Luminaire, and control unit for control electrical energy consumption of luminaires electrically supplied from a DC grid

Abstract

The invention relates to a luminaire configured to be supplied with a DC voltage, emit light in a normal operation state when the DC voltage is greater than a voltage threshold, and reduce its electrical energy consumption compared to its electrical energy consumption in the normal operation state when the DC voltage is equal to or smaller than the voltage threshold. Control unit for controlling an electrical energy consumption of luminaires supplied from a DC grid. The control unit is configured to control operation of the luminaires such that they are allowed to emit light in a normal operation state when the DC voltage of the DC grid is greater than a voltage threshold, and an electrical energy consumption of the luminaires is reduced compared with an electrical energy consumption of the luminaires in the normal operation state when the DC voltage of the DC grid is equal to or smaller than the voltage threshold.

Description

[0001] LUMINAIRE, AND CONTROL UNIT FOR CONTROL ELECTRICAL ENERGY CONSUMPTION OF LUMINAIRES ELECTRICALLY SUPPLIED FROM A DC GRID

[0002] Description:

[0003] The present invention relates to a luminaire configured to be electrically supplied with a DC voltage (e.g. from a DC grid); a system comprising one or more of such luminaires; a control unit for controlling an electrical energy consumption of luminaires electrically supplied from a DC grid; and a system comprising such a control unit and one or more luminaires.

[0004] Luminaires, such as luminaires for providing lighting (i.e. normal lighting), emergency luminaires for providing emergency lighting, safety sign luminaires for illuminate a safety sign etc., may be electrically supplied from a DC grid. That is, they may be electrically connected e.g. via a DC branch circuit, with the DC grid in order to be supplied with electrical energy and be able to provide their function, such as providing lighting, emergency lighting etc. Additional components may be electrical connected with the DC grid, wherein such additional components may use electrical energy from the DC grid and / or provide to the DC grid (i.e. supply to the DC grid) electrical energy. Such additional components may comprise energy storage(s) (e.g. one or more batteries, such as one or more rechargeable batteries) for storing electrical energy, renewable energy system(s) (e.g. photovoltaic (PV) system(s), wind energy system(s), etc.) for providing electrical energy, AC-to-DC power converters for providing electrical energy from an AC electrical energy source (such as mains). The term “DC network” may be used as a synonym for the term “DC grid”.

[0005] When a lighting system comprising luminaire(s) is electrically supplied with an AC voltage (alternating voltage) by an AC electrical energy source, such as mains, then failure or malfunction of the electrical supply may be detected by monitoring the AC voltage. For example, as soon as the AC voltage decreases below a threshold value,an emergency state may be recognized causing an emergency lighting. For this, emergency luminaires may be used, wherein each emergency luminaire comprises an electrical energy storage, such as a battery, and is configured to emit light in the emergency state by using the electrical energy stored in the respective electrical energy storage.

[0006] However, when luminaires are supplied from a DC grid (instead of an AC electrical energy source, such as mains), the above described detection of the emergency state cannot be used anymore. Namely, when the luminaires are supplied from the DC grid at no time an AC voltage is supplied to the luminaires and, thus, monitoring an AC voltage being provided by an AC electrical energy source, such as mains, cannot be used for detecting the emergency state and, thus, causing an emergency lighting. Especially, switching from an AC to a DC electrical energy supply cannot be used as an indicator for the emergency state.

[0007] Therefore, it is an object of the present invention to provide means that allow providing a system in which one or more luminaires are electrically supplied from a DC grid. It may be an object to provide means that allow providing an emergency lighting in a system in which one or more luminaires are electrically supplied from a DC grid.

[0008] These and other objects, which become apparent upon reading the following description, are solved by the subject-matter of the independent claim. The dependent claims refer to preferred embodiments of the invention.

[0009] According to a first aspect of the invention, a luminaire is provided. The luminaire is configured to be electrically supplied with a DC voltage. The luminaire is configured to emit light in a normal operation state when the DC voltage is greater than a voltage threshold. The luminaire is configured to reduce its electrical energy consumption compared to its electrical energy consumption in the normal operation state when the DC voltage is equal to or smaller than the voltage threshold.Thus, the first aspect proposes a luminaire that reduces its electrical energy consumption compared to its electrical energy consumption of the normal operation state when the DC voltage used for electrically supplying the luminaire reaches or falls below a voltage threshold. This allows countering an overload of an electrical energy source, such as a DC grid, that supplies the DC voltage. Therefore, the luminaire of the first aspect allows providing a system in which one or more luminaires of the first aspect are electrically supplied from a DC grid. Namely, in case the DC voltage electrically supplied from the DC grid to the one or more luminaires decreases to or below the voltage threshold, the one or more luminaires will reduce its energy consumption. This allows countering the reduction of the DC voltage and, thus, an overload of the DC grid causing the reduction of the DC voltage. The electrical energy consumption of the luminaire in the normal operation state may be understood as the electrical energy consumption of the luminaire when emitting light in the normal operation state.

[0010] The luminaire may be an indoor luminaire or an outdoor luminaire. The luminaire is not limited to a specific type of luminaire. The luminaire comprises lighting means and the luminaire is configured to operate the lighting means using the received DC voltage (with which the luminaire is configured to be electrically supplied) so that the lighting means provide a light emission of the luminaire. The luminaire may comprise a driver for driving the lighting means using the DC voltage with which the luminaire is configured to be electrically supplied. The lighting means may be one or more light emitting diodes (LEDs). In case of multiple LEDs, they may be electrically connected in series and / or in parallel. The present invention is not limited to a specific type of LEDs. The present invention is not limited to a specific type of lighting means.

[0011] The luminaire may be electrically supplied with the DC voltage from a DC electrical energy source, such as a DC grid and / or an electrical circuit (e.g. a DC branch circuit) being electrically connected with the DC grid and receiving the DC voltage from the DC grid. The luminaire may be configured to be electrically connected to theDC grid and / or an electrical circuit (e.g. a DC branch circuit) being electrically connected with the DC grid and receiving the DC voltage from the DC grid.

[0012] The normal operation state of the luminaire may be understood as an operation state in which the luminaire is allowed to operate according to its design. That is, in the normal operation state the luminaire does not actively reduce its electrical energy consumption in order to safe electrical energy.

[0013] In other words, in the normal operation state of the luminaire its maximum energy consumption may be defined by the operation for which the luminaire is designed for. That is, the maximum energy consumption of the luminaire in the normal operation state may be understood as the maximum possible energy consumption of the luminaire when the luminaire operates without any limitations in an effort to reduce the luminaire’s energy consumption. The luminaire may be configured to limit or reduce its maximum energy consumption when the DC voltage is equal to or smaller than the voltage threshold. In other words, the luminaire may be configured to reduce its maximum electrical energy consumption compared to its maximum electrical energy consumption of the normal operation state when the DC voltage is equal to or smaller than the voltage threshold.

[0014] The voltage threshold may be a voltage value at which a overload of the DC electrical energy source, such as a DC grid, providing the DC voltage (to the luminaire) begins. The smaller the DC voltage below the voltage threshold the greater the overload of the DC electrical energy source. The voltage threshold may be selected or set such that the DC voltage being greater than the voltage threshold is sufficient for the DC electrical energy source, e.g. the DC grid, providing the DC voltage to work properly (e.g. electrically supply one or more loads being electrically connected to the source) and, thus, not being in an overload state. For example, the voltage threshold may be equal to a DC voltage of 485 V. The state in which the DC electrical energy source (e.g. DC grid) works properly may be referred to as normal state of the DC electrical energy source.The term “direct voltage” may be used as synonym for the term “DC voltage”. The electrical energy consumption may be referred to as “energy consumption”. The term “decrease” may be used as a synonym for the term “reduce”.

[0015] The luminaire according to the first aspect may be a DC-lndustry compatible luminaire. It may be referred to as “DC-lndustry luminaire” or “DC-lndustry supply luminaire”. DC-lndustry is the name of a supply concept worked out by the DC Industry consortium. The term “DC Industry supply” may be used as a synonym for a supply grid (i.e. DC grid), which is according to the aforementioned concept.

[0016] Optionally, the luminaire is configured to, when the DC voltage is equal to or smaller than the voltage threshold, not emit light, or emit light in an energy saving operation state. In the energy saving operation state a maximum light intensity of the light emission is smaller than the maximum light intensity of the light emission in the normal operation state. In addition or alternatively, in the energy saving operation state a light quality of the light emission is reduced compared to the light quality of the light emission in the normal operation state such that the electrical energy consumption of the light emission (in the energy saving operation state) is reduced compared to the electrical energy consumption of the light emission in the normal operation state.

[0017] That is, in the energy saving operation state, the luminaire may reduce its electrical energy consumption compared to its electrical energy consumption in the normal operation state by reducing the electrical energy consumption of its light emission compared to the electrical energy consumption of its light emission in the normal operation state. The luminaire may be configured to reduce the electrical energy consumption of its light emission in the energy saving operation state compared to the electrical energy consumption of its light emission in the normal operation state by reducing the maximum light intensity of the light emission compared to the maximum light intensity of the light emission in the normal operation state and / or byreducing the light quality of the light emission compared to the light quality of the light emission in the normal operation state.

[0018] When the luminaire does not emit light, the luminaire has a smaller electrical energy consumption compared to a state in which the luminaire emits light. Thus, the luminaire may be configured to reduce its electrical energy consumption (compared to its electrical energy consumption of the normal operation state) by not emitting light when the DC voltage is equal to or smaller than the voltage threshold. In case the luminaire emits light while the DC voltage reduces to or below the voltage threshold, the luminaire may be configured to stop the light emission when the DC voltage reaches or reduces below the voltage threshold.

[0019] When in the energy saving operation state the maximum light intensity of the light emission of the luminaire is smaller than the maximum light intensity of the light emission of the luminaire in the normal operation state, the maximum electrical energy consumption of the luminaire in the energy saving operation state is smaller than the maximum electrical energy consumption of the luminaire in the normal operation state. The greater the light intensity of the light emission of the luminaire (i.e. its lighting means for providing the light emission) the greater the electrical energy consumption of the luminaire and vice versa (assuming that other optional function(s) of the luminaire do not change and, thus, do not have an effect on the electrical energy consumption). Namely, the luminaire, e.g. one or more drivers, provide a greater amount of electrical energy (e.g. in average over a certain time period) to the lighting means for achieving a greater light intensity of the light emitted by the lighting means and, thus, of the light emission of the luminaire. That is, the luminaire, e.g. one or more drivers, is configured to control the light intensity of its light emission (i.e. of the light emitted by its lighting means) by controlling the amount of electrical energy (e.g. in average over a certain time period) provided to the lighting means of the luminaire, wherein the greater the amount of electrical energy (e.g. in average over a certain time period) the greater the light intensity (e.g. in average over the certain time period) and vice versa. The more electrical energyused by the luminaire for providing its light emission the greater the electrical energy consumption and vice versa.

[0020] Thus, the luminaire may be configured to emit light in the energy saving operation state such that the light intensity of the light emitted by the luminaire in the energy saving operation is smaller than the maximum light intensity of the light emission of the luminaire emitting light in the normal operation state. The maximum light intensity of the luminaire in the normal operation state may be understood as the light intensity that is maximum possible due to the design of the luminaire or as the maximum light intensity (e.g. nominal light intensity) for which the luminaire is designed for. The maximum light intensity in the normal operation state may equal a dim level of 100% of the luminaire (i.e. of the light emission of the luminaire). The smaller the dim level the smaller the light intensity of the light emission of the luminaire and vice versa. The dim level may be percentage value between 0% and 100%. The dim level of 0% may mean that the luminaire does not emit light. Thus, the maximum light intensity in the energy saving operation state may equal a dim level that is smaller than 100%.

[0021] Optionally, when the luminaire operates in the energy saving operation state, the luminaire may be configured to emit light with a dedicated light intensity that is smaller than the maximum light intensity of the light emission in the normal operation state. In other words, the luminaire may be configured to emit light in the energy saving operation state such that the emitted light has a dedicated light intensity that is smaller than the maximum light intensity of the light emission in the normal operation state.

[0022] Optionally, when the luminaire operates in the energy saving operation state, the luminaire may be configured to emit light such that the smaller the DC voltage the smaller the light intensity of the emitted light and vice versa. In other words, the luminaire may be configured to emit light in the energy saving operation state such that the smaller the DC voltage the smaller the light intensity of the emitted light and vice versa.For example, when the luminaire operates in the energy saving operation state, the luminaire may be configured to emit light such that the light intensity of the emitted light equals between 5% and 30% of the maximum light intensity of the light emission in the normal operation mode (e.g. equals a dim level between 5% and 30%). In other words, the luminaire may be configured to emit light in the energy saving operation state such that the smaller the DC voltage the smaller the light intensity of the emitted light and vice versa.

[0023] Reducing the light quality of the light emission compared to the light quality of the light emission in the normal operation state means that the light emission with the reduced light quality requires less electrical energy and, thus, is more efficient compared to the light emission in the normal operation state. Optionally, the light emission with the reduced light quality may be a cold white light emission with a lower color rendering index (CRI) compared to a warm white light emission in the normal operation state. For example, the light emission with the reduced light quality in the energy saving operation state may be a cold white low CRI light emission and the light emission with the light quality (not being reduced) in the normal operation state may be a warm white high CRI light emission. Thus, reducing the light quality of the light emission (in the energy saving operation state) compared to the light quality of the light emission in the normal operation state may be achieved by changing from a warm white high CRI light emission to a cold white low CRI light emission.

[0024] Reducing the light quality of the light emission in the energy saving operation state compared to the light quality of the light emission in the normal operation state (such that the electrical energy consumption of the light emission in the energy saving operation state is reduced compared to the electrical energy consumption of the light emission in the normal operation state) may comprise increasing the color temperature, e.g. correlated color temperature (CCT), of the light emission and / or reducing the CRI of the light emission. In other words, the light emission with the reduced light quality in the energy saving operation state may have a greater color temperature compared to the color temperature of the light emission in the normaloperation state and / or may have a lower CRI compared to the CRI of the light emission in the normal operation state. Cold white light has a greater color temperature than warm white light.

[0025] Optionally, when the luminaire operates in the energy saving operation state, the luminaire may be configured to emit light with a dedicated color temperature, e.g. CCT, that is greater than the color temperature of the light emission in the normal operation state and / or with a dedicated CRI that is smaller than the CRI of the light emission in the normal operation state.

[0026] The luminaire may be configured to reduce its electrical energy consumption (compared to its electrical energy consumption of the normal operation state) by operating in the energy saving operation state and, thus, when light emission is wanted, to emit light in the energy saving operation state. In other words, the luminaire may be configured to, when the DC voltage is equal to or smaller than the voltage threshold not emit light (e.g. stop emitting light) or operate in the energy saving operation state. Thus, the luminaire may be configured to reduce its electrical energy consumption (compared to its electrical energy consumption of the normal operation state) when the DC voltage is equal to or smaller than the voltage threshold by not emitting light or operating in the energy saving operation state.

[0027] The term “reduced electrical energy operation state” may be used as a synonym for the term “energy saving operation state”.

[0028] Optionally, the luminaire is configured to emit light in the energy saving operation state when the DC voltage is equal to or smaller than the voltage threshold and greater than a second voltage threshold. The luminaire may be configured to not emit light when the DC voltage is equal to or smaller than the second voltage threshold. The second voltage threshold is smaller than the voltage threshold.The second voltage threshold may be a voltage value at which an overload of the DC electrical energy source, such as a DC grid, providing the DC voltage (to the luminaire) is critical and may cause failure of the DC electrical energy source. The second voltage threshold may be selected or set such that the DC voltage being equal to or smaller than the second voltage threshold is not sufficient for the DC electrical energy source, e.g. the DC grid, providing the DC voltage to work properly (e.g. electrically supply one or more loads being electrically connected to the source) and, thus, being close to failure or failing. For example, the second voltage threshold may be equal to a DC voltage between 40 V and 220 V (i.e. equal to 40 V, or greater than 40 V and smaller than 220 V, or equal to 220 V). Optionally the second voltage threshold may be equal to a DC voltage of 48 V or 216 V.

[0029] Optionally, the luminaire is an emergency luminaire or a safety sign luminaire. The luminaire is configured to emit light in an emergency operation state when the DC voltage is equal to or smaller than the voltage threshold. In the emergency operation state a minimum light intensity of the light emission is sufficient for an emergency / safety lighting and a maximum light intensity of the light emission is smaller than the maximum light intensity of the light emission in the normal operation state. In addition or alternatively, in the emergency operation state a light quality of the light emission is reduced compared to the light quality of the light emission in the normal operation state such that the electrical energy consumption of the light emission is reduced compared to the electrical energy consumption of the light emission in the normal operation state and the reduced light quality of the light emission is sufficient for the emergency / safety lighting.

[0030] In other words, the luminaire may be an emergency luminaire or a safety sign luminaire, and the luminaire may be configured to emit light in an emergency operation state when the DC voltage is equal to or smaller than the voltage threshold, wherein in the emergency operation state the luminaire reduces its electrical energy consumption compared to its electrical energy consumption in the normal operation state such that its reduced electrical energy consumption allows the luminaire toprovide an emergency / safety lighting. For example, the aforementioned reduction of its electrical energy consumption in the emergency operation state may be achieved in that in the in the emergency operation state the minimum light intensity of the light emission of the luminaire is sufficient for the emergency / safety lighting and the maximum light intensity of the light emission is smaller than the maximum light intensity of the light emission in the normal operation state. In addition or alternatively, the aforementioned reduction of its electrical energy consumption in the emergency operation state may be achieved in that the light quality of the light emission is reduced compared to the light quality of the light emission in the normal operation state such that the electrical energy consumption of the light emission is reduced compared to the electrical energy consumption of the light emission in the normal operation state and the reduced light quality of the light emission is sufficient for the emergency / safety lighting.

[0031] The emergency luminaire is configured to provide an emergency lighting. The safety sign luminaire is configured to provide a safety lighting to illuminate a safety sign and optionally provide the emergency lighting. An example of a safety sign luminaire is an escape sign luminaire, wherein the safety sign is an escape sign. The emergency operation state is a specific implementation of the aforementioned energy saving operation state. Thus the description with regard to the energy saving operation state may be correspondingly valid for the emergency operation state.

[0032] The minimum light intensity may equal between 5% and 30% of the maximum light intensity of the light emission in the normal operation mode (e.g. equals a dim level between 5% and 30%). The minimum light intensity being sufficient for the emergency / safety lighting may be defined by regulations, such as national and / or international regulations.

[0033] Optionally, the luminaire is configured to emit the light in the emergency operation state when the DC voltage is equal to or smaller than a second voltage threshold (the description of the above mentioned second voltage threshold may becorrespondingly valid, i.e. the aforementioned second voltage threshold may be the above mentioned second voltage threshold) such that the light intensity of the light emission equals the minimum light intensity and / or the reduced light quality of the light emission achieves a minimum electrical energy consumption of the light emission sufficient for the emergency / safety lighting. The second voltage threshold is smaller than the voltage threshold.

[0034] The luminaire may be configured to not use an optional internal energy storage of the luminaire (e.g. arranged in a housing of the luminaire) and / or an energy storage associated with the luminaire (e.g. arranged at a housing of the luminaire) for electrically supplying its light emission (i.e. its lighting means e.g. via driver(s)). An energy storage associated with the luminaire may be electrically connected with the luminaire and directed for providing electrical energy to the luminaire. For example, the luminaire may be configured to not use the optional internal energy storage of the luminaire and / or the energy storage associated with the luminaire for electrically supplying its light emission (i.e. its lighting means e.g. via driver(s)) in the emergency operation state. Optionally, the luminaire does not comprise an internal energy storage (e.g. arranged in a housing of the luminaire) and / or an energy storage associated with the luminaire (e.g. arranged at a housing of the luminaire) for electrically supplying its light emission (i.e. its lighting means e.g. via driver(s)). For example, the luminaire does not comprise the internal energy storage and / or the energy storage associated with the luminaire for electrically supplying its light emission (i.e. its lighting means e.g. via driver(s)) in the emergency operation state.

[0035] In order to achieve the luminaire according to the first aspect of the present invention, some or all of the above described optional features may be combined with each other.

[0036] According to a second aspect of the invention, a control unit for controlling an electrical energy consumption of luminaires electrically supplied from a DC grid is provided. The control unit is configured to monitor a DC voltage of the DC grid. Thecontrol unit is configured to control an operation of the luminaires such that the luminaires are allowed to emit light in a normal operation state when the DC voltage of the DC grid is greater than a voltage threshold, and an electrical energy consumption of the luminaires is reduced compared with an electrical energy consumption of the luminaires in the normal operation state when the DC voltage of the DC grid is equal to or smaller than the voltage threshold.

[0037] The above description with regard to the luminaire according to the first aspect of the present invention is also valid for the control unit according to the second aspect of the present invention.

[0038] The control unit may comprise or be at least one of a processor, microprocessor, controller, microcontroller, application specific integrated circuit (ASIC) and field programmable gate array (FPGA). The control unit may comprise or be a logic unit. It may be referred to as “lighting supply logic”. At least one of the aforementioned luminaires, optionally the aforementioned luminaires, may be luminaire(s) according to the first aspect of the present invention.

[0039] The control unit may be part or may be electrically connected with a DC branch circuit, the DC branch circuit being configured to electrically connect one or more luminaires to the DC grid. The control unit may be configured to control an electrical supply of DC voltage, such as the DC voltage of the DC grid, to the one or more luminaires. The control unit may be configured to receive the DC voltage of the DC grid. For example, the control unit may be configured to be electrically connected with the DC grid or be electrically connected via the DC branch circuit with the DC grid. The control unit may be configured to be electrically connected with the one or more luminaires.

[0040] Since the control unit is configured to monitor the DC voltage of the DC grid, it is configured to detect changes, e.g. a reduction, of the DC voltage of the DC grid. The description of the voltage threshold with regard to the luminaire of the first aspect iscorrespondingly valid for the voltage threshold with regard to which the control unit of the second aspect is configured to control the operation of the luminaires.

[0041] The control unit according to the second aspect may be a DC-lndustry compatible control unit. It may be referred to as “DC-lndustry control unit” or “DC-lndustry lighting control unit”.

[0042] Optionally, the control unit is configured to control the operation of the luminaires by communicating commands to the luminaires, and / or controlling a DC voltage electrically supplied to the luminaires.

[0043] The control unit may be configured to communicate with the luminaires wirelessly and / or in a wired manner. The present invention is not limited to a specific type of communication. For example, the control unit may be configured to communicate with the luminaire via an electrical supply path for providing the DC voltage to the luminaires. This is only by way of example and, thus, the control unit may be configured to communicate with the luminaires according to any other known method.

[0044] The control unit may be configured to control the DC voltage electrically supplied to the luminaires by at least one of forwarding the DC voltage of the DC grid to one or more of the luminaires, changing (e.g. reducing) the DC voltage of the DC grid and providing the changed DC voltage to one or more of the luminaires, and providing a DC voltage of an energy storage to one or more of the luminaires. The control unit may comprise or be configured to access the energy storage. Further information on the optional energy storage are described below.

[0045] Optionally, the control unit is configured to, when the DC voltage of the DC grid is equal to or smaller than the voltage threshold, perform at least one of the following steps: Stop the electrical supply of one or more luminaires of the luminaires, which are not emergency luminaire(s) and safety sign luminaire(s); reduce the electricalsupply of one or more luminaires of the luminaires from the DC grid; communicate to one or more luminaires of the luminaires, which are not emergency luminaire(s) and safety sign luminaire(s), a command to not emit light; and communicate to one or more luminaires of the luminaires a command to operate in an energy saving operation state. In the energy saving operation state a maximum light intensity of the light emission is smaller than the maximum light intensity of the light emission in the normal operation state. In addition or alternatively, in the energy saving operation state a light quality of the light emission is reduced compared to the light quality of the light emission in the normal operation state such that the electrical energy consumption of the light emission is reduced compared to the electrical energy consumption of the light emission in the normal operation state.

[0046] Optionally, the control unit is configured to, when the DC voltage of the DC grid is equal to or smaller than the voltage threshold, to reduce the electrical supply of one or more luminaires of the luminaires such that the smaller the DC voltage of the DC grid the more the electrical supply is reduced and vice versa.

[0047] Optionally, the control unit may be configured to communicate the value of the maximum light intensity of the energy saving operation state (that is reduced compared to the maximum light intensity of the normal operation state) to the one or more luminaires. Optionally, the control unit may be configured to communicate information on the reduced light quality of the light emission of the energy saving operation state to the one or more luminaires. The information on the reduced light quality of the light emission of the energy saving operation state may comprise changes of one or more parameters of the light emission, such as changes of at least one of the color temperature (e.g. CCT), color rendering index (CRI), etc., for achieving the reduced light quality of the light emission of the energy saving operation state.

[0048] The control unit may be configured to, when the DC voltage of the DC grid is equal to or smaller than the voltage threshold, communicate to one or more luminaires of theluminaires, which are emergency luminaire(s) and / or safety sign luminaire(s), a command to operate in the emergency operation state. In the emergency operation state the maximum light intensity of the light emission is smaller than the maximum light intensity of the light emission in the normal operation state and the minimum light intensity of the light emission is sufficient for an emergency / safety lighting. Optionally, the control unit may be configured to communicate the value of the minimum light intensity of the emergency operation state (being a type of energy saving operation state) to the one or more luminaires. In addition or alternatively, in the emergency operation state the light quality of the light emission is reduced compared to the light quality of the light emission in the normal operation state such that the electrical energy consumption of the light emission is reduced compared to the electrical energy consumption of the light emission in the normal operation state and the reduced light quality of the light emission is sufficient for the emergency / safety lighting. Optionally, the control unit may be configured to communicate information on the reduced light quality of the light emission of the emergency operation state (being a type of energy saving operation state) to the one or more luminaires. The information on the reduced light quality of the light emission of the emergency operation state may comprise changes of one or more parameters of the light emission, such as changes of at least one of the color temperature (e.g. CCT), color rendering index (CRI), etc., for achieving the reduced light quality of the light emission of the emergency operation state. The emergency operation state of emergency / safety sign luminaire(s) is an energy saving operation state, in which the minimum light intensity of the light emission is sufficient for an emergency / safety lighting and / or in which the reduced light quality of the light emission is sufficient for the emergency / safety lighting. Thus, the description of the energy saving operation state is correspondingly valid for the emergency operation state.

[0049] Optionally, the control unit is configured to, when the DC voltage of the DC grid is equal to or smaller than the voltage threshold and greater than a second voltage threshold, reduce the electrical supply of one or more luminaires of the luminaires from the DC grid, and / or communicate to one or more luminaires of the luminaires acommand to operate in an energy saving operation state. In the energy saving operation state a maximum light intensity of the light emission is smaller than the maximum light intensity of the light emission in the normal operation state. In addition or alternatively, in the energy saving operation state, a light quality of the light emission is reduced compared to the light quality of the light emission in the normal operation state such that the electrical energy consumption of the light emission is reduced compared to the electrical energy consumption of the light emission in the normal operation state. The control unit may be configured to, when the DC voltage of the DC grid is equal to or smaller than the second voltage threshold, stop the electrical supply of one or more luminaires of the luminaires, which are not emergency luminaire(s) and safety sign luminaire(s), and / or communicate to one or more luminaires of the luminaires, which are not emergency luminaire(s) and safety sign luminaire(s), a command to not emit light. The second voltage threshold is smaller than the voltage threshold.

[0050] The description of the second voltage threshold with regard to the luminaire of the first aspect is correspondingly valid for the second voltage threshold with regard to which the control unit of the second aspect is configured to control the operation of the luminaires.

[0051] Optionally, the control unit comprises or is configured to access an energy storage. The energy storage is configured to electrically supply the luminaires. The control unit may be configured to control a charging of the energy storage with electrical energy from the DC grid when the DC voltage of the DC grid is greater than the voltage threshold. The control unit may be configured to control the energy storage to electrically supply one or more luminaires of the luminaires when the DC voltage of the DC grid is equal to or smaller than the voltage threshold.

[0052] The energy storage may be an internal energy storage of the control unit. Optionally, the control unit may be electrically connected with the energy storage (e.g. via an galvanic isolation). The energy storage may be or may comprise at least one of oneor more rechargeable batteries, one or more capacitors for storing electrical energy, etc. The control unit may be configured to stop charging the energy storage with electrical energy from the DC grid when the DC voltage of the DC grid is equal to or smaller than the voltage threshold.

[0053] Optionally, the control unit is configured to detect a failure of the DC grid. The control unit may be configured to stop the electrical supply from the DC grid to the luminaires and control the energy storage to electrically supply the luminaires when the DC grid fails.

[0054] This allows reducing for the DC grid the electrical load represented by the electrical supply of the luminaires. Thus, this allows countering an overload of the DC grid. The control unit may be configured to stop charging of the energy storage with electrical energy from the DC grid when the DC grid fails. Optionally, the control unit is configured to detect the failure of the DC grid by detecting that the DC voltage of the DC grid is equal to or smaller than the second voltage threshold.

[0055] Optionally, the control unit is configured to control the energy storage to electrically supply the luminaires with a DC voltage that is equal to or smaller than the voltage threshold and greater than a second voltage threshold when the DC voltage of the DC grid is equal to or smaller than the voltage threshold and greater than a second voltage threshold. The control unit may be configured to control the energy storage to electrically supply the luminaires with a DC voltage that is equal to or smaller than the second voltage threshold when the DC grid fails. The second voltage threshold is smaller than the voltage threshold.

[0056] Optionally, the control unit is configured to control the energy storage to electrically supply the luminaires with a DC voltage that is equal to or smaller than 485 V and greater than the second voltage threshold being a DC voltage between 40 V and 220 V (i.e. equal to 40 V, or greater than 40 V and smaller than 220 V, or equal to 220 V), optionally a DC voltage of 48 V or 216 V. when the DC voltage of the DC grid isequal to or smaller than the voltage threshold and greater than then the second voltage threshold. The control unit may be configured to control the energy storage to electrically supply the luminaires with a DC voltage that is equal to or smaller than the aforementioned example of the second voltage threshold, when the DC grid fails. For example, the control unit is configured to control the energy storage to electrically supply the luminaires with a DC voltage that is equal to 485 V when the DC voltage of the DC grid is equal to or smaller than the voltage threshold and greater than then the second voltage threshold. The control unit may be configured to control the energy storage to electrically supply the luminaires with a DC voltage that is equal to the aforementioned example of the second voltage threshold when the DC grid fails.

[0057] In order to achieve the control unit according to the second aspect of the present invention, some or all of the above described optional features may be combined with each other.

[0058] The above description with regard to the control unit according to the second aspect of the present invention is also valid for the luminaire according to the first aspect of the present invention.

[0059] The control unit according to the second aspect of the present invention achieves the same advantages as the luminaire according to the first aspect of the present invention.

[0060] According to a third aspect of the invention, a system is provided. The system comprises a DC grid, and a DC branch circuit electrically connected with the DC grid The system comprises one or more luminaires according to the first aspect of the present invention, as described above. The one or more luminaires are configured to be electrically supplied from the DC branch circuit. The DC branch circuit is configured to supply a DC voltage of the DC grid to the one or more luminaires.The above description with regard to the luminaire according to the first aspect of the present invention is also valid for the system according to the third aspect of the present invention.

[0061] The one or more luminaires may be configured to be electrically connected via the DC branch circuit with the DC grid. For example, the one or more luminaires may be configured to be electrically connected with the DC branch circuit. Therefore, after installation of the system the one or more luminaires may be electrically connected with the DC branch circuit. The DC branch circuit may be configured to feed the electrical energy (DC voltage) from the DC grid to the luminaires. The DC branch circuit may be configured to adapt the electrical energy (DC voltage) from the DC grid and feed the adapted electrical energy to the luminaires 1. For example, the DC branch circuit may be configured to remove voltage spikes, adapt the electrical energy to the power of the luminaires etc.

[0062] The system may be referred to as lighting system. The system may be a busbar system or conductor rail system. The terms “busbar” and “conductor rail” may be used as synonyms. For example, at least a part of the DC grid may be part of a conductor rail to which the one or more luminaires may be mounted in order to be electrically supplied from the DC grid. The DC branch circuit may be part or may be mounted to the conductor rail. The one or more luminaires may be configured to be electrically connected via the DC branch circuit with the DC grid when the one or more luminaires are mounted to the conductor rail. The conductor rail represents a conductor rail for lighting and, thus, the one or more luminaire.

[0063] The system according to the third aspect may be a DC-lndustry compatible system. It may be referred to as “DC-lndustry system”.

[0064] In order to achieve the system according to the third aspect of the present invention, some or all of the above described optional features may be combined with each other.The above description with regard to the system according to the third aspect of the present invention is also valid for the luminaire according to the first aspect of the present invention.

[0065] The system according to the third aspect of the present invention achieves the same advantages as the luminaire according to the first aspect of the present invention.

[0066] According to a fourth aspect of the invention, a system is provided. The system comprises a DC grid, and a DC branch circuit electrically connected with the DC grid, and one or more luminaires. Optionally, the one or more luminaires are one or more luminaires according to the first aspect of the present invention, as described above. The one or more luminaires are configured to be electrically supplied from the DC branch circuit. The system comprises a control unit according to the second aspect of the present invention, as described above. The DC branch circuit is configured to supply a DC voltage of the DC grid to the one or more luminaires. The control unit is configured to monitor the DC voltage of the DC grid and control the operation of the one or more luminaires.

[0067] The above description with regard to the control unit according to the second aspect of the present invention, the luminaire according to the first aspect of the present invention and the system according to the third aspect of the present invention is also valid for the system according to the fourth aspect of the present invention.

[0068] The control unit may be part or may be electrically connected with the DC branch circuit. The control unit may be configured to control an electrical supply of DC voltage, such as the DC voltage of the DC grid, to the one or more luminaires. The control unit may be configured to receive the DC voltage of the DC grid. For example, the control unit may be configured to be electrically connected with the DC grid or be electrically connected via the DC branch circuit with the DC grid. The control unit may be configured to be electrically connected with the one or more luminaires.Optionally, at least a part of the DC grid may be part of a conductor rail to which the one or more luminaires may be mounted in order to be electrically supplied from the DC grid. The control unit may be part or may be mounted to the conductor rail.

[0069] The system according to the fourth aspect may be a DC-lndustry compatible system. It may be referred to as “DC-lndustry system”.

[0070] Optionally, the system comprises an energy storage configured to electrically supply the luminaires. The control unit is configured to control a charging of the energy storage with electrical energy from the DC grid and control the electrical supply of the luminaires from the energy storage.

[0071] The energy storage may be part or may be mounted to the conductor rail.

[0072] In order to achieve the system according to the fourth aspect of the present invention, some or all of the above described optional features may be combined with each other.

[0073] The above description with regard to the system according to the fourth aspect of the present invention is also valid for the control unit according to the second aspect of the present invention, the luminaire according to the first aspect of the present invention and the system according to the third aspect of the present invention.

[0074] The system according to the fourth aspect of the present invention achieves the same advantages as the control unit according to the second aspect of the present invention and the luminaire according to the first aspect of the present invention.

[0075] All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities.In the following, the invention is described exemplarily with reference to the enclosed Figures (FIGs.), in which

[0076] FIG. 1 shows an example of luminaires and a system according to the present invention,

[0077] FIG. 2 shows an example of a function of an optional implementation form of the luminaires of FIG. 1 ,

[0078] FIG. 3 shows an example of a function of an optional implementation form of the luminaires of FIG. 1 ,

[0079] FIG. 4 (a) shows an example of a function of an optional implementation form of the luminaires of FIG. 1 ,

[0080] FIG. 4 (b) shows an example of a function of an optional implementation form of the luminaires of FIG. 1 ,

[0081] FIG. 5 shows an example of a control unit and a system according to the present invention,

[0082] FIG. 6 shows an example of a function of an optional implementation form of the control unit of FIG. 5,

[0083] FIG. 7 shows an example of a function of an optional implementation form of the control unit of FIG. 5, and

[0084] FIG. 8 shows an example of a function of an optional implementation form of the control unit of FIG. 5.In the FIGs. (FIGs.), corresponding elements have the same reference signs. The size of elements in the FIGs. is not to scale and may be different compared to a real life implementation in order to highlight details of the embodiments.

[0085] FIG. 1 shows an example of luminaires and a system according to the present invention. The luminaires of FIG. 1 are examples of the luminaire according to the first aspect of the present invention. Thus, the description of the luminaire according to the first aspect of the present invention is correspondingly valid for the luminaires of FIG. 1. The system of FIG. 1 is an example of the system according to the third aspect of the present invention. Thus, the description of the system according to the third aspect of the present invention is correspondingly valid for the system of FIG. 1. As shown in FIG. 1 , the system 100a comprises a DC grid 4, and a DC branch circuit 5 electrically connected with the DC grid 4. The system 100a comprises one or more luminaires 1. For example, the one or more luminaires of the system 100a may be a luminaire 1a for a normal lighting (i.e. not for an emergency lighting) and a luminaire that is an emergency luminaire 1b or a safety sign luminaire Ic.This is only by way of example and, thus, the number of luminaires of the system may be different. Further, the type of luminaire(s) of the system may be different, i.e. the system may comprise at least one of luminaire(s) 1a for normal lighting, emergency luminaire(s) 1b and safety sign luminaire(s) 1 c. For the following description of the FIGs. it is assumed that the system comprise one luminaire 1a for normal lighting and one emergency luminaire 1b. The description is correspondingly valid in case of a different number and / or different type(s) of luminaires being used. The luminaires 1 are configured to be electrically supplied from the DC branch circuit 5. As shown in Figure 1, the luminaires 1 may be electrically connected with the DC branch circuit 5. The DC branch circuit 5 is configured to supply a DC voltage of the DC grid 4 to the luminaires 1.

[0086] In the following the luminaire 1 and, thus, the luminaires 1 of FIG. 1 are described. The description is correspondingly valid for the luminaire(s) 1 of the system 100a. The luminaire 1 is configured to be electrically supplied with a DC voltage, such asthe DC voltage of the DC grid 4. The luminaire 1 is configured to emit light in a normal operation state when the DC voltage is greater than a voltage threshold.

[0087] Irrespective of being configured to emit light in the normal operation state, optionally the luminaire may be controlled to not emit light when the DC voltage is greater than the voltage threshold. The luminaire 1 is configured to operate or be in the normal operation state when the DC voltage is greater than the voltage threshold. The luminaire 1 is configured to reduce its electrical energy consumption compared to its electrical energy consumption in the normal operation state when the DC voltage is equal to or smaller than the voltage threshold.

[0088] The voltage threshold may be a voltage value at which an overload of the DC grid 4 providing via the DC branch circuit 5 the DC voltage to the luminaires 1 begins. The smaller the DC voltage below the voltage threshold the greater the overload of the DC grid 4 and vice versa. The voltage threshold may be selected or set such that the DC voltage of the DC grid 4 being greater than the voltage threshold is sufficient for the DC grid 4 to work properly and, thus, not being in an overload state. For example, the voltage threshold may be equal to a DC voltage of 485 V.

[0089] In the following, optional implementation forms on how the luminaire 1 may reduce its electrical energy consumption are described with regard to FIGs. 2, 3, 4 (a) and 4 (b). Thus, FIGs. 2, 3, 4 (a) and 4(b) each show an example of a function of an optional implementation form of the luminaires of FIG. 1.

[0090] For further details on the luminaires 1 of FIG. 1 reference is made to the description of the luminaire according to the first aspect.

[0091] As shown in FIG. 2, when the DC voltage is greater than the voltage threshold VT1 the luminaire 1 may operate in the normal operation state and, thus, may emit light in the normal operation state. This corresponds to step S11 of FIG. 2. When the DC voltage is equal to or smaller than the voltage threshold VT1 the luminaire 1 may reduce its electrical energy consumption compared to its electrical energyconsumption in the normal operation state (step S12 of FIG. 2) by not emitting light (step 12b of FIG. 2) or operating in the energy saving operation state and, thus, emitting light in the energy saving operation state (step 12a of FIG. 2). In the energy saving operation state the maximum light intensity of the light emission of the luminaire 1 is smaller than the maximum light intensity of the light emission in the normal operation state. In addition or alternatively, in the energy saving operation state a light quality of the light emission is reduced compared to the light quality of the light emission in the normal operation state such that the electrical energy consumption of the light emission (in the energy saving operation state) is reduced compared to the electrical energy consumption of the light emission in the normal operation state.

[0092] Optionally, as shown in FIG. 3, when the DC voltage is greater than the voltage threshold VT1 the luminaire 1 may operate in the normal operation state and, thus, may emit light in the normal operation state. This corresponds to step S11 of FIG. 3. The luminaire 1 may operate and, thus, emit light in the energy saving operation state when the DC voltage is equal to or smaller than the voltage threshold VT1 and greater than a second voltage threshold VT2. This corresponds to step S12a of FIG.

[0093] 3. The second voltage threshold VT2 is smaller than the voltage threshold VT1. The second voltage threshold VT2 may be a voltage value at which an overload of the DC grid 4 is critical and may cause failure of the DC grid 4. The second voltage threshold VT2 may be selected or set such that the DC voltage being equal to or smaller than the second voltage threshold VT2 is not sufficient for the DC grid to work properly and, thus, being close to failure or failing. For example, the second voltage threshold VT2 may be equal to a DC voltage between 40 V and 220 V (i.e. equal to 40 V, or greater than 40 V and smaller than 220 V, or equal to 220 V). Optionally the second voltage threshold VT2 may be equal to a DC voltage of 48 V or 216 V.

[0094] Optionally, the luminaire 1 does not emit light when the DC voltage is equal to or smaller than the second voltage threshold VT2. This corresponds to step S12b of FIG. 3.FIGs. 4 (a) and (b) show optional implementation forms on how the luminaire 1 may reduce its electrical energy consumption, when the luminaire 1 is an emergency lum inaire 1 b or a safety sign lum inaire 1 c.

[0095] As shown in FIG. 4 (a), when the DC voltage is greater than the voltage threshold VT1 the luminaire 1 may operate in the normal operation state and, thus, may emit light in the normal operation state. This corresponds to step S11 of FIG. 4 (a). When the DC voltage is equal to or smaller than the voltage threshold VT1 , the luminaire 1 may emit light in an emergency operation state. This corresponds to step S13 of FIG.

[0096] 4 (a). In the emergency operation state a minimum light intensity of the light emission of the luminaire 1 is sufficient for an emergency / safety lighting and a maximum light intensity of the light emission is smaller than the maximum light intensity of the light emission in the normal operation state. In addition or alternatively, in the emergency operation state a light quality of the light emission is reduced compared to the light quality of the light emission in the normal operation state such that the electrical energy consumption of the light emission is reduced compared to the electrical energy consumption of the light emission in the normal operation state and the reduced light quality of the light emission is sufficient for the emergency / safety lighting. Thus, the emergency operation state corresponds to the energy saving operation state, wherein the light emission of the luminaire 1 in the energy saving operation has the minimum light intensity sufficient for the emergency / safety lighting and / or has the reduced light quality of the light emission sufficient for the emergency / safety lighting.

[0097] Optionally, as shown in FIG. 4 (b), when the DC voltage is greater than the voltage threshold VT1 the luminaire 1 may operate in the normal operation state and, thus, may emit light in the normal operation state. This corresponds to step S11 of FIG. 4 (b). When the DC voltage is equal to or smaller than the voltage threshold VT1 and greater than the second voltage threshold VT2, the luminaire 1 may emit light in the emergency operation state. This corresponds to step S13 of FIG. 4 (b). When the DC voltage is equal to or smaller than the second voltage threshold VT2, the luminaire 1may emit the light in the emergency operation state such that the light intensity of the light emission equals the minimum light intensity sufficient for the emergency / safety lighting and / or the reduced light quality of the light emission achieves a minimum electrical energy consumption of the light emission sufficient for the emergency / safety lighting. This corresponds to step S13a of FIG. 4 (b).

[0098] The implementation forms of FIGs. 2, 3, 4 (a) and 4 (b) may be combined with each other.

[0099] As shown in FIG. 1 , a renewable energy system 6 (e.g. photovoltaic (PV) system, wind energy system, etc.) for providing electrical energy may be electrically connected with the DC grid 4. Thus, the electrical energy provided by the renewable energy system 6 may be fed to the DC grid 4. An energy storage 7 (e.g. a battery, such as a rechargeable batteries) for storing electrical energy may be electrically connected with the DC grid 4. The energy storage 7 may provide stored electrical energy to the DC grid 4, e.g. in the case of an overload of the DC grid 4 in order to counter such overload. The energy storage 7 may store electrical energy from the DC grid 4, e.g. in case there is an energy excess due to a reduced load at the DC grid 4and optionally an increased electrical energy provision by the renewable energy system 6 to the DC grid 4. An AC-to-DC power converter 8 may be electrically connected with the DC grid 4 for providing electrical energy from an AC electrical energy source (such as mains) to the DC grid 4.

[0100] For further details on the system 100a of FIG. 1 reference is made to the description of the system according to the third aspect of the invention.

[0101] FIG. 5 shows an example of a control unit and a system according to the present invention. The control unit of FIG. 5 is an example of the control unit according to the second aspect of the present invention. Thus, the description of the control unit according to the second aspect is correspondingly valid for the control unit of FIG. 5. The system of FIG. 5 is an example of the system according to the fourth aspect ofthe present invention. Thus, the description of the system according to the fourth aspect of the present invention is correspondingly valid for the system of FIG. 5.

[0102] The system 100b of FIG. 5 corresponds to the system 100a of FIG. 1. Thus, the description of FIG. 1 is correspondingly valid for the system 100b of FIG. 5 and in the following mainly difference(s) are described.

[0103] As shown in FIG. 5, the system comprises the DC grid 4, and the DC branch circuit 5 electrically connected with the DC grid, and one or more luminaires 1. Optionally, the one or more luminaires 1 of the system of FIG. 5 are the one or more luminaires 1 according to FIGs. 1 , 2, 3, 4 (a) and 4 (b). Alternatively, they may be any type of luminaire(s) configured to communicate with a control unit 2 of the system 100b. The communication may be wireless and / or in a wired manner. The communication may be according to any known method(s). As it has been done already for the system 100a of FIG. 1 , for the following description of the FIGs. it is assumed that the system 110b comprises one luminaire 1 a for normal lighting and one emergency luminaire 1b. The description is correspondingly valid in case of a different number and / or different type(s) of luminaires being used. The luminaires 1 are configured to be electrically supplied from the DC branch circuit 5. As shown in FIG. 5, the system 100b comprises the control unit 2. The DC branch circuit 5 is configured to supply a DC voltage of the DC grid 4 to the luminaires 1. The control unit 2 is configured to monitor the DC voltage of the DC grid 4 and control the operation of the luminaires 1.

[0104] As shown in Figure 5, the control unit 2 may be electrically connected with the DC branch circuit 5 and, thus, via the DC branch circuit 5 with the DC grid 4. The luminaires 1 may be electrically connected with the control unit 2 and may be electrically supplied from the DC branch circuit 5 (and, thus, from the DC grid 4) via the control unit 2. Alternatively, the control unit 2 may be a part of the DC branch circuit 5 (not shown in Figure 5) and the luminaires may be electrically supplied from the DC grid 4 via the DC branch circuit 5 (e.g. via the control unit 2 of the DC branch circuit 5). The following description is valid irrespective how the control unit 2 and theDC branch circuit 5 are configured to electrically supply the luminaires 1 with the DC voltage from the DC grid 4.

[0105] Optionally, as shown in FIG. 5, the control unit 2 may comprise or be configured to access an optional energy storage 3. The energy storage 3 may be an internal energy storage of the control unit 2 (not shown in FIG. 5). Optionally, the control unit 2 may be electrically connected with the energy storage 3 (e.g. via an galvanic isolation). The energy storage 3 may be or may comprise at least one of one or more rechargeable batteries, one or more capacitors for storing electrical energy, etc. The energy storage 3 is arranged for electrically supplying the luminaire(s) 1. The energy storage 3 is not provided for electrically supplying electrical loads other than the lighting loads (e.g. the luminaire(s) 1).

[0106] The control unit 2 is configured to monitor the DC voltage of the DC grid 4. The control unit 2 is configured to control an operation of the luminaires 1 such that the luminaires 1 are allowed to emit light in a normal operation state when the DC voltage of the DC grid 4 is greater than the voltage threshold, and the electrical energy consumption of the luminaires 1 is reduced compared with an electrical energy consumption of the luminaires 1 in the normal operation state when the DC voltage of the DC grid 4 is equal to or smaller than the voltage threshold VT1.

[0107] The control unit 2 may control the operation of the luminaires 1 by communicating commands to the luminaires 1 , and / or controlling a DC voltage electrically supplied to the luminaires 1.

[0108] In the following, optional implementation forms on how the control unit 2 may contribute to reducing the electrical energy consumption of the luminaires 1 are described with regard to FIGs. 6, 7 and 8. FIGs. 6, 7 and 8 each show an example of a function of an optional implementation form of the control unit of FIG. 5.For further details on the control unit 2 of FIG. 5 reference is made to the description of the control unit according to the second aspect.

[0109] As shown in FIG. 6, when the DC voltage of the DC grid 4 is greater than the voltage threshold VT1 , the control unit 2 may control the operation of the luminaires 1 such that the luminaires 1 are allowed to emit light in the normal operation state. This corresponds to step S21 of FIG. 6. When the DC voltage of the DC grid 4 is equal to or smaller than the voltage threshold VT1 , the control unit 2 may reduce the electrical energy consumption of the luminaires 1 compared to the electrical energy consumption of the luminaires in the normal operation state (being the step S22 of FIG. 6) by performing at least one of the steps S22a, S22b, S22c and S22d.

[0110] According to the step S22a shown in FIG. 6, the control unit 2 may stop the electrical supply of at least one of the luminaires 1 , the at least one luminaire not being an emergency luminaire(s) 1b and safety sign luminaire(s) 1c. According to the step S22b shown in FIG. 6, the control unit 2 may reduce the electrical supply of at least one luminaire of the luminaires 1 from the DC grid. According to the step S22c shown in FIG. 6, the control unit 2 may communicate to at least one luminaire of the luminaires 1 a command to not emit light, the at least one luminaire not being an emergency luminaire(s) 1b and safety sign luminaire(s) 1c. According to the step S22d shown in FIG. 6, the control unit 2 may communicate to at least one luminaire of the luminaires a command to operate in an energy saving operation state. In the energy saving operation state a maximum light intensity of the light emission is smaller than the maximum light intensity of the light emission in the normal operation state. In addition or alternatively, in the energy saving operation state a light quality of the light emission is reduced compared to the light quality of the light emission in the normal operation state such that the electrical energy consumption of the light emission is reduced compared to the electrical energy consumption of the light emission in the normal operation state.

[0111] Optionally, as shown in FIG. 7, when the DC voltage of the DC grid 4 is greater than the voltage threshold VT1 , the control unit 2 may control the operation of theluminaires 1 such that the luminaires 1 are allowed to emit light in the normal operation state. This corresponds to step S21 of FIG. 7. When the DC voltage of the DC grid 4 is equal to or smaller than the voltage threshold VT1 and greater than the second voltage threshold VT2, the control unit 2 may reduce the electrical supply of at least one luminaire of the luminaires 1 from the DC grid 4, and / or communicate to at least one luminaire of the luminaires 1 a command to operate in the energy saving operation state. As outlined already above, in the energy saving operation state a maximum light intensity of the light emission is smaller than the maximum light intensity of the light emission in the normal operation state. In addition or alternatively, in the energy saving operation state a light quality of the light emission is reduced compared to the light quality of the light emission in the normal operation state such that the electrical energy consumption of the light emission is reduced compared to the electrical energy consumption of the light emission in the normal operation state. This corresponds to steps S22b and S22d, respectively, of FIG. 7.

[0112] When the DC voltage of the DC grid is equal to or smaller than the second voltage threshold VT2, the control unit 22 may stop the electrical supply of at least one luminaire of the luminaires 1, which is not emergency luminaire(s) and safety sign luminaire(s), and / or communicate to at least one luminaire of the luminaires 1, which is not emergency luminaire(s) and safety sign luminaire(s), a command to not emit light. This corresponds to steps S22a and S22c, respectively, of FIG. 7.

[0113] Optionally, the control unit 2 may comprise or be configured to access the optional energy storage 3. The energy storage 3 is configured to electrically supply the luminaires 1. The control unit 2 may be configured to control a charging of the energy storage 3 with electrical energy from the DC grid 4 when the DC voltage of the DC grid 4 is greater than the voltage threshold VT1. The control unit 2 may be configured to control the energy storage 3 to electrically supply one or more luminaires of the luminaires 1 when the DC voltage of the DC grid 4 is equal to or smaller than the voltage threshold VT 1.The control unit 2 may detect a failure of the DC grid 4. The control unit 2 may stop the electrical supply from the DC grid 4 to the luminaires 1 and control the energy storage 3 to electrically supply the luminaires 1 when the DC grid fails 4.

[0114] Optionally, as shown in Figure 8, when the DC voltage of the DC grid 4 is greater than the voltage threshold VT 1 , the control unit 2 may control the operation of the luminaires 1 such that the luminaires 1 are allowed to emit light in the normal operation state. This corresponds to step S21 of FIG. 8. When the DC voltage of the DC grid 4 is equal to or smaller than the voltage threshold VT1 and greater than the second voltage threshold V2, the control unit 2 may control the energy storage 3 to electrically supply the luminaires 1 with a DC voltage that is equal to or smaller than the voltage threshold VT1 and greater than the second voltage threshold VT2. When the DC grid 4 fails, the control unit 2 may control the energy storage 3 to electrically supply the luminaires 1 with a DC voltage that is equal to or smaller than the second voltage threshold VT2.

[0115] For further details on the system 100b of FIG. 5 reference is made to the description of the system according to the fourth aspect of the invention. The implementation forms of FIGs. 6, 7 and 8 may be combined with each other.

[0116] In the light of the above, the following example of operation of the system 100a of FIG. 1 and of the system 100b of FIG. 5 for providing a lighting to an area may be performed. In the following description, it is assumed that the one or more luminaires 1 of the system 100b are a luminaire 1a for normal lighting and a luminaire 1 that is an emergency luminaire 1b or a safety sign luminaire 1c. In the following the luminaire 1 being an emergency luminaire 1b or a safety sign luminaire 1c is referred to as safety type luminaire and is referenced by the reference signs “1b, 1c”. The description is correspondingly valid in case of a different number of luminaires and / or different luminaire type(s).In a normal state of the DC grid 4, the DC grid 4 is stable and is configured to draw sufficient electrical energy from other electrical energy source(s), such as one or more energy storages 7 (which may represent internal sources of the DC grid 4) and / or AC-to-DC power converter(s) 8 electrically connected with mains and providing electrical energy from outside the DC grid 4. For this, the DC grid 4 may be electrically connected via AC-to-DC power converter(s) 8 with mains. In the normal state of the DC grid 4, the luminaire 1a and the safety type luminaire 1b, 1c are electrically supplied by the DC branch circuit 5, which may feed the electrical energy (DC voltage) from the DC grid 4 to the luminaires 1 or adapt the electrical energy (DC voltage) from the DC grid 4 and feed the adapted electrical energy to the luminaires 1. For example, the DC branch circuit 5 may remove voltage spikes, adapt the electrical energy to the power of the luminaires 1 etc.

[0117] Since the normal state of the DC grid 4 is present, the DC voltage of the DC grid 4 will be greater than the first voltage threshold VT1 so that the luminaires 1 of the system 100a of FIG. 1 may operate in the normal operation state. In the system 100b of FIG. 5, the control unit 2 monitors the DC voltage of the DC grid 4 (i.e. monitors the state of the DC grid 4). In case of the optional energy storage 3 being present, the control unit 2 may charge the energy storage 3 with electrical energy from the DC grid 4 when the DC grid 4 is in the normal state. The control unit 2 may control the operation of the luminaires 1 such that the luminaires 1 are allowed to emit light in the normal operation state when the DC voltage of the DC grid 4 is greater than the first voltage threshold VT1. The control unit 2 may cause the DC voltage of the DC grid 4 to be provided to the luminaires 1b when the DC grid 4 is in the normal state. Thus, when the luminaires 1 of the system 100b of FIG. 5 are implemented according to the luminaires of the system 100a of FIG. 1, the luminaires 1 will operate in the normal operation state. Optionally, the control unit 2 may be configured to communicate commands to the luminaires 1 in order to cause the luminaires 1 to operate in the normal operation state. This also allows controlling the luminaires 1 of the system 100b of FIG. 5 when they are different compared to the luminaires of the system 100a of FIG. 1. The control unit 2 may communicate commands to theluminaires 1 irrespective of their implementation type, i.e. the luminaires 1 being implemented according to the luminaires 1 of the system 100a of FIG. 1 or being implemented differently.

[0118] In the systems 100a and 100b the luminaires do not provide electrical energy to the DC grid 4. In the system 100b the optional energy storage 3 does not provide electrical energy to the DC grid 4.

[0119] In case the DC grid 4 is overloaded and, thus, in an overload state (e.g. due to energy source(s), such as the renewable energy system 6, stopping to provide electrical energy to the DC grid 4), the DC voltage of the DC grid 4 will decrease below the voltage threshold VT1. Thus, in order to compensate the overload of the DC grid 4 the electrical components being electrically supplied by the DC grid 4 are desired to reduce electrical energy intake from the DC grid 4.

[0120] For this, in the system 100a of FIG. 1, the luminaire 1a may be configured to emit light in the energy saving operation state when the DC voltage of the DC grid 4 is equal to or smaller than the voltage threshold VT1 and, thus, the DC grid 4 is in the overload state. In the energy saving operation state the maximum light intensity of the light emission of the luminaire 1a is smaller than the maximum light intensity of the light intensity in the normal operation state of the luminaire 1a. In addition or alternatively, in the energy saving operation state the light quality of the light emission of the luminaire 1a is reduced compared to the light quality of the light emission of the luminaire 1a in the normal operation state such that the electrical energy consumption of the light emission of the luminaire 1a is reduced compared to the electrical energy consumption of the light emission in the normal operation state. Thus, the energy saving operation state of the luminaire 1a allows reducing the electrical energy consumption of the luminaire 1a compared to the electrical energy consumption of the normal operation state of the luminaire 1a.The safety type luminaire 1b, 1c may be configured to emit light in the emergency operation state when the DC voltage of the DC grid 4 is equal to or smaller than the voltage threshold VT1 and, thus, the DC grid 4 is in the overload state. In the emergency operation state the minimum light intensity of the light emission of the safety type luminaire 1b, 1c is sufficient for an emergency / safety lighting and the maximum light intensity of the light emission of the safety type luminaire 1b, 1c is smaller than the maximum light intensity of the light intensity in the normal operation state of the luminaire 1. In addition or alternatively, in the emergency operation state the light quality of the light emission of the safety type luminaire 1b, 1c is reduced compared to the light quality of the light emission in the normal operation state such that the electrical energy consumption of the light emission of the safety type luminaire 1b, 1c is reduced compared to the electrical energy consumption of the light emission in the normal operation state and the reduced light quality of the light emission of the safety type luminaire 1b, 1 c is sufficient for the emergency / safety lighting. Thus, the emergency operation state allows reducing the electrical energy consumption of the safety type luminaire 1b, 1c compared to the electrical energy consumption of the normal operation state of the safety type luminaire 1b, 1c.

[0121] That is, the luminaires 1 of the system 100a of FIG. 1, may detect the overload state of the DC grid 4 by detecting the reduction of the DC voltage to or below the voltage threshold VT1 and, thus, may react as outlined above in order to reduce the load on the DC grid 4 to counter the overload state of the DC grid 4. Thus, the luminaires 1 of FIG. 1 may detect the overload state of the DC grid on the basis of the amplitude of the DC voltage. The overload of the DC grid 4 may be caused by failure or interruption of the electrical supply of the DC grid 4 from mains (via the AC-to-DC power converter(s) 8) and / or failure or interruption of the electrical supply of the DC grid 4 from the renewable energy system 6. For example, the failure or interruption of the electrical supply of the DC grid 4 from mains (via the AC-to-DC power converter(s) 8) may be due to a power plant malfunctioning, a fire in the area (e.g. building) in which the DC grid 4 is installed etc. For example the failure or interruption of the electrical supply of the DC grid 4 from the renewable energy system 6 may bedue to a malfunctioning of the renewable energy stem 6, an absence of sun, wind etc. for making the renewable energy system 6 work, a fire in the area (e.g. building) in which the DC grid 4 is installed etc. Thus, the overload state of the DC grid may represent a type of emergency state of the DC grid 4.

[0122] In the system 100b of FIG. 5, the control unit 2 monitors the DC voltage of the DC grid 4 (i.e. monitors the state of the DC grid 4) and, thus, may detect the overload state of the DC grid 4. For example, the control unit 2 may detect the overload state of the DC grid 4 by detecting that the DC voltage of the DC grid 4 decrease to or below the voltage threshold VT1. The control unit 2 may control the operation of the luminaires 1 when the DC grid 4 is in the overload state (i.e. the DC voltage of the DC grid is equal to or smaller than the voltage threshold VT1) such that the luminaire 1a operates in the energy saving operation state and the safety type luminaire 1b, 1c operates in the emergency operation state. When the luminaires 1 of the system 100b of FIG. 5 are implemented according to the luminaires of the system 100a of FIG. 1 , the control unit 2 may provide the DC voltage of the DC grid 4 or a reduced value of the DC voltage of the DC grid 4 to the luminaires 1 in order to control the luminaire 1a to operate in the energy saving operation state and the safety type luminaire 1b, 1c to operate in the emergency operation state.

[0123] The control unit 2 may be configured to communicate command(s) to the luminaire 1a in order to cause the luminaire 1a to operate in the energy saving operation state. The control unit 2 may communicate the value of the maximum light intensity of the energy saving operation state to the luminaire 1a. In addition or alternatively, the control unit 2 may communicate information on the reduced light quality of the light emission of the energy saving operation state to the luminaire 1a. The information on the reduced light quality of the light emission of the energy saving operation state may comprise changes of one or more parameters of the light emission, such as changes of at least one of the color temperature (e.g. CCT), color rendering index (CRI), etc., for achieving the reduced light quality of the light emission of the energy saving operation state. The control unit 2 may be configured to communicatecommand(s) to the safety type luminaire 1b, 1c in order to cause the luminaire 1b, 1c to operate in the emergency operation state. The control unit 2 may communicate the value of the maximum light intensity and / or the minimum light intensity of the emergency operation state to the safety type luminaire 1b, 1c. In addition or alternatively, the control unit 2 may communicate information on the reduced light quality of the light emission of the emergency operation state to the safety type luminaire 1b, 1c. The information on the reduced light quality of the light emission of the emergency operation state may comprise changes of one or more parameters of the light emission, such as changes of at least one of the color temperature (e.g. CCT), color rendering index (CRI), etc., for achieving the reduced light quality of the light emission of the emergency operation state. The aforementioned examples of communication allow controlling luminaires 1 to operate in the energy saving operation state (e.g. emergency operation state), when the luminaires 1 are not configured to detect the overload state of the DC grid 4.

[0124] Optionally, the control unit 2 does not charge (e.g. it stop charging) the optional energy storage 3, when it detects the overload state of the DC grid 4.

[0125] Optionally, when the DC grid 4 is in the overload state and the DC voltage of the DC grid 4 continues decreasing, the control unit 2 may reduce the electrical supply of at least one of the luminaires 1 such that the smaller the DC voltage of the DC grid 4 the more the electrical supply is reduced and vice versa. In case this is done with regard to safety type luminaire(s) 1b, 1c, the electrical energy is reduced such that the reduced electrical energy is still sufficient for powering the emergency / safety light emission. Optionally, when the DC grid 4 is in the overload state and the DC voltage of the DC grid 4 continues decreasing, the control unit 2 may stop the electrical supply of at least one of luminaire(s) 1a, which is not safety type luminaire(s) 1b, 1c, and / or communicate a command to such at least one luminaire 1a to not emit light. This allows further reducing the electrical energy intake from the overloaded DC grid 4, while still allowing a sufficient emergency / safety lighting.A failed state of the DC grid 4 (i.e. the DC grid 4 being critical with regard to failure or the DC grid 4 having failed) may be detected when the DC voltage of the DC grid 4 decreases to or below the second voltage threshold VT2 that is smaller than the voltage threshold VT 1.

[0126] In the aforementioned case, the luminaires 1 of the system 100a of FIG. 1 may detect the failed state of the DC grid 4 by detecting that the DC voltage of the DC grid 4 has decreased to or below the second voltage threshold VT2. Optionally, the luminaire 1a of the system 100a of FIG. 1 does not emit light (e.g. it stops light emission) when the DC grid 4 is in the failed state (i.e. when the DC voltage of the DC grid 4 is equal to or smaller than the second voltage threshold VT2). When the DC grid 4 is in the failed state, the safety type luminaire 1 b, 1c of the system 100a may emit light in the emergency operation state such that the light intensity of the light emission equals the minimum light intensity of the emergency operation state and / or such that the reduced light quality of the light emission (of the emergency operation state) achieves a minimum electrical energy consumption of the light emission sufficient for the emergency / safety lighting.

[0127] In the system 100b of FIG. 5, the control unit 2 may detect the failed state of the DC grid 4 by detecting that the DC voltage of the DC grid 4 has decreased to or below the second voltage threshold VT2. When the DC grid 4 is in the failed state (i.e. when the DC voltage of the DC grid 4 is equal to or smaller than the second voltage threshold VT2) the control unit 2 may stop the electrical supply from the DC grid to the luminaires 1 and control the optional energy storage 3 to electrically supply the luminaires 1, e.g. the safety type luminaire 1b, 1c.

[0128] Optionally, when the DC grid 4 fails, the control unit 2 may control the energy storage 3 to electrically supply a DC voltage to the luminaires 1 that is equal to or smaller than the second voltage threshold VT2. When the luminaires 1 of the system 100b of FIG. 5 are implemented according to the luminaires 1 of the system 100a of FIG. 1, this may cause the luminaire 1a to not emit light (stop emitting light) and the safetytype luminaire 1b, 1c to emit light in the emergency operation state, optionally having a light intensity that equals the minimum light intensity of the emergency operation state and / or a reduced light quality that achieves a minimum electrical energy consumption of the light emission sufficient for the emergency / safety lighting.

[0129] Optionally, when the DC grid 4 is in the overload state (and not in the failed state, i.e. the DC voltage of the DC grid 4 is equal to or smaller than the voltage threshold VT1 and greater than the second voltage threshold VT2) the control unit 2 may control the energy storage 3 to electrically supply the luminaires 1 with a DC voltage that is equal to or smaller than the voltage threshold VT1 and greater than the second voltage threshold VT2. This allows the luminaires 1 to distinguish between the overload state and the failed state of the DC grid 4.

[0130] Thus, as outlined above, by changing or setting the DC voltage provided to the luminaires 1 (e.g. from the optional energy storage 3) the control unit 2 may electrically supply the luminaires 1 and communicate the state of the DC grid 4 to the luminaires 1.

[0131] In addition or alternatively to using voltage thresholds, such as the voltage threshold VT1 and second voltage threshold VT2, for changing the operation of the luminaires 1 and, thus, the electrical energy consumption of the luminaires 1, voltage ranges may be used accordingly.

[0132] The luminaires 1 according to any one of Figures 1 , 2, 4 (a) and 4 (b) may adapt their operation according to the value of the DC voltage of the DC grid 4 and, thus, the state of the DC grid 4 may be controlled without needing additional communication with the luminaires 1.

[0133] As shown above, the emergency luminaire(s) 1b and safety sign luminaire(s) 1c of the system 100a of FIG. 1 or the system 100b of FIG. 5 may provide emergency / safety lighting without needing an internal energy storage for poweringthe emergency / safety lighting. Further, there is no need of a separate wiring of luminaires 1a for normal lighting and safety type luminaires 1b, 1c. They all may be electrically connected to the DC branch circuit 5 and / or the control unit 2. The safety type luminaires 1b, 1c may be modularly adapted to needs and electrical energy storage capacity of the DC grid 4 and electrical storage(s) electrically connected with the DC grid 4 (e.g. internal energy storage(s) of the DC grid 4). The luminaires 1 may automatically detect emergency states, e.g. by detecting the overload state or the failed state of the DC grid 4. Optionally, the luminaires 1 may distinguish (i.e. automatically distinguish) between the overload state of the DC grid 4 (i.e. when the DC voltage of the DC grid 4 is equal to or smaller than the voltage threshold VT1 and greater than the second voltage threshold VT2) and the failed state of the DC Grid 4 (i.e. when the DC voltage of the DC grid 4 is equal to or smaller than the second voltage threshold VT2)

[0134] In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Claims

Claims:

1. A luminaire (1) configured tobe electrically supplied with a DC voltage,emit light in a normal operation state when the DC voltage is greater than a voltage threshold (VT1), andreduce its electrical energy consumption compared to its electrical energy consumption in the normal operation state when the DC voltage is equal to or smaller than the voltage threshold (VT1).

2. The luminaire (1 ) according to claim 1 , wherein the luminaire (1 ) is configured to, when the DC voltage is equal to or smaller than the voltage threshold (VT1),not emit light, oremit light in an energy saving operation state, whereinin the energy saving operation state:a maximum light intensity of the light emission is smaller than the maximum light intensity of the light emission in the normal operation state, and / ora light quality of the light emission is reduced compared to the light quality of the light emission in the normal operation state such that the electrical energy consumption of the light emission is reduced compared to the electrical energy consumption of the light emission in the normal operation state.

3. The luminaire (1) according to claim 2, wherein the luminaire (1) is configured toemit light in the energy saving operation state when the DC voltage is equal to or smaller than the voltage threshold (VT1) and greater than a second voltage threshold (VT2), andnot emit light when the DC voltage is equal to or smaller than the second voltage threshold (VT2), whereinthe second voltage threshold (VT2) is smaller than the voltage threshold (VT1).

4. The luminaire (1 ) according to claim 1 , whereinthe luminaire (1 ) is an emergency luminaire (1 b) or a safety sign luminaire (1c), andthe luminaire (1) is configured to emit light in an emergency operation state when the DC voltage is equal to or smaller than the voltage threshold (VT1), whereinin the emergency operation state:a minimum light intensity of the light emission is sufficient for an emergency / safety lighting and a maximum light intensity of the light emission is smaller than the maximum light intensity of the light emission in the normal operation state, and / ora light quality of the light emission is reduced compared to the light quality of the light emission in the normal operation state such that the electrical energy consumption of the light emission is reduced compared to the electrical energy consumption of the light emission in the normal operation state and the reduced light quality of the light emission is sufficient for the emergency / safety lighting.

5. The luminaire (1 ) according to claim 4, whereinthe luminaire (1 ) is configured to emit the light in the emergency operation state when the DC voltage is equal to or smaller than a second voltage threshold (VT1) such that the light intensity of the light emission equals the minimum light intensity and / or the reduced light quality of the light emission achieves a minimum electrical energy consumption of the light emission sufficient for the emergency / safety lighting, whereinthe second voltage threshold (VT2) is smaller than the voltage threshold (VT1).

6. A control unit (2) for controlling an electrical energy consumption of luminaires (1) electrically supplied from a DC grid (4), wherein the control unit (2) is configured tomonitor a DC voltage of the DC grid (4), andcontrol an operation of the luminaires (1) such thatthe luminaires (1 ) are allowed to emit light in a normal operation state when the DC voltage of the DC grid (4) is greater than a voltage threshold (VT1), andan electrical energy consumption of the luminaires (1 ) is reduced compared with an electrical energy consumption of the luminaires (1) in the normal operation state when the DC voltage of the DC grid (4) is equal to or smaller than the voltage threshold (VT 1 ).

7. The control unit (2) according to claim 6, wherein the control unit (2) is configured to control the operation of the luminaires (1) bycommunicating commands to the luminaires (1), and / orcontrolling a DC voltage electrically supplied to the luminaires (1 ).

8. The control unit (2) according to claim 6 or 7, wherein the control unit (2) is configured to, when the DC voltage of the DC grid (4) is equal to or smaller than the voltage threshold (VT1),stop the electrical supply of one or more luminaires of the luminaires (1 ), which are not emergency luminaire(s) (1b) and safety sign luminaire(s) (1c), reduce the electrical supply of one or more luminaires of the luminaires (1 ) from the DC grid (4),communicate to one or more luminaires of the luminaires (1 ), which are not emergency luminaire(s) (1b) and safety sign luminaire(s) (1c), a command to not emit light, and / orcommunicate to one or more luminaires of the luminaires (1 ) a command to operate in an energy saving operation state, whereinin the energy saving operation state:a maximum light intensity of the light emission is smaller than the maximum light intensity of the light emission in the normal operation state, and / ora light quality of the light emission is reduced compared to the light quality of the light emission in the normal operation state such that the electrical energy consumption of the light emission is reduced compared to the electrical energy consumption of the light emission in the normal operation state.

9. The control unit (2) according to any one of claims 6 to 8, whereinthe control unit (2) is configured to, when the DC voltage of the DC grid is equal to or smaller than the voltage threshold (VT1) and greater than a second voltage threshold (VT2),reduce the electrical supply of one or more luminaires of the luminaires (1) from the DC grid (4), and / orcommunicate to one or more luminaires of the luminaires (1 ) a command to operate in an energy saving operation state, wherein in the energy saving operation state:a maximum light intensity of the light emission is smaller than the maximum light intensity of the light emission in the normal operation state, and / ora light quality of the light emission is reduced compared to the light quality of the light emission in the normal operation state such that the electrical energy consumption of the light emission is reduced compared to the electrical energy consumption of the light emission in the normal operation state, andthe control unit (2) is configured to, when the DC voltage of the DC grid (4) is equal to or smaller than the second voltage threshold (VT2),stop the electrical supply of one or more luminaires of the luminaires (1), which are not emergency luminaire(s) (1b) and safety sign luminaire(s) (1c), and / orcommunicate to one or more luminaires of the luminaires (1 ), which are not emergency luminaire(s) (1b) and safety sign luminaire(s) (1c), a command to not emit light, whereinthe second voltage threshold (VT2) is smaller than the voltage threshold (VT1).

10. The control unit (2) according to any one of claims 6 to 9, whereinthe control unit (2) comprises or is configured to access an energy storage (3), the energy storage (3) being configured to electrically supply the luminaires (1), andthe control unit (2) is configured to controla charging of the energy storage (3) with electrical energy from the DC grid (4) when the DC voltage of the DC grid (4) is greater than the voltage threshold (VT1), andthe energy storage (3) to electrically supply one or more luminaires of the luminaires (1 ) when the DC voltage of the DC grid (4) is equal to or smaller than the voltage threshold (VT1).

11. The control unit (2) according to claim 10, wherein the control unit (2) is configured todetect a failure of the DC grid (4), andstop the electrical supply from the DC grid (4) to the luminaires (1 ) and control the energy storage (3) to electrically supply the luminaires (1) when the DC grid (4) fails.

12. The control unit (2) according to claim 11 , wherein the control unit (2) is configured to control the energy storage (3) to electrically supply the luminaires (1) witha DC voltage that is equal to or smaller than the voltage threshold (VT 1 ) and greater than a second voltage threshold (VT2) when the DC voltage of the DC grid (4) is equal to or smaller than the voltage threshold (VT 1 ) and greater than a second voltage threshold (VT2), and / ora DC voltage that is equal to or smaller than the second voltage threshold (VT2) when the DC grid (4) fails, whereinthe second voltage threshold (VT2) is smaller than the voltage threshold (VT1).

13. A system (100a) comprisinga DC grid (4),a DC branch circuit (5) electrically connected with the DC grid (4), and one or more luminaires (1) according to any one of claims 1 to 5 configured to be electrically supplied from the DC branch circuit (5), whereinthe DC branch circuit (5) is configured to supply a DC voltage of the DC grid (4) to the one or more luminaires (1).

14. A system (100b) comprisinga DC grid (4),a DC branch circuit (5) electrically connected with the DC grid (4), and one or more luminaires (1 ), optionally according to any one of claims 1 to 5, configured to be electrically supplied from the DC branch circuit (5), and a control unit (2) according to any one of claims 6 to 12, whereinthe DC branch circuit (5) is configured to supply a DC voltage of the DC grid (4) to the one or more luminaires (1), andthe control unit (2) is configured to monitor the DC voltage of the DC grid (4) and control the operation of the one or more luminaires (1).

15. The system (100b) according to claim 14, whereinthe system (100b) comprises an energy storage (3) configured to electrically supply the luminaires (1), andthe control unit (2) is configured to control a charging of the energy storage (3) with electrical energy from the DC grid (4) and control the electrical supply of the luminaires (1) from the energy storage (3).

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