Technical field

The present invention relates to charging a battery of a battery powered device. Especially, a battery-powered device is disclosed which battery-powered device is configured to communicate its need for being charged. Moreover, a control engine configured to handle charging requests from one or more battery-powered devices is disclosed.

Background

Many technical systems of today have various devices that communicates wirelessly with one or more other devices of the system. One example of such a technical system is a lighting system. In a lighting system a device that communicates wirelessly with one or more other devices of the system can be a button or dimmer configured to control a light intensity etc. for one or more luminaries of the lighting system. Another example of such a technical system is a monitoring system, e.g., monitoring an environment of a building. Such a monitoring system may comprise different devices such as camera(s), smoke detector(s), presence sensor(s), etc.

Many such devices of a technical system are battery powered. Even if such a battery powered device is made energy efficient, e.g., by low power wireless communication protocols such as Bluetooth Low Energy, BLE, battery replacement may still be a maintenance issue. Especially if there are many battery powered devices in the technical system.

Summary of the invention

It is an object to mitigate, alleviate or eliminate one or more of the above-identified deficiencies in the art and disadvantages singly or in any combination and solve at least the above-mentioned problem.

According to a first aspect a method for charging a battery of a battery powered device is provided. The method comprising: at the battery powered device, detecting that a state of charge of the battery of the battery powered device is below a first threshold; wirelessly transmitting, from the battery powered device, to a control engine, a charging-request signal; instructing, by means of the control engine, a luminaire to expose the battery powered device for light; and charging the battery of the battery powered device by harvesting energy from the light emitted from the luminaire.

The control engine and the battery powered device are embodied in different devices being at a distance from each other. The control engine may even be distributed among different devices. Hence, the battery powered device is wirelessly communicating with the control engine. The present invention is based on the concept of harvesting energy from light. Such harvesting is well known in the art and may, e.g., be made from visible light and/or UV-light.

According to the present invention a battery of a battery powered device may be charged when needed. Hence, the luminaire may be turned on only in case charging is actually requested for. This enables and energy efficient way of charging the battery. Moreover, by limiting the charging to be made upon need, i.e. , upon the state of charge, SOC, is below the first threshold the lifetime of the battery may be prolonged. This since most batteries is degraded less if they are not having a too high or too low SOC most of the time. For example, a SOC between 10% and 80% is more health for a battery.

By allowing recharging of the battery of a battery powered device as defined in the present invention maintenance of battery powered devices may be simplified and made less costly.

Using light as energy harvesting source facilitate in reduction of cost and technical complexity especially when the luminaire (s) is/are part(s) of an indoor lighting system. In such system signaling using light may also be a cost efficient and low complex solution by reusing the light sources etc.

The charging-request signal may comprise information pertaining to a frequency range of the light the energy-harvesting module is capable to harvest energy from. The method may further comprise, extracting, from the charging-request signal, information pertaining to a frequency range of desired light. Instructing a luminaire to expose the battery powered device for light may comprise sending information pertaining to the frequency range of desired light to the luminaire. This facilitate in selecting an luminaire that is capable of emitting light having a desired frequency range.

The method may further comprise selecting one or more luminaires among a plurality of luminaires based on a position of the battery-powered device, and instructing the selected one or more luminaires to expose the battery powered device for light. This facilitate in selecting an luminaire that is capable of emitting electromagnetic radiation to the battery powered device.

The method may further comprise: sending a positive charging request acknowledgment, ACK, to the battery powered device, and upon receipt of the ACK, activating an energy-harvesting energy module at the battery powered device. This may save lifetime of the battery powered device since the energy-harvesting energy module is only active when it is needed for charging. This may prolong the lifetime of the energy-harvesting energy module. This may also prolong the lifetime of the battery.

The method may further comprise: sending a negative charging request acknowledgment, NAK, to the battery powered device, and upon receipt of the NAK, setting the battery powered device in an energyconservation mode. Setting the battery powered device in an energyconservation mode upon charging is not made possible may allow the battery powered device to be limited to only perform some really crucial tasks. This may prolong the uptime of the battery powered device.

The method may further comprise: upon detecting, at the battery- powered device, that the state of charge of the battery of the battery powered device is above a second threshold, sending to the control engine a charging stop signal, upon detection of the charging stop signal, generating, at the control engine, a stop charging signal and transmitting it to the luminaire currently emitting light for charging the battery-powered device, upon receipt of the charging stop signal, at the luminaire, stop emitting light for charging the battery-powered device. Hence, it may be safeguarded that energy at the luminaire may be saved. Moreover, it may be safeguarded that the battery of the battery-powered device is not charged above a specific SOC, e.g., above 80%.

According to a second aspect a battery-powered device is provided. The battery-powered device comprising: a wireless communication unit; a battery; an energy-harvesting module configured to harvest energy from light; and control circuitry. The control circuitry is configured to execute: a state of charge function configured to determine a present state of charge of the battery, and a charging-request function configured to, upon the determined state of charge of the battery is below a first threshold, generate a chargingrequest signal. The wireless communication unit is configured to send the charging-request signal upon its generation.

The charging-request signal may comprise information pertaining to a frequency range of the light the energy-harvesting module is capable to harvest energy from.

The charging-request signal may further comprise information pertaining to one or more of: a device ID; a position of the battery-powered device; and a minimum amount of received power required for performing energy harvesting.

The wireless communication unit may be configured to communicate using a short-range communication protocol, such as one or more of Bluetooth; WiFi; LiFi; Cellular data, 2G-6G; and Zigbee.

The control circuitry is configured to further execute a confirmation function configured to receive a confirmation signal. The confirmation function may be configured to, upon the confirmation signal is indicative of a positive acknowledgement, ACK, set the battery-powered device in an energyharvesting mode. The confirmation function may be configured to, upon the confirmation signal is indicative of a negative acknowledgement, NAK, set the battery-powered device in an energy-conservation mode.

The charging-request function may further be configured to, upon the determined state of charge of the battery is above a second threshold, generate a charging stop signal. The confirmation function may be configured to deactivate the energy-harvesting module based on the charging stop signal. Hence, the charging stop signal may trigger deactivation of the energy-harvesting module. The wireless communication unit may be configured to transmit the charging stop signal upon its generation. By transmitting the charging stop signal deactivation of the luminaire providing the battery-powered device with light may be made.

The above-mentioned features and effects of the first aspect, when applicable, apply to this second aspect as well. In order to avoid undue repetition, reference is made to the above.

According to a third aspect a control engine is provided, the control engine comprising: a short-range wireless transceiver configured to detect a charging-request signal from a battery-powered device arranged at a distance from the control engine; and circuitry configured to execute: a charging function configured to, upon detection of a charging-request signal, generate a charging-initiation signal comprising charging information to a luminaire, and a communication function configured to transmit the charging-initiation signal to the luminaire.

The charging function may be configured to: extract, from the chargingrequest signal, information pertaining to a frequency range of desired light, and include information pertaining to the frequency range of desired light into the charging-initiation signal.

The charging function may further be configured to extract, from the charging-request signal, information pertaining to a position of the battery- powered device, select one or more luminaires among a plurality of luminaires based on the position of the battery-powered device, and send the charging-initiation signal to the selected one or more luminaires.

The circuitry may further be configured to execute a charging compliance function. The compliance function being configured to: confirm whether the control engine is able and/or allowed to provide the, in the charging-request signal, requested charging, upon positive confirmation, generate a confirmation signal comprising a positive acknowledgement, ACK, and send the ACK via the short-range wireless transceiver to the battery- powered device and/or instruct the charging function to generate the charging-initiation signal, and upon negative confirmation, generate a confirmation signal comprising a negative acknowledgement, NAK, and send the NAK via the short-range wireless transceiver to the battery-powered device and/or send the NAK to a maintenance server.

The short-range wireless transceiver may be configured to detect a charging stop signal from the battery-powered device. The charging function may further be configured to, upon detection of the charging stop signal, generate a stop charging signal and transmit it to a luminaire currently emitting light for charging the battery-powered device.

The above-mentioned features and effects of the first and second aspects, when applicable, apply to this second aspect as well. In order to avoid undue repetition, reference is made to the above.

According to a fourth aspect a system is provided. The system comprising: a battery-powered device according to the second aspect; a control engine according to the third aspect; and one or more luminaires each being arranged to expose the battery-powered device for light upon receipt of a charging-initiation signal.

The above-mentioned features and effects of the first, second and third aspects, when applicable, apply to this second aspect as well. In order to avoid undue repetition, reference is made to the above.

A further scope of applicability will become apparent from the detailed description given below. However, it should be understood that the detailed description and specific examples are given by way of illustration only.

It is to be understood that the terminology used herein is for purpose of describing particular embodiments only, and is not intended to be limiting. It must be noted that, as used in the specification and the appended claim, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements unless the context clearly dictates otherwise. Thus, for example, reference to "a unit" or "the unit" may include several devices, and the like. Furthermore, the words "comprising", “including”, “containing” and similar wordings does not exclude other elements or steps. Brief description of the drawings

The above and other aspects will now be described in more detail, with reference to appended figures. The figures should not be considered limiting; instead they are used for explaining and understanding.

As illustrated in the figures, the sizes of layers and regions may be exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures. Like reference numerals refer to like elements throughout.

Fig. 1 illustrate a technical system comprising a battery powered device, a control engine and a plurality of luminaires.

Fig. 2 is a block diagram of a method for charging a battery of a battery powered device.

Detailed description

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and to fully convey the scope of the invention to the skilled person.

The basic concept of the present innovation is that once a battery powered device detects a low state of charge it transmits a charging request via a wireless communication channel. The battery powered device having the ability to harvest energy from light, especially for charging the battery of the battery powered device. The charging request comprising information about the energy harvesting capabilities of the battery powered device, e.g., wavelength requirements and/or intensity requirements. A control engine detecting the charging request is then configured to expose the battery powered device for light (of the requested wavelength and/or intensity). The control engine is set to do this by instructing a luminaire to emit light (of the requested wavelength and/or intensity) onto the battery powered device requesting to be charged by energy harvesting from light.

Fig. 1 illustrates a technical system 10. The technical system comprises one or more battery powered devices 100, a control engine 200 and one or more luminaires 300. The one or more battery powered devices 100 are arranged at a distance from the control engine 200. Each battery powered device 100 is configured to wirelessly send information, e.g., comprising instructions, to the control engine 200. The control engine 200 is configured to act on information/instructions received from a battery powered device 100. The control engine 200 is further configured to send information, e.g., comprising instructions, to one or more of the one or more luminaires 300. The control engine 200 may communicate with the one or more luminaires 300 over a wireless communication channel and/or a wired communication channel. Each luminaire 300 is configured to act on information/instructions received from the control engine 200.

In case of a plurality of luminaires 300, each luminaire 300 may be of a same type. However, the technical system 10 may comprise different types of luminaires 300. The one or more luminaires 300 may belong to a lighting system. The luminaires 300 are typically stationary arranged in a building housing the technical system 10. The luminaires 300 are typically spread out in the building housing the technical system 10. Each luminaire 300 is configured to expose a sub-portion of a space for light. Hence, a specific luminaire 300 may be configured to expose one or more battery powered device 100 arranged in the portion of space it is exposing. The control engine 200 may be provided with information pertaining to a location of each luminaire 300. That is, the control engine 200 may be provided with information pertaining to a portion of the space which the specific luminaire 300 is configured to expose with light. Moreover, the control engine 200 may be provided with information pertaining to characteristics of each luminaire 300. Examples of such characteristics are: wavelength range of the luminaire 300; if the wavelength of the luminaire 300 is controllable or not; intensity range of the luminaire 300; if the intensity of the luminaire 300 is controllable or not; beam shaping ability of the luminaire 300.

A specific battery powered device 100 may be a control device configured to control other devices of the technical system 10. For example, the battery powered device 100 can be one or more of: an on/off switch and/or dimmer for one or more luminaries of a lighting system, a temperature controller for devices of a heating/cooling system, an air flow controller in a ventilation system. A specific battery powered device 100 may be a sensor. Such a sensor may be configured to monitor presence of moving objects (such as a person or animal). Alternatively, or in combination, such a sensor may be configured to monitor environmental data, such as smoke, concentration of a specific gas, etc. A specific battery powered device 100 may be stationary arranged in the building housing the technical system 10. A specific battery powered device 100 may be a non-stationary device. In case of a battery powered device 100 being stationary arranged, the control engine 200 may be provided with information pertaining to a location of the battery powered device 100 within the housing the technical system 10. In case of a battery powered device 100 being non-stationary, the control engine 200 may be configured to keep track of a location of the battery powered device 100, at least as long as the battery powered device 100 is within the building housing the technical system 10.

In connection with Fig. 1 the technical system 10 is illustrated in a situation when one of the luminaires 300 is instructed to emit light towards a battery powered device 100. This is illustrated by the dashed lines. The luminaire 300 have received instructions from the control engine 200 to expose the battery powered device 100 with light. This since the battery powered device 100 sent a charging-request signal to the control engine 200. The charging-request signal was generated due to that a state-of charge of the battery powered device 100 was below a first threshold. The chargingrequest signal may comprise a desired wavelength of light. The chargingrequest signal may comprise a location of the battery powered device 100. The control engine 200 may be configured to decided which luminaire 300 to instruct for exposing the battery powered device 100 for light based on one or more of the desired wavelength of light and the location of the battery powered device. The control engine 200 may further be configured to decided which luminaire 300 to instruct for exposing the battery powered device 100 for light based on a location of the luminaire 300.

The battery powered device 100, the control engine 200, the luminaire 300 and a method for charging a battery 110 of the battery powered device 100 will below be discussed in more detail.

With reference to Fig. 1 , a battery powered device 100 will be discussed in more detail. The battery-powered device 100 comprises a battery 110 powering the battery powered device 100. The battery 110 is a rechargeable battery.

The battery-powered device 100 further comprises an energyharvesting module 120. The energy-harvesting module 120 is configured to harvest energy from light. For example, the energy-harvesting module 120 may comprise solar/light cells. The solar/light cells being configured to transform light to electricity. The energy-harvesting module 120 is connected to the battery 110 in such manner so that upon harvesting energy, the energy-harvesting module 120 is configured to charge the battery 110.

The battery-powered device 100 further comprises control circuitry 130. The control circuitry 130 may be hardware or software implemented. The control circuitry 130 may even be a combination of hardware and software portions. The software may be executed by a processor being part of the control circuitry 130. In case of being full or partly software implemented the control circuitry 130 may comprise a memory storing software code portions. The control circuitry 130 is configured to perform one or more functions of the battery-powered device 100.

The control circuitry 130 is configured to execute a state of charge function 132. The state of charge function 132 is configured to determine a present state of charge of the battery 110.

The control circuitry 130 is further configured to execute a chargingrequest function 134. The charging-request function 134 is configured to generate a charging-request signal. Especially, the charging-request function 134 is configured to generate the charging-request signal upon the determined state of charge of the battery 110 is below a first threshold. The charging-request signal may comprise information pertaining to a frequency range of the light the energy-harvesting module 120 is capable to harvest energy from. The charging-request signal may further comprise information pertaining to one or more of: a device ID for the battery powered device 100; a position of the battery-powered device 100; and a minimum amount of received power required for performing energy harvesting.

The charging-request function 134 may further be configured to, upon the determined state of charge of the battery is above a second threshold, generate a charging stop signal. The second threshold is above the first threshold. According to a non-limiting example, the first threshold is 10% state of charge, SOC, and the second threshold is 80% SOC. The charging stop signal may be triggering deactivation of the energy-harvesting module 120. Moreover, the charging stop signal may be transmitted to the control engine 200.

The battery-powered device 100 further comprises a wireless communication unit 180. The wireless communication unit 180 is configured to transmit the charging-request signal upon its generation. Hence, the battery powered device 100 monitors the state of charge of the battery 110 and once it passes below a first threshold, the battery powered device 100 wirelessly sends out a charging request. The wireless communication unit 180 is configured to transmit the charging stop signal upon its generation. Hence, the battery powered device 100 monitors the state of charge of the battery 110 and once it passes above a second threshold, the battery powered device 100 wirelessly sends out a stop charging request. The wireless communication unit 180 may be configured to communicate using a short-range communication protocol. Examples of short-range communication protocols are: Bluetooth, especially BLE; WiFi; LiFi; Cellular data, e.g. 2G-6G; and Zigbee. However, it is understood that other short-range communication protocols may as well be used. There might even be a future protocol dedicated for energy harvesting.

The control circuitry 130 may further be configured to execute a confirmation function 136. The confirmation function 136 is configured to receive a confirmation signal. The confirmation signal carrying information pertaining to if light required by the battery-powered device 100, e.g., compatible with the energy-harvesting module 120, can be provided to the battery-powered device 100 or not. The confirmation signal may be a dedicated signal. Alternatively, the confirmation signal may be receipt of light of “correct” wavelength impinging the energy-harvesting module 120. The confirmation function 136 may be configured to, upon the confirmation signal is indicative of a positive acknowledgement, ACK, set the battery-powered device 100 in an energy-harvesting mode. Setting the battery-powered device 100 in an energy-harvesting mode may comprise activating the energyharvesting module 120. Hence, the energy-harvesting module 120 may be set in a normally-off mode and only be activated upon being impinged with light of “correct” wavelength and/or intensity. Further, the confirmation function 136 may be configured to, upon the confirmation signal is indicative of a negative acknowledgement, NAK, set the battery-powered device 100 in an energyconservation mode. The energy-conservation mode may be a sleep mode of the battery-powered device 100. Upon the confirmation signal being a NAK, the battery-powered device 100 may further be configured to generate and send a battery-replacement signal. Such a battery-replacement signal is typically addressed to a maintenance service of the building housing the technical system 10.

In connection with Fig. 1 the control engine 200 will be discussed in more detail. The control engine 200 comprises a wireless transceiver 280. The wireless transceiver 280 is configured received and possibly also transmit data over a wireless short-range communication protocol, such as Bluetooth, especially BLE; WiFi; LiFi; Cellular data, e.g., 2G-6G; and Zigbee. However, it is understood that other short-range communication protocols may as well be used. Especially, the wireless transceiver 280 is configured to receive a charging-request signal transmitted from a battery-powered device 100. Hence, the wireless transceiver 280 is configured to detect a chargingrequest signal. The wireless transceiver 280 may further be configured to receive a charging stop signal transmitted from the battery-powered device 100. Hence, the wireless transceiver 280 is configured to detect a charging stop signal.

The control engine 200 further comprises circuitry 230. The circuitry 230 may be hardware or software implemented. The circuitry 230 may even be a combination of hardware and software portions. The software may be executed by a processor being part of the circuitry 230. In case of being full or partly software implemented the circuitry 230 may comprise a memory storing software code portions. The circuitry 230 is configured to perform one or more functions of the control engine 200.

The circuitry 230 is configured to execute a charging function 232. The charging function 232 is configured to generate a charging-initiation signal. Especially, the charging function 232 is configured to generate the charginginitiation signal upon the wireless transceiver 280 has received/detected a charging-request signal. Typically, the charging-initiation signal comprises charging information bound for a specific luminaire 300 among the one or more luminaires 300. On that note, the charging function 232 may be configured to, from the charging-request signal, extract information pertaining to a position of the battery-powered device 100 having generated the charging-request signal. Based on the information pertaining to the position of the battery-powered device 100, the charging function 232 may be configured to select one or more luminaires 300 to which a charging-initiation signal is to be sent. As an alternative to, or in combination with, the charging function 232 may be configured to, from the charging-request signal, extract information pertaining to an ID of the battery-powered device 100 having generated the charging-request signal. Based on the information pertaining to the ID of the battery-powered device 100, the charging function 232 may be configured to select one or more luminaires 300 to which a charging-initiation signal is to be sent. This selection may, e.g., be made by accessing a look-up table comprising which one or more luminaires 300 that are being able to emit light bound for a specific battery-powered device 100.

The charging function 232 may further be configured to extract information pertaining to a frequency range of desired light to be emitted from the luminaire 300. Typically, the information pertaining to a frequency range of desired light is extracted from the charging-request signal. The charging function 232 may further be configured to include information pertaining to the frequency range of desired light into the charging-initiation signal.

The charging function 232 may further be configured to generate a stop charging signal. Especially, the charging function 232 is configured to generate the stop charging signal upon the wireless transceiver 280 has received/detected a charging stop signal.

The circuitry 230 is further configured to execute a communication function 234. The communication function 234 is configured to transmit the charging-initiation signal. Especially, the communication function 234 is configured to transmit the charging-initiation signal to the specific luminaire 300 among the one or more luminaires 300. The transmitting of the charginginitiation signal may be made by means of the wireless transceiver 280. In such case the wireless transceiver 280 is configured to establish a communication channel to the specific luminaire 300 and possibly also to other luminaires 300 among the one or more luminaires 300. Alternatively, the transmitting of the charging-initiation signal may be made by means of another wired or wireless transceiver 290.

The communication function 234 may further be configured to transmit the stop charging signal to a luminaire 300. Especially to the luminaire 300 currently emitting light for charging the battery-powered device 200 having issued the charging stop signal.

The circuitry 230 may further be configured to execute a charging compliance function 236. The charging compliance function 236 is configured to confirm that a luminaire 300 is present that is able and/or allowed to provide the, in the charging-request signal, requested charging. In this context “is able to” has the meaning of: does there exist a luminaire 300 being able to emit light onto the battery-powered device 100 that issued the chargingrequest signal; can that luminaire 300 provide the requested wavelength of light; and/or can that luminaire 300 provide enough power of the requested wavelength of light. In this context “is allowed to” has the meaning of: is the requesting battery-powered device 100 on a list of battery-powered devices that are allowed to receive power. The device ID may be used for checking this. The ID may be stored in a data base of allowed devices. Allowed devices may be configured for instance during a commissioning of the system. The advantage of such check is that only allowed devices or devices belonging to the system is allowed to charge. Upon positive confirmation, the charging compliance function 236 is configured to generate a confirmation signal comprising a positive acknowledgement, ACK. The charging compliance function 236 may be configured to and send the ACK to the requesting battery-powered device 100. Such sending of the ACK may be made using the wireless transceiver 280. Alternatively, or in combination, the charging compliance function 236 is also configured to instruct the charging function 232 to generate the charging-initiation signal. Upon negative confirmation, the charging compliance function 236 is configured to generate a confirmation signal comprising a negative acknowledgement, NAK. The charging compliance function 236 may be configured to and send the NAK to the requesting battery-powered device 100. Such sending of the NAK may be made using the wireless transceiver 280. The charging compliance function 236 may, alternatively, or in combination, be configured to and send the NAK to a maintenance server.

Upon a luminaire 300 is receiving a charging-initiation signal it is configured to initiate emission of light, thereby exposing a battery-powered device 100 for light. Upon a luminaire 300 is receiving a stop charging signal it is configured to stop emission of light, thereby stop exposing a battery- powered device 100 for the emitted light.

In connection with Fig. 2 a method 400 for charging a battery 110 of a battery powered device will be discussed. The method 400 comprises a plurality of steps. The steps may be performed in any suitable order. The method 400 comprising, at the battery powered device 100, detecting S402 that a state of charge of the battery 110 of the battery powered device 100 is below a first threshold. Hence, the battery powered device 100 obtains information about state of charge of its battery 110. This can for instance be made by measuring the current or voltage level over the battery 110. Once the state of charge of the battery 110 is below the first threshold it is determined that the battery 110 is in need for being charged. This in order to safeguard future operation of the battery powered device 100.

The method further comprises wirelessly transmitting S404, from the battery powered device 100, to a control engine 200, a charging-request signal. Hence, the battery powered device 100 transmits a charging request over a wireless communication protocol as described above. The charging request signal may comprise energy harvesting capabilities as well as other information needed for successful wireless charging (spatial position info, device ID etc. as also described above).

The method may further comprise, at the control engine 200, detecting S405 a charging request signal transmitted over the wireless communication protocol.

The method further comprises instructing S406, by means of the control engine 200, a luminaire 300 to expose the battery powered device 100 for light. Hence, the control engine initiates a charging action. As discussed above, the charging action can be based on charging request information in the charging request signal. How to select a luminaire 300 to instruct and how to instruct the selected luminaire 300 is discussed above in connection with Fig. 1 and the discussion of the control engine 200. In order to avoid undue repletion reference is made to the above discussion.

The method further comprises charging S408 the battery 110 of the battery powered device 100 by harvesting energy from the light emitted from the luminaire 300. The harvesting is made by the energy-harvesting module 120 of the battery powered device 100 as discussed above.

The method may further comprise, at the control engine, monitoring whether the charging action failed or not. In case of success, the method may comprise sending, from the control engine 200 to the battery powered device 100, a positive charging request acknowledgment, ACK. This is further discussed above. In case of failed charging action, the method may comprise, sending, from the control engine 200 to the battery powered device 100, a negative charging request acknowledgement, NAK, and/or reporting the failed charging action to a system maintenance server.

The method may further comprise, at the battery powered device 100, monitoring for a charging request acknowledgment. Upon receiving a positive charging request acknowledgment, ACK, start the charging S408. Upon receiving a negative charging request acknowledgement, NAK, setting the battery powered device 100 in an energy-conservation mode.

The person skilled in the art realizes that the present invention by no means is limited to what is explicitly described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

For example, a single device may have capabilities to both act as a control engine 200 and as a luminaire 300. Alternatively, the control engine 200 and the luminaire 300 are different devices. Hence, the control engine 200 may be embodied in a specific device, such as a server. Alternatively, the control engine 200 may be arranged in one of the one or more luminaires 300. Yet alternatively, the control engine 200 may be distributed over a plurality of different devices.

The control engine 200 and the one or more battery powered device 100 may be configured to communicate using a first wireless communication protocol. The control engine 200 and the one or more luminaires 300 may be configured to communicate using a second communication protocol, the second communication protocol being different from the first wireless communication protocol. The second communication protocol does not even need to be wireless, also wired communication protocols may be used.

The control engine 200 may broadcast the charging-initiation signal. If so, the charging-initiation signal may, e.g., comprise information on where the battery powered device 100 that is requesting to be exposed to light is located and/or by which wavelength(s) the battery powered device 100 is requesting to be exposed to. Each luminaire 300 receiving the broadcasted charging-initiation signal may then act upon the received information. That is, if it can fulfil the requests, i.e. , if it can emit the desired wavelength(s) and/or expose the desired location.

The control engine 200 may unicast the charging-initiation signal. That is, the control engine 200 can direct the charging-initiation signal to one specific luminaire 300. The selection of specific luminaire 300 to unicast to may, e.g., be decided by having knowledge of which locations the different luminaire (s) 300 are able to expose for light and/or which wavelength it may emit.

Additionally, variations can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.