FIELD OF THE INVENTION

The present invention relates in general to a lighting system comprising a plurality of lighting units, and provided with power backup facilities.

BACKGROUND OF THE INVENTION

Figure 1 is a block diagram schematically showing a lighting system 1 comprising a plurality of lighting units 10 receiving power from a power line 2, 3. The power line 2, 3 typically carries mains powers which, in any case in Europe, can be characterized as 230 VAC @ 50 Hz.

One generally known problem is associated by power failure. For any reason, the mains power supply may fail, causing the lights to go out. To mitigate this problem, power backup facilities have been developed, taking over the power supply in case of failure of the mains power supply. Depending on requirements, such power backup facilities may include an engine-driven generator or a unit based on batteries. The capacity of such backup facilities may vary, and the duration of the backup power depends on the one hand on this capacity and on the other hand on the power consumption by the connected power consumers.

The power backup facilities may be associated with individual lighting units, may be associated with groups of lighting units, and may in fact even be common to an entire building.

Figure 1 illustrates a possibility of a power backup unit 4 associated with the power line 2, 3. The original power line is indicated by reference numeral 2, whereas the power line behind the power backup unit 4 is indicated by reference numeral 3. In case the mains power fails in power line 2, the mains power will remain to be available in power line 3 for some time, provided by backup unit 4. This power line 3 will be indicated as buffered power line.

Figure 1 also shows outlet sockets 6, 7 of the power lines 2, 3, respectively. The figure shows that a lighting unit 10 can be connected to an outlet socket 7 of the buffered power line 3. The figure also shows that a lighting unit 10 can be connected to the non-buffered power line 2 via an individual backup unit 5 that is connected to an outlet socket 6 of the non-buffered power line 2. Multiple lighting units 10 may be coupled to one single power backup unit 5, but this is not shown. In each case, the lighting unit 10 receives buffered power. It is possible that each lighting unit 10 has its own dedicated power backup unit 5. The power backup unit 5 may be a separate unit, having its output coupled to the power input 11 of the lighting unit 10. It Is also possible that each lighting unit 10 has its own integrated power backup unit.

In any case, in the normal operating condition, mains power is available on non-buffered power line 2 as well as on buffered power line 3, and therefore normal mains power is supplied to the various lighting units 10 of the lighting system 1.

Figure 1 only shows two lighting units 10, but is to be understood that the lighting system 1 may include a vast plurality of lighting units.

SUMMARY OF THE INVENTION

When a power failure occurs, the system enters a backup condition, in which power is continued to be supplied to the individual lighting units 10 either by a common power backup unit 4 or by individual power backup units 5, or both. This means that, In the rooms provided with these lighting units, illumination is ensured to continue. But this continued illumination only lasts for a limited time. A power backup unit 4, 5 has power stored in its batteries up to a certain level, and power

consumption will drain the stored power. In practice, power backup units are provided with sound alarms, causing users on the one hand to realize that a power failure has occurred and on the other hand to take steps for repair. But repair may take longer than expected, in any case longer than the time period bridged by the power capacity of the power backup units. In any case, it is desirable to extend the operating time of the power backup units as much as possible.

An object of the present invention is to provide a solution to this problem.

A first aspect of the present invention involves reducing the power

consumption of the lighting units 10 when a power failure is detected.

Another aspect of the present invention involves detecting the occurrence of power failure.

Another aspect of the present invention involves a prediction of an

approaching power failure.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features and advantages of toe present Invention will be further explained by the following description of one or more preferred embodiments with reference to the drawings, in which same reference numerals indicate same or similar parts, and in which:

Figure 1 is a block diagram schematically showing a lighting system comprising a plurality of lighting units receiving power from a power line. DETAILED DESCRIPTION OF THE INVENTION

The lighting system 1 is provided with a communication system 30 In mesh topology. This means that each lighting unit 10 comprises a communication device, schematically illustrated at reference numeral 13, for communicating with other lighting units of the system. The communication may be wired, via the power line or via separate communication lines, but the communication preferably is wireless.

Each lighting unit 10 forms a node in the communication network. It is characteristic of a mesh topology that each node can communicate to each other node and can receive messages from each other node.

Such communication systems are known per se, and mesh topology in general is known per se, therefore an elaborate explanation thereof will be omitted here. It Is noted that the individual nodes may have individual addresses, so that a specific communication from one node may be directed exclusively to a selected one of the other nodes, but in the context of the present invention communications do not discriminate between receivers and a communication is received by all other nodes, as far as allowed by external circumstances.

Each lighting unit 10 comprises a control device 20, for instance implemented as a microcontroller. The controller 20 has an input receiving messages from communication receiver 13, and has an output coupled to the one or more light sources 12 of the lighting unit 10 to control the light output thereof. According to the invention, if the controller receives a signal indicating a power failure, it will control the light sources 12 to reduce the output level thereof. The output level may for instance be reduced to 10% of the nominal output level.

It will be understood by persons skilled in the art that this will reduce power consumption by the lighting unit 10 and hence will extend the time that can be bridged by the power backup unit 4, 5.

An aspect of the present invention involves the detection of a power failure. Figure 1 also shows a non-buffered lighting unit 110 connected directly to a non- buffered power line 2, i.e. without an intermediary power back up unit. The controller 20 of the non-buffered lighting unit 110 is adapted to, via the communication system 30, at intervals which may be regular or irregular, send a predefined okay signal. This signal will be received by the buffered lighting units 10, signalling to the controllers 20 of those lighting units 10 that the power supply is still okay. As soon as power fails, the non-buffered lighting unit 110 will stop operating due to lack of supply, and hence it can no longer generate the okay signal. The buffered lighting units 10 will note the omission of okay signals received, and their respective control devices 20 will draw the conclusion that power has failed and will switch over to backup mode. Depending on lay out and implementation of the lighting system, it may happen that communication signals are blocked and/or disturbed, so that signals are not received or are not understood. If this happens with the okay signal from the non- buffered power unit 110, which will also be indicated as sensor unit, it may happen that lights are reduced without proper cause. It is also possible that the non-buffered power unit 110 does not send any signals due to failure of the non-buffered power unit 110. In order to reduce the risk of this to happen, the lighting system 1 preferably comprises two or more sensor units 110. Even if one or more sensor units fail, as long as there is still at least one sensor unit properly functioning to generate the okay signal, proper functioning of the lighting system as a whole Is ensured.

it is also possible that the signal from a certain sensor unit 110 is not received by all normal units 10, because of distance between these units and/or because of walls or other objects preventing the signal from the sensor unit 110 from reaching the lighting unit 10. For such cases, it may be useful if each control device 20 has a repeat facility, meaning that this control device will also send the okay signal after having received an okay signal. In order to prevent an avalanche of okay messages caused by control devices repeating each and every received okay message, each control device is preferably adapted to send an okay message at a maximum of once per predetermined time interval, which time interval may suitably be chosen between one and five minutes, for instance. Likewise, the sensor unit 110 is also suitably adapted to send its okay message only once per predetermined time interval.

It may happen that the okay signal from a sensor unit 1 10 is blocked temporarily. It would be undesirable if this causes the system to respond by lowering the lighting level. This problem can be overcome by either one or both of the following features. On the one hand it is possible to have two or more sensor units. On the other hand, it is possible that the lighting units only respond to the omission or lack of okay signals after having missed a predetermined number of okay signals, for instance two, three, four, five or more of the expected okay signals.

In practice, the delayed response by the individual control devices may be implemented in the form of a timer. A control device will have an associated timer, timing a time period of for instance ten minutes, which timer will be reset by the received okay signal, which may for instance be received every two minutes.

All in all, this will reduce the chances of the system erroneously lowering the light output level if no power failure has occurred, but it delays the response time between an actual power failure and the response action of lowering the light output level. In order to provide a further improvement of system response In this respect, in a preferred embodiment of the lighting system according to the present invention the sensor units 110 are adapted to monitor the input voltage, and to send a warning signal as soon as it Is detected that the input voltage drops below a predetermined threshold. This serves to predict a possible power failure. In response to receiving such warning signal, the control devices 20 may decide to lower the light output ievel immediately, to have a quick and even pro-active response to power failures.

However, the voltage drop may only be temporary, or the warning signal may have been sent erroneously, for instance due to failure of a sensor unit 110. To reduce the probability of the system erroneously lowering the light output ievel, the control devices 20 may be adapted to wait until the next expected moment for an okay signal. Then, if no okay signal is received at the expected moment, the control devices 20 may conclude from the combination of these two facts, i.e. the warning signal followed by the lacking okay signal, that the chances are high that power has failed indeed, and switch over to reduced power consumption. If on the other hand, after having received such a warning signal, the next okay signal is received, the control devices know that they may ignore the warning signal because apparently the power has not failed.

In an alternative embodiment, there are two or more sensor units. If a power drop actually occurs, this should be sensed by all sensor units, and they should all send their respective warning signals. In such embodiment, foe control devices 20 may be adapted to only switch over to reduced power consumption after having received said warning message from at least two or more, or even all, sensor units within a certain timeframe. If an okay signal is received, the control devices 20 may conclude that the power has been restored.

It is noted that the sensor units 110 and the normal units 10 are implemented differently, specially adapted to their specific tasks. However, it Is preferred that the sensor units 110 and the normal units 10 are implemented identically, and are provided with a user-interface such as a simple switch for indicating whether the unit should operate as a normal unit or as a sensor unit. While normal units are allowed to repeat a communication signal, they are not permitted to initiate a communication signal, because they would continue doing that even after power failure for foe simple reason that their power is buffered.

Summarizing, a lighting system comprises buffered and non-buffered power lines. At least one lighting unit 110 receives power from a non-buffered power line, and is adapted to transmit a communication signal either continuously or repetitively. At least one lighting unit 10 receives power from a buffered power line, and is adapted to monitor receipt of foe communication signal and to reduce output power if it does not receive the communication signal. it should be clear to a person skilled in the art that the present invention is not limited to the exemplary embodiments discussed above, but that several variations and modifications are possible within the protective scope of the invention as defined in the appending claims. For instance, two or more functions may be performed by one single entity, unit or processor. Even if certain features are recited in different dependent claims, the present invention also relates to an embodiment comprising these features in common. Even if certain features have been described in

combination with each other, the present invention also relates to an embodiment in which one or more of these features are omitted. Features which have not been explicitly described as being essential may also be omitted. Any reference signs in a claim should not be construed as limiting the scope of that claim.

In the above, the present invention has been explained with reference to block diagrams, which illustrate functional blocks of the device according to the present invention. It is to be understood that one or more of these functional blocks may be implemented in hardware, where the function of such functional block is performed by individual hardware components, but it is also possible that one or more of these functional blocks are implemented in software, so that the function of such functional block is performed by one or more program lines of a computer program or a programmable device such as a microprocessor, microcontroller, digital signal processor, etc.