Improved-low-voltage connected light source control for stable operation in a system with long cables

Abstract

A light source (typically LED based) and a method for operation a light source in a lighting system comprising a plurality of light sources electrically connected in parallel by a cable. A light output of the light source is adjustable by two or more LED channels, each arranged to alternate between a low voltage and a high voltage at a duty cycle. The light source is arranged to determine if an input voltage is sufficient to supply a required output voltage for each of the LED channels. The duty cycle of one or more of the LED channels is adjusted if it is determined that the input voltage to the light source is insufficient to supply the required output voltage for each of the LED channels. On the other hand, the light is turned on or kept on without adjusting the duty cycle if the input voltage is sufficient.

Description

[0001] Improved-low-voltage connected light source control for stable operation in a system with long cables

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a light source, preferably a low-voltage light source, e.g., including one or more LEDs, for operation in a lighting system comprising a plurality of such light sources that are electrically connected in parallel by a cable. The present disclosure further relates to a lighting system comprising a plurality of such light sources and a method for operating such light source.

[0004] BACKGROUND

[0005] Low-voltage connected light sources may be used in lighting systems with long cables. An example of such lighting system 100 is shown in Fig. 1. In Fig. 1, the lighting system 100 includes three light sources 110, 112, 114 that are connected to a bus including cable portions 122, 124, 126 and connectors 104, 106. It will be understood that different number of light sources may be included in the lighting system and that the topology may be different from what is shown in Fig. 1. Different cable portions may have different lengths, e.g., 2.0m for cable portion 122, 5.0m for cable portions 124 and 0.6m for cable portions 126, or any other length for any or each of the cable portions. The light sources 110-114 may be LED light sources operating on direct current (DC), in which case an alternating current (AC) to DC converter 104 may be used to transform AC from a power source into DC. In the example of Fig. 1, the lighting system 100 is plugged into an AC providing wall socket by a plug and socket 102, with an AC cable 120 connecting the plug to the AC to DC converter 104.

[0006] In known low-voltage light source designs, a high LED voltage, close to the bus voltage, is typically used to maximize driver efficiency. Current may then be regulated by a resistor, which can disadvantageous^ affect other performance parameters, such as current sensitivity to voltage and temperature variation, space vector modulation (SVM), color variation and lumen decay.

[0007] Additionally, switching of a load (e.g., a light source 110-114 switching ON / OFF) in a low-voltage lighting system can cause fluctuations in the DC bus voltage. This, in turn, can directly affect the light output of light sources that are already ON. This phenomenon is known as load induced flicker.

[0008] To improve light source performance, a DC / DC buck converter or a linear regulator may be used to stabilize the voltage provided at a light source. A voltage drop across a cable, which can become significant with longer cables, e.g., when using a plurality of cable portions 124, 126 to connect a plurality of light sources 110-114, in combination with high LED forward voltage can disrupt the operation of the DC / DC buck converter or linear regulator. In such a case, a light source may not operate at all or at least not as intended.

[0009] SUMMARY

[0010] A summary of aspects of certain examples disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects and / or a combination of aspects that may not be set forth.

[0011] The present disclosure aims to overcome the drawbacks identified in the background section. In particular, the present disclosure aims to provide a solution for operating connected light sources, preferably low-voltage light sources, e.g., including one or more LEDs, in a lighting system while minimizing disruption of normal operation of the light sources in the lighting system.

[0012] According to an aspect of the present disclosure, a light source is presented for operation in a lighting system. The lighting system includes a plurality of light sources that are electrically connected in parallel by a cable. A light output of the light source may be adjustable by two or more LED channels. Each of the LED channels may be arranged to alternate between a low voltage and a high voltage at a duty cycle. The light source may be arranged to determine whether or not an input voltage to the light source is sufficient to supply a required output voltage for the LED channels. The light source may be arranged to adjust the duty cycle of one or more of the LED channels if it is determined that the input voltage to the light source is insufficient to supply the required output voltage for the LED channels. The light source may further be arranged to turn on or keep the light source turned on without adjusting the duty cycle of one or more of the LED channels if it is determined that the input voltage to the light source is sufficient to supply the required output voltage for the LED channels. In an embodiment, the light source is further arranged to turn off or keep the light source turned off after a further determination, after adjusting the duty cycle of one or more of the LED channels, that the input voltage to the light source is insufficient to supply the required output voltage for the LED channels.

[0013] In an embodiment, the two or more LED channels may include a warm white channel and a cool white channel.

[0014] In an embodiment, the light source may include a control module arranged to supply the two or more LED channels from the input voltage. The light source may further include a level detection module arranged determine whether or not the LED channels can be supplied from the input voltage. The light source may further include a duty cycle adjustment module arranged to have the duty cycle of one or more of the LED channels adjusted if it is determined that the input voltage to the light source is insufficient to supply the required output voltage for the LED channels.

[0015] In an embodiment, the duty cycle adjustment module may signal the control module to adjust the duty cycle of the one of more LED channels.

[0016] In an embodiment, the duty cycle adjustment module is arranged to adjust the duty cycle of the one of more LED channels.

[0017] In an embodiment, the level detection module and / or the duty cycle adjustment module may be parts of the control module.

[0018] In an embodiment, the light source may include a buck converter to supply the output voltage for the channel voltages from the input voltage.

[0019] According to an aspect of the present disclosure, a lighting system is presented. The lighting system includes a plurality of light sources and a cable electrically connecting the plurality of light sources in parallel. At least one of the plurality of light sources may be a light source having one or more of the above described features.

[0020] According to an aspect of the present disclosure, a method is presented of operating a light source in a lighting system including a plurality of light sources that are electrically connected in parallel by a cable. The method may include receiving an input for turning on the light source. The method may further include setting duty cycles of LED channels for a light output of the light source. The method may further include determining whether or not an input voltage to the light source is sufficient to supply a required output voltage for the LED channels. The method may further include adjusting the duty cycle of one or more of the LED channels if it is determined that the input voltage to the light source is insufficient to supply the required output voltage for the LED channels. The method may further include or turning on or keeping the light source turned on without adjusting the duty cycle of one or more of the LED channels if it is determined that the input voltage to the light source is sufficient to supply the required output voltage for the LED channels.

[0021] In an embodiment, the method may further include turning off or keeping the light source turned off after a further determination, after adjusting the duty cycle of one or more of the LED channels, that the input voltage to the light source is insufficient to supply the required output voltage for the LED channels.

[0022] In an embodiment, the method may further include receiving a further input comprising a new light setting resulting in the duty cycle of one or more of the channels to be changed. The method may further include determining if there is an overlap between two or more of the LED channels after applying the new light setting. The method may further include, if it is determined that there is no overlap between the two or more of the LED channels after applying the new light setting, setting the duty cycle of the one or more channels in accordance with the new light setting. The method may further include, if it is determined that there is an overlap between the two or more of the LED channels after applying the new light setting, repeating the steps following the setting of the duty cycles for LED channels of the light output of the light source, with the duty cycles set to the new light settings.

[0023] In an embodiment, the determining whether or not the input voltage to the light source is sufficient to supply the required output voltage for the LED channels may include: determining if the sum of channel voltages exceeds a high voltage of one of the LED channel voltages at one moment in time, or, if an inverse logic is used, determining if the sum of channel voltages is equal or below a high voltage of one of the channel voltages at one moment in time.

[0024] In an embodiment, the LED channels may include a warm white channel and a cool white channel. The determining whether or not the input voltage to the light source is sufficient to supply the required output voltage for the LED channels may include determining whether Vww+Vcw>Vn, or, if an inverse logic is used, determining whether VWW+VCW<VH.

[0025] In a preferred embodiment, the light source may be an LED-based light source. The LED channels may be LED channels. The low voltage may correspond to an OFF state of the LED channel. The high voltage may correspond to an ON state of the LED channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbol indicate corresponding parts, in which:

[0027] Fig. 1 shows an example of a lighting system including three light sources, which can benefit from the solution of the present disclosure;

[0028] Fig. 2 shows a simplified schematics of (a part) of a light source of an example embodiment of the present disclosure;

[0029] Fig. 3 shows a flow chart of an example embodiment of the operation of a light source of an example embodiment of the present disclosure; and

[0030] Fig. 4 and Fig. 5 show time-voltage graphs of channels of a light source of an example embodiment of the present disclosure.

[0031] The figures are intended for illustrative purposes only, and do not serve as restriction of the scope of the protection as laid down by the claims.

[0032] DETAILED DESCRIPTION

[0033] It will be readily understood that the components of the embodiments as generally described herein and illustrated in the appended figures could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of various embodiments, as represented in the figures, is not intended to limit the scope of the present disclosure but is merely representative of various embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

[0034] The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the present disclosure is, therefore, indicated by the appended claims rather than by this detailed description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

[0035] Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present disclosure should be or are in any single example of the present disclosure. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present disclosure. Thus, discussions of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same example.

[0036] Furthermore, the described features, advantages, and characteristics of the present disclosure may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize, in light of the description herein, that the present disclosure may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the present disclosure. Reference throughout this specification to "one embodiment," "an embodiment," or similar language means that a particular feature, structure, or characteristic described in connection with the indicated embodiment is included in at least one embodiment of the present disclosure. Thus, the phrases "in one embodiment," "in an embodiment," and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0037] The solution of the present disclosure enables operating connected light sources, preferably low-voltage light sources, e.g., light sources including one or more LEDs, in a lighting system while minimizing disruption of normal operation of the light sources. For example, the lighting system may keep on operating at a relatively large voltage to keep efficiency high while also preventing light flicker when changing the characteristics of a light source in the lighting system. Such changing of characteristics may include turning a light source on or off, changing the intensity (flux) of a light source and / or changing the color of a light source. Changing the color point and / or flux level is also known as changing the scene of a light source.

[0038] A control method and system will be presented that improves operation of connected light sources, preferably low-voltage light sources, e.g., including one or more LEDs, in a lighting system, such as light sources 110-114 of lighting system 100 as shown in Fig. 1. The lighting system 100 may include a long total cable length, e.g., 35 meter (m) or more, that can result in a significant voltage drop along the cable. Connected LED-based light sources typically have a high LED forward voltage to improve driver efficiency that can compromise other performance parameters, such as sensitivity to voltage and temperature change. Moreover, connected light sources, such as LED-based light sources, may include a DC / DC converter, such as a DC / DC buck convert and / or a linear regulator, to generate the output voltage for the LED channel. When such light source is connected to a power supply unit (PSU), e.g., a 24V PSU, with a long cable in between the PSU and the light source, a significant voltage drop along the cable can cause the DC / DC converter of the light source to stop working or malfunction.

[0039] In an embodiment, the operation of low-voltage connected light sources may be improved by detecting that the input voltage is too low to for the DC / DC converter to provide the required output voltage to the light source. The output voltage is typically provided for one or more channels, also referred to as LED channels, which includes a voltage signal operating at a voltage level and on a duty cycle. In case of LEDs such LED channels may be referred to as LED channels. In an example embodiment, which will be further detailed below, duty cycles of one or more LED channels may be scaled down to avoid overlap in voltages provided by different channels, e.g., to avoid overlap of warm white (WW) and cool white (CW) channels. Advantageously, this may significantly reduce the voltage drop along the cable, making it more likely for a light source to resume normal operation, be it at a lower lumen output. Note that when the input voltage is sufficient for operating the light source in the desired mode of operation, the duty cycles may overlap and no scaling down need to be applied.

[0040] A simplified schematics of (a part) of a light source 200 of an example embodiment of the present disclosure is shown in Fig. 2. The light source 200 may be used as one or more of the light sources 110-114 in Fig. 1. The light source 200 may include one or more LEDs 210, which operation is controlled by a control module 202. The control module 202 typically includes a DC / DC converter, such as a DC / DC buck converter, for converting an input voltage Vin into an output voltage Vout for LED channels controlling the individual LED(s) 210. The output voltage Vout may alternatively be referred to as a bus voltage Vbus. In the example of Fig. 2, two LED channels are shown: a warm white LED channel Vww for setting a flux level and a cool white LED channel Vcw for setting a color temperature of the LED(s) 210. Depending on the type of light source 200, further or other LED channels may be present, such as LED channels for red, green and blue controlling the color of the LED(s) 210.

[0041] The overall light intensity (flux level) and / or color temperature of the light source 200 may be adjusted by changing the duty cycle of the warm white channel (i. e. , that of Vww) and / or the cool white channel (i. e. , that of Vcw). The term duty cycle refers to the proportion of time each channel (e.g., WW or CW) is active within a given period. The duty cycle may be expressed as a percentage: duty cycle (%) = (time on / total period) * 100. LEDs are often controlled using pulse width modulation (PWM), where the power delivered to an LED is modulated by switching it on and off at a high frequency. The duty cycle then determines the average power and, consequently, the brightness of the LED. By varying the duty cycles of the WW and CW channels, the combined light output may be adjusted to achieve different color temperatures.

[0042] An end user may be provided with a control unit, e.g., in the form of a remote control, a wall mounted control unit, an app on a mobile device or a voice controlled interface, to manually adjust the flux level, the color temperature and / or the light color to achieve a desired lighting effect. In some lighting systems, sensors and / or smart controls may automatically adjust the flux level, the color temperature and / or the light color, e.g., based on the time of day, ambient light conditions or user preferences. Moreover, a light source 200 may be configured to provide feedback to the end user, e.g., to an output device such as a display of the control unit, to report a current mode of operation of the light source 200. For example, the current on / off state, brightness, color temperature and / or color, possibly including details on the individual WW, CW and color channels, may be presented to the end user. Manual and / or automatic control of the light source 200 and feedback control may be implemented into the light source 200 in any manner known per se, e.g., within the control module 202 or in another module (not shown) that is operably connected to the control module 202.

[0043] When the light source 200 is turned on and / or when the light source 200 receives a command for a scene change (e.g., a new flux level, another color temperature or another color), a level detection module 204 may determine whether the desired channel voltage levels, in the example of Fig. 2 that of Vww and Vcw, can be realized using Vin, in which case the LED(s) 210 may be driven by the channel voltage levels Vww and Vcw. This is indicated in Fig. 2 as Vww ok and Vcw ok being used to drive the LED(s) 210, which may be the same as Vww and Vcw. If it is detected that Vin is too low, a duty cycle adjustment module 206 may adjust or signal the control module 202 to adjust the duty cycle of one or more of the channels, such as the WW, CW and / or one or more color channels. The thus obtained updated channel voltage levels may then be detected and verified again by the level detection module 204.

[0044] In Fig. 2, the level detection module 204 and the duty cycle adjustment module 206 are shown as separate modules. Alternatively, these modules may be integrated. Alternatively, these modules may be part of the control module 202. In an example, the detection module 204 and / or the duty cycle adjustment module 206 may be implemented as an extension to a DC / DC buck converter. A flow chart of an example embodiment of the operation of the light source 200 is shown in Fig. 3. The method 300 of Fig. 3 may be used to control the duty cycle of one or more channels (such as the Vww channel and / or the Vcw channel) in case Vin is determined to be insufficient. When Vin is sufficient, the duty cycles may remain as is.

[0045] In step 302, the light source may be turned on after being in an off state. Default duty cycles, e.g., preconfigured in the light source 200, may then be applied by generating the default duty cycles in step 304 and setting the duty cycles in step 306. Steps 304 and 306 may be implemented in any known manner and may be combined in a single step. Steps 304 and 306 may be implemented by the control module 202, e.g., involving a DC / DC buck converter for converting Vin into Vout for Vww and Vcw, such as illustrated in Fig. 2.

[0046] After setting the duty cycles in step 306, in step 308 it may be determined whether or not the input voltage, e.g., Vin in Fig. 2, is sufficient for supplying the channel voltages for the light source. In the example of Fig. 2, step 306 may be performed by the detection module 204 to determine whether or not Vin is sufficient for supplying Vww ok and Vcw_ok.

[0047] If it is determined that the input voltage is insufficient, the flow may continue with step 310. If it is determined that the input voltage is sufficient, the flow may continue with step 318 to keep the current duty cycles.

[0048] In step 310, new duty cycles may be generated for one or more of the channels. In the example of Fig. 2, this may involve generating new duty cycles for Vww and / or Vcw. In step 310, the duty cycles may be changed such that there are no more overlapping voltages between two or more channels, such as between the WW and the CW channel. This will be further explained with Fig. 4 and Fig. 5 below. In the example of Fig. 2, step 310 may be performed by the duty cycle adjustment module 206.

[0049] In step 312, the new duty cycles may be applied by setting the duty cycles, similar to step 306, and in step 314 it may be determined whether or not the input voltage is sufficient for supplying the channel voltages with the adjusted duty cycles, similar to step 308.

[0050] If the input voltage is still determined to be insufficient, the light source may be turned off or kept off in step 316, or optionally further measures may be taken in step 340. When turned off, the flow chart may start again at step 302.

[0051] In optional step 340, the voltage levels of one or more channels may be scaled down. Step 340 is shown as a dashed box, indicating it to be an optional step. For example, one or more LED channels may be scaled down by reducing the voltage level of the channel. Thus, e.g., the voltage level of Vww and / or VCM may be lowered. In one example, the voltage levels are scaled down by 10%. In another example, the voltage levels are scaled down by 20%. In another example, the voltage levels are scaled down by any percentage. After scaling down the voltage(s) in step 340, it may be determined again in step 314 whether or not the input voltage is sufficient for supplying the channel voltages (now set at the scaled down voltages). Step 340 may be repeated if the input voltage is still determined to be insufficient. If the voltages are at a preset minimum voltage level, a further scaling down may be impossible and the flow chart may continue at step 316 by turning off of keeping off the light source.

[0052] If the input voltage is determined to be sufficient, the light source may be turned on or kept on and the flow may advance to step 322, possibly via step 320.

[0053] In optional step 320, the light source may be turned on using the then supplying channel voltages at the set duty cycles. Step 320 is shown as a dashed box, indicating it to be an optional step. When step 320 is included in the flow chart 300, then at this stage the light source 200 is turned on. Alternatively, when step 320 is omitted from the flow chart 300, the light source may already be turned on at any of the ‘setting of the duty cycle’ steps 306, 312, which would result in the light source being turned on in step 306 and possibly getting adjusted while being turned on in steps 312 and 340 or getting turned off in step 316.

[0054] Steps 306-318 and 340 may be considered an initialization phase, where the light is set to be turned on with specific duty cycles for each of the channels and it is verified whether or not the light can be turned on with these settings. If turning the light on with its settings is determined to be impossible using the input voltage, to avoid disruption of other light sources in the lighting system, duty cycles (in steps 310-312) and possibly voltage levels (in step 340) may be adjusted. If it is then still not possible to turn on the light, the light may be turned off or kept of (in step 316). Otherwise, the light may be turned on (in step 320) or kept on (if turned on already in steps 306 and / or 312).

[0055] Steps 322-328 may be considered an operational phase, where the light is turned on and light settings may be changed.

[0056] In step 322, the light source waits for a new light setting, e.g., through a manual (user input) or an automatically generated control command. The feedback loop from step 322 to step 322 indicates that no new light setting has been received and the light source keeps waiting for a command. When a new light setting has been received, e.g., an input for changing a flux level, a color temperature and / or a light color, new duty cycles for one or more of the channels may be generated in step 324. For example, the duty cycles for Vww and / or Vcw may be changed in response to an input for changing the light intensity.

[0057] In step 326, it may be determined whether or not there is an overlap in voltages between two or more channels, such as between the WW and the CW channel.

[0058] If there is not overlap, it can be assumed that the input voltage will be sufficient and that there will be no disruption to other light sources when applying the adjusted light setting. In step 328, the new duty cycles may then be applied by setting the duty cycles, similar to step 306, and the flow chart may return to step 322, possibly via step 320. I.e., with step 328 the new light settings may be adjusted while being in the on state, or the new light settings may be applied by step 320.

[0059] If on the other hand there is an overlap, it need to be determined again whether or not the input voltage will be sufficient for applying the new light setting. The initialization phase may then be rerun with the new light settings by returning to step 306 of the flow chart 300.

[0060] Whether or not there is an overlap between voltages of two or more different channels, such as determined in step 310 or in step 326, may be performed by determining if the sum of channel voltages exceeds the high voltage of one of the channel voltages. This will be further explained in the examples of Fig. 4 and Fig. 5.

[0061] Optionally, when the light source failed to turn on or failed to apply desired light settings, a change in settings of another light source may trigger the current light source to rerun the initialization phase to try to apply the desired settings again. This is indicated by optional step 330, which represents a trigger from another light source being received when the other light source changed its settings. Step 330 is shown as a dashed box, indicating it to be an optional step. When, e.g., the other light source is set to a lower output power, the available input voltage of the current light source may have increased in the lighting system, possibly enabling the desired light settings where they were not possible before.

[0062] The end-user may be informed about the operation of the light source, e.g., via an app on a smartphone or any other software running on any device. For example, the enduser may be informed via an app that a higher flux level is not possible with the current system configuration and required light output, or more generally that the desired light settings cannot be applied. In another example, in case that the light source cannot resume normal operation after one (or more) atempts, it may stay off and the end-user may be informed that operation is not possible under the current system configuration.

[0063] Fig. 4 shows an example of a time-voltage graph 400 of two channels. In this example, line 402 represents the voltage over time of a first channel and line 404 represents the voltage over time of a second channel. The first channel is, e.g., a WW channel and the second channel is, e.g., a CW channel. In this example, the time-voltage graph 400 shows a Vww 402 and a Vcw 404.

[0064] Along the y-axis, two voltage levels are shown: VL indicating a low voltage (e.g., 0V) and Vn indicating a high voltage (e.g., 1.0V). VL may be the voltage at which the channel is turned off; in case of LEDs VL may correspond to an OFF state of an LED. Vn may represent a maximum voltage of the channel; in case of LEDs Vn may correspond to an ON state of an LED. Typically, the maximum voltages of the channels is the same, but they may differ.

[0065] In the time-voltage graph 400, Vww 402 switches from Vn to VL at time tl, switches from VL to Vn at time t2 and switched from Vn to VL at t4. Vcw 404 switches from VL to Vn at time tl, switches from Vn to VL at time t3 and switched from VL to Vn at t4. It will be understood that this periodicity of Vww and Vcw repeats in time.

[0066] In this example, the duty cycle of Vww 402 is set at (time on / total period) * 100% = ((t4-t2) / (t4-tl))*100% and the duty cycle of Vcw 404 is set at ((t3-tl ) / (t4-tl ))* 100%. In an example, tl=49.00ms, t2=49.40ms, t3=49.55ms and t4=50.00ms. The duty cycles of Vww 402 and Vcw 404 are then as follows: duty_cycleww=60% and duty_cyclecw=55%. This seting of the duty cycles of Vww 402 and Vcw 404 may be representative of a 4000K light output at maximum brightness.

[0067] Between t2 and t3 there is an overlap in voltage between Vww 402 and Vcw 404. This overlap may result in the input voltage Vin of the light source to be insufficient to supply the desired Vww 402 and Vcw 404 at the duty cycles as set in the example of Fig. 4. Note that in step 326 of Fig. 3, it may be determined that there is an overlap between two or more channels by determining Vchanneis>Vn at any moment in time. In the example of Fig. 4, VWW+VCW=2*VH>VH between t2 and t3, thus there is an overlap between the channels. It will be understood that in step 326 of Fig. 3, alternatively, it may be determined that there is no overlap between two or more channels by determining Vchanneis<Vn resulting in an inverted logic to determine the outcome of step 326.

[0068] When Vin is insufficient to supply the voltages for the different channels, the duty cycles of one or more of the channels may be adjusted to a level where there is no overlap between the channels. The time-voltage graph 500 of Fig. 5 shows the result of adjusting the duty cycles of channels to a level where there is no overlap. In this example, line 502 represents the voltage over time of a first channel and line 504 represents the voltage over time of a second channel. The first channel is, e.g., the WW channel and the second channel is, e.g., the CW channel. In this example, the time-voltage graph 500 shows a Vww 502 and a Vcw 504, which may represent the same WW and CW channels of Fig. 5, after adjusting the duty cycles.

[0069] In Fig. 5, Vww 502 switches from Vn to VL at time t5, switches from VL to Vn at time t6 and switched from Vn to VL at t7. Vcw 504 switches from VL to Vn at time t5, switches from Vn to VL at time t6 and switched from VL to Vn at t7. It will be understood that this periodicity of Vww and Vcw repeats in time.

[0070] In this example, the duty cycle of Vww 502 is set at ((t7-t6) / (t7-t5))* 100% and the duty cycle of Vcw 504 is set at ((t6-t5) / (t7-t5))* 100%. In an example, t5=47.00ms, t6=47.50ms and t7=28.00ms. The duty cycles of Vww 502 and Vcw 504 are then as follows: duty_cycleww=50% and duty_cyclecw=50%. This setting of the duty cycles of Vww 502 and Vcw 504 may be representative of a 4000K light output at a brightness level that is reduced from 100% to 88%.

[0071] Without the overlap in channel voltages, the input voltage Vin may be sufficient to have the light source on at the new duty cycles, wherein, in this example, the output voltage Vout never exceeds Vn.

[0072] In a lighting system, such as the lighting system 100, the solution of the present disclosure can significantly reduce the voltage drop (e.g., by a factor of about two) along the cable, making it more likely for a light source, e.g., any or all of the light sources 110, 112, 114, to operate or resume normal operation, be it possibly at lower lumen output.

[0073] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope thereof.

Claims

CLAIMS:

1. A light source (200) for operation in a lighting system (100) comprising a plurality of light sources (110, 112, 114, 200) that are electrically connected in parallel by a cable (122-126), the plurality of light sources (110, 112, 114, 200) comprising the light source (200), the light source (200) comprising two or more LED channels (Vww, Vcw, 402, 404, 502, 504), wherein a light output of the light source (200) is adjustable by the two or more LED channels (Vww, Vcw, 402, 404, 502, 504); wherein each of the LED channels is arranged to alternate between a low voltage (VL) and a high voltage (Vn) at a duty cycle; wherein the light source (200) is arranged to determine whether or not an input voltage (Vin) to the light source (200) is sufficient to supply a required output voltage (Vout) for the LED channels; wherein the light source (200) is arranged to adjust the duty cycle of one or more of the LED channels if it is determined that the input voltage to the light source (200) is insufficient to supply the required output voltage for the LED channels; and wherein the light source (200) is arranged to turn on or keep the light source (200) turned on without adjusting the duty cycle of one or more of the LED channels if it is determined that the input voltage to the light source (200) is sufficient to supply the required output voltage for the LED channels.

2. The light source according to claim 1, wherein the light source is further arranged to turn off or keep the light source turned off when, after the adjusting of the duty cycle of one or more of the LED channels, the input voltage to the light source is insufficient to supply the required output voltage for the LED channels.

3. The light source according to any one of the preceding claims, wherein the two or more LED channels comprise a warm white channel (Vww) and a cool white channel (Vcw).

4. The light source according to any one of the preceding claims, wherein the light source is an LED-based light source, wherein the low voltage corresponds to an OFF state of the LED channel, and wherein the high voltage corresponds to an ON state of the LED channel.

5. The light source according to any one of the preceding claims, comprising: a control module (202) arranged to supply the two or more LED channels from the input voltage; a level detection module (204) arranged to determine whether or not the LED channels can be supplied from the input voltage; and a duty cycle adjustment module (206) arranged to have the duty cycle of one or more of the LED channels adjusted if it is determined that the input voltage to the light source is insufficient to supply the required output voltage for the LED channels.

6. The light source according to claim 5, wherein the duty cycle adjustment module signals the control module to adjust the duty cycle of the one of more LED channels.

7. The light source according to claim 5, wherein the duty cycle adjustment module is arranged to adjust the duty cycle of the one of more LED channels.

8. The light source according to any one of the claims 5-7, wherein the level detection module and the duty cycle adjustment module are parts of the control module.

9. The light source according to any one of the preceding claims, comprising a buck converter to supply the output voltage for the channel voltages from the input voltage.

10. A lighting system (100) comprising a plurality of light sources (110, 112, 114, 200) and a cable (122-126) electrically connecting the plurality of light sources in parallel, wherein at least one of the plurality of light sources (200) is a light source according to any one of the claims 1-9.

11. A method (300) of operating a light source (200) in a lighting system (100) comprising a plurality of light sources (110, 112, 114, 200) that are electrically connected in parallel by a cable (122-126), the plurality of light sources (110, 112, 114, 200) comprisingthe light source (200), the light source (200) comprising two or more LED channels (Vww, Vcw, 402, 404, 502, 504) the method comprising: receiving (302) an input for turning on the light source; setting (306) duty cycles of LED channels for a light output of the light source; determining (308) whether or not an input voltage (Vin) to the light source is sufficient to supply a required output voltage (Vout) for the LED channels; and adjusting (310-312) the duty cycle of one or more of the LED channels if it is determined that the input voltage to the light source is insufficient to supply the required output voltage for the LED channels, or turning on or keeping the light source turned on (318, 320) without adjusting the duty cycle of one or more of the LED channels if it is determined that the input voltage to the light source is sufficient to supply the required output voltage for the LED channels.

12. The method according to claim 11, further comprising: turning off or keeping the light source turned off (316) when, after adjusting the duty cycle of one or more of the LED channels, the input voltage to the light source is insufficient to supply the required output voltage for the LED channels.

13. The method according to any one of the claims 11-12, further comprising: receiving (322) a further input comprising a new light setting resulting in the duty cycle of one or more of the LED channels to be changed; determining (326) if there is an overlap between two or more of the LED channels after applying the new light setting; if it is determined that there is no overlap between the two or more of the LED channels after applying the new light setting, setting (328) the duty cycle of the one or more LED channels in accordance with the new light setting; and if it is determined that there is an overlap between the two or more of the LED channels after applying the new light setting, repeating the steps following the setting (306) of the duty cycles for LED channels of the light output of the light source, with the duty cycles set to the new light settings.

14. The method according to any one of the claims 11-13, wherein the determining (308) whether or not the input voltage (Vin) to the light source is sufficient to supply the required output voltage for the LED channels comprises: determining if the sum of channel voltages exceeds a high voltage (Vn) of one of the channel voltages at one moment in time, or, if an inverse logic is used, determining if the sum of channel voltages is equal or below a high voltage (VH) of one of the channel voltages at one moment in time.

15. The method according to claim 14, wherein the LED channels comprise a warm white channel (Vww) and a cool white channel (Vcw), and the determining (308) whether or not the input voltage (Vin) to the light source is sufficient to supply the required output voltage for the LED channels comprises: determining whether Vww+Vcw>Vn, or, if an inverse logic is used, determining whether Vww+Vcw<Vn.

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