WO2009133505A1

WO2009133505A1 - Illumination unit responsive to objects

Info

Publication number: WO2009133505A1
Application number: PCT/IB2009/051681
Authority: WO
Inventors: Lorenzo Feri; Tim C. W. Schenk; Martinus T. Bennebroek; Paulus H. A. Damink; Cornelis R. Ronda
Original assignee: Philips Intellectual Property & Standards Gmbh; Koninklijke Philips Electronics N.V.
Priority date: 2008-04-29
Filing date: 2009-04-24
Publication date: 2009-11-05
Also published as: TW200952559A

Abstract

The invention relates to an illumination unit (10, 10') comprising a light source, a light detector, and a control unit by which the presence of objects (4) in an operation area(3a) can be detected and the operation of the light source (11) can be adapted according to the detection results. In preferred embodiments, a plurality of such illumination units constitutes an illumination system (100) with each of its light sources repetitively emitting test emissions comprising a characteristic, individual code pattern that allows to identify light from said light source in a superposition of light from various origins. By detecting the presence of persons (4) in a roomitis for example possible to dim the lightemissions to a low level if nobody is present, thus saving power.

Description

ILLUMINATION UNIT RESPONSIVE TO OBJECTS

FIELD OF THE INVENTION

The invention relates to an illumination unit that is responsive to the presence of objects in an operation area, to an illumination system comprising a plurality of such units, and to a method for controlling illumination in response to the presence of an object.

BACKGROUND OF THE INVENTION

The US 2005/281030 Al discloses an LED (light emitting diode) lamp with an autonomously operating occupancy sensor for detecting the presence of e.g. a person in the room where the lamp is installed. When the sensor detects nobody, the lamp is dimmed or switched off to save power.

SUMMARY OF THE INVENTION

Based on this situation it was an object of the present invention to provide more robust and reliable means for illuminating an area of interest that are responsive to the presence of objects in said area.

This object is achieved by an illumination unit according to claim 1, an illumination system according to claim 9, and a method according to claim 15. Preferred embodiments are disclosed in the dependent claims. The illumination unit according to the present invention shall be responsive to the presence of objects in an operation area, for example to the presence of persons in a room, of passengers on a pathway, or of cars on a lane. The illumination unit comprises the following components: a) At least one light source for illuminating an area of interest, particularly the operation area or a part of it. The light source may comprise any device that is suited for the generation of light, for example LEDs, phosphor converted LEDs, organic LEDs (OLEDs), LASERs, phosphor converted LASERs, fluorescent lamps, halogen lamps, high intensity discharge (HID) lamps, and/or Ultra High Performance (UHP) lamps (wherein these light sources may additionally be used with filters and/or as a colored light source if desired). Moreover, the light source may be composed of a plurality of single elements, e.g. LEDs of different or identical colors, which are typically commonly or synchronously controlled and treated as one single entity in the context of the present invention. b) At least one light detector for detecting light and for providing a detection signal associated to said detected light, wherein the detected light may particularly comprise light that was emitted by the aforementioned light source and that was reflected by an object in the operation area. The light detector may for example comprise a photodiode, photocell or photosensor that is sensitive in the complete spectral range of visible light or a part of it. The detection signal will usually be an electrical signal like a voltage or a current that is indicative of the total amount of detected light. It should be noted that the term "reflected light" is to be understood in a broad sense here, i.e. as comprising light having interacted with an object in any way, for example (and most importantly) by reflection in the narrower sense, but also by refraction or diffraction. c) A control unit for evaluating the aforementioned detection signal with respect to the presence of an object in the operation area and for adapting the operation of the light source according to the evaluation result. The control unit may for example be realized in dedicated electronic hardware, in digital data processing hardware with associated software, or a mixture of both. The described illumination unit has the advantage that it uses light that was emitted by its own light source for detecting the presence of an object in the operation area. It is therefore not dependent on autonomous radiation of the object (e.g. the emission of infrared light by living beings) or on the availability of sufficient ambient light. Moreover, hardware effort is minimized as the very light source that shall illuminate the operation area (and that is therefore already present) is additionally used for detection purposes. Using the light of the own light source has furthermore the advantage to provide controllable, reproducible and well known illumination conditions that help to increase the reliability of the detection results. Moreover, the power emitted by the light source can typically be much higher than that of a secondary source that would typically be used for presence detection, e.g. an infrared LED, and this will consequently result in a much higher signal level at the detector and reliability in detection.

According to a preferred embodiment of the illumination unit, the control unit is designed such that the operation of the light source is dimmed from a high to a low level (including a level "zero", i.e. a complete switching off) if no objects are present in the operation area and vice versa (i.e. from a low to a high level if objects are present). This procedure is particularly useful if the objects of interest are persons in a room (e.g. employees in an office), passengers on a pathway, or cars on a road which require a high-level operation of the light source. Accordingly, power can be saved and the light source can be dimmed to a low level if no such users of the light are present in the operation area. The control unit may detect or infer the presence of objects in the operation area in various ways, for example from an increase of reflected light above a given threshold. In a preferred embodiment, the control unit is adapted to detect changes in the detection signal. Such changes in the detection signal will be indicative of changes taking place in the operation area, which will typically be due to the movement of an object like a person or a vehicle that is of interest for the illumination unit. Moreover, the detection of signal changes makes the procedure independent of a static baseline signal which may for example be affected by ambient light. It should be noted that the detection of changes will usually refer to some given timescale, for example to the interval between two subsequent regular detection periods of the light source for which the corresponding detection signals are compared. Objects will therefore usually only be detected if their movement velocity lies within a given range (e.g. between 1 m/h and 50 m/s).

According to a preferred embodiment of the invention, the light source repetitively emits test emissions of light into the operation area or into a part of it. Thus the operation area can continuously be monitored or scanned even in times when the "normal" illumination operation of the light source is dimmed to a (non-zero) low level or completely switched off. Moreover, the use of test emissions has the advantage that their occurrence, duration, intensity etc. are well known and adjustable, thus allowing to reliably detect this light falling on the light detector after reflection in the operation area. The test emissions are preferably integrated into the "normal" illumination operation of the illumination unit, i.e. without a change in the average intensity of the light source. The aforementioned test emissions may optionally comprise an individual code pattern. The pattern may for example comprise a particular spectral composition of the test emissions (e.g. red, green and blue) and/or a modulated intensity. The test emissions therefore carry a characteristic fingerprint that allows to assign measured reflections to the associated light source. The individual code pattern is particularly useful if a plurality of illumination units is used, as it allows to distinguish the test emissions of different light sources.

According to a further development of the invention, the illumination unit may be adapted to separately evaluate detected light that was emitted by another light source than the light source of the illumination unit and that was reflected by an object. The light detector and the control unit are then able to use for their detection procedure also light from other light sources, thus allowing to increase the reliability of their detection results, to the controlled spatial zone, and the scenarios they can cope with. A convenient way to achieve such a separate detection is the aforementioned use of coded test emissions. The control unit preferably comprises a memory for tracking (i.e. determining and storing) the actual number and/or the spatial position/distribution of objects in the operation area. The control unit may for example infer the (approximate) spatial position of an object based on the intensity of the light reflected by said object (a higher intensity would e.g. be an indication of the object being nearer to the light source/light detector). Moreover, knowing the net number of objects that are presently in the operation area will help to avoid errors, for example the misinterpretation of immobile objects as the absence of objects.

According to another embodiment of the invention, the illumination unit comprises an alarm unit that can be activated by the control unit, for example a loudspeaker, an alarm light, and/or a wireless alarm transmitter. The capability of the illumination unit to survey an operation area with respect to the presence of objects can then not only be used for the adaptive control of a light source, but also for the triggering of an alarm in case a predefined emergency situation has been detected. Possible applications of such an alarm unit are in an hospital, emergency, or (elderly) home application where e.g. a sudden breathing stop of small children shall be detected, where a minute sleep of car drivers, pilots, etc. shall be detected, where sudden movement changes or the complete absence of movements of persons shall be detected (e.g. at intensive care units), or where the intrusion of unauthorized persons shall be detected.

The invention further relates to an illumination system that is responsive to the presence of objects in an associated operations field, said illumination system comprising a plurality of illumination units each of which comprises : a) at least one light source; b) at least one light detector for detecting light and for providing an associated detection signal, wherein the detected light may particularly comprise light that was emitted by said light source and reflected by an object in an operation area associated to the illumination unit; c) a control unit for detecting the presence of an object in at least a part of the operation field taking into account said detection signal (and perhaps further information), and for adapting the operation of the light source accordingly. The illumination system may particularly be composed of a plurality of the illumination units of the kind described above, wherein the operation field is the sum of all operation areas of said units. Due to this correspondence, reference can be made to the above description of the illumination unit for more information on the details, advantages and modifications of the illumination system. According to a preferred embodiment of the illumination system, its illumination units are adapted to distinguish light reflected from an object with respect to the illumination unit that is the origin of this light. In this way the illumination units get the capability of a new and much more elaborated evaluation of their detection signals, for example with respect to a spatial resolution of the whereabouts of an object and/or to the movement direction and speed of an object.

In another embodiment of the illumination system, its illumination units are adapted to repetitively emit test emissions that comprise individual, linearly independent code patterns. It will then be possible to identify each illumination unit as the origin of a measured light contribution based on the imprinted code pattern. The "linear independence" of the code patterns means in this context that none of the coded test emissions can be generated by a weighted superposition of the residual coded test emissions. It will therefore always be possible to unambiguously identify the contribution of a particular light source even if all light sources contribute with their test emissions to a measurement.

According to a further development of the illumination system, the illumination units of that system comprise transmitter units and receiver units for exchanging information signals, for example RF or IR transmitter/receiver units.

The aforementioned information signals that are exchanged between the illumination units may particularly be encoded in light emissions of their light sources. Thus the already available hardware, i.e. the light sources and the light detectors, is advantageously used as transmitter and receiver for the information exchange. The information signals may in general encode any kind of information that shall be communicated between the illumination units, for example information about their dimming level. In a preferred embodiment, the signals comprise information about the detection of objects in the operation field, for instance their number and (approximate) location and/or the identity of the illumination unit by which they were detected. Moreover, the illumination units are adapted in this case to take this information into account when controlling their own light source. If one illumination unit detects the presence of an object, this information can thus be communicated to other illumination units that may not yet have detected the object. The coordinated operation of the components of the illumination system can thus generate synergy effects that considerably increase the performance of the system. This may optionally also comprise the combination of information coming from several illumination units.

The aforementioned coordinated operation may particularly comprise that, based on the object detection in the operation area of one first illumination unit, also all illumination units in a given range of that first unit can be dimmed. The "given range" can in this context optionally further be classified into different sub-ranges according to the distance of the illumination units from the first one. Thus it is for example possible to define sub-ranges with respect to the number of relay-stations via which the information about the detection of an object was forwarded, i.e.

"sub-range 1" comprises all illumination units that can directly communicate with the first illumination unit (which detected the object in its operation area), e.g. via optical signals, "sub-range N" comprises all illumination units that can directly communicate with illumination units of sub-range N-I (and that are not yet members of an already defined sub-range with number < N) for N = 2, 3, ... .

Based on their sub-range number, illumination units can then be dimmed to a certain level after an object detection. For instance in sub-range 1 they can be dimmed to 70% and in sub-range 2 to 50% etc.

The illumination system may further comprise an occupancy detector for detecting the presence of an object and for activating the illumination units accordingly. The occupancy detector may use any technology for its purpose, for example a passive IR detection, ultrasonic detection, RF (radiofrequency) detection or the like, and it may particularly be a low-cost device that is only used in a standby mode to switch on the fine tuning capabilities of the illumination system if necessary.

The invention further relates to a method for controlling illumination in response to the presence of an object in an operation area, the method comprising the following steps: a) Emitting test light into the operation area by at least one light source. b) Detecting emitted test light that was reflected by an object. c) Evaluating the detected test light with respect to the presence of an object in the operation area and adapting the operation of the light source accordingly.

The method comprises, in general form, the steps that can be executed with an illumination unit and system of the kind described above. Therefore, reference is made to the preceding description for more information on the details, advantages and improvements of that method. In the following various exemplary approaches will be summarized by which a single illumination unit or an illumination system can localize an object in the operation area/field. In a first particular embodiment, the illumination unit may be adapted to determine the individual contributions of different light sources to the detection signal of a light detector. This approach is based on the observation that the light received and determined by a particular light detector - and thus also the associated detection signal - will usually comprise a superposition of contributions from all (active) light sources. For some localization approaches it is however necessary to know the amount of reflected light that corresponds to a particular light source. This information can be obtained if the illumination unit is adapted in the aforementioned way. The determination of individual contributions of the light sources may for example be based on different colors of the light sources, wherein the light detector should be able to provide spectrally resolved measurements in this case. Preferably, the distinction between different contributions is however based on individual code patterns of the kind mentioned above that are imprinted onto the emissions of the light sources. Thus the light sources may for example be modulated with different frequencies such that the illumination unit can discriminate their contributions based on a Fourier analysis of a recorded detection signal. Knowing the spatial arrangement of the light sources and the light detector(s) as well as the individual contributions of the light sources to an observed detection signal allows in principle to determine the position of the object of interest (e.g. if all light sources emit with a known intensity and if the reflectivity of the object is known or at least the same for the light of all light sources, then the position of an object may be estimated with a triangulation like procedure.)

In another embodiment, the illumination unit is adapted to identify the light source with the largest contribution to the detection signal, preferably the largest normalized contribution. This approach is related to the aforementioned one, but requires only the identification of one particular contribution and not the (quantitative) determination of various contributions (if the latter are known, it is however readily possible to identify the largest contribution). The "normalization" refers in this context to the intensity of the initial light emission of the individual light sources, i.e. the absolute value of a contribution of a light source to the detection signal is normalized with the original emission intensity of said light source as the weakness/strength of the emissions is neutralized by the normalization. A nearby but weak light source will therefore not be surpassed by a remote but strong light source. Knowing the light source with the largest normalized contribution allows to locate the object of interest approximately "at" said light source (e.g. vertically below a light source embedded in the ceiling). It should be noted that the normalization can be skipped if all light sources emit test emissions with the same intensity. According to another approach, the illumination unit may be adapted to determine the time-of-flight that a particular light ray needs from its emission by a light source via its reflection by the object to its detection by a light detector. Via the speed of light, the time-of-flight is related to the distance the light had to travel, which already provides a (coarse) positional information about the object with respect to the considered light source and light detector.

In a further development of the aforementioned approach, the illumination unit is further adapted to determine the desired spatial information from a triangulation of at least three different times-of- flight which were determined as described above. Thus the complete spatial coordinates of the object can be determined, wherein the accuracy increases with the number of considered times-of- flight.

According to still another approach, the illumination system is adapted to determine the light detector that received the highest amount of light which was emitted by (any number of) the light sources and reflected by the object. This approach is based on the fact that the total amount of light that stems from different light sources and is reflected by the object usually propagates with decaying intensity isotropically from the object in all directions. The light detector closest to the object will therefore see the highest intensity of this light, and its position can be taken as an estimation of the position of the object. An advantage of this approach is that the individual contributions of the light sources need not be separated from each other. Two or more of the different approaches to determine spatial information about the object that were described above can of course be combined in order to increase the accuracy and robustness of the localization.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. These embodiments will be described by way of example with the help of the accompanying drawings in which: BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic perspective view of a room comprising an illumination system according to the present invention;

Figure 2 is a view onto the ceiling of the room in Figure 1; Figure 3 illustrates an On-Off-Keying modulation of the light emissions;

Figure 4 illustrates a Duty-Cycle BiPhase modulation of the light emissions.

Like reference numbers in the Figures refer to identical or similar components.

DETAILED DESCRIPTION OF EMBODIMENTS

Many conventional systems that allow for the detection of human presence or motion are based on passive infrared (PIR) sensors attached to the ceiling, which detect the IR radiation from human bodies. Such PIR sensors offer however poor resolution, i.e., usually the resolution equals the room size. Hence, these sensors are mainly used to detect the presence of a human, rather than to determine an exact position in a room. Cameras would allow for higher resolution estimation of the position of persons in a room, but have other shortcomings like cost and privacy issues. Moreover, conventional cameras need background light to be able to record images with reasonable contrast.

To address the above issues, a method and an illumination unit/system are proposed here that provide reliable and high resolution information about the (3D) position of (moving) objects, e.g. humans or vehicles, in indoor or outdoor environments, based on lamps with an integrated photosensor. Other (optional) features of this proposal include:

Each light source sends regular invisible test emissions into the environment, while at the same time the integrated photosensor measures the reflected signals. In this way, each illumination unit can have an updated estimation of the channel (i.e. of the part of the total detected light that is due to one particular light source) around it.

A change in the strength of the received test emissions indicates the presence of an object, e.g. a person, near the illumination unit sending that test emission.

By measuring and combining all channel responses, a high resolution "map" of the objects in the environment can be made. With a high number of light sources and sensors, this allows for 3D imaging.

Preferably each light source outputs orthogonal test emissions, which allows for independent measurements. Various multiple access techniques can be used for this, e.g. Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), or Frequency Division Multiple Access (FDMA). - The different illumination units may communicate the observed

(change in) channel values with each other to come to a higher resolution observations.

The aforementioned communication between the illumination units may be carried out using the visible light of the actual light sources. - The automatic control of light sources.

Figure 1 illustrates in a schematic perspective view a room 1 comprising an illumination system 100 according to the above general concepts. The illumination system 100 comprises of a plurality of illumination units 10, 10' that are distributed in a regular array on the ceiling 2 of the room 1. Each of the illumination units comprises a light source and an associated light detector (photosensor). The light sources of the illumination units repetitively emit test emissions into the room 1 to detect the presence of objects of interest in the room, e.g. of persons 4 moving on the floor 3.

Figure 2 shows in a plan view some illumination units 10 of the illumination system 100 in more detail. Each illumination unit 10 comprises several components, namely: a light source 11, e.g. an LED; a light detector 12, e.g. a photodiode; a control unit 13, e.g. a microcontroller or a dedicated integrated circuit (IC), with a memory 14 (e.g. RAM); - optionally an alarm unit 15, e.g. a loudspeaker or an antenna for transmitting wireless communication signals.

Returning to Figure 1, the operation of the illumination system 100 will now be described in more detail. It was already mentioned that each of the illumination units 10, 10' (or, more precisely, its light source) repetitively emits test emissions into the room 1. The test emissions of the illumination unit with reference number 10 will for example cover an associated "operation area 3 a" of the floor 3. The environment and objects 4 in said operation area 3a will reflect the test emissions, and a part of the reflected light will return to the illumination unit 10 from which it was emitted. The light detectors 12 of the illumination unit 10 can then detect the reflections (together with other, e.g. ambient light) and communicate corresponding detection signals to the associated control unit 13. The control unit 13 will thus be able to detect an object 4, for example due to changes in detection signals associated to a movement of said object, and to control the light source 11 of the illumination unit 10 accordingly. This control may particularly include the powering up of the average intensity of the light source if a person 4 is in the associated operation area 3a; similarly, it may include the dimming of the light source if no person 4 is detected. Figure 1 also indicates that test emissions by the illumination unit 10 may also reach, e.g. via the reflection by the object 4, another illumination unit 10'. In order to allow the illumination units 10, 10' to distinguish between reflections from different light sources/illumination units, it is preferred that the test emissions of each illumination unit will carry a characteristic fingerprint that allows to distinguish them from all other test emissions that might be superposed in one of the light detectors.

The spatial distribution of the illumination units 10, 10' together with the physical properties of their light sources and light detectors will define the resolution and coverage area of the illumination system 100. Since each illumination unit can operate independently and orthogonally with respect to the others, a safe choice is to have partial overlaps in the operation areas 3a that each individual illumination unit 10 covers. That is very convenient also, since for the lighting purpose the illumination units have to be placed at a similar distance anyway.

It is further noted that it is possible to make an illumination unit "listen" to only the test emissions from the light source in the same illumination unit or to all test emissions from all illumination units. In the former case each illumination unit will simply discard the portion of the signal orthogonal to its own test emission, whereas in the latter case each illumination unit will detect all the test emissions. As exemplified in Figure 1, part of the signal from illumination unit 10 may leak into a neighboring illumination unit 10'. In this situation, this neighboring illumination unit 10' has the option of estimating or discarding the received signal.

By gathering the information obtained in all illumination units, it is possible to draw conclusions about the (movements/locations of) objects in the monitored environment. This can be done in a centralized solution, where all illumination units 10, 10' communicate their findings to a master controller (not shown), e.g. using a wired or wireless backbone. Alternatively, however, it can also be done in an ad hoc manner, where each illumination unit shares its observations with its neighboring illumination units. For this again a RF wireless link could be used. Since the light of the light sources is modulated anyway, it is however preferred to embed the information in the visible light of the illumination unit. The receiving illumination units can then combine that information with their own observations and propagate it further or just relay the original message further. The following table gives an example of information available in (and optionally to be forwarded by) the illumination unit 10 having the neighbors 10', 10a, 10b, 10c. The table contains which test emissions the illumination unit 10 observed in the previous time slot, together with the strength at which the test emissions were observed and whether there was a variation observed in the strength compared to the previous observation period. Additionally, the illumination unit 10 relays the information it received from another illumination unit 10'.

More simple systems can be implemented that only locally observe the variations in the channel or simply the variations in the received total signal (a figure of merit for this can be the variation in the reflected power). In that way each illumination unit can draw a conclusion about the presence of moving objects in its close surroundings. Merging of decisions and observations do not take place in such a simple system.

The above procedures can be applied in the illumination system 100 to switch on, or change the dimming level of, the light sources in the illumination units that observe a change in their channel due to moving objects. When the observations are shared between the illumination units, also the changes in reflections ending up at other illumination units can be taken into account. This will result in a more accurate switching of the illumination units.

As mentioned above, for a good operation of the system, it is necessary that different illumination units use different and orthogonal test emissions. Borrowing from communication theory, it is possible to use time/frequency/code division multiple access techniques. It should be noticed that the system could operate properly also in the case when non-perfect orthogonality is ensured between the various signals. In that case, signal processing should compensate for that.

Figure 3 illustrates in this context different binary control signals ("0", " 1 ") over one basic time unit T that may be used in combination with a pulse width modulation (PWM) control of the light sources 11 to encode data (e.g. an individual number identifying the light source and/or information that shall be exchanged between the illumination units). In order to guarantee the required illumination, one can modify the duration of pulses (i.e. the duty cycle of the signal) - mo dify the amplitude A o f pulses .

In this scheme, "0" and "1" will have different widths. Nevertheless, one can compensate this by using balanced codes (i.e. having the same number of bits 0 and 1). Therefore the width of pulses, averaged over a code-word, will be exactly the average value between the "0" and "1" widths. Figure 4 illustrates the different control signals ("0", "1") for one basic time unit T in case of a generalization of BiPhase (BP) modulation, to allow an arbitrary duty cycle. When the duty cycle equals 50%, this "Duty Cycle BiPhase" (DC-BP) approach degenerates to BP modulation. In this case, the unique code that each LED is assigned is carried in the signal by transmitting "0" and "1" (as in Figure 3) accordingly. In order to guarantee the required illumination, one can modify the duration of pulses (i.e. the duty-cycle of the signal) - modify the amplitude A of pulses.

It should be noticed that in a large environment, a cheap presence- detector 50 can be used to wake-up all illumination units 10 and set them in a monitoring state (at a low level of illumination and transmitting test emissions), whereas the disclosed illumination system 100 can allow higher resolution detection and fine-tuned illumination.

Since the resolution of the presented illumination system is much higher than that of traditional presence detection systems, also other application scenario become possible, e.g.:

Detection of the presence of people in environments: The system could detect and track whether people entering a room have also left the room.

This is of relevance in e.g. museums or shops before closing time. This information could also be used to not switch off the light when people are hardly moving (e.g. behind their PC), which currently often happens in PIR systems. The system can also be used as surveillance system and home protection (e.g. thief detection). The user can switch the alarm system on and off.

If it is on, no person should enter the rooms etc., and an alarm can be sent when this is nevertheless occurring.

The system can be used for automatic navigation in large buildings, wherein the route to follow may be indicated by activated lights. - The system could be generalized to a distributed 3D imaging system of a room using illumination units installed in the room.

Applications of the invention are in the area of smart/energy efficient lighting systems that can adapt the illumination depending on the occupancy of the environment or more generally 3D indoor or outdoor imaging systems. Such systems are of particular interest in office buildings, where automatic control of light sources is desirable in order to avoid misuse of light sources (illumination units left in an on-state although nobody is benefiting from that) and, consequently, cut electrical costs. In summary, the invention discloses a method and system that can provide high resolution information about the position of (moving) objects, e.g. humans, in indoor or outdoor environments. When coupled to a lighting system, the aforementioned system allows a very precise control of the light sources that are relevant for the people occupying the environment, e.g., only the light sources in the close surrounding of people are switched on. This brings a clear advantage in terms of consumed electrical power.

The invention discloses the use of an array of transceiver devices that can independently monitor the environment and take independent decisions about the presence/movement of people. In the preferred embodiment the transmitter is a visible light source and the receiver is a photosensor built in the illumination unit/luminaire. Each transmitter sends regular test emissions into the environment while at the same time the receiver coupled to the transmitter measures the reflected signals. To this end, the illumination unit transmits invisible identifiers in the light, using "coded light". In this way, each transceiver can have an updated estimation of the channel around it. The sensor can then distinguish the relevant variations in the channel of its own illumination unit and, subsequently, decide about the illumination status of the illumination unit. When illumination units also observe the variations in the channel originating for the other illumination units and share that, a more precise system can be constructed. Finally it is pointed out that in the present application the term

"comprising" does not exclude other elements or steps, that "a" or "an" does not exclude a plurality, and that a single processor or other unit may fulfill the functions of several means. The invention resides in each and every novel characteristic feature and each and every combination of characteristic features. Moreover, reference signs in the claims shall not be construed as limiting their scope.

Claims

CLAIMS:

1. An illumination unit (10, 10') that is responsive to the presence of objects (4) in an operation area (3a), comprising a) at least one light source (11); b) at least one light detector (12) for detecting light and for providing an associated detection signal, wherein said detected light may comprise light that was emitted by said light source and reflected by an object (4) in the operation area; c) a control unit (13) for evaluating said detection signal with respect to the presence of an object (4) in the operation area and for adapting the operation of the light source accordingly.

2. The illumination unit (10, 10') according to claim 1, characterized in that the operation of the light source (11) is dimmed from a high to a low level if there are no objects (4) in the operation area (3a) and vice versa.

3. The illumination unit (10, 10') according to claim 1, characterized in that the control unit (13) is adapted to detect changes in the detection signal.

4. The illumination unit (10, 10') according to claim 1, characterized in that the light source (11) repetitively emits test emissions into the operation area (3a) or a part of it.

5. The illumination unit (10, 10') according to claim 4, characterized in that the test emissions comprise an individual code pattern.

6. The illumination unit (10, 10') according to claim 1, characterized in that it is adapted to separately evaluate detected light that was emitted by another a light source and reflected by an object (4).

7. The illumination unit (10, 10') according to claim 1, characterized in that the control unit (13) comprises a memory (14) for tracking the actual number and/or spatial position of objects (4).

8. The illumination unit (10, 10') according to claim 1, characterized in that it comprises an alarm unit (15) that can be activated by the control unit (13).

9. An illumination system (100) that is responsive to the presence of objects (4) in an associated operation field (3), comprising a plurality of illumination units (10, 10') each of which comprises: a) at least one light source (11); b) at least one light detector (12) for detecting light and for providing an associated detection signal, wherein said detected light may comprise light that was emitted by said light source and reflected by an object (4) in an associated operation area (3a); c) a control unit (13) for detecting the presence of an object (4) in at least a part of the operation field taking into account said detection signal, and for adapting the operation of the light source accordingly.

10. The illumination system (100) according to claim 9, characterized in that the illumination units (10, 10') are adapted to distinguish light components with respect to the illumination unit (10, 10') by which they were emitted.

11. The illumination system (100) according to claim 9, characterized in that the illumination units (10, 10') repetitively emit test emissions that comprise individual, linearly independent code patterns.

12. The illumination system (100) according to claim 9, characterized in that the illumination units (10, 10') comprise transmitter units and receiver units for exchanging information signals, particularly information signals that are encoded into light emissions of the illumination units (10, 10').

13. The illumination system (100) according to claim 12, characterized in that the information signals comprise information about the detection of objects (4) in the operation field (3), and that the illumination units (10, 10') are adapted to take this information into account when controlling their own light source (11).

14. The illumination system (100) according to claim 9, characterized in that it comprises an occupancy detector (50) for detecting the presence of an object (4) and for activating the illumination units (10, 10').

15. A method for controlling illumination in response to the presence of an object (4) in an operation area (3a), comprising a) emitting test light into the operation area (3 a) by at least one light source (11); b) detecting emitted test light that was reflected by an object (4); c) evaluating the detected test light with respect to the presence of an object (4) in the operation area (3a) and adapting the operation of the light source (11) accordingly.