Biosafety Control of LED Light Sources

Abstract

The present invention includes a light source control method and a related lighting device. The light source has a control signal for controlling the intensity of the emitted light. The control signal is PWM modulated in time, where the PWM modulation includes PWM pulses and PWM periods associated with the PWM pulses. Here, the PWM pulse instantaneous frequency of the PWM pulse is the reciprocal of the instantaneous PWM period of the PWM pulse. The PWM pulse instantaneous frequency of the PWM pulse of the PWM modulation depends on the PWM duty cycle of the PWM pulse of the PWM modulation of the control signal: the PWM pulse instantaneous frequency of the PWM pulse of the PWM modulation is a first PWM pulse instantaneous frequency at a first PWM duty cycle of the PWM pulse of the PWM modulation of the control signal, and is a second PWM pulse instantaneous frequency different from the first PWM pulse instantaneous frequency at a second PWM duty cycle of the PWM pulse of the PWM modulation of the control signal that is different from the first PWM duty cycle. At least in one operating state, the value of the first PWM duty cycle is less than the value of the second PWM duty cycle, and the value of the first PWM pulse instantaneous frequency is less than the value of the second PWM pulse instantaneous frequency.

Description

Technical Field

[0001] The present invention provides an LED lighting device using a light emitting diode (LED) as a light source, which minimizes the risks of IEEE1789-2015 and simultaneously achieves good intensity setting and good diagnostic capabilities. The present invention provides a method for increasing the PWM frequency of a PWM-controlled light source, in which short pulse times can be avoided in order to enable diagnosis and reduce the influence of edges on dimming, i.e., intensity setting is performed by a predetermined value transmitted externally. Background Art

[0002] The IEEE 1789-2015 cited herein reports health risks when using PWM to control an LED driver.

[0003] According to the current state of the art, an LED is controlled by PWM controlling a constant current source. The advantage of this method is that since the LED current is not modulated, the color shift of the color perception of the light emitted by the LED as a light source is minimized.

[0004] This modulation type is described in the IEEE 1789-2015 standard and is referred to as 100% modulation.

[0005] Depending on the technical possibilities of the LED driver and PWM generator used, a PWM pulse instantaneous frequency higher than 100 Hz is used. The IEEE 1789-2015 standard recommends a PWM pulse instantaneous frequency greater than 2000 Hz for the modulation type used. According to the current state of the art, LEDs are driven by a PWM-controlled constant current source. Here, the constant current source drives the light source with a current that is set to a predetermined current value either by design or by means of a control value signal. Here, the light source typically comprises one LED or an LED string containing a plurality of LEDs connected in series or a parallel connection of a plurality of LED strings. Preferably, the constant current source uses the PWM period to repeatedly turn on and off in pulses. If the constant current source is turned on during the PWM pulse duration within the PWM period, the constant current source thus feeds the preset current into the light source only during the on-time of this PWM pulse duration. Therefore, for the remaining time outside the PWM pulse duration of the PWM period, the constant current source generally does not feed current into the light source. If the constant current source feeds the preset current into the light source during the PWM pulse duration, the constant current source supplies power to the light source during this PWM pulse duration, causing the light source to emit light. Here, the preset amount of current affects the human perception of the color of the emitted light (i.e., the color temperature). The advantage of this method is that the color shift is minimal because the predetermined value of the LED current is not modulated. The light source is either on or off. Depending on the technical possibilities of the LED driver and PWM generator used as the light source driver, a PWM pulse instantaneous frequency higher than 100 Hz is used to avoid an unwanted flicker effect for the viewer. Therefore, the PWM modulation of the control signal used by the light source driver when supplying power to the light source (here an LED) includes PWM pulses. In the sense of this text, for better illustration, exactly one PWM period is assigned to each PWM pulse, and conversely, exactly one PWM pulse is assigned to each PWM period in order to be able to precisely define the PWM pulse instantaneous frequency. In the sense of this text, the PWM modulation of the energy supply of the constant current source to the light source has a PWM period, and each PWM period is assigned a PWM pulse. In the sense of this text, this PWM period of the PWM pulse starts at the rising edge of the PWM pulse in time and ends at the rising edge of the immediately following PWM pulse of the PWM modulation. In the sense of this text, the PWM pulse instantaneous frequency of the PWM pulse is the reciprocal of the PWM period of the relevant PWM pulse. Furthermore, in the sense of this text, the PWM duty cycle of the PWM pulse is understood as the ratio obtained by dividing the time value of the PWM pulse duration in the PWM period of the PWM modulation of the control signal by the time value of the PWM period duration of this PWM period of the PWM modulation of the control signal.

[0006] For example, at the time of filing this application, a PWM pulse instantaneous frequency of 300 Hz is typically used in the field of RGB interior lighting of motor vehicles. A PWM pulse instantaneous frequency higher than 500 Hz is currently under discussion. However, since in the case where a 16-bit resolution is usually required for the PWM duty cycle, the minimum current source effective time when the corresponding light source driver of the corresponding LED supplies power to the LED is in the nanosecond range, the increase in the PWM pulse instantaneous frequency is limited by technology. However, due to parasitic capacitance, the LED cannot be controlled by such a short PWM pulse duration. In addition, due to the non-ideal edge shape, the error in intensity setting increases.

[0007] At the same time, due to the shorter effective time, diagnosis becomes more difficult. This is understood as measuring the operating parameters of the LED or LED string during operation in order to detect the following errors, for example, by detecting the LED current and / or LED voltage and their time characteristics: an interruption that already exists or an indication of such an interruption that is occurring, or a short circuit or a short circuit that is occurring.

[0008] Current light source drivers use a PWM generator based on a configurable PWM clock generator and / or duty cycle timer. The basis of the PWM generator is usually a counter that operates with a PWM clock and restarts cyclically with the current PWM period. This restart is usually triggered at the first count of the PWM counter by the reset logic of the PWM counter. Then, an exemplary PWM counter jumps back to the restart value. For example, when the PWM counter restarts and / or when the PWM counter is at the restart value of the PWM counter, the PWM counter can turn on a constant current source to supply power to the light source. At a second count value where the PWM counter typically takes values between the restart value and the first count value, the PWM counter usually turns off the constant current source again, so that the light source no longer emits light before the PWM counter reaches the first count value. Usually, the value obtained by dividing the first number of counts between the restart value of the PWM counter and the first count value of the PWM counter by the PWM clock corresponds to the PWM period. Usually, the value obtained by dividing the second number of counts between the restart value of the PWM counter and the second count value of the PWM counter by the PWM clock corresponds to the PWM pulse duration. However, in addition to this PWM generator based on a PWM counter, other PWM generators can also be considered, and the use of other PWM generators is also claimed here. Usually, the PWM frequency can only be set by an integer divider. If it is required that the PWM pulse instantaneous frequency cannot be generated as an integer according to the PWM clock used to operate the PWM generator in the light source driver, the PWM resolution of the PWM modulation of the control signal used by the light source driver when supplying power to the light source is reduced.

[0009] Therefore, the problem that now arises is that the individual light sources cannot be switched on and off arbitrarily quickly. First, the current flowing through the light source shows a typical exponential increase during switching on and a typical exponential decrease during switching off. Therefore, compared with the ideal control signal of the PWM modulation provided by the corresponding light source driver for supplying power to the light source, the time curve (Verlauf) of the light intensity emitted by the light source has at least a low-pass behavior. Then, because the short PWM pulses cause changes in the light radiation of the light source due to the low-pass characteristics and non-linear characteristic curve of the light source, and the light intensity of this light source is no longer proportional to the time variation of the PWM pulse duration, this low-pass behavior and typical non-linear characteristics of the light source result in non-linear distortion of the light intensity for small light intensities.

[0010] Therefore, substantially increasing the instantaneous frequency of the PWM pulses to a value above 500 Hz results in significant, from the perspective of the application software unknown non-linearity of the effective current in the low dimming range (i.e., in the low light intensity range), because the edge control of the light source driver causes an increase in errors at short PWM pulses in this range.

[0011] In the current embodiment, using a PWM frequency greater than 2000 Hz would mean a significant reduction in the PWM resolution, or that the PWM clock of the PWM generator (e.g., PWM counter) would require a very high clock frequency. Summary of the Invention

[0012] Therefore, the object of the present invention is to create a solution that does not have the disadvantages of the prior art and has other advantages.

[0013] The present invention relates to a method for controlling a light source using a control signal, wherein the intensity of the light emitted by the light source depends on the value and value curve of the control signal, and wherein the value curve of the control signal is PWM modulated in time using PWM modulation, and wherein the PWM modulation of the control signal comprises PWM pulses, and wherein the PWM modulation comprises PWM periods respectively associated with the PWM pulses, and wherein the PWM period of a PWM pulse starts at the rising edge of the PWM pulse and ends at the rising edge of the immediately following PWM pulse of the PWM modulation, and wherein the PWM pulse instantaneous frequency of the PWM pulse is the reciprocal of the PWM period of the PWM pulse, and wherein the PWM duty cycle of the PWM pulse is the ratio obtained by dividing the time value of the PWM pulse duration in the PWM period of the PWM modulation of the control signal by the time value of the PWM period duration of the PWM period of the PWM modulation of the control signal, characterized in that the PWM pulse instantaneous frequency of the PWM pulses of the PWM modulation depends on the PWM duty cycle of the PWM pulses of the PWM modulation of the control signal, and at a first PWM duty cycle of the PWM pulses of the PWM modulation of the control signal, the PWM pulse instantaneous frequency of the PWM pulses of the PWM modulation is a first PWM pulse instantaneous frequency, and at a second PWM duty cycle of the PWM pulses of the PWM modulation of the control signal different from the first PWM duty cycle, the PWM pulse instantaneous frequency of the PWM pulses of the PWM modulation is a second PWM pulse instantaneous frequency different from the first PWM pulse instantaneous frequency, and at least in one operating state, the value of the first PWM duty cycle is less than the value of the second PWM duty cycle, and thus, in this operating state, the value of the first PWM pulse instantaneous frequency is less than the value of the second PWM pulse instantaneous frequency.

[0014] The invention further relates to an illumination device, the illumination device comprising a light source, a light source driver and a control signal, wherein the light source driver supplies power to the light source at least secondly (zweitweise) via the control signal, and wherein the light source driver generates the control signal, and wherein the intensity of the light emitted by the light source depends on the value and the value-time curve of the control signal, and wherein the value-time curve of the control signal generated by the light source driver and thus the intensity of the light emitted by the light source depends on a predetermined value generated or received or made ready by the light source driver, and wherein the light source driver PWM-modulates the value-time curve of the control signal in time by PWM modulation, and wherein the PWM modulation of the control signal comprises PWM pulses, and wherein the PWM modulation of the light source driver comprises PWM periods respectively associated with the PWM pulses, and wherein the PWM period of a PWM pulse starts at the rising edge of this PWM pulse and ends at the rising edge of the immediately following PWM pulse of the PWM modulation, and wherein the PWM pulse instantaneous frequency of a PWM pulse is the reciprocal of the PWM period of this PWM pulse, and wherein the PWM duty cycle of a PWM pulse is the ratio obtained by dividing the time value of the PWM pulse duration in the PWM period of the PWM modulation of the control signal by the time value of the PWM period duration of this PWM period of the PWM modulation of the control signal, characterized in that the PWM duty cycle and / or the PWM pulse instantaneous frequency depends on the predetermined value, and for a first predetermined value, at a first PWM duty cycle of the PWM pulses of the PWM modulation of the control signal, the PWM pulse instantaneous frequency of the PWM pulses of the PWM modulation is a first PWM pulse instantaneous frequency, and for a second predetermined value different from the first predetermined value, at a second PWM duty cycle different from the first PWM duty cycle of the PWM pulses of the PWM modulation of the control signal, the PWM pulse instantaneous frequency of the PWM pulses of the PWM modulation is a second PWM pulse instantaneous frequency different from the first PWM pulse instantaneous frequency, and at least the value of the first PWM duty cycle is less than the value of the second PWM duty cycle, and thus, in this operating state, the value of the first PWM pulse instantaneous frequency is less than the value of the second PWM pulse instantaneous frequency. Detailed Description

[0015] A method is proposed for establishing an adaptive PWM pulse instantaneous frequency related to the light intensity. This corresponds to the matching of the current PWM period to the light intensity to be emitted currently.

[0016] Generally, the lighting device receives a predetermined value for the light intensity to be emitted externally. From this, the duty cycle of the PWM modulation of the control signal utilized by the light source driver when powering the light source is derived. Preferably, the light source driver includes a PWM generator that generates the PWM modulation.

[0017] Preferably, the light source driver has a first computing means for determining the PWM period to be set according to the predetermined value. For example, this first determination can be performed by calculation, e.g., in a microcomputer of the light source driver, or by using a corresponding table in the memory of the light source driver, or by a constructively predetermined logic.

[0018] Preferably, the light source driver has a second computing means for determining the PWM duty cycle to be set according to the predetermined value. For example, this second determination can be performed by calculation, e.g., in a microcomputer of the light source driver, or by using a corresponding table in the memory of the light source driver, or by a constructively predetermined logic.

[0019] Very particularly preferably, at least the first computing means of the light source driver performs the first determination or at least the second computing means of the light source driver performs the second determination such that the duty cycle of the PWM modulation of the control signal and / or the PWM period of the PWM modulation of the control signal are at least corrected according to the non-linear distortion of the light radiation of the light source.

[0020] Then, the light source driver uses the PWM period and / or the PWM duty cycle that may be determined in this way to generate a control signal that is PWM modulated with these values to power the light source.

[0021] The IEEE 1789-2015 reports negative physiological effects that depend on the light intensity. The negative effects at high light intensities are greater than those at low light intensities. This characteristic allows for the selection of a very high PWM pulse instantaneous frequency at high intensities (= large duty cycle) and a smaller PWM pulse instantaneous frequency at low intensities (= small duty cycle). Thus, there is the possibility that when using a DDS-PWM generator (e.g., also see US 7 284 025B2), an adaptive PWM pulse instantaneous frequency control can be used in a range above, for example, 100 Hz (lower limit to avoid perceptible flicker of light sources such as LEDs) according to the configured duty cycle (i.e., the duty cycle to be configured), thereby minimizing the health risks far exceeding 2 kHz mentioned in the IEEE. By reducing the PWM pulse instantaneous frequency, the minimum PWM pulse duration can be extended, thus minimizing the influence of the edge time, because the ratio value obtained by dividing the time value of the PWM pulse duration by the time value of the PWM period duration remains constant as the PWM period duration is extended in time. However, the time proportion of the edges within the PWM period is reduced.

[0022] A method for establishing an adaptive PWM pulse instantaneous frequency is proposed.

[0023] In the case of high light intensity, the PWM pulse duration of the final PWM pulse is long enough in time such that the PWM edge effect can be ignored because the total duration of the edge rise or edge fall is short compared to the corresponding PWM pulse duration.

[0024] In the case of low light intensity, the PWM pulse duration of the final PWM pulse is very short in time so that the PWM edge effect can no longer be ignored now because the total duration of the edge rise or edge fall is longer or at least relevant compared to the corresponding PWM pulse duration. However, in this case of low light intensity, the PWM pulse instantaneous frequency can now be selected to be lower, for example, by means of the corresponding table or the first logic, such that the minimum PWM pulse duration when the light source driver supplies energy to the light source over a period of time is extended by the lower PWM pulse instantaneous frequency. Preferably, it does not exceed the minimum PWM pulse duration. Alternatively or additionally, in this case of low light intensity, the PWM period can be selected to be longer, for example, by means of the corresponding table or the logic, such that the minimum PWM pulse duration when the light source driver supplies energy to the light source over a period of time is extended by the lower PWM pulse instantaneous frequency. However, it is clearly more preferable to change the PWM period duration. Thus, the proportional effect of the edge time can be minimized by reducing the PWM pulse instantaneous frequency, and the time for performing diagnostic functions (e.g., detecting the voltage drop across the light source during the PWM pulse duration or detecting the current passing through the light source during the PWM pulse period) becomes longer. Therefore, stabilization of the current passing through the light source or stabilization of the voltage drop across the light source can be achieved before measurement, for example, by means of the analog-to-digital converter of the light source driver, during the PWM pulse duration outside the edge time when the control signal changes its voltage or current state. For example, the light source driver can have a microcomputer. Preferably, the microcontroller detects the diagnostic values determined by the analog-to-digital converter for the light source current amount and / or light source voltage amount during the PWM pulse duration and outside the edge time, and outputs the diagnostic value, or transmits the diagnostic value via the data bus, for example, or holds the diagnostic value for query by a superior system. Generally, devices such as a shunt resistor for current-to-voltage conversion are connected in series with the light source, and the current of the light source flows through the shunt resistor such that the analog-to-digital converter can detect the current and voltage at least temporarily and with a time delay in a time-division multiplexing manner through a multiplexer at its input.

[0025] This method allows for an adaptive PWM pulse instantaneous frequency to improve the diagnosis and dimming of a light source, which in this case is an LED or an LED string or multiple LED strings. Here, an LED string is understood as a series connection of multiple LEDs.

[0026] Therefore, in the following text, methods and devices for implementing this idea are proposed. The proposed method is a method for controlling a light source through a control signal. Here, the intensity of the light emitted by the light source depends on the value and the value curve (Wertverlauf) of the control signal. In this method, the value curve of the control signal is PWM modulated in time. As a result of this PWM modulation, this temporal PWM modulation of the control signal respectively has PWM pulses and PWM periods associated with the PWM pulses. In the sense of this text, the PWM period of a PWM pulse starts in time at the rising edge of the PWM pulse and ends in time at the rising edge of the immediately following PWM pulse of the PWM modulation. In the sense of this text, the value of the PWM pulse instantaneous frequency of a PWM pulse is the reciprocal of the duration value of the PWM period of the PWM pulse. In the sense of this text, the PWM duty cycle of a PWM pulse is the ratio obtained by dividing the PWM pulse duration value in the PWM period of the PWM modulation of the control signal by the time value of the PWM period duration of the PWM period of the PWM modulation of the control signal.

[0027] The method is characterized in that the PWM pulse instantaneous frequency of the PWM modulation of the PWM pulses depends on the PWM duty cycle of the PWM pulses of the PWM modulation of the control signal. This means that at a first PWM duty cycle of the PWM pulses of the PWM modulation of the control signal, the PWM pulse instantaneous frequency of the PWM modulation of the PWM pulses is a first PWM pulse instantaneous frequency, and at a second PWM duty cycle of the PWM pulses of the PWM modulation of the control signal that is different from the first PWM duty cycle, the PWM pulse instantaneous frequency of the PWM modulation of the PWM pulses is a second PWM pulse instantaneous frequency that is different from the first PWM pulse instantaneous frequency. At least in one operating state of the device that executes the method, the numerical value of the first PWM duty cycle is less than the numerical value of the second PWM duty cycle. Then, precisely in this operating state, the numerical value of the first PWM pulse instantaneous frequency is less than the numerical value of the second PWM pulse instantaneous frequency. Preferably, the light source includes at least one LED, an LED string, or is an LED or an LED string.

[0028] Corresponding to this method is a related lighting device including a sub-device that executes the above method. Such a lighting device includes at least one light source, a light source driver, and a control signal. The light source driver supplies power to the light source at least secondarily through the control signal. The light source driver generates the control signal. Here, the intensity of the light emitted by the light source depends on the value and the value-time curve of the control signal. The light source driver may, for example, have the microcomputer that can receive a predetermined value from a superior system via a data bus, for example. Preferably, the value-time curve of the control signal generated by the light source driver and thus the intensity of the light emitted by the light source depend on such a predetermined value. If necessary, the light source driver can generate the predetermined value, or receive the predetermined value and / or make it ready, for example, from a superior computer system via a data bus. Preferably, but not necessarily, the predetermined value is a predetermined value of the duty cycle. The light source driver performs PWM modulation on the value-time curve of the control signal in terms of time. The PWM modulation of the control signal of the light source driver has the PWM pulses in a time sequence that generally do not overlap. In addition, the PWM modulation of the light source driver also includes corresponding PWM periods, where, in the sense of this text, each PWM period is exactly assigned to one PWM pulse. In the sense of this text, the PWM period of a PWM pulse starts from the rising edge of the PWM pulse and ends at the rising edge of the immediately following PWM pulse in the PWM modulation. Here, in the sense of this text, the PWM pulse instantaneous frequency of a PWM pulse is the reciprocal of the PWM period of the PWM pulse.

[0029] In the sense of this text, the PWM duty cycle of a PWM pulse is the ratio obtained by dividing the value of the PWM pulse duration in the PWM period of the PWM modulation of the control signal by the value of the PWM period duration of this PWM period of the PWM modulation of the control signal. As mentioned above, the PWM duty cycle and / or the PWM pulse instantaneous frequency preferably depend on the predetermined value. For a first predetermined value, at a first PWM duty cycle of the PWM pulse in the PWM modulation of the control signal, the PWM pulse instantaneous frequency of the PWM modulation of the PWM pulse is the first PWM pulse instantaneous frequency. For a second predetermined value different from the first predetermined value, at a second PWM duty cycle different from the first PWM duty cycle of the PWM pulse in the PWM modulation of the control signal, the PWM pulse instantaneous frequency of the PWM modulation of the PWM pulse is a second PWM pulse instantaneous frequency different from the first PWM pulse instantaneous frequency.

[0030] Here, the value of at least the first PWM duty cycle is less than the value of the second PWM duty cycle. Then, in this operating state, the value of the first PWM pulse instantaneous frequency is less than the value of the second PWM pulse instantaneous frequency. The light source also preferably includes at least one LED and / or an LED string.

[0031] Advantages

[0032] Higher PWM pulse instantaneous frequencies under PWM control become possible. However, the advantages are not limited to this.

Claims

1. A method for controlling a light source using a control signal, wherein, the intensity of the light emitted by the light source depends on the value and value curve of the control signal, and wherein, PWM modulation is used to perform PWM modulation on the value curve of the control signal in time, and wherein, the PWM duty cycle of the PWM modulation of the control signal for driving the light source is determined based on a predetermined value of the light intensity, and the PWM period of the PWM modulation of the control signal for driving the light source is determined based on the determined PWM duty cycle, or the PWM period of the PWM modulation of the control signal for driving the light source is determined based on a predetermined value of the light intensity, and the PWM duty cycle of the PWM modulation of the control signal for driving the light source is determined based on the determined PWM period, and wherein, the PWM modulation of the control signal includes PWM pulses, and wherein, the PWM modulation includes PWM periods respectively associated with the PWM pulses, and wherein, the PWM period of a PWM pulse starts from the rising edge of the PWM pulse and ends at the rising edge of the immediately following PWM pulse in the PWM modulation, and wherein, the PWM pulse instantaneous frequency of a PWM pulse is the reciprocal of the PWM period of the PWM pulse, and wherein, the PWM duty cycle of a PWM pulse is a ratio obtained by dividing the time value of the PWM pulse duration in the PWM period of the PWM modulation of the control signal by the time value of the PWM period duration of the PWM period of the PWM modulation of the control signal, characterized in that, the PWM pulse instantaneous frequency of the PWM pulses of the PWM modulation depends on the PWM duty cycle of the PWM pulses of the PWM modulation of the control signal, and at a first PWM duty cycle of the PWM pulses of the PWM modulation of the control signal, the PWM pulse instantaneous frequency of the PWM pulses of the PWM modulation is a first PWM pulse instantaneous frequency, and at a second PWM duty cycle of the PWM pulses of the PWM modulation of the control signal different from the first PWM duty cycle, the PWM pulse instantaneous frequency of the PWM pulses of the PWM modulation is a second PWM pulse instantaneous frequency different from the first PWM pulse instantaneous frequency, and at least in one operating state, the value of the first PWM duty cycle is less than the value of the second PWM duty cycle, and therefore, in this operating state, the value of the first PWM pulse instantaneous frequency is less than the value of the second PWM pulse instantaneous frequency.

2. The method according to claim 1, wherein, the light source includes at least one LED.

3. An illumination device, the illumination device includes a light source, a light source driver, and a control signal, wherein, the light source driver supplies power to the light source at least secondarily through the control signal, and wherein, the light source driver generates the control signal, and wherein, the intensity of the light emitted by the light source depends on the value and value time curve of the control signal, and wherein the value-time curve of the control signal generated by the light source driver and thus the intensity of the light emitted by the light source depend on a predetermined value generated or received or made ready by the light source driver, and wherein the light source driver PWM-modulates the value-time curve of the control signal in time by PWM modulation, and wherein the PWM modulation of the control signal comprises PWM pulses, and wherein the PWM modulation of the light source driver comprises PWM periods respectively associated with the PWM pulses, and wherein the PWM period of a PWM pulse starts at the rising edge of the PWM pulse and ends at the rising edge of the immediately following PWM pulse of the PWM modulation, and wherein the PWM pulse instantaneous frequency of a PWM pulse is the reciprocal of the PWM period of the PWM pulse, and wherein the PWM duty cycle of a PWM pulse is a ratio obtained by dividing the time value of the PWM pulse duration in the PWM period of the PWM modulation of the control signal by the time value of the PWM period duration of the PWM period of the PWM modulation of the control signal, characterized in that the PWM duty cycle and / or the PWM pulse instantaneous frequency depend on the predetermined value, wherein the PWM duty cycle is determined based on the predetermined value, and the PWM pulse instantaneous frequency is determined based on the determined PWM duty cycle, or the PWM pulse instantaneous frequency is determined based on the predetermined value, and the PWM duty cycle is determined based on the determined PWM pulse instantaneous frequency, and for a first predetermined value, at a first PWM duty cycle of the PWM pulses of the PWM modulation of the control signal, the PWM pulse instantaneous frequency of the PWM pulses of the PWM modulation is a first PWM pulse instantaneous frequency, and for a second predetermined value different from the first predetermined value, at a second PWM duty cycle different from the first PWM duty cycle of the PWM pulses of the PWM modulation of the control signal, the PWM pulse instantaneous frequency of the PWM pulses of the PWM modulation is a second PWM pulse instantaneous frequency different from the first PWM pulse instantaneous frequency, and at least the value of the first PWM duty cycle is less than the value of the second PWM duty cycle, and consequently, the value of the first PWM pulse instantaneous frequency is less than the value of the second PWM pulse instantaneous frequency.

4. The lighting device according to claim 3, wherein the light source comprises at least one LED.