FIELD OF THE INVENTION

The present invention generally relates to lighting and presence sensing. In particular, the present invention relates to a processing module for use in a presence sensing system.

BACKGROUND OF THE INVENTION

Lighting systems are becoming increasingly sophisticated, for example with regards to efficiency of energy usage. For example, lighting systems are known which utilize presence sensors that can switch on and/or off lights in the lighting system depending on whether presence of a person or object is sensed by the presence sensors. An example of such a lighting system is the LumiMotion system from Philips Lighting, where camera-based sensors are used for presence detection. The Philips LumiMotion street lighting module includes a camera sensor, which is used to sense presence of a person in the proximity of a street light. In case the camera sensor senses presence of a person in the proximity of a street light, the street light, which is normally dimmed or switched off, may be switched on or activated so as to emit light.

In many application scenarios, it is desired that the presence sensor triggers, i.e. performs the sensing of the object or person and establishes whether an object or person is present within the sensing region of the presence sensor, in a relatively short period of time, so that a sufficient level of light can be provided relatively fast to pedestrians, riders of bicycles, and/or drivers of other vehicles when approaching or being in proximity to the street light. At the same time, it is desired that the presence sensor should not trigger responsive to movements or changes in the surroundings that are caused by events in the surroundings of the presence sensor that should be ignored with respect to switching on the street light. For example, movement of tree branches, large bushes, etc. that may be present in the surroundings of the presence sensor and/or street light caused by winds may possibly cause a false triggering of the presence sensor. Thereby, the street light may be switched on, thereby consuming energy, although there is no actual need at the moment for illumination by the street light. In general, presence of different, possibly movable, objects in the surroundings of the presence sensor and/or street light, may make it difficult to accurately discriminate between changes in the surroundings of the presence sensor and/or street light that should give rise to triggering of the presence sensor, such as people or vehicles moving in the proximity of the street light, and changes in the surroundings of the presence sensor and/or street light that should not give rise to triggering of the presence sensor. This problem may be aggravated by a relatively short observation period available to the presence sensor, which relatively short observation period may be required to keep the activation time of the street light, i.e. the time required to sense presence of the object or person and responsive to the sensing activate the street light, relatively low, as may be required in some applications.

Presence or motion detectors or sensors may use different techniques for detecting presence or motion. Examples include but are not limited to Passive Infrared (PIR) detectors, Ultrasonic (US) motion detectors, detectors based on a combination of PIR and US techniques, and camera-based sensors. Further examples include detectors based on radar, sound and pressure. Applications of presence or motion detectors are numerous, including for example, apart from lighting control systems as discussed above, e.g. for switching one or more light sources on and/or off based on detection of presence or motion of a person in the proximity of the light source or light sources, burglar alarms, where detection of presence or motion by the detector of a person in the proximity of the detectors causes an alarm to go off.

WO 2011/055261 Al discloses an intelligent control system for an object- sensing lighting network and a control system for an outdoor lighting fixture that

dynamically determines a relationship to a plurality of other lighting fixtures. The control system of a lighting fixture dynamically determines its relationship to a plurality of other lighting fixtures along one or more normal paths of activity by monitoring travel times of an object between the lighting fixture and a plurality of other lighting fixtures during periods of low activity.

SUMMARY OF THE INVENTION

In view of the above discussion, a concern of the present invention is to provide a lighting system having a presence sensing system which has an increased robustness in the presence sensing with respect to changes in the surroundings of the presence sensing system that should not give rise to triggering of the presence sensing system compared to known presence sensing systems. A further concern of the present invention is to provide a lighting system having a presence sensing system which has a lower reaction time for presence sensing compared to known presence sensing systems.

A further concern of the present invention is to provide a lighting system having a presence sensing system for sensing presence of an object or person, which presence sensing system comprises a plurality of presence sensors and allows for an increased accuracy in determining whether the object or person is a true object or person, such that the detection of its presence is to be accepted, or a false object or person, such that the detection of its presence is to be rejected, compared to known presence sensing systems.

A further concern of the present invention is to provide a lighting system equipped with a presence sensing system, which lighting system has an increased

performance with respect to efficiency of energy usage compared to known lighting systems.

A further concern of the present invention is to provide a processing module, or alternatively some other entity or unit, for use in a presence sensing system adapted to sense presence of an object or person, which processing module (or other entity or unit) allows for an increased robustness in the presence sensing with respect to changes in the surroundings of the presence sensing system that should not give rise to triggering of the presence sensing system, i.e. false triggers, compared to known presence sensing systems.

To address at least one of these concerns and other concerns, a processing module, a presence sensing system, a sensor, a lighting system, a controller, a method, a computer program product and a computer-readable storage medium in accordance with the independent claims are provided. Preferred embodiments are defined by the dependent claims.

According to a first aspect of the present invention, there is provided a processing module for use in a presence sensing system adapted to sense presence of an object or person and to effect a change of a state of operation of a lighting system in response to sensing presence of the object or person and on a condition that the object or person has been determined as being a true object or person, such that the detection of its presence is to be accepted. The presence sensing system comprises a plurality of sensors, each of which is adapted to sense whether the object or person is present within a corresponding sensing region and on a condition that presence of the object or person is sensed, detect at least one physical characteristic of the sensed object or person. The processing module is adapted to receive at least one physical characteristic of the sensed object or person detected by respective ones of at least two sensors of the plurality of sensors. The processing module is adapted to, based on the received physical characteristics of the sensed object or person, derive at least one three-dimensional physical characteristic of the sensed object or person, and, based on the derived at least one three-dimensional physical characteristic, determine whether the object or person is a true object or person, such that the detection of its presence is to be accepted, or a false object or person, such that the detection of its presence is to be rejected.

Hence, according to embodiments of the present invention, three-dimensional information about an object or person is used to determine whether the object or person is an object or person which a presence sensing system should ignore or react to, e.g. with respect to determining whether the object or person should trigger a change of a state of operation of a lighting system. As described further in the following, the three-dimensional information may for example include information about the object's or person's distance from a ground plane or the object's or person's height above a ground plane, or possibly some other plane, e.g. defined in relation to the ground. According to embodiments of the present invention, the three-dimensional information can be derived by a processing module, by means of receiving and processing sensor output from at least two sensors of a plurality of sensors included in a presence sensing system, which three-dimensional information then can be used by the processing module to determine whether the object or person should be ignored or if it should trigger a reaction.

For example with respect to an example where the three-dimensional information includes information about the object's or person's height above a ground plane (or the ground), an evaluation may be made (e.g. by the processing module) whether the object or person has a height with respect to the ground plane within a selected or predefined height interval which is acceptable for the type of objects or targets for which the presence sensing system should react to. Based on the evaluation, it may then be determined whether the object or person is a true object or person, such that the detection of its presence is to be accepted, or a false object or person, such that the detection of its presence is to be rejected. For example in a street lighting application, the use of three-dimensional information may facilitate discriminating between movement caused by winds of tree branches, large bushes, etc. that may be present in the surroundings of the presence sensing system and/or the lighting system, since, for example, the center of mass of persons (e.g., pedestrians) above ground generally differs from the height of tree branches, etc. above ground. Responsive to the object or person being determined as being a true object or person, the presence sensing system may effect a change of a state of operation of the lighting system. If the object or person is determined as being a false object or person, the sensing of its presence by the sensors may be rejected and no change of a state of operation of the lighting system is effected.

By deriving three-dimensional information by means of receiving and processing sensor output from at least two sensors of a plurality of sensors included in a presence sensing system, which three-dimensional information then can be used by the processing module to determine whether the object or person should be ignored or if it should trigger a reaction (validation or rejection of the object or target), an increased presence sensing robustness with respect to changes in the surroundings of the sensors of the presence sensing system that should not give rise to triggering of a change of a state of operation of the lighting system may be achieved compared to known presence sensing systems. In turn, by an increased presence sensing robustness, a higher confidence in the presence sensing operation may be achieved, which may allow for a decreased activation time of the lighting system and/or reduction in the number of false triggerings of a change of a state of operation of the lighting system, or even elimination of false triggering of a change of a state of operation of the lighting system.

The processing module may be adapted to combine the received physical characteristics of the sensed object or person by means of triangulation so as to derive the at least one three-dimensional physical characteristic of the sensed object, wherein the derived least one three-dimensional physical characteristic comprises a triangulated physical characteristic of the sensed object or person.

The processing module may be adapted to compare the derived least one three-dimensional physical characteristic with a predefined criterion for the derived at least one three-dimensional physical characteristic, the predefined criterion being determinative of whether the detection of the presence of the object or person is to be accepted or rejected. The processing module may be adapted to, based on the comparison, determine whether the object or person is a true object or person, such that the detection of its presence is to be accepted, or a false object or person, such that the detection of its presence is to be rejected.

The processing module may be adapted to determine a correlation between the received physical characteristics of the sensed object or person, which determined correlation may be compared with a predefined correlation criteria. On a condition that the determined correlation complies with the predefined correlation criteria, the detection of the presence of the object or person may be accepted. On a condition that the determined correlation does not comply with the predefined correlation criteria, the detection of the presence of the object or person may be rejected.

The predefined correlation criteria may for example be defined by a value of a correlation coefficient deduced or derived from the determined correlation between the received physical characteristics of the sensed object or person compared to a predefined correlation coefficient. There may for example be relatively strong correlation between physical characteristics such as appearance, e.g. brightness and/or surface texture, and/or shape, with respect to the received physical characteristics of the sensed object or person. In case there is a relatively strong correlation between the received physical characteristics of the sensed object or person, this may indicate that the object or person is a true object or person, such that the detection of its presence should be accepted. In case there is a relatively weak correlation between the received physical characteristics of the sensed object or person, this may indicate that the object or person is a false object or person, such that the detection of its presence should be rejected.

The changing of a state of operation of the lighting system in response to sensing presence of the object or person and on a condition that the object or person has been determined as being a true object or person, such that the detection of its presence is to be accepted, may for example comprise activating at least one light-emitting module included in the lighting system. The at least one light-emitting module may for example be included in a lighting fixture. Activation of the at least one light-emitting module may for example comprise switching the light-emitting module from a state in which it is not emitting any light at all or emits light having a first level of luminous flux to a state in which it emits light, e.g. having a second level of luminous flux, which may be higher than the first level of luminous flux.

The physical characteristics of the sensed object or person received by the processing module may be different or the same. Hence, different sensors of the plurality of sensors may detect different physical characteristics. However, it is possible that different sensors detect the same physical characteristic.

According to a second aspect of the present invention, there is provided a presence sensing system adapted to sense presence of an object or person and to effect a change of a state of operation of a lighting system in response to sensing presence of the object or person and on a condition that the object or person has been determined as being a true object or person, such that the detection of its presence is to be accepted. The presence sensing system comprises a plurality of sensors, each of which is adapted to sense whether the object or person is present within a corresponding sensing region and on a condition that presence of the object or person is sensed, detect at least one physical characteristic of the sensed object or person. The presence sensing system comprises a processing module according to the first aspect of the present invention, which processing module is adapted to determine whether the object or person is a true object or person, such that the detection of its presence is to be accepted, or a false object or person, such that the detection of its presence is to be rejected.

The at least one physical characteristic of the sensed object or person may for example include an exterior appearance of the object or person, a size of the object or person, a shape of the object or person, a width of the object or person, a size, shape and/or orientation of a shadow of the object or person, a direction to at least a portion of the object or person from the respective sensor, a speed of movement of the object or person, and/or the center of mass of the object or person.

The derived least one three-dimensional physical characteristic may for example include a location of the object or person, a height of the object or person above a reference plane, and/or a distance between the center of mass of the object or person and a reference plane. The reference plane may for example comprise a plane corresponding to or representing the ground level. For example where the lighting system includes or is constituted by a street lighting system, the reference plane may comprise the street level.

Each sensor of the plurality of sensors in the presence sensing system may be arranged at a distance from the other sensors such that the sensing region of the sensor at least partly overlaps with respective sensing regions of neighboring sensors.

Each sensor of the plurality of sensors in the presence sensing system may for example include at least one Passive Infrared Sensor, at least one acoustic and/or ultrasound sensor, and/or at least one imaging sensor adapted to capture at least one image of the sensing region of the imaging sensor.

According to a third aspect of the present invention, there is provided a sensor for use in a presence sensing system according to the second aspect of the present invention, which sensor comprises a processing module according to the first aspect of the present invention.

In case the processing module according to the first aspect of the present invention is, in accordance with the third aspect of the present invention, included in a sensor of a presence sensing system according to the second aspect of the present invention, the processing module may for example be adapted to receive at least one physical characteristic of the sensed object or person detected by the sensor in which the processing module is arranged, and at least one physical characteristic of the sensed object or person detected by at least one other sensor in the presence sensing system. The embodiments of the present invention described below with reference to the accompanying drawings relate mainly to that example. However, this should not be seen as limiting the present invention, the scope of which is defined by the appended claims.

According to a fourth aspect of the present invention, there is provided a lighting system including a presence sensing system according to the second aspect of the present invention, the presence sensing system being adapted to sense presence of an object or person and to effect a change of a state of operation of the lighting system in response to sensing presence of the object or person and on a condition that the object or person has been determined as being a true object or person, such that the detection of its presence is to be accepted.

According to a fifth aspect of the present invention, there is provided a controller for controlling at least a portion of a lighting system including a presence sensing system according to the second aspect of the present invention adapted to sense presence of an object or person and to effect a change of a state of operation of the at least a portion of the lighting system in response to sensing presence of the object or person and on a condition that the object or person has been determined as being a true object or person, such that the detection of its presence is to be accepted. The controller may comprise a processing module according to the first aspect of the present invention.

The at least a portion of the lighting system may for example include at least one light-emitting module of a plurality of light-emitting modules included in the lighting system.

According to a sixth aspect of the present invention, there is provided a method in a presence sensing system adapted to sense presence of an object or person and to effect a change of a state of operation of a lighting system in response to sensing presence of the object or person and on a condition that the object or person has been determined as being a true object or person, such that the detection of its presence is to be accepted. The presence sensing system comprises a plurality of sensors, each of which is adapted to sense whether the object or person is present within a corresponding sensing region and on a condition that presence of the object or person is sensed, detect at least one physical characteristic of the sensed object or person. The method comprises receiving at least one physical characteristic of the sensed object or person detected by respective ones of at least two sensors of the plurality of sensors. Based on the received physical characteristics of the sensed object or person, at least one three-dimensional physical characteristic of the sensed object or person is derived. Based on the derived at least one three-dimensional physical characteristic, there is determined whether the object or person is a true object or person, such that the detection of its presence is to be accepted, or a false object or person, such that the detection of its presence is to be rejected.

According to a seventh aspect of the present invention, there is provided a computer program product adapted to, when executed in a processing module according to the first aspect of the present invention, perform a method according to the sixth aspect of the present invention.

According to an eight aspect of the present invention, there is provided a computer-readable storage medium on which there is stored a computer program product adapted to, when executed in a processing module according to the first aspect of the present invention, perform a method according to the sixth aspect of the present invention.

According to a ninth aspect of the present invention, there is provided a lighting system. The lighting system comprises a presence sensing system for sensing presence of an object or person. The presence sensing system comprises a plurality of sensors. Each sensor of the plurality of sensors comprises a communication module adapted to transmit information to any one of at least neighboring sensors and receive information from any one of at least neighboring sensors by means of a communication link. Each sensor is adapted to sense whether an object or person is present within a corresponding sensing region. Each sensor is arranged at a distance from the other sensors, and information on the extent of the sensing region of each sensor is available at least to neighboring sensors. Each sensor of the plurality of sensors is adapted to, on a condition that presence of the object or person is sensed by the sensor, detect at least one physical characteristic of the sensed object or person. Based on the extents of the respective sensing regions corresponding to at least neighboring sensors, the sensor determines whether there is at least one other sensor that potentially can sense presence of the object or person. On a condition that at least one other sensor is identified that potentially can sense presence of the object or person, the sensor transmits the at least one physical characteristic of the sensed object or person to the at least one other sensor. The at least one other sensor is adapted to, on a condition that presence of the object or person is sensed by the at least one other sensor, detect at least one physical characteristic of the sensed object or person. The at least one other sensor is adapted to, based on a combination of the detected at least one physical characteristic with received at least one physical characteristic or characteristics, determine whether the object or person is a true object or person, such that the detection of its presence is to be accepted, or a false object or person, such that the detection of its presence is to be rejected. The lighting system comprises a plurality of lighting fixtures. Each lighting fixture is arranged at a distance from the other lighting fixtures. Each lighting fixture comprises a light-emitting module adapted to emit light, and a control module adapted to control operation of the light-emitting module of the lighting fixture. Each sensor of the presence sensing system is comprised in a corresponding lighting fixture. The control module of each lighting fixture is adapted to activate the light- emitting module of the lighting fixture on a condition that the object or person has been determined by the sensor corresponding to the lighting fixture as being a true object or person such that the detection of its presence is to be accepted.

According to embodiments of the present invention, in a lighting system having a presence sensing system including a plurality of sensors capable of sensing presence of an object or person or target within respective sensing regions, whenever a sensor in the system senses presence of a potential object or person within its corresponding sensing region, the sensor may share information to other sensors, such as sensors that are neighboring the particular sensor within the presence sensing system. The choice of which sensor or sensors, if any, to share the information with, may be based on topology

information of the sensors within the presence sensing system. Such topology information, which may include information on possible overlapping of respective sensing regions of the sensors, may be available from a calibration procedure being a part of the installation process of the presence sensing system, or may be established via a self-learning or machine learning procedure or the like. The information may for example comprise measurement data from the presence sensing operation of the particular sensor, indicative of presence of non-presence of the object or person, or information based on which presence of non-presence of the object or person may be established. The other sensor or sensors which receive the information may perform presence sensing measurements on its or their own, which in combination with the received information may be used by the other sensor or sensors to validate or reject the detection of the object or person. In other words, the other sensor or sensors may combine the received information with its or their own presence sensing measurements, e.g. using triangulation principles, based on which each of the other sensor or sensors may determine whether the object or person is a true object or person, such that the detection of its presence is to be accepted, or a false object or person, such that the detection of its presence is to be rejected. By means of the sharing of presence sensing information between sensors and subsequent validation or rejection of the object or target, an increased presence sensing robustness with respect to changes in the surroundings of the sensors of the presence sensing system that should not give rise to triggering of the sensors of the presence sensing system may be achieved, as compared to known presence sensing systems.

By an increased presence sensing robustness of the presence sensing system, a higher confidence in the presence sensing operations may be achieved. In turn, this may allow for a decreased activation time and/or reduction in the number of false triggerings of the sensors or even elimination of false triggering of the sensors.

By an increased presence sensing robustness of the presence sensing system included in the lighting system, a higher confidence in the presence sensing operations may be achieved. In turn, this may allow for a decreased activation time and/or reduction in the number of false triggering of the sensors or even elimination of false triggering of the sensors, which may improve overall lighting system performance with regards to user comfort and/or safety, and/or efficiency in energy usage.

The lighting system may for example comprise a street lighting system, wherein each lighting fixture comprises a street light.

Triangulation principles or methods as mentioned or described herein, generally referring to combining observations and/or measurements from at least two sensors arranged at different positions and on basis thereof deduce or determine three-dimensional information, are known to a skilled person, and will therefore not be described in great detail herein.

The combination of a detected at least one physical characteristic with received at least one physical characteristic or characteristics as described in the foregoing may be a combination of different physical characteristics. In other words, different sensors may detect different physical characteristics. However, it is possible that different sensors may detect the same physical characteristic.

According to a tenth aspect of the present invention, there is provided a method in a lighting system comprising a presence sensing system and a plurality of lighting fixtures, each lighting fixture being arranged at a distance from the other lighting fixtures and each lighting fixture comprising a light-emitting module adapted to emit light. The presence sensing system comprises a plurality of sensors. Each sensor comprises a communication module adapted to transmit information to any one of at least neighboring sensors and receive information from any one of at least neighboring sensors by means of a communication link. Each sensor is adapted to sense whether an object or person is present within a corresponding sensing region. Each sensor is arranged at a distance from the other sensors. The sensors are configured such that information on the extent of the sensing region of each sensor is available at least to neighboring sensors. Each sensor is comprised in a corresponding lighting fixture. The method comprises, for each sensor, sensing whether the object or person is present in the sensing region of the sensor. On a condition that presence of the object or person is sensed by the sensor, at least one physical characteristic of the sensed object or person is detected. Based on the extents of the respective sensing regions corresponding to at least neighboring sensors, there is determined whether there is at least one other sensor that potentially can sense presence of the object or person. On a condition that at least one other sensor is identified that potentially can sense presence of the object or person, the at least one physical characteristic of the sensed object or person is transmitted to the at least one other sensor. For each sensor that has sensed presence of the object or person and determined that there is at least one other sensor that potentially can sense presence of the object or person, the method further comprises, for each of the at least one other sensor, sensing whether the object or person is present. On a condition that presence of the object or person is sensed by the sensor, at least one physical characteristic of the sensed object or person is detected. Based on a combination of the detected at least one physical characteristic with received at least one physical characteristic, there is determined whether the object or person is a true object or person such that the detection of its presence is to be accepted or a false object or person such that the detection of its presence is to be rejected. The light-emitting module of a lighting fixture is activated on a condition that the object or person has been determined by the sensor corresponding to the lighting fixture as being a true object or person such that the detection of its presence is to be accepted.

Activation of the light-emitting module of a lighting fixture may for example comprise switching the light-emitting module from a state in which it is not emitting any light at all or emits light having a first level of luminous flux to a state in which it emits light having a second level of luminous flux, which may be higher than the first level of luminous flux.

In the context of the present application, by "physical characteristic" of an object or person it is meant a feature, property and/or attribute of or associated with the object or person that may be sensory, i.e. perceptible to the senses, and is measurable. For example, the physical characteristic may include, but is not limited to, one or more of a geometrical property, position, speed of movement, texture, brightness, shape, length and/or width, etc. Alternatively or optionally, the physical characteristic may include, but is not limited to, a size, shape, and/or orientation of a shadow of an object or person.

In the context of the present application, by the presence sensing system comprising a plurality of sensors it is meant that the presence sensing system comprises at least two sensors.

As previously mentioned, each sensor is adapted to sense whether an object or person is present. Each sensor may be adapted to sense whether an object or person is present within a sensing region corresponding to the particular sensor. As further described in the following, there may be at least partial overlap, e.g. spatial and/or temporal overlap, between sensing regions corresponding to different sensors of the plurality of sensors.

For enabling each sensor to transmit information to any one of at least neighboring sensors, and receive information from any one of at least neighboring sensors, the plurality of sensors may for example be in wired and/or wireless network communication with respect to each other so as to enable transmitting information between different sensors of the plurality of sensors. The information transmitted between different sensors may for example comprise measurements made by at least one sensor, data and/or commands for controlling operation of a sensor.

For each sensor of the plurality of sensors, information on the extent of the sensing region of the sensor, or spatial extent, bounds, scope or coverage of the sensing region of the sensor, may be available at least to neighboring sensors of the respective sensor, which may be all or only some neighboring sensors, or sensors that are situated or arranged close or closest to the location of the respective sensor as compared to the location of other sensors of the plurality of sensors. Hence, for each sensor, information on the extent of the sensing region of the sensor may be available to neighboring sensors, and possibly also to sensors of the plurality of sensors other than the neighboring one or ones.

The extent, spatial extent, bounds, scope or coverage of the sensing region of each sensor of the plurality of sensors may be known to each of the other sensors.

The extent, spatial extent, bounds, scope or coverage of the sensing region of each sensor of the plurality of sensors may be known to at least neighboring sensors for example by means of a calibration step or steps possibly as a part of an installation procedure of the presence sensing system or lighting system, or by a self learning procedure or machine learning algorithm.

The presence sensing system may for example be included in a lighting system comprising a plurality of lighting fixtures arranged at a distance relatively each other so as to enable lighting over a relatively large area or in a relatively large region, where each lighting fixture comprises a light-emitting module adapted to emit light, and where each sensor of the plurality of sensors in the presence sensing system is comprised in a corresponding lighting fixture of the lighting system. Such a lighting system may for example be a street lighting system.

As previously mentioned, each sensor is adapted to, on a condition that presence of the object or person is sensed by the sensor, detect at least one physical characteristic of the sensed object or person. The at least one physical characteristic may for example include a position of the sensed object or person. The position may for example be a position in relation to a relative reference system or an absolute position.

The detection of at least one physical characteristic of the sensed object or person by a sensor of the plurality of sensors may be performed or implemented in several ways.

For example, each sensor of the plurality of sensors may include at least one Passive Infrared Sensor (PIR), at least one acoustic and/or ultrasound sensor, at least one imaging sensor adapted to capture at least one image of the sensing region of the sensor or imaging sensor, and/or any other sensor capable of sensing whether an object or person is present, e.g. within a sensing region of the sensor.

The acoustic and/or ultrasound sensor may be adapted to emit at least one acoustic and/or ultrasound pulse from the sensor, and receive at least one reflected and/or scattered acoustic and/or ultrasound pulse generated by reflection and/or scattering of an acoustic and/or ultrasound pulse emitted by the sensor from structures in the surroundings of the sensor.

According to one example, the acoustic and/or ultrasound sensor comprises a transmitting module comprising at least one actuatable transducer element configured to produce an acoustic and/or ultrasound pulse when actuated, wherein the transmitting module is configured to emit the acoustic and/or ultrasound pulse from the sensor. The sensor comprises a receiving module configured to receive at least one reflected and/or scattered acoustic and/or ultrasound pulse generated by reflection and/or scattering of an acoustic and/or ultrasound pulse emitted by the transmitting module from structures in the

surroundings of the sensor. The sensor comprises a processing module configured to, for each reflected and/or scattered acoustic and/or ultrasound pulse, generate a received signal corresponding to the reflected and/or scattered acoustic and/or ultrasound pulse. The received signal, e.g. an electrical signal, can subsequently be processed, e.g. digitally processed, for example for detecting at least one physical characteristic of an object or person in the sensing region of the sensor.

The imaging sensor may comprise an image processing module adapted to convert the captured at least one image into an image representation, which subsequently can be digitally processed, e.g. using image analysis tools and/or techniques, for example for detecting at least one physical characteristic of an object or person in the sensing region of the sensor.

The imaging sensor may for example comprise an active-pixel image sensor, a charge-coupled device (CCD) based sensor and/or a complementary metal-oxide- semiconductor (CMOS) based sensor.

Principles of detection of at least one physical characteristic of an object or person using a sensor or sensors as described herein are known to a skilled person and are therefore not discussed in greater detail in the following.

Each sensor may be adapted to, on a condition that presence of the object or person is sensed by the sensor, determine whether there is at least one other sensor that potentially can sense presence of the object or person. The determination may be performed based on the extents of the respective sensing regions corresponding to at least sensors neighboring the respective sensor.

The determination may for example be based on any overlap that exists between the respective sensing regions, or observation areas, corresponding to the sensors. Thus, each sensor may be adapted to, on a condition that presence of the object or person is sensed by the sensor, determine whether there is at least one other sensor that potentially can sense presence of the object or person in its corresponding region based on the extents of the of the respective sensing regions corresponding to at least sensors neighboring the respective sensor.

Alternatively or optionally, the determination may for example be based on distance between any adjacent non-overlapping sensing regions, or observation areas, or portions thereof, corresponding to the sensors. For example, the determination may be performed by assessing whether a shadow of the object or person potentially can be sensed, or observed, by an imaging sensor or camera-based sensor operating in a sensing region which is at least partly non-overlapping with, and possibly neighboring to, the sensing region of the sensor which did first sense presence of the object or person in its sensing region. Each sensor may be arranged at a distance from the other sensors such that the sensing region of the sensor at least partly overlaps with respective sensing regions of neighboring sensors.

The sensors may be aware of any overlap that exists between the respective sensing regions corresponding to the sensors, or even any overlapping regions of the sensing regions, prior to performing any sensing operation by one or several calibration steps as a part of installation of the presence sensing system, or by means of a self learning procedure or machine learning algorithm.

Alternatively or optionally, the sensors may be aware of any overlap that exists between the respective sensing regions corresponding to the sensors, or even any overlapping regions of the sensing regions, by each sensor being adapted to transmit the extent of its sensing region to the other sensors. However, in principle each sensor may transmit the extent of its sensing region to only one or some of the other sensors, e.g. to a neighboring sensor or sensors. The sensor or sensors receiving the information regarding the extent of the sensing region may then pass on the information to another sensor or other sensors, and so on. In such a manner, the extent, bounds, scope or coverage of the sensing region of each sensor of the plurality of sensors may be known to each of the other sensors. Information on the extent of the sensing region of a sensor may be available at least to a neighboring sensor or neighboring sensors.

The determination of whether the object or person is a true object or person, such that the detection of its presence is to be accepted, or a false object or person, such that the detection of its presence is to be rejected, at a sensor, based on a combination of detected at least one physical characteristic with received at least one physical characteristic or characteristics, may be performed in different alternative ways. In the following some examples are described.

For example, for each sensor that has sensed presence of the object or person and determined that there is at least one other sensor that potentially can sense presence of the object or person in its corresponding sensing region, on a condition that presence of the object or person is sensed by the at least one other sensor, the detected at least one physical characteristic may be combined with received at least one physical characteristic or characteristics by means of triangulation so as to obtain a triangulated physical characteristic of the sensed object or person. The triangulated physical characteristic may be compared with a predefined criteria for the triangulated physical characteristic, which predefined criteria may be determinative of whether the detection of the presence of the object or person is to be accepted or rejected. Based on the comparison, it may be determined whether the object or person is a true object or person, such that the detection of its presence is to be accepted, or a false object or person, such that the detection of its presence is to be rejected.

The detected at least one physical characteristic may be stored locally, i.e. at the respective sensor performing the detection, in a memory means arranged in the sensor. Stored physical characteristics may be utilized in the obtaining of a triangulated physical characteristic of the sensed object or person in addition to combination of the detected at least one physical characteristic with received at least one physical characteristic or characteristics by means of triangulation. This may facilitate or enable an increased accuracy in determining the triangulated physical characteristics.

According to one example, initially no triangulation information is available at the sensors. Then, whenever two sensors detect an object or person, a physical characteristic of the object or person, e.g. its position, as determined by both of the two sensors is stored or saved in respective memory means in the two sensors, which subsequently may be used to incrementally update the triangulation parameters for those two sensors.

The memory means may for example comprise a semiconductor based memory including non- volatile memory such as read-only memory (ROM), magnetoresistive random-access memory (MRAM), a flash memory, etc., or volatile memory such as static random-access memory (SRAM), dynamic random-access memory (DRAM), etc.

The at least one physical characteristic of the sensed object or person may for example include an exterior appearance of the object or person, such as brightness and/or texture, a size of the object or person, a shape of the object or person, a width of the object or person, a direction to at least a portion of the object or person from the respective sensor, a speed of movement of the object or person, and/or the center of mass, or barycenter, of the object or person. Alternatively or optionally, the at least one physical characteristic of the sensed object or person may for example include a size, shape and/or orientation of a shadow of the object or person.

The triangulated physical characteristic may for example include a location of the object or person, a height of the object or person above a reference plane; and/or a distance between the center of mass of the object or person and a reference plane. The reference plane may for example comprise a plane corresponding to or representing the ground level above which the sensors are located. For example where the presence sensing system is included in a street lighting system, the reference plane may comprise the street level. Alternatively or optionally, for each sensor that has sensed presence of the object or person and determined that there is at least one other sensor that potentially can sense presence of the object or person in its corresponding sensing region, on a condition that presence of the object or person is sensed by the at least one other sensor, a height of the object or person above a reference plane may be estimated based on a combination of the detected at least one physical characteristic with received at least one physical characteristic. On a condition that the estimated height of the object or person above the reference plane is within a predefined range of values, the detection of the presence of the object or person may be accepted. On a condition that the estimated height of the object or person above the reference plane is outside the predefined range of values, the detection of the presence of the object or person may be rejected.

Alternatively or optionally, the at least one physical characteristic may include at least a direction to an upper portion of the sensed object or person from the respective sensor and a direction to a lower portion of the sensed object or person from the respective sensor.

For each sensor, information on the position of the sensor in relation to at least neighboring sensors may be available at least to neighboring sensors.

For each sensor that has sensed presence of the object or person and determined that there is at least one other sensor that potentially can sense presence of the object or person in its corresponding sensing region, on a condition that presence of the object or person is sensed by the at least one other sensor, a location of the upper portion of the sensed object or person may be determined based on a combination of the detected direction to the upper portion of the sensed object or person from the at least one other sensor, the received direction to the upper portion of the sensed object or person, and the respective positions of the sensors having sensed presence of the object or person.

A location of the lower portion of the sensed object or person may be determined based on a combination of the detected direction to the lower portion of the sensed object or person from the at least one other sensor, the received direction to the lower portion of the sensed object or person, and the respective positions of the sensors having sensed presence of the object or person.

Based on a difference between the determined locations of the upper and lower portions of the sensed object or person, a height of the object or person above a reference plane may be estimated. The acceptance or rejection of the detection of the presence of the object or person may be based on the estimated height of the object or person. For example, on a condition that the estimated height of the object or person above the reference plane is within a predefined range of values, the detection of the presence of the object or person may be accepted. On a condition that the estimated height of the object or person above the reference plane is outside the predefined range of values, the detection of the presence of the object or person may be rejected.

For each sensor that has sensed presence of the object or person and determined that there is at least one other sensor that potentially can sense presence of the object or person in its corresponding sensing region, on a condition that presence of the object or person is sensed by the at least one other sensor, a correlation between the detected at least one physical characteristic and received at least one physical characteristic or characteristics may be determined. The determined correlation may be compared with a predefined correlation criteria. The predefined correlation criteria may for example be defined by a value of a correlation coefficient deduced from the determined correlation between the detected at least one physical characteristic and received at least one physical characteristic or characteristics compared to a predefined correlation coefficient. On a condition that the determined correlation complies with the predefined correlation criteria, the detection of the presence of the object or person may be accepted. On a condition that the determined correlation does not comply with the predefined correlation criteria, the detection of the presence of the object or person may be rejected.

In particular, there may be relatively strong correlation between physical characteristics such as appearance, e.g. brightness and/or surface texture, and/or shape, with respect to detected at least one physical characteristic and received at least one physical characteristic or characteristics. In case there is a relatively strong correlation between detected and received physical characteristics, this may indicate that the object or person is a true object or person, such that the detection of its presence should be accepted. In case there is a relatively weak correlation between detected and received physical characteristics, this may indicate that the object or person is a false object or person, such that the detection of its presence should be rejected. Hence, a correlation between the detected at least one physical characteristic and received at least one physical characteristic or characteristics may be used to further increase the robustness of presence sensing with respect to changes in the surroundings of the sensors of the presence sensing system that should not give rise to triggering of the sensors of the presence sensing system, as compared to known presence sensing systems. Each of the plurality of sensors may comprise a processing module or the like adapted to process information received from another sensor and/or data or values deduced from measurements made by the sensor, etc.

The light-emitting module of a lighting fixture may for example comprise at least one solid state light source such as a light-emitting diode (LED). The LED may for example comprise an organic LED (OLED) or an inorganic LED. Alternatively or optionally, the light-emitting module of a lighting fixture may comprise a light-emitting element other than a LED or LEDs.

According to an eleventh aspect of the present invention, there is provided a computer program product adapted to, when executed in a processor unit or processing module, perform a method according to the present invention.

According to a twelth aspect of the present invention, there is provided a computer-readable storage medium on which there is stored a computer program product adapted to, when executed in a processor unit or processing module, perform a method according to the present invention.

According to a thirteenth aspect of the present invention, there is provided a presence sensing system included in a lighting system according to the present invention.

Further objects and advantages of the present invention are described in the following by means of exemplifying embodiments.

It is noted that the present invention relates to all possible combinations of features recited in the claims. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. Those skilled in the art realize that different features of the present invention can be combined to create embodiments other than those described in the following.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplifying embodiments of the invention will be described below with reference to the accompanying drawings, in which:

Fig. 1 is a schematic a schematic view from above of a presence sensing system in accordance with an embodiment of the present invention;

Fig. 2 is a schematic block diagram of a presence sensing system in

accordance with an embodiment of the present invention;

Fig. 3 is a schematic side view of a lighting system according to an embodiment of the present invention; Fig. 4 is a schematic side view of a lighting system according to an

embodiment of the present invention;

Fig. 5 is a schematic view of a computer-readable storage medium according to an embodiment of the present invention;

Fig. 6 is a schematic flowchart of a method according to an embodiment of the present invention; and

Fig. 7 is a schematic block diagram of a lighting system according to an embodiment of the present invention.

In the accompanying drawings, the same reference numerals denote the same or similar elements throughout the views.

DETAILED DESCRIPTION

The present invention will now be described hereinafter with reference to the accompanying drawings, in which exemplifying embodiments of the present invention are shown. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example. Furthermore, like numbers refer to like or similar elements or components throughout.

Referring now to Fig. 1, there is shown a schematic view from above of a presence sensing system 100 in accordance with an embodiment of the present invention. The presence sensing system 100 is capable of sensing presence of an object or person 101. The presence sensing system 100 is intended to be included in a lighting system (not shown in

Fig. 1, see Fig. 3).

The presence sensing system 100 comprises two sensors 102. Each sensor 102 comprises a communication module (not shown in Fig. 1, see Fig. 2) adapted to transmit information to the other sensor 102 and receive information from the other sensor 102 by means of a communication link 106. The communication link 106 may be wireless or wired. For example, the sensors 102 may be included in a local area network (LAN), e.g. a wireless LAN (WLAN) or the like, or an ad hoc network using Bluetooth technology, etc. Other possibilities of effecting a wired or wireless communication link or network communication between the sensors are known to a skilled person and are therefore not discussed in greater detail herein.

Although Fig. 1 depicts two sensors 102, it is to be understood that the present invention is not limited to the case of two sensors being included the presence sensing system 100. In general, the presence sensing system 100 may comprise any integer number of sensors 102 exceeding one - i.e. a plurality of, or at least two, sensors 102, e.g. three, four, five, six, eight, ten, fifteen or twenty or more sensors 102.

According to the example depicted in Fig. 1, the person or object 101 is located on a road, a corridor, a hallway or the like, schematically indicated by reference numeral 110.

Each of the sensors 102 is adapted to sense whether an object or person 101 is present within a sensing region corresponding to the sensor 102. The respective sensing regions are schematically and exemplary indicated by dashed lines indicated by reference numerals 108. The sensors 102 are configured such that information on the extent of the sensing region 108 of each sensor 102 is available to the other sensor 102. It is understood that the shapes of the respective sensing regions 108, i.e. the outline of their spatial extents, are according to an example only and other shapes are possible as required by circumstances and/or application.

As depicted in Fig. 1, the sensors 102 are arranged at a distance from each other.

A principle of the present invention will now be described with reference to

Fig. 1.

Each of the sensors 102 is adapted to, on a condition that presence of the object or person 101 is sensed by the sensor 102, detect at least one physical characteristic of the sensed object or person 101.

The at least one physical characteristic of the sensed object or person 101 may for example be at least one of an exterior appearance of the object or person 101, a size of the object or person 101, a shape of the object or person 101, a width of the object or person 101, a direction to at least a portion of the object or person 101 from the respective sensor 102, a speed of movement of the object or person 101 and the center of mass of the object or person 101.

Then, based on the extents of the respective sensing regions 108 corresponding to the neighboring sensor 102, each sensor 102 is adapted to determine whether the other sensor 102 can potentially sense presence of the object or person 101. The determination may for example be based on any overlap that exists between the respective sensing regions 108, as indicated in Fig. 1. The sensors 102 may be aware of any overlap that exists between the respective sensing regions 108 prior to performing any sensing operation for example by means of one or several calibration steps possibly as a part of installation of the presence sensing system 100, or by means of a self learning procedure or machine learning algorithm.

Each sensor 102 is adapted to transmit the at least one physical characteristic of the sensed object or person 101 to the other sensor 102, on a condition that the other sensor 102 is identified as potentially being able to sense presence of the object or person 101. In the case depicted in Fig. 1, the object or person is located in a region where the respective sensing regions 108 overlap, so for the situation depicted in Fig. 1, each sensor 102 will identify the other sensor 102 as potentially being able to sense presence of the object or person 101.

Consider now a first case where the left sensor 102 in Fig. 1 has sensed presence of the object or person 101, detected at least one physical characteristic of the sensed object or person 101, and transmitted the at least one physical characteristic of the sensed object or person 101 to the right sensor 102, since the left sensor 102 identifies the right sensor 102 as potentially being able to sense presence of the object or person 101.

The right sensor 102 is adapted to, on a condition that presence of the object or person 101 is sensed by the right sensor 102, detect at least one physical characteristic of the sensed object or person 102 in the sensing region 108 of the right sensor 102. Based on a combination of the detected at least one physical characteristic by the right sensor 102 with the received at least one physical characteristic or characteristics from the left sensor 102, the right sensor 102 is adapted to determine whether the object or person 101 is a true object or person, such that the detection of its presence is to be accepted, or a false object or person, such that the detection of its presence is to be rejected.

To this end, the right sensor 102 may be adapted to combine the detected at least one physical characteristic with received at least one physical characteristic or characteristics by means of triangulation, so as to obtain a triangulated physical characteristic of the sensed object or person 101. The right sensor 102 may be adapted to compare the triangulated physical characteristic with a predefined criteria for the triangulated physical characteristic, which predefined criteria is determinative of whether the detection of the presence of the object or person 101 is to be accepted or rejected, and based on the comparison, determine whether the object or person 101 is a true object or person, such that the detection of its presence by the right sensor 102 is to be accepted, or a false object or person, such that the detection of its presence by the right sensor 102 is to be rejected.

The triangulated physical characteristic may for example be at least one of a location of the object or person 101, a height of the object or person 101 above a reference plane (not shown in Fig. 1) and a distance between the center of mass of the object or person

101 and a reference plane (not shown in Fig. 1).

A second case is analogous to the first case: the right sensor 102 in Fig. 1 senses presence of the object or person 101, detects at least one physical characteristic of the sensed object or person 101, and transmits the at least one physical characteristic of the sensed object or person 101 to the left sensor 102, which based on a combination of a detected at least one physical characteristic with received at least one physical characteristic or characteristics from the left sensor 102 determines whether to accept or reject the detection of the presence of the object or person 102 by the left sensor 102.

The same principles apply analogously to presence sensing systems having a number of sensors exceeding two.

Referring now to Fig. 2, there is shown a schematic block diagram of a presence sensing system 100 in accordance with an embodiment of the present invention. The presence sensing system 100 is capable of sensing presence of an object or person (not shown in Fig. 2) using principles as described in the foregoing, such as the same or similar principles as described above with reference to Fig. 1. The presence sensing system 100 is intended to be included in a lighting system (not shown in Fig. 2, see Fig. 3).

The presence sensing system 100 comprises four sensors 102. Each sensor 102 comprises a communication module 104 adapted to transmit information to each of the other sensors 102 and receive information from the other sensors 102 by means of communication links 106. The communication links 106 may be wireless or wired. For example, the sensors

102 may be included in a local area network (LAN), e.g. a wireless LAN (WLAN), or the like, or an ad hoc network using Bluetooth technology, etc.

Although Fig. 2 depicts four sensors 102, it is to be understood that the present invention is not limited to the case of four sensors being included the presence sensing system 100. In general, the presence sensing system 100 may comprise any integer number of sensors 102 exceeding one - i.e. a plurality of, or at least two, sensors 102, e.g. two, three, five, six, eight, ten, fifteen or twenty or more sensors 102.

With reference to Figs. 1 and 2, each sensor 102 may for example include or be constituted by at least one Passive Infrared Sensor (PIR), at least one ultrasound sensor, at least one imaging sensor adapted to capture at least one image of the sensing region 108 of the sensor 102 or imaging sensor, and/or any other sensor capable of sensing whether an object or person 101 is present within a sensing region 108 of the sensor 102. Referring now to Fig. 3, there is shown a schematic side view of a lighting system 200 according to an embodiment of the present invention. The lighting system comprises two lighting fixtures 201. The lighting fixtures 201 are arranged at a distance from each other. Each lighting fixture 201 comprises a light-emitting module 202 adapted to emit light. According to the embodiment depicted in Fig. 3, the light-emitting modules 202 are adapted to illuminate a road or pavement 110, and are arranged on poles 205 or the like at a height above the road or pavement 110. Each lighting fixture 201 comprises a control module (not shown in Fig. 3) adapted to control operation of the light-emitting module 202.

The lighting system 200 comprises a presence sensing system according to an embodiment of the present invention for sensing presence of an object or person. In Fig. 3, there is shown in accordance with an example three possible objects or persons 101a, 101b, 101c whose presence possibly may be sensed by the presence sensing system. According to the embodiment depicted in Fig. 3, the objects or persons 101a, 101b, 101c are two birds 101a, 101b and a person or pedestrian 101c. The presence sensing system comprises two sensors 102, wherein each sensor 102 is comprised in a corresponding lighting fixture 201. Each of the sensors 102 is adapted to sense whether an object or person 101a, 101b, 101c is present within a corresponding sensing region 108, indicated by the dashed lines in Fig. 3.

The sensors 102 are aware of any overlap that exists between their respective sensing regions 108, e.g. by one or several calibration steps as a part of installation of the presence sensing system and/or lighting system 200, or by means of a self learning procedure or machine learning algorithm.

Each of the sensors 102 comprises a communication module (not shown in Fig. 3) adapted to transmit information to the other sensor 102 and receive information from the other sensor 102 by means of a communication link (not shown in Fig. 3). The communication link may be wired or wireless such as described in the foregoing.

The control module of each lighting fixture 201 is adapted to activate the light- emitting module 202 of the lighting fixture 201 on a condition that the object or person 101a, 101b, 101c has been determined by the sensor 102 corresponding to the lighting fixture 201 as being a true object or person, such that the detection of its presence is to be accepted.

A principle of the present invention will now be described with reference to

Fig. 3.

According to the embodiment depicted in Fig. 3, each of the sensors 102 comprises an imaging sensor adapted to capture at least one image of the respective sensing region 108 of the sensor 102. Each of the sensors 102 may further comprise a processing module or the like (not shown in Fig. 3) adapted to process information received from the other sensor 102 and/or data or values deduced from measurements made by the sensor 102, etc.

The bird 101a is located on the intersection of rays or lines R _a i and RM. Both of the rays or lines R _a i and RM are outside either of the sensing regions 108. Hence, presence of the bird 101a will not be detected by any one of the sensors 102.

The bird 101b and the person or pedestrian 101c are within the sensing region 108 of the left sensor 102. The presence of both the bird 101b and the person or pedestrian 101c may hence be sensed by the left sensor 102. Since the imaging sensor of the sensor 102 projects a three-dimensional scene onto a two-dimensional plane or image, the distance to the bird 101b and the person or pedestrian 101c, respectively, may be difficult or even impossible to directly deduce from an image of the sensing region 108 of the left sensor 102 captured by the left sensor 102. In view of this, and since the bird 101b and the person or pedestrian 101c are situated at different distances with respect to the position of the left sensor 102, both the bird 101b and the person or pedestrian 101c may have a similar position and size in the image captured by the left sensor 102. It may be difficult or even impossible to directly deduce from an image of the sensing region 108 of the left sensor 102 captured by the left sensor 102 a position on the road or pavement 110 or on the ground of an object or person and distinguish between objects or persons that are moving on the road or pavement 110 or on the ground and objects or persons that are flying or hovering above the road or pavement 110 or the ground.

As illustrated in Fig. 3, the person or pedestrian 101c is located both in the sensing region 108 of the left sensor 102 and in the sensing region 108 of the right sensor 102. In other words, the person or pedestrian 101c is located in a region where the respective sensing regions 108 of the sensors 102 overlap.

Since, as previously mentioned, the sensors 102 are aware of any overlap that exists between their respective sensing regions 108, the left sensor 102 may, once it has detected presence of the person or pedestrian 101c in the sensing region 108 of the left sensor 102 and detected at least one physical characteristic of the person or pedestrian 101c, transmit the detected at least one physical characteristic of the person or pedestrian 101c to the right sensor 102 via the communication link.

Based on a combination of the detected at least one physical characteristic of the person or pedestrian 101c by the left sensor 102 as received from the left sensor 102 and a detected at least one physical characteristic of the person or pedestrian 101c by the right sensor 102, the right sensor 102 may validate or reject the detection of the person or pedestrian 101c. For example, received information from the left sensor 102 may be combined at the right sensor 102 with presence sensing measurements of the right sensor 102, e.g. using triangulation principles. Based on such a combination, the right sensor 102 may determine whether the person or pedestrian 101c is a true person, such that the detection of his or her presence should be accepted, or a false person, such that the detection of his or her presence should be rejected.

According to one example, the at least one physical characteristic includes a direction to a lower portion of the person or pedestrian 101c from the respective sensors 102, indicated by rays or lines Ra ₃ and Rt, ₃ in Fig. 3.

For example at the right sensor 102, a location of the lower portion of the person or pedestrian 101c with reference to the road or pavement 110 level or ground level may be determined based on a combination of the detected direction to the lower portion of the person or pedestrian 101c from the right sensor 102, the direction to the lower portion of the person or pedestrian 101c from the left sensor 102 received by the right sensor 102 from the left sensor 102, and the respective positions of the sensors 102. The determined location of the lower portion of the person or pedestrian 101c with reference to the road or pavement 110 level or ground level will be close to or coincidental with the road or pavement 110 level or ground level. If the location of a sensed object or person would not be close to or coincidental with the road or pavement 110 level or ground level, the detection of the presence of the object or person should be rejected or discarded.

Referring now to Fig. 4, there is shown a schematic side view of a lighting system 200 according to an embodiment of the present invention, for describing a principle of the present invention.

According to one example, the at least one physical characteristic includes a direction to a lower portion of the person or pedestrian 101c from the respective sensors 102, indicated by rays or lines Rai and RM, respectively, in Fig. 4, and a direction to an upper portion of the person or pedestrian 101c from the respective sensors 102, indicated by rays or lines R^ and Rb2, respectively, in Fig. 4.

For example, a location of the upper portion of the person or pedestrian 101c with reference to the road or pavement 110 level or ground level may be determined at the right sensor 102 based on a combination of the detected direction to the upper portion of the person or pedestrian 101c from the right sensor 102, the direction to the upper portion of the person or pedestrian 101c from the left sensor 102 received by the right sensor 102 from the left sensor 102, and the respective positions of the sensors 102. In addition, a location of the lower portion of the person or pedestrian 101c with reference to the road or pavement 110 level or ground level may be determined at the right sensor 102 based on a combination of the detected direction to the lower portion of the person or pedestrian 101c from the right sensor 102, the direction to the lower portion of the person or pedestrian 101c from the left sensor 102 received by the right sensor 102 from the left sensor 102, and the respective positions of the sensors 102.

Based on a difference between the determined locations of the upper and lower portions of the person or pedestrian 101c, the right sensor 102 may then estimate a height of the person or pedestrian 101c above the road or pavement 110 level or ground level.

Subsequently, the acceptance or rejection of the detection of the presence of the person or pedestrian 101c may be based on the estimated height of the person or pedestrian 101c above the road or pavement 110 level or ground level. For example, on a condition that the estimated height of the person or pedestrian 101c above the road or pavement 110 level or ground level is within a predefined range of values, the detection of the presence of the person or pedestrian 101c may be accepted, and on a condition that the estimated height of the person or pedestrian 101c above the road or pavement 110 level or ground level is outside a predefined range of values, the detection of the presence of the person or pedestrian 101c may be rejected. The predefined range of values may be values of heights that are acceptable for the type of 'targets' for which the presence sensing system should trigger, and hence for which the light-emitting units should be activated.

Referring now to Fig. 5, there is shown a schematic view of a computer- readable storage medium 500 according to an embodiment of the present invention, comprising a floppy disk 500. On the floppy disk 500 there may be stored a computer program comprising computer code adapted to, when executed in a processor unit, perform a method according to the present invention, such as a method 600 as described in the following with reference to Fig. 6.

Although only one type of computer-readable storage medium has been described above with reference to Fig. 5, the present invention encompasses embodiments employing any other suitable type of computer-readable digital storage medium, such as, but not limited to, a non-volatile memory, a hard disk drive, a CD, a DVD, a flash memory, magnetic tape, a USB stick, a Zip drive, etc.

Referring now to Fig. 6, there is shown a schematic flowchart of a method 600 for operating a presence sensing system according to an embodiment of the present invention. The presence sensing system comprises a plurality of sensors. Each sensor comprises a communication module adapted to transmit information to any one of at least neighboring sensors and receive information from any one of at least neighboring sensors by means of a communication link. Each sensor is adapted to sense whether an object or person is present within a corresponding sensing region. Each sensor is arranged at a distance from the other sensors. The sensors are configured such that information on the extent of the sensing region of each sensor is available at least to neighboring sensors.

The method comprises, for each sensor, sensing whether the object or person is present in the sensing region of the sensor, 601.

On a condition that presence of the object or person is sensed by the sensor,

609, at least one physical characteristic of the sensed object or person is detected, 602.

Based on the extents of the respective sensing regions corresponding to at least neighboring sensors, it is determined whether there is at least one other sensor that potentially can sense presence of the object or person, 603.

On a condition that at least one other sensor is identified that potentially can sense presence of the object or person, 610, the at least one physical characteristic of the sensed object or person is transmitted to the at least one other sensor, 604.

For each sensor that has sensed presence of the object or person and determined that there is at least one other sensor that potentially can sense presence of the object or person, the method 600 comprises, for each of the at least one other sensor, sensing whether the object or person is present, 605.

On a condition that presence of the object or person is sensed by the sensor, 611, at least one physical characteristic of the sensed object or person is detected, 606.

Based on a combination of the detected at least one physical characteristic with received at least one physical characteristic, it is determined whether the object or person is a true object or person such that the detection of its presence is to be accepted or a false object or person such that the detection of its presence is to be rejected, 607.

The light-emitting module of a lighting fixture is activated, 608, on a condition that the object or person has been determined by the sensor corresponding to the lighting fixture as being a true object or person such that the detection of its presence is to be accepted.

Referring now to Fig. 7, there is shown a schematic block diagram of a lighting system 200 according to an embodiment of the present invention. The lighting system 200 comprises four lighting fixtures 201. However, the lighting system 200 may comprise any integer number of lighting fixtures exceeding two, such as two, three, five, eight, ten, twelve, fifteen or twenty or more. Each lighting fixture 200 is arranged at a distance from the other lighting fixtures 201. Each lighting fixture 201 comprises a light-emitting module 202 adapted to emit light and a control module 203 adapted to control operation of the light-emitting module 202. The lighting system comprises a presence sensing system 100 such a described with reference to Fig. 2, for sensing presence of an object or person (not shown in Fig. 7). Each sensor 102 of the plurality of sensors 102 of the presence sensing system 100 is comprised in a corresponding lighting fixture 201. The control module 203 of each lighting fixture 201 is adapted to activate the light-emitting module 202 of the lighting fixture 201 on a condition that the object or person has been determined by the sensor 102 corresponding to the lighting fixture 201 as being a true object or person such that the detection of its presence is to be accepted.

In conclusion, a processing module is disclosed, which is for use in a presence sensing system adapted to sense presence of an object or person and to effect a change of a state of operation of a lighting system in response to sensing presence of the object or person and on a condition that the object or person has been determined as being a true object or person, such that the detection of its presence is to be accepted. The presence sensing system comprises a plurality of sensors, each of which is adapted to sense whether the object or person is present. The processing module is adapted to receive at least one physical characteristic of the sensed object or person detected by respective ones of at least two sensors of the plurality of sensors, and, based on the received physical characteristics of the sensed object or person, derive at least one three-dimensional physical characteristic of the sensed object or person. Based on the derived at least one three-dimensional physical characteristic, there is determined whether the object or person is a true object or person, such that the detection of its presence is to be accepted, or a false object or person, such that the detection of its presence is to be rejected.

While the present invention has been illustrated and described in detail in the appended drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplifying and not restrictive; the present invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.