WO2009093191A2

WO2009093191A2 - Lighting system comprising a light source, a controller and a light sensor

Info

Publication number: WO2009093191A2
Application number: PCT/IB2009/050239
Authority: WO
Inventors: Marcellinus P. C. M. Krijn; Ramon P. Van Gorkom; Martin J. J. Jak
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2008-01-25
Filing date: 2009-01-22
Publication date: 2009-07-30
Also published as: WO2009093191A3

Abstract

The invention relates to a lighting system (10), a controller (100) for use in the lighting system, a light sensor (20) for use in the lighting system, a method of determining the contribution of the light emitted by the light source (30) to an illumination level and a computer program product. The lighting system comprises a light source for emitting modulated light (40), a light sensor for sensing the illumination level over time to capture the modulation of the modulated light, and a controller being configured for receiving a sense signal (SS) and for receiving a parameter (P) defining the modulated light to determine the contribution of the modulated light to the sensed illumination level. The effect of the measures according to the invention is that due to the known modulation of the modulated light emitted by the light source, the contribution of the light source in the sensed illumination level can be reconstructed relatively accurately.

Description

LIGHTING SYSTEM COMPRISING A LIGHT SOURCE, A CONTROLLER AND A LIGHT SENSOR

FIELD OF THE INVENTION:

The invention relates to a lighting system comprising a light source, a controller and a light —sensor.

The invention also relates to a controller and a sensor for use in the lighting system.

BACKGROUND OF THE INVENTION:

Such lighting systems are known per se. They are used, inter alia, as indoor lighting systems for general lighting purposes, for example, for office lighting or shop lighting, for example, shop window lighting.

Such a lighting system is known from, for example, US patent application US 2005/0047133. In this patent application an illumination management system is disclosed which includes a first LED that outputs a first signal when exposed to a first spectrum of light. The first signal indicates the intensity of light of the first spectrum. Also included is a second LED that outputs a second signal when exposed to a second spectrum of light. The second signal indicates the intensity of light of the second spectrum. The second spectrum includes at least some wavelengths that are not in the first spectrum. Also included is a light control circuitry coupled to the first and second LEDs, and configured to generate a lighting control signal that can be output to one or more lights to adjust the lights to a desired level. The illumination management system further includes an infrared LED for detecting the contribution of the sunlight to the overall illumination.

A disadvantage of the known lighting system is that the determination of the contribution of the artificial light to the overall illumination is not accurate enough.

SUMMARY OF THE INVENTION:

It is an object of the invention to provide a lighting system which relatively accurately determines the contribution of light emitted by the light source to the overall illumination level. According to a first aspect of the invention the object is achieved with a lighting system comprising: a light source for emitting modulated light, a light sensor for sensing the illumination level over time to capture the modulation of the modulated light, and to provide a sense-signal to a controller, the controller being configured for receiving the sense-signal, the controller further comprising a parameter defining the modulated light from the light source to determine the contribution of the modulated light to the sensed illumination level.

An effect of the lighting system according to the invention is that the use of a light source emitting modulated light and the use of a light sensor arranged for capturing the modulation of the modulated light enables the controller to substantially directly and accurately reconstruct the modulated light impinging on the light sensor by using the parameter defining the modulated light. As a result, the controller is able to relatively accurately determine the contribution of the light emitted by the light source to the overall illumination level. The illumination level sensed by the light sensor is the sum of the light emitted by the light source and the ambient light which impinges on the light sensor. The ambient light may, for example, include daylight which is transmitted by a window or may include light emitted by other light sources, or may include light reflected from walls or objects. The controller comprises the parameter or, for example, receives the parameter from the light source or from a database connected to the controller. The parameter defines the modulated light. Because this parameter is known, the controller can reconstruct the modulated light as emitted by the light source and as such determine the contribution of the modulated light to the measured illumination level at the light sensor. This contribution may, for example, be subtracted from the sensed illumination level to determine, for example, the contribution of the ambient light which impinges on the light sensor.

In the known illumination system a mathematical algorithm is used to ascertain from the first LED, the second LED and the infrared LED the contribution of artificial lights and of natural sunlight. The use of an infrared LED to determine the contribution of sunlight to the overall illumination level is not very accurate, as the contribution to the overall illumination due to reflection of the sunlight is not considered. Furthermore, the distinction between artificial light sources and sunlight is made by using the different spectral characteristics of the artificial light sources and by using the fact that the artificial light sources do not emit infrared light. These assumptions limit the usability of the known illumination system and require an extensive calibration of the illumination system, which may even depend on the position of the light sensor relative to the light source to allow accurate determination of the contribution of the light emitted by the light source to the overall sensed illumination level. In the lighting system according to the invention, the contribution of the light emitted by the light source can be reconstructed using the sense- signal and the parameter defining the modulated light. The parameter enables the controller to reconstruct the modulated light emitted by the light source which impinges on the light sensor. By using this reconstruction of the modulated light the controller can relatively accurately determine the contribution of the light emitted by the light source to the overall, sensed illumination level and thus can relatively accurately determine the level of the ambient light. Subsequently, the controller may control the light source such that the illumination level as measured by the light sensor substantially corresponds to a predetermined illumination level.

A further benefit of the lighting system according to the invention is that the lighting system is able to regulate the illumination level, while efficiently utilizing the ambient light. The lighting system according to the invention is able to determine the contribution of the light emitted by the light source to the illumination level sensed by the light sensor. As a result, the lighting system can relatively quickly and accurately determine the ambient light contribution to the illumination level at the light sensor and may adapt the light emitted by the light source such that the light source only contributes the light required to generate the predetermined illumination level at the light sensor. Consequently, the lighting system is able to substantially fully utilize the daylight contribution to the illumination level, while maintaining a substantially constant illumination level in the light sensor, for example, at a desk in an office or at a predetermined location in the office. An even further benefit of the lighting system according to the invention is that the controller of the lighting system according to the invention is able to determine the contribution of the light emitted by the light source to the overall sensed light at substantially any location relative to the light source. As a result, the light sensor may be moved to the location where the illumination level should substantially comply with a predetermined illumination level. The local change in ambient illumination can directly be compensated by the light source, using the sense-signal, as the controller is able to discriminate between the contribution of the light emitted by the light source and the remainder of the light impinging on the light sensor. Thus, continuous measurement of the illumination level and the determination of the contribution of the artificial light to this overall illumination level may be used to locally control the illumination level without the need for extensive calibration procedures. A user may, for example, change from one desk to another, and by only taking his light sensor with him, the lighting system is able to locally determine the contribution of the ambient light and the modulated light to the overall sensed illumination and adapt the modulated light such that the sensed illumination at the new location substantially corresponds to the predetermined level.

In this document, "illumination level" is intended to mean a luminous flux incident on a unit area and is used throughout this document to include both the intensity level of the light and/or the spectrum of the light sensed or generated by the lighting system. In an embodiment of the lighting system, the light sensor is configured for sensing spectral information from the sensed illumination level, and the light source is configured for altering the spectrum of the emitted modulated light. A benefit of this embodiment is that the lighting system is able to adapt both the intensity and the spectrum of the illumination level as sensed by the light sensor. This enables the lighting system to be regulated such that the illumination level at the light sensor comprises a predefined color temperature, or comprises a predetermined variation of the color temperature, while the determination of the contribution of the modulated light to the overall illumination level makes it possible to substantially fully utilize the ambient light.

In an embodiment of the lighting system, the controller is configured for generating a drive signal for driving the light source to determine the modulation of the modulated light. A benefit of this embodiment is that the controller, for example, may adapt the modulation of the modulated light to better match the local requirements. For example, in a room in which a 100Hz television system is running, modulation of the modulated light may interfere with the modulation of the television system. By tuning the modulation frequency away from the frequency used by the television system, the interference may be reduced or prevented. Furthermore, other modulated light sources which are not controlled by the controller of the lighting system may be present in a room. These may interfere with the determination of the contribution of the modulated light emitted by the light source to the overall illumination level. By altering the modulation mode, the discrimination between light originating from the light source and light originating from other modulated light sources may be improved.

In an embodiment of the lighting system, the drive signal comprises at least one of the group comprising: amplitude modulation, frequency modulation, phase modulation, pulse-height modulation, pulse-width modulation, or a combination thereof, and the parameter comprises at least one of the group comprising: modulation frequency, modulation depth, modulation phase, pulse-height, pulse-width and spectral information. The modulation may be, for example, an analog modulation and/or a digital modulation. For example, a combination of pulse-width and pulse-height modulation enables the controller to drive the light source to provide modulated light which may be used to discriminate between light emitted by the light source and ambient light, while the average lumen output of the light source remains substantially constant.

In an embodiment of the lighting system, the modulation is imperceptible by human senses. Imperceptible by human senses in this context means that the modulation does not impose a physical sensation on any of the human senses directly, such that the human would be aware of the modulation. The human senses include, for example, sight, hearing and feeling. Preferably the modulation is chosen such that the frequency, for example, exceeds 100 Hz, so that the modulation of the light source is not perceivable by sight. Alternatively, the modulation of the light emitted by the light source, for example, exceeds 10 kHz to prevent the modulation frequency from being perceived via audible noise generated by the light source or by the power converter of the light source.

In an embodiment of the lighting system, the controller is configured for driving at least two light sources by generating at least two drive signals, a phase of the at least two drive signals being different. By altering the phase of the at least two drive signals, the controller can relatively easily discriminate between the light emitted individually by the at least two light sources. For example, at a first point in time the sense signal only comprises ambient light and modulated light from a first light source, while at a second point in time (different from the first point) the sense-signal comprises either a combination of the modulated light from the first and a second light source together with ambient light, or the sense-signal comprises modulated light from the second light source together with ambient light. Knowing the phase difference enables the controller to clearly discriminate between the light emitted by the at least two light sources and enables the controller to individually control the contribution of each of the at least two light sources to the overall illumination level sensed at the light sensor. In an embodiment of the lighting system, the parameter comprises at least one of the group comprising: modulation frequency, modulation depth, modulation phase, pulse- height, pulse-width and spectral information.

In an embodiment of the lighting system, the lighting system is configured to periodically calibrate the lighting system to update the parameters. The periodic calibration may, for example, be used to relate the sensed modulation depth of the modulated light emitted by the light source to the drive signal provided by the controller. This calibration may, for example, be done at night when the offices are empty and would only require a few seconds. This periodical calibration would also reduce inaccuracy of the lighting system due to aging effects of the light source or of the plurality of light sources. Furthermore, the calibration may include a spectral calibration of the light emitted by the light source. Especially when the light emitted by the light source is not a substantially primary color but comprises a multi-color output spectrum or even a substantially continuous spectrum, the spectrum may alter due to aging effects, which may be taken into consideration after the calibration. The calibration may require an update of the parameter or parameters which define the modulated light from the light source.

In an embodiment of the lighting system, the controller is connected to a database for storing and/or retrieving the parameter.

In an embodiment of the lighting system, the controller uses the spectral information from the light sensor to control the spectrum of the light emitted by the light source to maintain the spectrum of the light impinging on the light sensor substantially constant. The spectrum of the light impinging on the light sensor may change due to several reasons: for example, the contribution of sunlight changes, for example, when the sun is blocked by clouds or by sun-screens. Alternatively, the spectrum of the light impinging on the sensor may change because a user switches on another lamp in the room, of which part of the light also impinges on the sensor. If the other lamp emits a different spectrum of light, the spectrum as measured by the light sensor changes. Also people moving through a room may alter the spectrum of the light due to reflections from these people and/or due to blocking of specific contributions to the light impinging on the light sensor. The controller receiving the altered sense signal may adapt the spectrum of the light emitted by the light source to substantially correct for the altered sense-signal.

Alternatively, the controller uses the spectral information from the light sensor to control the spectrum of the light emitted by the light source to maximize the color rendering index of the light impinging on the light sensor. The color rendering index indicates the ability of light to reproduce the color of an object illuminated by the light. The color rendering index is determined by the spectrum of the light impinging on the object. Two light sources which emit, for example, substantially the same color may have a different color rendering index depending on the individual spectral content of the light emitted by the two light sources. The color rendering is compared with the color rendering when the object is illuminated by a black-body-radiator. When the color of the light impinging on the sensor changes, the color rendering ability of the light changes. The controller may use the modulated light to amend the spectrum of the light sensed by the light sensor such that the sensed illumination level has the highest color rendering index possible. In a further embodiment, the controller uses the spectral information from the light sensor to ensure that the light impinging on the light sensor comprises a predetermined intensity and/or variation of light of a specific color blue, the specific color blue reducing the melatonin concentration in a human. It is well known in the art that light of the specific color blue influences the melatonin production in humans and that the level of melatonin influences the alertness of humans. So, the light illuminating a room may comprise a predetermined intensity of light of the specific color blue and/or may comprise a predetermined variation of the light of the specific color blue during a day. When the light source has, for example, a surplus of different light emitters, the light source may have several means to generate light of a predetermined color. The controller may, for example, choose to generate the predetermined color while maintaining the level of light of the specific color blue to the required level to influence the level of alertness of the humans in the room. In a further embodiment, the controller uses the spectral information from the light sensor to maximize the efficiency for generating a predetermined color of the light impinging on the light sensor. The light source may, for example, comprise different light emitters, for example, a combination of a low-pressure gas discharge lamp and a plurality of light emitting diodes. The controller may choose a specific combination of light emitters such that the predetermined color is produced at a minimum energy consumption. Light emitting diodes typically emit light of a predominant color having a relatively narrow spectral bandwidth around a center wavelength. The use of light emitting diodes enables the controller to efficiently add light of the predominant color at the relatively narrow bandwidth and at a specific intensity to the emission spectrum of the light source to generate the predetermined color. Especially when the lighting system is used in office buildings, the energy consumption is a very important issue and should be controlled for environmental and cost reasons. Light of a predominant color comprises light of a predefined spectral bandwidth around a center wavelength. For example, a light emitting diode emitting light of the predominant color Blue emits light at the center wavelength of, for example, 470 nanometer, having a spectral bandwidth of, for example, 10 nanometer. When using light emitters which emit the predominant colors Red, Green and Blue in the lighting system according to the invention, the lighting system according to the invention is able to emit substantially any color (including white) within a triangle as defined by the three predominant colors in the CIE color diagram. The predominant colors Red, Green and Blue are also indicated as primary colors. Also other combinations of light emitters emitting other predominant or primary colors may be used in the lighting system, for example, Red, Green, Blue, Cyan, Yellow and White.

In an embodiment of the lighting system, the controller generates the drive signal in dependence on a clock. The clock determines the time of day and thus may be used to determine, for example, the required stage in the circadian rhythm of a human. Such a lighting system may also be useful for plants, for example in horticulture and/or for animals, for example, animal well-being and/or productivity on animal farms. The light emitted by the lighting system may be adapted to comply with the light associated with the required stage in the circadian rhythm.

Alternatively, the controller generates the drive signal in dependence on a calendar. The controller may take specific seasonal variations into account when controlling the light emitted by the light source. Again, the use of the calendar may aid in providing light corresponding to the circadian rhythm or may aid in changing the circadian rhythm of a human.

The controller may also generate the drive signal in dependence on manual input from manual input means. A human may, for example, override the programming of the controller to generate the lighting levels and colors of his choice.

The controller may further generate the drive signal in dependence on biosensor input from a bio-sensor, the bio-sensor being arranged for sensing the biological state and/or emotional state of a user. By measuring the biological state of the user, the current state of the circadian rhythm may be determined and/or a general state of well-being of the user may be determined. The controller may anticipate on the sensed signals and adapt the color and/or intensity of the light emitted by the light source to correspond to the sensed biological state. In this context, a bio-sensor is any sensor which provides an indication of the well-being or the biological state of the user. This, for example, includes heart-beat sensors and temperature sensors worn on the body of the user. This may also include a feedback signal indicating, for example, the typing speed of somebody working behind a computer. The speed variation in his typing may be an indication of the level of alertness of the person behind the computer. This information may, for example, be used by the controller to adapt the drive signal accordingly. The controller may also generate the drive signal in dependence on a maintained history stored in the database. The user may, for example, override the current program of the controller via manual inputs. The controller logs the history of, for example, the manual inputs in the database and uses this history to adapt the standard programming so as to correspond more closely to the requirements of the user as indicated via the manual overrides. Alternatively, a history of the sensed biological state of the user may be stored in the database and used to anticipate the light color and/or level which may currently be preferred by the user.

In an embodiment of the lighting system, the light source comprises at least two light emitters, each emitting modulated light, the spectrum of the modulated light emitted by the at least two light emitters being different from each other. By adapting the intensity of the modulated light emitted by the at least two light emitters individually, the spectrum of the light emitted by the light source can be altered.

In an embodiment of the lighting system, the light sensor is arranged for sensing the direction of the impinging light and for providing a further sense-signal to the controller, the further sense-signal comprising the directional information sensed by the light sensor. The directional information may be used by the controller to further control the light source to, for example, compensate the directional content of the light such that a surface is substantially uniformly illuminated. The controller may also use the directional information to activate, for example, sunscreens for blocking the impinging directional light. The directional information, for example, provides information as to which sunscreens should be activated to block the impinging directional light, while maintaining the remainder of the sunscreens open to receive as much as possible ambient light such that the ambient light is used optimally.

In addition, the lighting system may use additional information, such as the date, daytime and geographical location to calculate the expected direction of the sunlight. This embodiment may be beneficial when the sun is temporarily blocked by clouds and when the adaptation of the lighting system to compensate for the directional light takes time. The part of the lighting system which has to compensate for the directional light may be preset depending on the date, daytime and geographical location and may be switched on as soon as the sun is no longer blocked by the clouds. The geographical location may be inputted by hand or may be retrieved from a GPS system, after which the geographical location is, for example, stored in the controller or in the database connected to the controller. Alternatively, the lighting system comprises an additional light sensor providing a further sense-signal to the controller, the additional light sensor being arranged for sensing the direction of the impinging light, and the further sense-signal comprising the directional information sensed by the additional light sensor. Using a different sensor for the illumination level and the directional information has the advantage that both sensors may be optimized for gathering the illumination and directional information, respectively, so that the individual sensors are more accurate.

In an embodiment of the lighting system, the controller emits a further drive signal for driving screens for selectively blocking daylight. The daylight may, for example, be blocked using variable screens. These variable screens may, for example, vary the intensity of the light transmitted through the screens (using, for example, a kind of light valve such as an array of liquid crystal cells), or, for example, vary a wavelength transmitted through the screens (for example, using different color filters) via which a specific color may be removed from the daylight contribution which is allowed to enter into a room. The invention also relates to a controller according to claim 14, and a light sensor according to claim 15.

BRIEF DESCRIPTION OF THE DRAWINGS:

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. In the drawings:

Fig. 1 shows a schematic overview of a lighting system according to the invention,

Fig. 2A and Fig. 2B show a sense-signal representing a sensed illumination level over time,

Fig. 3 shows a schematic overview of a controller of the lighting system according to the invention, and

Fig. 4A and 4B show embodiments of a light sensor according to the invention. The figures are purely diagrammatic and not drawn to scale. Particularly for clarity, some dimensions are exaggerated strongly. Similar components in the figures are denoted by the same reference numerals as much as possible. DETAILED DESCRIPTION OF EMBODIMENTS:

Fig. 1 shows a schematic overview of a lighting system 10 according to the invention. The lighting system 10 as shown in Fig. 1 is arranged inside a room 50, for example a living room 50 in a house, or, for example, an office 50, a shop or a factory. The lighting system 10 comprises a light source 30, a light sensor 20 and a controller 100. The light source 30 emits modulated light 40. The modulation of the light may, for example, be determined by the controller 100 via the drive signal DS. Alternatively, the modulation of the light may be a fixed modulation of the light source 30, for example, caused by the AC mains power supply. The light sensor 20 senses the illumination level over time to capture the modulation of the modulated light 40 and provides a sense-signal SS to the controller 100 representing the sensed illumination level. The controller 100 comprises a parameter P and is configured for receiving the sense-signal SS. The parameter P defines the modulated light 40 from the light source 30. From the sense-signal SS and the parameter P, the controller 100 is able to determine the contribution of the modulated light 40 to the overall sensed illumination level. The parameter P may, for example, be stored in a database 110 connected to the controller 100.

The controller 100 uses the parameter P to reconstruct the modulated light 40 impinging on the light sensor 20. As a result, the controller 100 is able to relatively accurately determine the contribution of the light emitted by the light source 30 to the overall, sensed illumination level. The illumination level sensed by the light sensor 30 is a sum of the light emitted by the light source 30 and ambient light which impinges on the light sensor 20. The ambient light may, for example, include daylight which is transmitted by a window 56 or may include light emitted by other light sources (not shown), or may include light reflected from walls or objects. The controller 100 receives the parameter P which defines the modulated light. Because this parameter P is known, the controller 100 can reconstruct the modulated light 40 as emitted by the light source 30 and thus determine the contribution of the modulated light 40 to the illumination level measured by the light sensor 20. If, for example, an amplitude modulation of the light emitted by the light source 30 is known, the sensed amplitude modulation by the light sensor 20 may be used to reconstruct the modulated light 40 emitted by the light source 30 and from this the exact contribution of the light emitted by the light source 20 to the sensed illumination level may be determined. This contribution may, for example, be subtracted from the sensed illumination level to determine, for example, the contribution of the ambient light which impinges on the light sensor 20. In an embodiment of the lighting system 10, the controller 100 generates a drive signal DS for determining the modulation of the modulated light 40. The drive signal DS may, for example, drive the light source 30 such that the modulation of the modulated light 40 comprises amplitude modulation, frequency modulation, pulse-height modulation, pulse-width modulation, or a combination thereof. In such an embodiment where the controller 100 generates the drive signal DS, the parameter P defining the modulated light is typically known by the controller 100 as the drive signal DS determines the modulation of the modulated light. When, for example, the modulated light 40 comprises pulse-height modulation, the parameter P may, for example, include a value defining the difference between the maximum light amplitude and the minimum light amplitude of the modulated light 40. Knowing the absolute difference between the maximum light amplitude and the minimum light amplitude, the controller 100 can reconstruct what part of the light emitted by the light source 30 impinges on the light sensor 20. Alternatively, the drive signal DS may, for example, provide a combination of pulse-height and pulse-width modulation (see for example Fig. 2A). The parameter P may thus comprise both the pulse-height difference and the pulse-width difference of the modulated light 40, which again enables the controller 100 to reconstruct the modulated light 40. An advantage of this combined pulse-height and pulse- width modulation of the modulated light 40 is that the pulse-height and pulse-width variation may be chosen such that the average contribution of the light emitted by the light source 30 over time remains substantially constant (as is illustrated in Fig. 2A).

Preferably, the modulation of the modulated light 40 is imperceptible by human senses. Imperceptible by human senses in this context means that the modulation does not impose a physical sensation on any of the human senses directly such that the human would be aware of the modulation. The human senses include, for example, sight, hearing and feeling. Preferably, the modulation is chosen such that the frequency, for example, exceeds 100 Hz, so that the modulation of the light source 30 is imperceptible by sight. Alternatively, the modulation of the modulated light 40, for example, exceeds 10 kHz to prevent the modulation frequency from being perceived via audible noise generated by the light source 30 or by the power converter (not shown) of the light source 30. The light source 30, for example, comprises a plurality of light emitters 32, 34,

36. The light source 30 as shown in Fig. 1 comprises a low-pressure gas discharge lamp 32 which, for example, operates on a fixed frequency determined by the transformer of the low- pressure gas discharge lamp 32. This fixed frequency may be the parameter P of the low- pressure gas discharge lamp 32 which may be provided to the controller 100 from the light source 30 or from the database 110 into which the parameter P of the low-pressure gas discharge lamp 32 has been added, for example, manually. Furthermore, the light emitted by the low-pressure gas discharge lamp comprises a specific spectrum of light which typically depends on a mixture of the luminescent materials used in the low-pressure gas discharge lamp 32. The spectrum emitted by the low-pressure gas discharge lamp 32 may also be defined via a further parameter P of the low-pressure gas discharge lamp 32, which is provided to the controller 100. From this spectrum information, the controller can determine the spectral contribution of the modulated light 40 from the low-pressure gas discharge lamp 32 to the overall, sensed illumination level. The light source 30 as shown in Fig.l further comprises a plurality of light emitting diodes 34, 36 as light emitters. These light emitting diodes 34, 36 may be driven by a different drive signal DS, which has a modulation such that it is possible to clearly distinguish the modulated light 40 originating from the light emitting diodes 34, 36 from the remainder of the illumination level sensed by the light sensor 20. This modulation may be different in frequency, in phase, in modulation depth, in pulse-height and pulse-width and in spectral information. If, for example, the light sensor 20 comprises a plurality of sub-sensors Sr, Sg, Sb (see Fig. 4A) which are each sensitive to a different part of the spectrum, the light emitted by one of the light emitting diodes 34; 36 may be sensed by one sub-sensor Sr; Sg; Sb, while the light of another light emitting diode 34; 36 may be sensed by a further sub-sensor Sr; Sg; Sb. The light emitting diodes 34, 36 may be rows of light emitting diodes 34, 36 which are arranged, for example, substantially parallel to the elongated tube of the low-pressure gas discharge lamp 32.

An advantage of using a combination of a low-pressure gas discharge lamp 32 and a light emitting diode 34, 36 is that it provides the possibility to alter the color of the light emitted by the light source 30, while requiring a relatively low energy contribution. This is due to the typical emission spectrum of the light emitting diode 34, 36 which comprises the predominant color having a relatively narrow bandwidth. Only the required amount of the predominant color is admixed to the other light emitter 32 such that the color of the modulated light emitted by the light source 30 comprises the required color.

Preferably, the light source 30 comprises a light-mixing element (not shown) to mix the contributions of the different light emitters 32, 34, 36 such that the light emitted by the light source 30 is substantially homogeneous and uniform.

Alternatively, the light source 30 may comprise means (not shown) to alter the direction of the individual light emitters 32, 34, 36. The light source 30 may, for example, be arranged for receiving a further drive signal FDS (see Fig. 3) from the controller 100 for controlling the direction of the individual light emitters 32, 34, 36. The means to alter the direction may be used to compensate for a sensed directionality or may be used to induce a directionality of the light emitted by the light source 30. The means for altering the direction of the light may, for example, be motors (not shown) for altering the orientation of the light emitters 32, 34, 36 inside the light source 30, or may for example, be moving lens-elements, mirrors or collimators for altering the direction of the light emitted by the individual light emitters 32, 34, 36.

The light sensor 20 is arranged for sensing an illumination level over time to capture the modulation of the modulated light 40. The illumination level may, for example, comprise an intensity variation over time and/or may, for example, comprise a spectral variation over time. The light sensor 20 subsequently provides a sense-signal SS to the controller 100. The sense-signal SS represents the sensed illumination level over time. As can be seen by the schematic arrangement in Fig.l, the light impinging on the light sensor 20 is not only light from the light source 30, but also contains contributions of the light emitted by the sun 54 which passes through the window 56 and impinges on the light sensor 20. The light sensed by the light sensor 20 may also comprise light which is reflected from any of the walls of the room 50, or reflected from any object inside the room 50. To efficiently use the ambient light which impinges on the light sensor 20 and at the same time have good control over the illumination level (in intensity and/or spectrum) at the location of the light sensor 20, a clear distinction between the contribution of the ambient light and the light emitted by the light source 30 is required. By using a light source 30 which emits modulated light 40, and by providing the modulation information to the controller 100 via the parameter P, the controller 100 can reconstruct the modulated light 40 and, from this reconstruction, the controller 100 can determine the contribution of the light source 30 to the illumination level (in intensity and/or spectrum). As a result, the modulated light 40 may be adapted such that the required illumination level at the light sensor 20 is generated, using as much of the ambient light as possible.

The light sensor 20 may alternatively be a portable light sensor 20, for example, comprising wireless connection means (not shown) for providing the sense-signal S S to the controller 100.

In an alternative embodiment, the light sensor 20 may also sense the directionality of the light impinging on the light sensor 20. In such an embodiment, the light sensor 20 is arranged to generate a further sense-signal FSS which comprises the directional information as sensed by the light sensor 20. The sense-signal SS and/or the further sense- signal FSS are sent to the controller 100 and are used by the controller 100 to generate the drive signal DS which is sent to the light source 30 for determining the spectrum of the light emitted by the light source 30 and/or for determining the direction of the light emitted by the light source 30. Alternatively, the further sense-signal FSS may be used to control screens and shutters (not shown) which may block or filter directional sunlight.

The controller 100 generates the drive signal DS for driving the light source 30. The drive signal DS may be generated by the controller 100 such that the light emitted by the light source 30 ensures a uniform spectrum and/or intensity of the light which impinges on the light sensor 20. When the sun 54 is partially covered by a cloud 52, the contribution of the sunlight which enters through the window 56 changes, which is sensed by the light sensor 20. The controller 100 receives the changed illumination level via the sense-signal SS of the light sensor 20 and alters the spectrum and/or intensity of the light emitted by the light source 30 such that the spectrum and/or intensity of the light impinging on the light sensor 20 remains substantially constant.

Alternatively, the controller 100 may generate the drive signal DS for driving the light source 30 such that the light impinging on the light sensor 20 has a maximized color rendering index. When, for example, part of the impinging light from the sun 54 is shielded by the cloud 52, the controller may adapt the drive signal DS such that the color of the light in the room 50 substantially remains the same. However, the spectral contribution of the light inside the room 50 may have changed and thus the color rendering possibilities of the light may have changed. The controller 100 may adapt the drive signal DS such that the color rendering of the light inside the room 50 always has a maximum color rendering index that can be achieved with the current light source 30. This may be especially beneficial in shops where, for example, showing the true color of an object is very important.

In a further embodiment of the controller 100, the drive signal DS may be generated to obtain a predetermined intensity and/or variation of the light of the specific color blue. Typically, this is only possible when the light source 30 comprises light emitters 32, 34, 36 able to produce this specific color blue. In such a lighting system 10, the controller 100 may influence the well-being, alertness and circadian rhythm of a person who is in the room 50.

In a further alternative embodiment of the controller 100, the drive signal DS may be generated to generate the required color of the light in the room 50 in a most energy- efficient way. Because light emitting diodes 34, 36 typically have a relatively narrow spectrum (not shown), the use of light emitting diodes 34, 36 enables a very specific contribution of light of a certain color to the light emitted by the light source 30, such that the color of the light emitted by the light source 30 can be changed in a relatively efficient way. The sense-signal SS, the further sense-signal FSS, the drive signal DS and the further drive signal FDS may be signals which are transmitted via a wire or wirelessly (not indicated) and continuously or periodically. When the signals are transmitted continuously, the lighting system 10 responds relatively rapidly to changes in the lighting conditions in the room 50, while, when the signals are transmitted periodically, the lighting system 10 responds relatively slowly to changing lighting conditions. The light sensor 20 may, for example, comprise a plurality of sub-sensors Sr,

Sg, Sb arranged at a distance from each other. From the differences between the intensities of the sub-sensors Sr, Sg, Sb a direction may be derived.

The light source 30 may, for example, include light emitting diodes 34, 36, and the number of light emitting diodes 34, 36 which emit different primary colors exceeds three. Generally, by using three primary colors substantially every color which lies within the triangle defined by the three primary colors, including white, can be made. Adding a further primary color has the advantage that the gamut of colors that can be produced by the system is increased. A further advantage is that when more than three colors are used, a substantially infinite combination of intensities of the different light emitting diodes may be present to generate a specific color. Due to this advantage, the lighting system is able to choose the combination and the intensity of light emitters which produce the required color in addition to a further constraint, for example, to maximize the contribution of the specific color blue or to vary the contribution of the specific color blue according to a predefined variation during the day. Alternatively, the light source may adapt the color of the light emitted by the lighting system, while complying with the further constraint of, for example, maximizing the color rendering index of the light emitted by the lighting system, or maximizing the efficiency to generate the required color of the light emitted by the lighting system.

Fig. 2 A and Fig. 2B show a sense-signal SS representing a sensed illumination level over time t. In a first embodiment the light source 30 comprises three light-emitters 34, 36, for example, three light emitting diodes 34, 36 emitting light having the primary colors red, green and blue. The controller 10 provides three different drive signals DSr, DSg, DSb which cause an amplitude modulation in each of the three light emitting diodes 34, 36. The amplitude modulation causes a difference in amplitude over time. This amplitude difference need not be large but preferably is known and is provided to the controller 100 via the parameter P. Furthermore, the phase of the individual drive signals DSr, DSg, DSb is provided as a further parameter P to the controller 100 to enable the distinction between the different contributions of the different light-emitters 34, 36 to the sensed illumination level. The sensed signal SS is indicated in Fig. 2A and comprises a contribution of ambient light and of the different colors SSr, SSg, SSb of the modulated light 40 emitted by the light emitting diodes 34, 36. By indicating the sense-signal SS in luminance values L, a mathematical representation of the sense-signal SS may be:

L Total (^) = ^ Artificial (^) + ^ Ambient (^) , where L represents the luminance, and λ represents the wavelength of the sensed light.

In this mathematical representation, the contribution of the modulated light 40 may be described as:

^L _Arti_fici_al ^ ^) = L₀(X) + Z_r(λ) - cos(2π v ϊ +φ_r) + Z_g(λ) - cos(2π v ϊ +φ_g) + Z₆(λ) - cos(2π v ϊ +φ₆) , where Lo, L_r, L_g, Lb represent the sensed luminance of the ambient light (Lo)and of the primary colors Red, Green and Blue, respectively, Φ_r, Φ_g, Φb represent a phase of the sensed signal and the sensed luminance of the primary color Red to the luminance, and v represents the modulation frequency of the sensed light.

The different parameters P provided to the controller 100 indicate for every light emitting diode 34, 36 the amplitude differences L₁ZL₀, L_g/L₀, Lb/L₀ and the phase Φ_r, Φ_g, Φb. Subsequently, the controller 100 may determine from the sense-signal SS the sensed amplitude differences ΔAr, ΔAg, ΔAb and use the sensed amplitude differences ΔAr, ΔAg, ΔAb at specific time-periods t_ls t₂, t3, t₄ in the sense-signal SS to reconstruct the modulated light 40 emitted by the individual light emitters 34, 36. From the reconstructed modulated light 40 of the individual light emitters 34, 36 the exact contribution of each of the light emitting diodes 34, 36 is determined and the ambient light contribution may be derived. Instead of amplitude modulation with a phase that differs for the different colors, also frequency modulation may be used. In that case, in the mathematical representation, the contribution of the modulated light 40 may be described as: t t

L_Artlflaal(λ,t) = L₀(λ) + L_r(λ) - cos(2π JK +Δv_r(τ)]Λ) + Z_g(λ) - cos(2π J>₀ + Δv_g(τ)]Jτ)

0 0 t

+ Z_δ(λ) - cos(2π ^_O + Av_b(τ)]dτ), where Vo is the frequency of the carrier wave that is common to the different colors and Δv_r(t), Δv_g(t), Δv_b(t) denote the modulation of the carrier wave frequency for the different colors. For example, Δv _r{t) = cos(2πv_r ) for a periodic modulation with frequency v_rof the carrier wave. The light sensor 20 may, for example, be able to sense the intensity variation of the individual light emitting diodes 34, 36, using different sub-sensors Sr, Sg, Sb (see Fig. 4), or the light sensor 20 may sense the integrated intensity over time across the whole spectrum (not shown). When the integrated intensity is measured, the phase Φ_r, Φ_r, Φ_r of the drive signals DSr, DSg, DSb to the individual light emitting diodes 34, 36 may be used to discriminate between the different contributions of the light emitted by the individual light emitting diodes 34, 36 to the sensed illumination level.

In the embodiment shown in Fig. 2A, the amplitude modulation is used to determine the contribution of the different light emitters. In Fig. 2A the amplitude difference between the red ΔAr, green ΔAg and blue ΔAb contribution is used to determine the color of the modulated light 40 emitted by the light source 30.

In a second embodiment the modulation of the light source 30 comprises both pulse-height modulation ΔA1, ΔA2 and pulse-width wl, w2 modulation. An advantage of this embodiment is that the average contribution of the light source 30 to the illumination level is substantially constant. The sense-signal SS again comprises a contribution of the ambient light and a contribution of the modulated light 40 indicated in Fig. 2B by SSc. A first light-pulse emitted by the light source 30 generates an amplitude difference ΔA1 having a first width wl and a second light-pulse emitted by the light source 30 generates a second amplitude difference ΔA2 having a second width w2. Knowing this modulation of the modulated light 40 enables the controller 100 to reconstruct the contribution of the modulated light 40 from the sensed illumination level. The overall contribution of the modulated light 40 is substantially equal to the average amplitude difference ΔAa having an average width wa.

Fig. 3 shows a schematic overview of a controller 100 of the lighting system 10 according to the invention. The controller 100 as shown in Fig. 3 comprises a clock 102 for determining the time of day, which may be used as a timer, for example, for switching off the system to save energy, or which may be used to adapt or control the circadian rhythm of a human. The controller further comprises a calendar 104 which enables the controller 100 to implement specific seasonal variations to the light emitted by the light source 30. For example, when the light source 30 is able to generate UV-A and/or UV-B radiation, the controller 100 may add some UV-A and/or UV-B light to the light emitted by the light source 30, for example, to ensure a healthy vitamine-D concentration in a human inside the room 50 (see Fig. 1). The controller 100 may further comprise input means for receiving manual input from manual input means 106. These manual input means 106 enable a user to override the programming of the controller 100 to generate the light levels and/or colors of his choice. A further input means, for example, is arranged for receiving an input signal from a bio-sensor 108. The bio-sensor 108 senses a biological state of a user; for example, it measures the well- being of the human, or the concentration of melatonin in the human or it measures bio- parameters from which the location in the circadian rhythm of the human can be determined. A bio-sensor may be any sensor which provides an indication of the bio-parameters of a human, such as his heartbeat, his temperature, etc. The controller 100 shown in Fig. 3 further may comprise a database 110 to store, for example, the history of the manual inputs of the user and/or to store the bio-sensor signal. The database 110 may also be located away from the controller 100 and be connected to the controller 100 via a wired or wireless connection. The controller 100 further comprises sensor input means via which the sense- signal SS is received from the light sensor 20 and via which the further sense-signal FSS is received from the additional light sensor 25. The light sensor 20, for example, senses the illumination level over time to capture the modulation of the modulated light 40. The illumination level may be sensed via spectral information and/or via intensity information. The additional light sensor 25, for example, senses the directionality of the light impinging on the additional light sensor 25. The further sense-signal FSS comprises the directional information sensed by the additional light sensor 25.

The controller 100 further comprises output means for providing the generated drive signals DS; DSr, DSg, DSb; DSc and the further drive signal FDS to the light source 30 (see Fig. 1). The drive signals DS; DSr, DSg, DSb; DSc determine the modulation of the modulated light 40 emitted by the light source 30. The further drive signal FDS determines the direction of the light emitted by the light source 30. The drive signal DS and the further drive signal FDS may also be combined in a single signal sent by the controller 100 to the light source 30. Figs. 4 A and 4B show embodiments of a light sensor 20 according to the invention. In the embodiments of the light sensor 20a, 20b shown in Figs. 4A and 4B, the sensor consists of a number of photo-diodes 22 (or pixels of a CCD or CMOS image sensor), each of them covered by a spectral filter 24r, 24g, 24b which transmits only a part of the spectrum. Preferably, the transmission spectra of the individual filters 24r, 24g, 24b do not overlap and together they substantially span the full visual spectrum. The best spectral resolution can be obtained with interference filters 24r, 24g, 24b (e.g. dichroic filters). However, the transmission spectra of these interference filters 24r, 24g, 24b depend relatively strongly on the angle at which the light impinges on the interference filters 24r, 24g, 24b, which is undesirable. This has been solved in Fig. 4A by adding separating walls 26 between the individual photo-diodes 22, thus generating a light-absorbing tunnel. These separating walls 26 limit the angle at which the light impinges on the interference filters 24r, 24g, 24b to a maximum angle θ_max. A diffuse-reflecting layer 28 near the entrance of the light-absorbing tunnel ensures a more or less uniform angular distribution of the light which reaches the photo-diode 22 via the interference filters 24r, 24g, 24b, irrespective of the angle at which the light is directed towards the light sensor 20a.

Alternatively, Fig. 4B shows a light sensor 20b having a collimator 27 that collects the light originating mainly from a direction in line with the orientation of the collimator. The collimator 27 comprises a diffuser 29 to tune the angular range of the light that is able to reach the photo-diode 22 via the filters 24r, 24g, 24b. In a preferred embodiment, the color filters 24r, 24g, 24b are absorption color filters.

The invention further relates to a method of determining the contribution of the light emitted by a light source 30 to the illumination level sensed by a light sensor 20 of a lighting system 10, the lighting system 10 comprising a light source 30 for emitting modulated light 40, a light sensor 20 for sensing the illumination level over time to capture the modulation of the modulated light 40 and to provide a sense-signal SS to a controller 100, the controller 100 being configured for receiving the sense-signal SS and comprising a parameter P defining the modulated light 40 from the light source 30, the method comprising the step of: reconstructing the modulated light 40 emitted by the light source 30 from the sense-signal SS, using the parameter P, and determining the contribution of the modulated light 40 to the sensed illumination level, using the reconstruction of the modulated light 40 and the sense-signal SS. The invention further relates to a computer program product stored on a computer readable medium, the computer program product being arranged to perform the method as indicated above.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. 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.

Claims

CLAIMS:

1. Lighting system (10) comprising: a light source (30) for emitting modulated light (40), a light sensor (20) for sensing the illumination level over time to capture the modulation of the modulated light (40), and to provide a sense-signal (SS) to a controller (100), the controller (100) being configured for receiving the sense-signal (SS), the controller further comprising a parameter (P) defining the modulated light (40) from the light source (30) to determine the contribution of the modulated light (40) to the sensed illumination level.

2. Lighting system (10) as claimed in claim 1, wherein the light sensor (20) is configured for sensing spectral information from the sensed illumination level.

3. Lighting system (10) as claimed in claim 1, wherein the controller (100) is configured for generating a drive signal (DS; DSr, DSg, DSb; DSc) for driving the light source (30) to determine the modulation of the modulated light (40).

4. Lighting system (10) as claimed in claim 3, wherein the drive signal (DS; DSr, DSg, DSb; DSc) comprises at least one of the group comprising: amplitude modulation, frequency modulation, phase modulation, pulse-height modulation, pulse-width modulation, or a combination thereof, and wherein the parameter (P) comprises at least one of the group comprising: modulation frequency, modulation depth, modulation phase, pulse-height, pulse- width and spectral information.

5. Lighting system (10) as claimed in claim 4, wherein the modulation is imperceptible by human senses.

6. Lighting system (10) as claimed in claim 3, 4 or 5, wherein the controller

(100) is configured for driving at least two light sources (30) by generating at least two drive signals (DS; DSr, DSg, DSb; DSc), the phase of the at least two drive signals (DS; DSr, DSg, DSb; DSc) being different.

7. Lighting system (10) as claimed in any of the previous claims, wherein the lighting system (10) is configured to periodically calibrate the lighting system (10) to update the parameters (P).

8. Lighting system (10) as claimed in any of the previous claims, wherein the controller (100) is connected to a database (110) for storing and/or retrieving the parameter (P).

9. Lighting system (10) as claimed in any of the previous claims, wherein the controller (100) uses the spectral information from the light sensor (20) to control the spectrum of the light emitted by the light source (30): to maintain the spectrum of the light impinging on the light sensor (20) substantially constant, and/or to maximize the color rendering index of the light impinging on the light sensor (20), and/or to ensure that the light impinging on the light sensor (20) comprises a predetermined intensity and/or variation of light of a specific color blue (Bs), the specific color blue (Bs) reducing the melatonin concentration in a human, and/or to maximize the efficiency for generating a predetermined color of the light impinging on the light sensor (20).

10. Lighting system (10) as claimed in any of the previous claims, wherein the controller (100) generates the drive signal (DS; DSr, DSg, DSb; DSc) in dependence on: a clock (102), and/or a calendar (104), and/or manual input from manual input means (106), and/or bio-sensor input from a bio-sensor (108), the bio-sensor (108) being arranged for sensing the biological and/or emotional state of a user, and/or the maintained history stored in the database (110).

11. Lighting system (10) as claimed in any of the previous claims, wherein the light source (30) comprises at least two light emitters (32, 34, 36) each emitting modulated light (40), the spectrum of the modulated light (40) emitted by the at least two light emitters (32, 34, 36) being different.

12. Lighting system (10) as claimed in any of the previous claims, wherein the light sensor (20) is arranged for sensing the direction of the impinging light and for providing a further sense-signal (FSS) to the controller (100), the further sense-signal (FSS) comprising the directional information sensed by the light sensor (20), or wherein the lighting system (10) comprises an additional light sensor (25) providing the further sense-signal (FSS) to the controller (100), the additional light sensor (25) being arranged for sensing the direction of the impinging light, and the further sense-signal (FSS) comprising the directional information sensed by the additional light sensor (25).

13. Lighting system (10) as claimed in any of the previous claims, wherein the controller (100) emits a further drive signal (FDS) for driving screens for selectively blocking daylight.

14. A controller (100) for use in the lighting system (10) as claimed in any of the previous claims.

15. A light sensor (20) for use in the lighting system (10) as claimed in any of the previous claims.