7]13 shows a chromaticity diagram showing schematic coordinates of light from three LED channels having different color temperatures of an LED lighting system according to another embodiment of the present invention. [Figure 8] 8 shows a chromaticity diagram showing a locus of mixed light that can be realized by combining two lights having relatively high color temperatures among the three lights shown in the chromaticity diagram of FIG. 7. [Figure 9] 8 shows a chromaticity diagram showing a locus of mixed light that can be realized by combining two lights having relatively low color temperatures among the three lights shown in the chromaticity diagram of FIG. 7. [Figure 10] 8 shows an example of a graph showing target brightness and target color temperature according to dimming levels using three lights shown in the chromaticity diagram of FIG. 7. [Figure 11] 11 shows an example of a graph showing the brightness of three lights according to dimming levels for realizing the target brightness and the target color temperature shown in FIG. [Figure 12] 1 shows a chromaticity diagram illustrating exemplary coordinates of light of three LED channels having different color temperatures according to an embodiment of the present invention. [Figure 13] 1 shows a chromaticity diagram in which the coordinates of two lights having different color temperatures according to the prior art are displayed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0026] Fig. 1 shows a block diagram of an LED lighting system according to an embodiment of the present invention. Referring to Fig. 1, an LED light source 10 includes three or more, for example, N (a natural number equal to or greater than 3) LED channels 11, 12, and 13. Each of the LED channels 11, 12, and 13 includes one or more LEDs and is configured to emit light having different color temperatures from the highest color temperature to the lowest color temperature. Here, color temperature means correlated color temperature (CCT), and will be simply referred to as color temperature hereinafter.

[0027] The LED lighting system according to the embodiment of the present invention may be embodied as any type of lighting device, such as a desk lamp, a lamp installed on a ceiling or a wall, or the like.

[0028] The LED channel #1 11 emits light with the highest color temperature among the N LED channels, and the remaining LED channels emit light with progressively lower color temperatures as the channel number increases. Thus, the LED channel #N 13 emits light with the lowest color temperature. Although two embodiments including three LED channels will be described below, the number of LED channels is not limited thereto, and four or more LED channels may be provided. Each of the LED channels 11, 12, and 13 may include one or more LEDs that emit light with a corresponding color temperature, and may include LEDs that emit light with various color temperatures and colors, such as white LEDs, red and amber LEDs, as light sources.

[0029] The driver 20 is configured to electrically drive each of the LED channels 11, 12, and 13. For example, the driver 20 may be configured with an electric circuit that can selectively drive each of the LED channels 11, 12, and 13 by applying a driving current to each of the LED channels 11, 12, and 13. For example, the driver 20 may be configured with a current driver that can supply a desired amount of current, a constant voltage driver that can apply a constant voltage, and an electric circuit that can drive the LEDs of the LED channels in any manner. As shown in FIG. 1, the driver 20 may include three or more drivers 21, 22, and 23 provided for each of the LED channels 11, 12, and 13 so as to drive each of the LED channels 11, 12, and 13, respectively.

[0030] The control unit 30 is configured to control the driver 20 so that the brightness of the light emitted from each of the LED channels 11, 12, and 13 is adjusted according to an input dimming signal. The dimming signal may be input to the control unit 30 through a control interface 40. The control unit 30 may include a microprocessor, memory, and related hardware and software, and may be programmed to control the driver 20 according to the control logic described below.

[0031] The control interface 40 is configured to receive a desired dimming level from a user. When a user inputs a desired dimming level using the control interface 40, the control interface 40 generates a dimming signal corresponding to the input dimming level and outputs it to the control unit 30, and the control unit 30 can output a control signal for driving the driver 20 according to the transferred dimming signal. At this time, the control unit 30 can obtain a driving current for driving each of the LED channels 11, 12, and 13 to realize the input dimming level from the dimming table 50. The dimming table 50 can be configured as a lookup table including data on the driving current of each of the LED channels 11, 12, and 13 to realize a dimming level (i.e., a brightness level of light) corresponding to each dimming signal. As another example, the control unit 30 can calculate a driving current corresponding to the input dimming level using a predetermined function.

[0032] The control interface 40 may be formed integrally with elements constituting the main body of the lighting system, such as the control unit 30, the driver 20, and the LED light source 30, or may be formed separately and remotely and connected in a wired or wireless manner. The control interface 40 may be embodied as any interface configured to allow a user to input a desired dimming level, such as a rotary or sliding knob, or a touch screen input means.

[0033] The control unit 30 controls the brightness and color temperature of the mixed light emitted from the LED light source 10 to decrease together as the dimming level indicated by the dimming signal increases. Here, the increase in the dimming level means that the brightness of the light gradually becomes darker. For example, the dimming level may have a total of 21 levels from 1 to 21, and the 1st dimming level may indicate a state where the brightness is maximum, and the 21st dimming level may indicate a state where the brightness is zero. In this process, the brightness may be set to gradually decrease as the dimming level increases from 1 to 21. In the embodiment of the present invention, the brightness is decreased as the dimming level increases, and the color temperature is also decreased in conjunction with the brightness. As a result, the color temperature is decreased in conjunction with the decrease in brightness due to dimming, so that a warm light with a low color temperature can be created as the dimming progresses, thereby implementing a dim-to-warm function. At low dimming levels, a bright mixed light with a high color temperature is produced, making it suitable for use in work, study, etc. At high dimming levels, a dark mixed light with a low color temperature is produced, making it suitable for use in rest, sleep, etc.

[0034] Further, according to an embodiment of the present invention, the control unit 30 is configured to control the driver 20 according to consecutive N-1 control periods set according to an increase in dimming level. At least one of two LED channels having adjacent color temperatures are used to obtain mixed light in each control period. For example, when N LED channels from 1 to N arranged in the order of increasing color temperature are used, at the control period with the lowest dimming level, at least one of the 1st and 2nd LED channels are used to generate mixed light, and at the control period with the next dimming level, at least one of the 2nd and 3rd LED channels are used to generate mixed light. In this manner, dimming is performed by sequentially using two LED channels having adjacent color temperatures in each control period, and at the last control period, mixed light is generated by using the Nth LED channel having the lowest color temperature and at least one of the LED channel before it. Since mixed light is generated using two LED channels having adjacent color temperatures in each control period in this manner, light characteristics that approximate a desired locus on a chromaticity diagram during dimming can be realized. This will be described again later.

[0035] Each LED channel 11, 12, 13 can emit light whose coordinates lie within a 10-step MacAdam ellipse on the black body locus on the chromaticity diagram.

[0036] The LED channel 11 emitting light having the highest color temperature among the N LED channels may emit light having a light spectrum with a maximum relative emission intensity of 60% or more in a 380 to 500 nm band, and the LED channel 13 emitting light having the lowest color temperature among the N LED channels may emit light having a light spectrum with a maximum relative emission intensity of 30% or less in a 380 to 500 nm band. When the brightness of the mixed light is at a low dimming level, light having a high color temperature that occupies a large portion of the mixed light contains a large amount of spectrum around 460 nm that suppresses melatonin secretion, and when the brightness of the mixed light is at a high dimming level, light having a low color temperature that occupies a large portion of the mixed light contains a small amount of spectrum around 460 nm, thereby suppressing melatonin secretion in a high brightness state and improving concentration, and when the brightness is at a low dimming level, helping melatonin secretion and sleep.

[0037] Meanwhile, according to an embodiment of the present invention, the control unit 30 may be configured to implement a timer function. When the timer function is activated, the LED channel having the lowest color temperature among the N LED channels may be driven to perform dimming, and more specifically, the light with the lowest color temperature may be automatically dimmed for a predetermined time and then turned off. Meanwhile, in another example, when the timer function is activated, the LED channel emitting the light with the lowest color temperature among the N LED channels (i.e., the Nth LED channel) and the LED channel emitting the light with the next lowest color temperature (i.e., the N-1th LED channel) may be both driven to gradually dim as the color temperature decreases and then turned off.

[0038] Meanwhile, the LED lighting system according to another embodiment of the present invention may have a wireless charging function for wirelessly charging a mobile phone, etc. When the LED lighting system according to the embodiment of the present invention is embodied in the form of a desk lamp, etc., it may have a mobile phone rest pad for wireless charging, and the mobile phone may be wirelessly charged when the user places the mobile phone on the rest pad. A detailed description of the electric circuit for implementing the wireless charging function will be omitted.

[0039] In a system consisting of N LED channels, if the color temperature decreases linearly with an increase in the dimming level and the change in brightness is expressed as decreasing with an m-th order polynomial, the mixing ratio of the kth LED channel to the k-1th LED channel (y k ) can be expressed by the following Equation 1.

number

[0040] The brightness ratio of the kth channel to the maximum brightness of the 1st channel with the highest color temperature (L k ) is expressed by the following formula 2.

number

[0041] At this time, the overall system brightness (L total ) is x mTherefore, the brightness ratio of the kth channel to the maximum brightness of the 1st channel (L k ) is expressed by the following Equation 3.

number

number

number

number

[0042] Therefore, the maximum brightness of the k-th LED channel is preferably smaller than that in the case of a first-order polynomial where m = 1. Substituting m = 1 into the above Equation 6, the maximum brightness (L k_max ) of the k-th LED channel is represented by the following Equation 7.

Equation

[0043] Therefore, according to an embodiment of the present invention, the ratio of the maximum brightness of the k-th LED channel to the maximum brightness of the LED channel that emits light with the highest color temperature among the N LED channels can be set to be smaller than the value calculated by (N - k + 1) 2 / (4 * (N - 1)) (where 1 < k <= N).

[0044] The LED lighting system according to an embodiment of the present invention includes three LED channels that respectively emit light with three different color temperatures. In this case, the highest color temperature among the three color temperatures is a value between 10,000K and 4,000K, the intermediate color temperature is a value between 3,500K and 2,500K, and the lowest color temperature can be a value between 2,500K and 1,000K. Also, the three lights having each color temperature can be lights located within a 10-step MacAdam ellipse at coordinates on the blackbody locus on the chromaticity diagram. By using three LED channels having such three different color temperatures respectively, in a section corresponding to a relatively bright low dimming level, mixed light is created by the light having the highest color temperature belonging to the range between 10,000K and 4,000K and the light having the next highest color temperature belonging to the range between 3,500K and 2,500K. In a section corresponding to a relatively dark high dimming level, mixed light is created by the light having a color temperature belonging to the range between 3,500K and 2,500K and the light having the lowest color temperature belonging to the range between 2,500K and 1,000K. Since dimming is performed by sequentially using LED channels with consecutive color temperatures among such three LED channels having different color temperatures from each other, color expression that follows the blackbody locus on the chromaticity diagram is possible.

[0045] More specifically, general lighting products using existing tunable white LEDs are configured to be able to change brightness and color temperature independently within the range of 6,500K to 2,700K, in which case color expression is performed along a straight line section connecting the coordinates corresponding to 6,500K and 2,700K on the blackbody locus of the chromaticity diagram shown in Figure 2, and since the line does not deviate significantly from the blackbody locus, color expression that closely follows the blackbody locus is possible. However, if the range is expanded to below 2,500K in order to further expand the color temperature expression range, the blackbody locus bends significantly around 2,500K as shown in Figure 2, making it impossible to express colors that closely follow the blackbody locus. 13, when light corresponding to a coordinate 601 of approximately 6,500K on the blackbody locus 301 on the chromaticity diagram and light corresponding to a coordinate 602 of approximately 2,050K are mixed in a known manner, a mixed light having coordinates on a line 603 connecting the two coordinates 601, 602 is obtained. At this time, the coordinates of a portion of the line 603 deviate significantly from the blackbody locus, and the 10-step MacAdam ellipse of a portion of the coordinate 604 deviates from the blackbody locus, and therefore it is not possible to express colors that closely follow the blackbody locus. As another example of the conventional technology, there is a dimming technology that mixes three lights of different colors, for example, green light, blue light, and red light, to express a color that follows a desired locus on a chromaticity diagram, for example, a blackbody locus, but this existing technology can express a color within the entire area of ​​a triangle that connects the coordinates of the three lights on the chromaticity diagram, and can express a color that precisely follows the blackbody locus if necessary, but there is a problem that the brightness and color temperature according to the dimming are not controlled in conjunction with each other, making the control complicated and significantly increasing the manufacturing cost of the lighting system. The present invention solves this problem and provides a method that allows a wide range of color temperature expression and a color expression that similarly follows the blackbody locus, and the LED lighting system according to the embodiment of the present invention uses three or more LED channels having different color temperatures, but by using two LED channels with adjacent color temperatures for each section, it is possible to express a color in a wide color temperature range while similarly following the blackbody locus.For example, in the embodiment of the present invention, as shown in Fig. 12, a light corresponding to a coordinate 501 of about 6,500K on the blackbody locus 301 in the chromaticity diagram, a light corresponding to a coordinate 502 of about 3,000K, and a light corresponding to a coordinate 503 of about 1,750K are used, and the two lights corresponding to the coordinates 501 and 502 with high color temperatures are mixed in a dimming section where the brightness is relatively bright, and the two lights corresponding to the coordinates 502 and 503 with low color temperatures are mixed in a dimming section where the brightness is relatively low, thereby making it possible to express colors on two straight lines 504 and 505 that similarly follow the blackbody locus 301 over a wide color temperature range. Although the background portion showing the color temperature in the chromaticity diagram shown in Fig. 2 etc. is displayed in black and white, it can be understood that it has the same distribution as the color temperature of a commonly used chromaticity diagram.

[0046] Hereinafter, an embodiment including three LED channels each emitting light of three different color temperatures will be described. As specific examples, two embodiments using three LED channels each generating light of different color temperatures, that is, an embodiment using three white LED channels each generating white light having different color temperatures, and an embodiment using two white LED channels generating white light and one amber LED channel generating amber light having different color temperatures will be described. Table 1 and FIGS. 2 to 6 are for explaining an embodiment using three white LED channels, and Table 2 and FIGS. 7 to 11 are for explaining an embodiment using two white LED channels and one amber LED channel. These two examples are illustrative for explaining the embodiments of the present invention, and the number of LED channels, the color temperature of the generated light, etc. may be variously changed.

[0047] Example 1: White 6,500K - White 3,000K - White 2,000K An LED channel that generates white light with a color temperature of 6,500 K (Kelvin), an LED channel that generates white light with a color temperature of 3,000 K, and an LED channel that generates white light with a color temperature of 2,000 K are used. Each LED channel can contain one or more LEDs that generate white light with the corresponding color temperature.

[0048] 2 shows a chromaticity diagram in which coordinates (xy scale) 101 of 6,500K white light, coordinates 102 of 3,000K white light, and coordinates 103 of 2,000K white light generated by three LED channels are displayed on a CIE (International Commission on Illumination) color chart, and further shows a black body locus 301. As shown in the drawing, the three white lights used are white lights having coordinates on the black body locus 301.

[0049] When there are three LED channels emitting light of different color temperatures, i.e., N=3, dimming control is performed by dividing into N-1 control sections, i.e., 2 control sections. In a relatively bright control section with a low dimming level, mixed light is generated using two adjacent lights with high color temperatures, i.e., two LED channels that generate 6,500K white light and 3,000K white light, and in a relatively dark control section with an increased dimming level, mixed light is generated using two adjacent lights with low color temperatures, i.e., two LED channels that generate 3,000K white light and 2,000K white light.

[0050] 3 shows a light coordinate locus 111 that can be obtained by mixing 6,500K white light and 3,000K white light in a relatively bright first control section, and one coordinate 112 of the locus 111 is shown as an example. At this time, the light coordinate locus 111 that can be obtained by mixing 6,500K white light and 3,000K white light coincides with a straight line connecting the coordinate 101 of the 6,500K white light and the coordinate 102 of the 3,000K white light. The ellipse designated by reference numeral 113 in FIG. 3 indicates a 10-step MacAdam ellipse of the light coordinate 112 of the mixed light. In an embodiment of the present invention, the mixed light obtained by mixing light generated by LED channels of adjacent color temperatures is configured to lie within a 10-step MacAdam ellipse at coordinates on the blackbody locus on a chromaticity diagram, which can be interpreted as being equivalent to a 10-step MacAdam ellipse at any coordinate on the coordinate locus 111 of the mixed light in FIG. 3 including at least a portion of the blackbody locus 301.

[0051] Meanwhile, Fig. 4 shows a light coordinate locus 121 that can be obtained by mixing 3,000K white light and 2,000K white light in a relatively dark second control section, and one coordinate 122 of the locus 121 is exemplarily shown. At this time, the light coordinate locus 121 that can be obtained by mixing 3,000K white light and 2,000K white light coincides with a straight line connecting the coordinate 102 of the 3,000K white light and the coordinate 103 of the 2,000K white light. The ellipse designated by reference numeral 123 in Fig. 4 indicates a 10-step MacAdam ellipse of the light coordinate 122 of the mixed light. Similar to the first control section, in the second control section, the mixed light obtained by mixing the light generated by the LED channels of adjacent color temperatures is configured to be located within a 10-step MacAdam ellipse at coordinates on the blackbody locus on the chromaticity diagram, which can be interpreted as being equivalent to a 10-step MacAdam ellipse at any coordinate on the coordinate locus 121 of the mixed light in FIG. 4 including at least a portion of the blackbody locus 301.

[0052] By making the mixed light obtainable by mixing light of adjacent color temperatures lie within a 10-step MacAdam ellipse in coordinates on the blackbody locus, the mixed light approximating the blackbody locus can be maintained during the dimming process.

[0053] Table 1 shows an example of the brightness of each light for realizing the target brightness and the target color temperature according to the dimming level using 6,500K white light, 3,000K white light, and 2,000K white light. In Table 1, the brightness of each white light is calculated as a value that can achieve the target brightness and the target color temperature, and is listed as a value rounded off to the nearest tenth. The dimming level No. is a sequential numbering of each dimming level step, and the % value is a value obtained by sequentially decreasing the dimming step by the same amount from 100% to 0%. For example, the target brightness is a value obtained by adding up the brightness of each light, and the target color temperature is roughly calculated as a weighted average value according to the brightness of the color temperature of each light, and the brightness of each light can be determined as a value that satisfies these conditions.

[0054] [Table 1] Meanwhile, Fig. 5 is a graph showing the target brightness and the target color temperature percentage for each dimming level in Table 1, and Fig. 6 is a graph showing the brightness of each light for each dimming level in Table 1. In Table 1, the target brightness is set to the maximum brightness of the system at dimming level No. 1, which is the lowest dimming level, and is set to be turned off at dimming level No. 21, which is the highest dimming level, and Fig. 5 shows the target brightness as a percentage of the brightness of the corresponding dimming level relative to the maximum brightness. In Table 1, the target color temperature is set to 6,500K, which is the highest color temperature of the three lights used in dimming level No. 1, and 2,000K, which is the lowest color temperature, at dimming level No. 21. Fig. 6 shows the target brightness as a percentage of the target color temperature for each dimming level when the color temperature of 6,500K is set to 100% and the color temperature of 2,000K is set to 0%. Referring to Table 1, Figures 5 and 6, when implementing the dim-to-warm function using three (N=3) different LED channels, dimming control is performed by dividing into two (N-1) control sections C11 and C12. In Figures 5 and 6, the horizontal axis indicates the dimming level as a percentage, with 100% on the far right corresponding to the lowest dimming level where the LEDs are lit to maximum brightness, and 0% at the origin corresponding to the highest dimming level where the LEDs are turned off. In other words, as the dimming level increases, the horizontal axis in Figures 5 and 6 follows a path that moves from the right to the left.

[0055] First, in the first control section C11, a mixed light is generated by mixing the light having the highest color temperature of 6,500K with the light having the next highest color temperature of 3,000K. The first control section C11 is a section where the dimming level ranges from 100% to 25%. In the first control section C11, as the dimming level increases, the brightness of the 6,500K white light having a relatively high color temperature gradually decreases, and the brightness of the 3,000K white light having a relatively low color temperature gradually increases and then decreases again.

[0056] Next, in the second control section C12, the light having a middle color temperature of 3,000K is mixed with the light having the lowest color temperature of 2,000K to generate a mixed light. The second control section C12 is a section from dimming level 20% to 0%. In this control section C12, as the dimming level increases, the brightness of the 3,000K white light having a relatively high color temperature is gradually decreased, and the brightness of the 2,000K light having a relatively low color temperature is increased and then decreased. As such, when the dimming level increases in each of the control sections C11 and C12, the brightness of the LED channel having a higher color temperature among two adjacent LED channels is gradually decreased, and the brightness of the LED channel having a lower color temperature is gradually increased and then decreased, so that the brightness percentage tends to decrease nonlinearly with the increase in the dimming level as shown in FIG. 5. If the brightness percentage changes nonlinearly with the linear change in the dimming level as shown in FIG. 5, the user will recognize that the brightness changes linearly with the linear change in the dimming level. This is because the human eye is insensitive to brightness changes when it is relatively bright, but is sensitive to brightness changes when it is relatively dark. At a relatively bright low dimming level, the brightness change increases with the change in dimming level, so that the user perceives the brightness as changing linearly similar to the linear change in the dimming level. This provides a high-quality lighting system in which the brightness can be perceived as changing linearly in response to the linear change in the dimming level.

[0057] As shown in Fig. 5, the brightness of each light changes nonlinearly with the dimming level in the two control sections C11 and C12, and the percentage of the target brightness changes linearly with the dimming level. For example, the percentage of the target brightness may change nonlinearly in the form of a polynomial function or exponential function of a quadratic or higher order with respect to the dimming level, and the percentage of the target color temperature may change in the form of a linear function. In particular, by changing the percentage of the target brightness nonlinearly with the dimming level, it is possible to make it possible for the naked eye to recognize that the brightness change during the dimming process changes linearly with the linear change of the dimming level.

[0058] Example 2: White 6,500K - White 2,700K - Amber 1,700K An LED channel that generates white light with a color temperature of 6,500K (Kelvin), an LED channel that generates white light with a color temperature of 2,700K, and an LED channel that generates amber light with a color temperature of 1,700K are used. Each LED channel may include one or more LEDs that generate white light or amber light with a corresponding color temperature. Descriptions that overlap with those of the first embodiment will be omitted. In another embodiment of the present invention, red light may be used instead of amber light.

[0059] 7 shows a chromaticity diagram in which coordinates 201 of 6,500K white light, coordinates 102 of 2,700K white light, and coordinates 203 of 1,700K white light generated by three LED channels are plotted on a CIE color chart, and additionally shows a blackbody locus 301. As shown in the drawing, the two white lights used are white lights having coordinates on the blackbody locus 301, and the amber light is a light having coordinates that lie within a 10-step MacAdam ellipse at one coordinate on the blackbody locus 301.

[0060] As in the first embodiment, dimming control is performed by dividing into two control sections. In the relatively bright control section where the dimming level is low, mixed light is generated using two adjacent lights with high color temperatures, i.e., two LED channels that generate 6,500K white light and 2,700K white light, and in the relatively dark control section where the dimming level is increased, mixed light is generated using two adjacent lights with low color temperatures, i.e., two LED channels that generate 2,700K white light and 1,700K amber light.

[0061] 8 shows a light coordinate locus 211 that can be obtained by mixing 6,500K white light and 2,700K white light in a relatively bright first control section, and one coordinate 212 of the locus 211 is shown as an example. At this time, the light coordinate locus 211 that can be obtained by mixing 6,500K white light and 2,700K white light coincides with a straight line connecting the coordinate 201 of the 6,500K white light and the coordinate 202 of the 2,700K white light. An ellipse designated by reference numeral 213 in FIG. 8 indicates a 10-step MacAdam ellipse of the light coordinate 212 of the mixed light. In an embodiment of the present invention, the mixed light obtained by mixing light generated by LED channels of adjacent color temperatures is configured to be located within a 10-step MacAdam ellipse at coordinates on the blackbody locus on a chromaticity diagram, which can be interpreted as being equivalent to a 10-step MacAdam ellipse at any coordinate on the coordinate locus 211 of the mixed light in FIG. 8 including at least a portion of the blackbody locus 301.

[0062] Meanwhile, Fig. 9 shows a light coordinate locus 221 that can be obtained by mixing 2,700K white light and 1,700K amber light in a relatively dark second control section, and one coordinate 222 of the locus 221 is exemplarily shown. At this time, the light coordinate locus 221 that can be obtained by mixing 2,700K white light and 1,700K amber light coincides with a straight line connecting the coordinate 202 of the 2,700K white light and the coordinate 203 of the 1,700K amber light. The ellipse designated by reference numeral 223 in Fig. 9 indicates a 10-step MacAdam ellipse of the light coordinate 222 of the mixed light. Similar to the first control section, in the second control section, the mixed light obtained by mixing the light generated by the LED channels of adjacent color temperatures is configured to be located within a 10-step MacAdam ellipse at coordinates on the blackbody locus on the chromaticity diagram, which can be interpreted as being equivalent to a 10-step MacAdam ellipse at any coordinate on the coordinate locus 221 of the mixed light in FIG. 9 including at least a portion of the blackbody locus 301.

[0063] By making the mixed light obtainable by mixing light of adjacent color temperatures lie within a 10-step MacAdam ellipse in coordinates on the blackbody locus, the mixed light approximating the blackbody locus can be maintained during the dimming process.

[0064] Table 2 shows an example of the brightness of each light to realize the target brightness and target color temperature according to the dimming level using 6,500K white light, 2,700K white light, and 1,700K amber light. The brightness of each light in Table 2 is calculated based on the value that can achieve the target brightness and target color temperature, and is listed with the value rounded off to the first decimal place.

[0065] [Table 2] Meanwhile, FIG. 10 is a graph showing the percentage of the target brightness and the target color temperature for each dimming level in Table 2, and FIG. 11 is a graph showing the brightness of each light for each dimming level in Table 2.

[0066] Referring to Table 2, FIG. 10 and FIG. 11, as in the first embodiment, the dimming control is performed by dividing into two control sections C21 and C22. First, in the first control section C21, a light having the highest color temperature of 6,500K and a light having the second highest color temperature of 2,700K are mixed to generate a mixed light. The first control section C21 is a section from dimming level 100% to 40%. In the first control section C21, as the dimming level increases, the brightness of the 6,500K white light having a relatively high color temperature is gradually decreased, and the brightness of the 2,700K white light having a relatively low color temperature is gradually increased and then decreased again. Next, in the second control section C22, a light having an intermediate color temperature of 2,700K and a light having the lowest color temperature of 1,700K are mixed to generate a mixed light. The second control section C22 is a section from dimming level 35% to 0%. In this control section C22, as the dimming level increases, the brightness of the 2,700K white light, which has a relatively high color temperature, gradually decreases, and the brightness of the 1,700K amber light, which has a relatively low color temperature, increases and then decreases. By controlling the brightness of each light in this manner, as described above, the brightness percentage may tend to change nonlinearly with the linear change in the dimming level, and therefore the user may perceive the brightness as changing linearly similar to the linear change in the dimming level.

[0067] Although the embodiments of the present invention have been described above, the scope of the invention is not limited thereto, and includes all changes and modifications that can be easily modified from the embodiments of the present invention by a person having ordinary knowledge in the technical field to which the present invention belongs and are deemed to be equivalent. [Industrial Applicability]

[0068] INDUSTRIAL APPLICABILITY The present invention relates to an LED lighting system and can be applied to lighting devices, and therefore has industrial applicability.

Claims

1. In an LED lighting system capable of implementing a dimming function for adjusting the brightness of output light to be reduced, An LED light source including three or more LED channels each configured to emit light of a different color temperature; and an electrical circuit configured to electrically drive the three or more LED channels; a ratio of a maximum brightness of a k-th LED channel, which is arranged in order from highest to lowest color temperature among the three or more LED channels, to a maximum brightness of an LED channel emitting light of the highest color temperature among the three or more LED channels is smaller than a value calculated by (N-k+1)2 / (4*(N-1)) (where 1<k<=N, N is the number of LED channels); The electric circuit is configured to drive the three or more LED channels such that the brightness and color temperature of the output light obtained by the LED light source are decreased in conjunction with each other during dimming in which the brightness of the output light is decreased. LED lighting system.

2. 2. The LED lighting system of claim 1, wherein the electric circuit operates to drive the remaining LED channels except for at least one of the three or more LED channels at all dimming levels according to the dimming function to generate output light according to the dimming levels.

3. The electric circuit is configured to drive the three or more LED channels by dividing the three or more LED channels into dimming control sections, the number of which is one less than the number of the three or more LED channels; 2. The LED lighting system of claim 1, wherein the electrical circuit is configured to selectively use any one of combinations of two LED channels selected from the three or more LED channels in each dimming control period to realize brightness and color temperature of the output light according to a dimming level by the dimming function.

4. The LED lighting system according to claim 3 , wherein the combination of two LED channels is made up of two LED channels having adjacent color temperatures among the three or more LED channels.

5. 5. The LED lighting system of claim 3, wherein the electrical circuit is configured to drive one or more of the two LED channels constituting the selected LED combination at each dimming level to realize brightness and color temperature of the output light according to the dimming level.

6. 5. The LED lighting system of claim 3, wherein the light generated by the combination of the two LED channels is configured to generate light whose coordinates on the blackbody locus on a chromaticity diagram lie within a 10-step MacAdam ellipse.

7. 7. The LED lighting system of claim 6, wherein each of the LED channels emits light whose coordinates on the blackbody locus lie within a 10-step MacAdam ellipse on a chromaticity diagram.

8. Among the three or more LED channels, an LED channel emitting light having the highest color temperature has a light spectrum in which a maximum value of a relative emission intensity is 60% or more in a 380 to 500 nm band; The LED channel emitting light having the lowest color temperature among the three or more LED channels has a light spectrum in which the maximum value of the relative luminous intensity is 30% or less in a 380 to 500 nm band.

5. An LED lighting system according to claim 1.

9. 5. The LED lighting system of claim 1, further comprising a control interface configured to receive a desired dimming level from a user and to output a dimming signal corresponding to the input dimming level to the electric circuit.

10. The electrical circuit is configured to implement a timer function, When the timer function is activated, the electric circuit controls the LED channel having the lowest color temperature among the three or more LED channels so that the light having the lowest color temperature is automatically dimmed and then turned off for a predetermined time, or controls the LED channel emitting the lowest color temperature and the LED channel emitting the next lowest color temperature among the three or more LED channels so that the light is automatically dimmed and then turned off while the color temperature is decreased for a predetermined time.

5. An LED lighting system according to claim 1.

11. The three or more LED channels include a first LED channel having at least one first LED emitting light having a first color temperature, a second LED channel having at least one second LED having a second color temperature lower than the first color temperature, and a third LED channel having at least one third LED having a third color temperature lower than the second color temperature, The electric circuit selectively uses any one of the combinations of two LED channels selected from the first to third LED channels according to the brightness of the mixed light emitted from the LED light source corresponding to the dimming level of the dimming function, thereby controlling to realize a desired brightness and color temperature.

2. The LED lighting system of claim 1.

12. the first and second LED channels emit white light; The third LED channel emits amber or red light.

12. An LED lighting system according to claim 11.

13. 13. The LED lighting system of claim 12, wherein the first color temperature is between 10,000K and 4,000K, the second color temperature is between 3,500K and 2,500K, and the third color temperature is between 2,500K and 1,000K.

14. 14. The LED lighting system according to claim 11, wherein the first to third LED channels emit light whose coordinates on the blackbody locus on a chromaticity diagram lie within a 10-step MacAdam ellipse.

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