Light-emitting diode arrangement, and method for dimming a light-emitting diode of a light-emitting diode arrangement

Abstract

Light-emitting diode arrangement comprising at least - a light-emitting diode (1), - a control device (4) which is designed to dim the at least one light-emitting diode (1) by means of pulse width modulation, wherein the pulse width modulation is characterized by a clock cycle (T) and a pulse duration (τ) during a clock cycle, - wherein the control device (4) is designed to control the at least one light-emitting diode (1) with packets (P) of at least two clock pulses, wherein - wherein the control device (4) is selectively configured to control the at least one light-emitting diode (1) in a first operating mode (B 1,p ) and at least one second operating mode (B 2,p ), - wherein the at least one light-emitting diode (1) is controlled in the second operating mode with at least one different pulse duration within the package (P), characterized in that - that in the first operating mode the pulse durations (τ) are equal within the packet (P) and - that the light-emitting diode arrangement is designed to illuminate at least one point (6), wherein the light-emitting diode arrangement is equipped with a detection device (5) which is designed to detect the relative movement speed (v), in particular angular speed (ω), of the at least one point (6) with respect to the detection device (5).

Description

[0001] The present invention relates to a light-emitting diode arrangement according to the preamble of claim 1, as well as a method for dimming a light-emitting diode of a light-emitting diode arrangement according to claim 6.

[0002] The brightness of light-emitting diodes (LEDs) can be adjusted using pulse-width modulation (PWM). Essentially, the LED's current is periodically switched on and off using pulse-width modulation (PWM). Here, the duty cycle (the time spent on versus off) is changed, while the current and pulse frequency remain constant.

[0003] Such dimmable LEDs are used today in many areas for lighting purposes, for example in PWM-dimmed LED traffic signs, LED car taillights, LED daytime running lights, but also in so-called matrix systems, which are used as main headlights in motor vehicles and consist of, for example, 100×100 LEDs or even 1000×1000 LEDs. In the latter matrix systems, for example, some LEDs are dimmed because otherwise glare could occur. For example, those LEDs whose light is directed at highly reflective traffic signs can be dimmed. Ultimately, the light emitted by a matrix system can be dynamically adapted to the area to be illuminated.

[0004] If the PWM method is used to dim the respective LEDs, the so-called pearl necklace effect can occur.

[0005] "The pearl-string effect is an optical illusion caused by rapid eye movements toward or away from a pulsed light source. Due to the inertia of the receptors in the eye, this leads to the multiple appearance of the light source, for example, PWM-dimmed LED traffic signs or LED car taillights. Depending on the pulse frequency, this effect can occur even when no flicker is perceptible upon direct observation, which can lead to irritation." (Source: www.emk.tu-darmstadt.de).

[0006] For this reason, among others, the LEDs are switched at such a high frequency (PWM frequency) that the human eye cannot perceive any flicker. Typically, 250 Hz or more is an acceptable value.

[0007] The matrix systems mentioned above are often controlled via video interfaces. One standard, for example, is the RGB interface. Based on RGB666 and the dimming information per LED of 6 bits, this results in 64 dimming levels (2 6 ). At a PWM frequency of 250 Hz, the resulting clock would be 4 ms. With 64 dimming levels, the resolution is 4 ms / 64 = 62.5 µs. For example, if a dimming of 50% is to be applied, the result is an on-time for an LED of 2 ms and an off-time of 2 ms. With a resolution of 64 levels, the next higher possible dimming would be 2.0625 ms / 4 ms = 51.5%. This corresponds to an increment of 1.5%, which is too high for many applications. With multiple LEDs of different brightness, for example, clearly visible grids result. Many OEMs therefore require resolutions of < 1%.

[0008] Another LED arrangement is known from document DE 10 2009 041 943 A1. This comprises at least - a light-emitting diode, - a control device which is designed to dim the at least one light-emitting diode by means of pulse width modulation, wherein the pulse width modulation is characterized by a clock pulse and a pulse duration during a clock pulse, - wherein the control device is configured to control the at least one light-emitting diode with packets of at least two clock pulses, - wherein the control device is configured to control the at least one light-emitting diode in an operating mode, - wherein the at least one light-emitting diode is controlled in this operating mode with at least one different pulse duration within the package.

[0009] With the LED arrangement known from this document, a better resolution is possible.

[0010] This is where the present invention comes in. Its objective is not only to propose an improved LED array, in particular to propose an LED array that, on the one hand, avoids the pearl-string effect or exhibits only a minimal pearl-string effect and, on the other hand, enables finer dimming, in particular < 1% increments, but also allows for individual adaptation to lighting situations. The control unit can accordingly implement the control that is optimal for the detected movement speed, in particular the angular velocity, of the illuminated point.

[0011] According to the invention, this object is achieved by a light-emitting diode arrangement having the characterizing features of claim 1. Due to the fact that the control device is configured to control the at least one light-emitting diode with packets of at least two pulses, wherein the control device is selectively configured to control the at least one light-emitting diode in a first operating mode and at least one second operating mode, wherein the at least one light-emitting diode is controlled with identical pulse durations within the packet in the first operating mode and is controlled with at least one different pulse duration within the packet in the second operating mode, finer dimming can be achieved and / or the string of pearls effect can be avoided. One possible procedure is as follows.

[0012] Based on the otherwise constant PWM frequency of 250Hz and the resulting clock T of 4ms, 51.5% brightness could be applied in the first clock T1 of 4ms. This corresponds to a resolution of 64 dimming levels (2 6 ) a pulse duration or on-time of (33 / 64)*4ms = 2.0625ms and a corresponding off-time of (31 / 64)*4ms = 1.9375ms. In the next three cycles T2 to T4, for example, 50% brightness can be applied, i.e. 2ms on-time and 2ms off-time each. In the four 4ms cycles, which are combined into a packet P, the average value for the eye is (51.5% + 3*50%) / 4 = 50.375%. Accordingly, in this second operating mode, with packets with different pulse durations, an increment of 0.375% can be achieved, thus increasing the resolution.

[0013] On the other hand, in the first operating mode, where no different pulse durations are provided within the packet, the pearl-string effect can be advantageously counteracted if a correspondingly high PWM frequency is selected.

[0014] According to the invention, the LED array is configured to illuminate at least one point, wherein the LED array is equipped with a detection device configured to detect the relative movement speed, in particular the angular velocity, of the at least one point with respect to the detection device. This measure allows for individual adaptation to lighting situations, with the control unit correspondingly implementing the control that is predefined as optimal for the detected movement speed, in particular the angular velocity, of the illuminated point.

[0015] Further advantageous embodiments of the proposed invention emerge in particular from the features of the subclaims. The subject matter and features of the various claims can, in principle, be combined with one another in any desired way.

[0016] In an advantageous embodiment of the proposed invention, the LED array can comprise a plurality of LEDs, in particular 100×100 or 1000×1000 LEDs combined as a matrix system. An LED array configured in this way can be advantageously used, for example, as the main headlight of a vehicle.

[0017] It can preferably be provided that the control device is configured to control the at least one LED according to the first operating mode or the second operating mode depending on the movement speed, in particular the angular speed. Here, the control unit will, for example, control the at least one LED or groups of LEDs using the first operating mode when the illuminated point is moving very quickly relative to the detection device. A stationary point, in contrast, would, for example, be controlled in the second operating mode.

[0018] In a further advantageous embodiment of the proposed invention, it can be provided that the control device is configured to control the number of clock pulses combined into a packet, in particular as a function of the movement speed, in particular the angular speed. This technical feature enables a further intervention option of the control device with regard to the control of the at least one light-emitting diode. This allows the resulting brightness modulation to be adjusted via the number of clock pulses combined into a packet, whereby packets consisting of fewer clock pulses tend to have a higher probability that the resulting brightness modulation is so high-frequency that it is not perceived by the human eye.

[0019] In a further advantageous embodiment of the proposed invention, the detection device can be a camera, a radar system, or a laser system. Such systems offer numerous possibilities for detecting the movement of the point(s) and processing them accordingly for the control device.

[0020] A further object of the present invention is to propose an improved method for dimming a light-emitting diode of a light-emitting diode array, in particular to propose a method that counteracts a string-of-pearls effect and enables finer dimming of the at least one light-emitting diode. According to the invention, this object is achieved by the method according to claim 6.

[0021] Further advantageous embodiments of the proposed invention emerge in particular from the features of the subclaims. The subject matter and features of the various claims can, in principle, be combined with one another in any desired way.

[0022] The invention is explained in more detail below with reference to the accompanying drawings. In the drawings: Fig. 1 Summary of the period durations with at least one different pulse duration in packets (second operating mode); Fig. 2 Summary of period durations with equal pulse durations in packets (first operating mode); Fig. 3 shows a schematic representation of a light-emitting diode arrangement according to the invention with a light-emitting diode; Fig. 4 shows a schematic representation of a light-emitting diode arrangement according to the invention with a light-emitting diode and a detection device (point stationary); Fig. 4a shows a schematic representation of a light-emitting diode arrangement according to the invention with a light-emitting diode and a detection device (moderate movement of the point); Fig. 4b shows a schematic representation of a light-emitting diode arrangement according to the invention with a light-emitting diode and a detection device (rapid movement of the point); Fig. 5 shows a light-emitting diode arrangement according to the invention in the form of a matrix system without a detection device; Fig. 6 shows a schematic representation of a light-emitting diode arrangement according to the invention with a plurality of light-emitting diodes and a detection device (points in the first movement pattern); List of reference symbols 1 light-emitting diode (light-emitting diode) 2 second LED 3 third LED 4 Control device 5 Recording device 6 point 7 point 8 point P Package τ pulse duration / switch-on time T cycle / period duration f frequency B 1,p first operating mode (p = number of clock pulses combined into a packet) B 2,p second operating mode (p = number of clock pulses combined into a packet)

[0023] A light-emitting diode arrangement according to the invention essentially comprises at least one light-emitting diode 1 and a control device 4 which is designed to dim the at least one light-emitting diode by means of pulse width modulation, wherein the pulse width modulation is essentially determined by a clock T and a pulse duration τ within the clock T.

[0024] A light-emitting diode arrangement according to the invention is characterized in that the control device 4 is designed to control the at least one light-emitting diode 1 with packets P of at least two clock pulses T, wherein the pulse durations τ within the clock pulses T of a packet P are the same (first operating mode) or at least one different pulse duration τ is provided within a packet P (second operating mode).

[0025] As already indicated, this essentially results in two operating modes for controlling the LED. For the sake of simplicity, the following explanation will refer to a first operating mode when the pulse durations τ are the same within the clock pulses T of a packet P, and a second operating mode when at least one different pulse duration τ is provided within a packet P.

[0026] Using the example of four cycles, the two operating modes are in the Fig. 1 and Fig. 2 shown.

[0027] The light-emitting diode arrangement can comprise more than one light-emitting diode, for example a plurality of light-emitting diodes which are combined in a so-called matrix system of 100×100 or 1000×1000 LEDs.

[0028] The control device can further be configured to control the number of clock pulses combined into a packet. The packet can generally comprise an integer multiple of the clock pulse, for example, two or four clock pulses.

[0029] The light-emitting diode arrangement can further be configured to illuminate at least one point 6, wherein the light-emitting diode arrangement is equipped with a detection device 5 which is configured to detect the relative movement speed of the at least one point 6 with respect to the detection device 5.

[0030] In principle, any reflective object that reflects the light emitted by at least one LED can be considered a point.

[0031] In this context, the control device 4 can be configured to evaluate this movement information in order to control the at least one light-emitting diode 1 according to the first operating mode or the second operating mode and / or to control the number of clock pulses T combined into a packet P as a function of the movement speed of the at least one point 6.

[0032] These control options result in numerous possibilities, not exhaustively listed here, for designing the light-emitting diode arrangement according to the invention or the method proposed according to the invention.

[0033] Pulse width modulation can be described in principle by its pulse duration τ and the clock pulse T. The clock pulse, also called period duration, ultimately results from the PWM frequency as T = 1 / f.

[0034] To dim an LED, the pulse duration τ, also known as the on-time, is changed. Simply put, the longer the pulse duration τ within a cycle, the brighter the LED, and the shorter the pulse duration τ, the dimmer it.

[0035] The light-emitting diode arrangement, in particular the control device 4, often receives its dimming information from a video interface, for example in RGB666 format, so that the dimming information is available in a resolution of 6 bits and 64 dimming levels (2 6 ) result.

[0036] With 64 dimming levels for LED 1 and a PWM frequency of 250 Hz for pulse width modulation, the resolution is 4 ms / 64 = 62.5 µs. For example, if a dimming level of 50% is to be applied, the turn-on time for LED 1 would be 2 ms and the turn-off time 2 ms. With a resolution of 64 levels, the next highest possible dimming level would be 2.0625 ms / 4 ms = 51.5%. This corresponds to an increment of 1.5%.

[0037] Smaller dimming steps can now be achieved by controlling at least one LED 1 in the second operating mode.

[0038] Based on the otherwise constant PWM frequency of 250Hz and the resulting clock T of 4ms, 51.5% brightness could be applied in the first clock T1 of 4ms. This corresponds to a resolution of 64 dimming levels (2 6) a pulse duration or switch-on time of (33 / 64)*4ms = 2.0625ms and a corresponding switch-off time of (31 / 64)*4ms = 1.9375ms. In the next three cycles T2 to T4, for example, 50% brightness can be applied, i.e. 2ms switch-on time and 2ms switch-off time each. In the four 4ms cycles, which are combined into a packet P, the average value for the eye is (51.5% + 3*50%) / 4 = 50.375%. Accordingly, in this second operating mode with packets with different pulse durations, an increment of 0.375% can be achieved, thus increasing the resolution. This process could also be referred to as dithering. A disadvantage of this operating mode could be that a modulation of the brightness of, in this example, 62.5 Hz results, since the length of a packet P is 16ms and this packet P is repeated every 16ms.

[0039] In conjunction with the example mentioned at the beginning, packets P with the same pulse duration τ can also be generated in the clock pulses. This is shown in the Fig. 2 is schematically indicated by four clock pulses T1 to T4, which are combined into a packet P and all contain the same pulse duration. This ultimately corresponds to the first operating mode.

[0040] The LED array offers advantageous properties for both operating modes. In the first mode, dimming gradations are less fine, but there is no modulation in the burst cycle, and the pearlescent effect is reduced or even imperceptible depending on the selected clock frequency.

[0041] In contrast, the second operating mode allows for finer dimming gradations. However, it cannot be ruled out that brightness modulations perceptible to the human eye may result. Furthermore, it cannot be ruled out that this could result in a—albeit weak—pearl-like effect.

[0042] Typically, packets consisting of fewer clock pulses are more likely to produce brightness modulation at such a high frequency that it is undetectable by the human eye. For example, if a PWM frequency of 250 Hz is used, the repetition rate of packets consisting of two clock pulses will be 125 Hz, whereas the repetition rate of packets consisting of four clock pulses will be 62.5 Hz. The latter may be perceptible to the human eye, whereas a modulation of 125 Hz may not be.

[0043] A light-emitting diode arrangement in a simple embodiment with a light-emitting diode and a control device is described in Fig. 3. The reference symbols B 1,p and B 2,p It is indicated that the LED can be controlled in the first operating mode and in the second operating mode, with, for example, p = 2 or 4 clock pulses per packet.

[0044] As already indicated above, the light-emitting diode arrangement can comprise a detection device 5 in addition to the light-emitting diode 1 and the control device 4. In Fig. 4, Fig. 4a and Fig. Figure 4b shows a schematic representation of such a light-emitting diode arrangement.

[0045] In principle, at least one LED 1 should be controlled in the second operating mode (dithering) when the dot is not moving ( Fig. 4) or only moderately active ( Fig. 4a, v1) and in the first operating mode ( Fig. 4b) when the point is moving rapidly (v2), whereby the angular velocity ω1 or ω2 of the point relative to the detection device should be taken into account. Furthermore, a corresponding control can be implemented with regard to the clock pulses combined into a packet, for example, four clock pulses when the point is stationary and two clock pulses when the point is moving moderately fast. The result is the advantages already outlined above regarding resolution, pearlescent effect, and brightness modulation.

[0046] The principles outlined above can also be applied to more than one LED, particularly to matrix systems comprising, for example, 100×100 or 1000×1000 LEDs. In this case, the control device controls not just one LED, but every LED in the matrix system.

[0047] In one embodiment of the LED array as a matrix system, but without a detection device, frequently occurring lighting situations can be taken into account in order to use the operating modes outlined above in a targeted and advantageous manner. Certain zones of LEDs of the matrix system can be combined, for example, a zone in which the LEDs are controlled in the first operating mode B1, a second zone in which the LEDs are controlled in the second operating mode with two clock pulses per packet B 2,2 and a third zone in which the LEDs in the second operating mode with four clocks per package B 2,4The number of cycles per package is, of course, only an example. The control device can be individually configured and, for example, define a maximum number of cycles that can be combined into packages. Such a lighting arrangement is in the Fig. 5 shown schematically.

[0048] The light-emitting diode device outlined above can be advantageously illustrated by a practical example.

[0049] Starting with a matrix system, such as the headlights of a motorcycle, the edges of the matrix system can be equipped with LEDs, for example, which are controlled in the first operating mode, thus forming the first zone Z1. These outer zones Z1 typically illuminate the roadside, which moves very quickly past the matrix system when a motorcycle is moving. The expected modulation effect and a string of pearls effect are extremely undesirable here. On the other hand, fine dimming gradations are not necessary, so these LEDs can be controlled in the first operating mode.

[0050] In contrast, the middle area of ​​the matrix system illuminates objects that are further away but move less or not at all, such as the middle of the road, etc. In this respect, for example, the middle area of ​​the matrix system in the second operating mode B 2,4controlled with the maximum number of clock pulses per packet, allowing for finer brightness gradations. The second zone is formed by the middle area.

[0051] LEDs of the third zone can be arranged between the edges and the central area, for example, because these LEDs usually illuminate moderately moving points. It is therefore advantageous to use these LEDs in the second operating mode B. 2,2 with, for example, two clock cycles per packet.

[0052] The previously outlined LED array in the form of a matrix system can also be equipped with a detection device. The LED array illuminates a plurality of points accordingly. The detection device can be configured to detect the movement of each point illuminated by the matrix system. This can be refined to the extent that, for each LED, it can be detected which point is currently illuminated. Based on the movement of the point, the control device is configured to control the corresponding LED with the appropriate operating mode and / or to make appropriate settings regarding the number of pulses combined into a packet.

[0053] To give a concrete example, let's take the example of a motorcycle's headlight again. The motorcycle is traveling along a country road, the first LED illuminates a point on the roadside, such as a curb post. The second LED illuminates a vehicle approaching in cross traffic, and the third LED zone illuminates a bridge some distance away. The detection device detects this scenario and controls the zones or LEDs in the appropriate operating mode and with the appropriate number of pulses within the packets.

[0054] If the scenario changes, for example, the first LED illuminates a point that is stationary relative to the detection device, the control device controls the first LED in the second operating mode (dithering), and so on.

[0055] The example outlined above assumes a very ideal assignment of LEDs and the points they illuminate. In principle, this level of detail can be achieved. In practice, however, LEDs in the matrix system can also be grouped into zones, which are controlled by the control device according to the movement of the illuminated points.

[0056] With regard to the relative motion between the detection device and the point, the angular velocity should be used as a first approximation. A point moving directly toward the detection device or the LED array does exhibit a relative motion to the detection device, but this is negligible with regard to the string of pearls effect, since no transverse motion occurs.

Claims

[1] Light-emitting diode arrangement, comprising at least - a light-emitting diode (1), - a control device (4) which is designed to dim the at least one light-emitting diode (1) by means of pulse width modulation, wherein the pulse width modulation is characterized by a clock cycle (T) and a pulse duration (τ) during a clock cycle, - wherein the control device (4) is designed to control the at least one light-emitting diode (1) with packets (P) of at least two clock pulses, wherein - wherein the control device (4) is selectively configured to control the at least one light-emitting diode (1) in a first operating mode (B 1,p ) and at least one second operating mode (B 2,p ), - wherein the at least one light-emitting diode (1) is controlled in the second operating mode with at least one different pulse duration within the package (P), characterized by , - that in the first operating mode the pulse durations (τ) are equal within the packet (P) and - that the light-emitting diode arrangement is designed to illuminate at least one point (6), wherein the light-emitting diode arrangement is equipped with a detection device (5) which is designed to detect the relative movement speed (v), in particular angular speed (ω), of the at least one point (6) with respect to the detection device (5). [2] Light-emitting diode arrangement according to claim 1, characterized by that the light-emitting diode arrangement comprises a plurality of light-emitting diodes (6, 7, 8), in particular 100×100 or 1000×1000 light-emitting diodes which are combined as a matrix system. [3] Light-emitting diode arrangement according to at least one of the preceding claims, characterized by that the control device for controlling the at least one light-emitting diode (1) in the first operating mode (B 1,p) or the second operating mode (B 2,p ) depending on the speed of movement (v), in particular angular velocity (ω). [4] Light-emitting diode arrangement according to at least one of the preceding claims, characterized by that the control device is designed to control the number of clock pulses (T) combined to form a packet (P), in particular as a function of the movement speed (v), in particular angular speed (ω). [5] Light-emitting diode arrangement according to at least one of the preceding claims, characterized by that the detection device is a camera, a radar system or a laser system. [6] Method for dimming a light-emitting diode of a light-emitting diode arrangement, in particular according to one of claims 1 to 5, comprising at least one light-emitting diode with a control device (4) which is designed to dim the at least one light-emitting diode (1) by means of pulse width modulation, wherein the pulse width modulation is characterized by a clock cycle (T) and a pulse duration (τ) during a clock cycle, characterized by following procedural steps: Formation of packets from at least two clock pulses and control of the at least one light-emitting diode in a first operating mode, which is characterized in that the at least one light-emitting diode is controlled with the same pulse duration (τ) within the packet (P) or in a second operating mode, which is characterized in that the at least one light-emitting diode is controlled with at least one different pulse duration within the packet (P), wherein the light-emitting diode arrangement illuminates at least one point, wherein the light-emitting diode arrangement is equipped with a detection device, wherein the detection device detects the relative movement speed (v), in particular angular speed (ω), of the at least one point with respect to the detection device. [7] Method according to claim 6, characterized by that the number of clock pulses (T) combined into a packet (P) is controlled by the control device. [8] Method according to at least one of the two preceding claims, characterized bythat the light-emitting diode arrangement comprises a plurality of light-emitting diodes, in particular 100×100 or 1000×1000 light-emitting diodes which are combined as a matrix system, wherein each light-emitting diode or groups of light-emitting diodes is controlled individually by the control device with regard to the first operating mode or the second operating mode and is controlled in particular with regard to the number of clock pulses (T) combined to form a packet (P). [9] Method according to at least one of claims 6 to 8, characterized by that the operating mode and / or the number of clock pulses (T) combined into a packet (P) is controlled as a function of the movement speed (v), in particular angular speed (ω), detected by the detection device.

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