System and method for calibrating a multi-channel lighting system

Abstract

Systems and methods are disclosed for calibrating a multi-channel lighting system. The multi-channel lighting system may have a plurality of channels, each channel of the plurality of channels being configured to emit radiation at a respective control in a respective spectral band from a plurality of first spectral bands. The method comprises receiving or determining a set of calibration settings, each calibration setting defining a respective control value for each channel of the multi-channel lighting system. The set of calibration settings comprises a number of linearly independent calibration settings equal to a number of channels of the multi-channel lighting system. The method further comprises, for each calibration setting in the set of calibration settings: selecting a calibration setting from the set of calibration settings, configuring the multi-channel lighting system to emit radiation according to the selected calibration setting, and measuring, for each spectral band in a plurality of second spectral bands different from the plurality of first spectral bands, an irradiance value at a specified position relative to the multi-channel lighting system. Based on the set of calibration settings and the measured irradiance values, a calibration matrix is determined. The calibration matrix allows to convert a set control values for the plurality of channels into a set of irradiance values for the plurality of second spectral bands and / or vice versa.

Description

[0001] SYSTEM AND METHOD FOR CALIBRATING A MULTI-CHANNEL LIGHTING

[0002] SYSTEM

[0003] FIELD OF THE INVENTION

[0004] This disclosure relates to a system and method for calibrating a multi-channel lighting system, and in particular to a computer-implemented method for calibrating a multichannel lighting system and to a computer program and computer-readable storage medium for performing such method.

[0005] BACKGROUND OF THE INVENTION

[0006] In many applications, different colors of light must be mixed with a specific light intensity. For example, in horticulture, mixing light colors with different intensities per light color can be used to create a specific light recipe that results in an optimal light combination for the crop (vegetable, fruit, plant, seed, or any other living vegetative product). This light recipe can be created to for example, boost crop growth, increase shelf life, adjust vitamin or mineral level in the crop, or change the color of the crop. Similar light recipes may be used for, e.g., growing livestock or fish, therapeutic lighting applications, or light performances

[0007] These light recipes may be defined in photon flux densities, or light intensities per color; for example, in horticulture applications, light recipes are often defined in Photosynthetic Photon Flux Density (PPFD). More in general, the light intensity (also referred to as irradiance) can be measured in micromoles (of photons) per second per square meter (pmol / s / m2). For the end customer, it is important to have the correct intensity and light distribution towards the crop, for optimal results. The light flux provided by a luminaire in such contexts is measured in micromoles per second (pmol / s) and it is called Photosynthetic Photon Flux (PPF). This is the total light (or radiation) output in all directions of the luminaire or any other light or radiation emitting device (hereinafter also referred to as just a ‘luminaire’ for the sake of brevity) per unit of time. In horticulture application, the PPF is typically used as the control value set by the user to control the luminaires.

[0008] The irradiance or PPFD can then be determined based on the number of luminaires used in an area and by understanding the specifics of that area, e.g., height, reflection index, etc. The procedure to enable measurement in micromoles per second per square meter is called calibration. Thus, this calibration allows a user to know how many micromoles per second will ‘arrive’ on that specific square meter, for any set of control values.

[0009] To create a light recipe, mixing light colors with a specific light intensity per light color is possible by powering the LED-chips typically used in a luminaire in a variety of ways. To realize the desired light recipe with a luminaire, the following aspects are important: (1) the combination of LED-chips used in the luminaire, (2) the maximum power that the luminaire can handle, and (3) the colors (usually expressed in wavelength nanometer ranges) that are being radiated by the various LED-chips, in particular multi-color radiation of a single LED-chip.

[0010] Regarding the third aspect, a LED-chip provides a specific spectral distribution, in this example blue, white, deep red, or far-red (which is not uncommon for a horticulture luminaire). In some cases, a LED-chip is emitting light in more than one spectral band used to define light recipes, and different LED-chips may have completely or partially overlapping spectral bands; for example, the deep red and far-red spectra may partially overlap. This behavior is seen even more with LED-chips with a white (or whitish) spectrum. White is a combination of colors, comprising blue, green, red and, optionally, far-red. When a light recipe is to be created, it is important to realize the exact combination of light colors with a specific light intensity. Hence, when powering the ‘white’ LED-chip, a variety of light colors is being emitted. This is also called multi-color radiation. Other chips may have dual peaks, e.g., NIR and green or far-red and blue.

[0011] Current calibration methods typically perform a light measurement at the canopy level of the crop for a specific light setting in the luminaire in order to convert a set PPF in pmol / s into a PPFD in pmol / s / m2in a horticulture facility (such a greenhouse or a multi-layered indoor farm). Since a typical luminaire has from one to four dimmable LED channels, a specific calibration dimming value is set (usually 50-70% level for all LED channels) on all luminaires in the crop area, resulting in a set PPF value. The next step is to use a so-called light-spectrum-measurement device that can measure the total irradiance at the canopy level, e.g., in the range of 400 nm to 800 nm. Once the measurement is done, a single calibration constant k is calculated: where lca\ is the measured PPFD at calibration setting, andca[is the calculated (or set) PPF at calibration setting based on luminaire technical specifications. With the calibration constant k, it is possible to convert a desired PPFD into a luminaire PPF setting, as well as converting current luminaire PPF into current PPFD in the crop. However, this equation assumes that the calibration constant is the same for all channels, which is not necessarily the case.

[0012] To solve this problem, WO 2022 / 106515 Al describes a calibration procedure that uses a calibration matrix rather than a single calibration scalar. The method described herein requires knowledge of the luminaire specification, in particular the spectral mapping of the LED channels, which is not always available to a user performing the calibration.

[0013] In light of the above, there is a need in the art for a system and method for calibrating a multi-channel luminaire that does not require a spectral mapping of the multichannel luminaire.

[0014] SUMMARY OF THE INVENTION

[0015] To that end, a method for calibrating multi-channel lighting system is disclosed. The multi-channel lighting system may have a plurality of channels, each channel of the plurality of channels being configured to emit radiation at a respective control in a respective spectral band from a plurality of first spectral bands. The method comprises receiving or determining a set of calibration settings, each calibration setting defining a respective control value for each channel of the multi-channel lighting system. The set of calibration settings comprises a number of linearly independent calibration settings equal to a number of channels of the multi-channel lighting system. The method further comprises, for each calibration setting in the set of calibration settings: selecting a calibration setting from the set of calibration settings, configuring the multi-channel lighting system to emit radiation according to the selected calibration setting, and receiving, for each spectral band in a plurality of second spectral bands different from the plurality of first spectral bands, a measurement value representing an irradiance value at a specified position relative to the multi-channel lighting system. Based on the set of calibration settings and the measured irradiance values, a calibration matrix is determined. The calibration matrix allows to convert a set of control values for the plurality of channels into a set of irradiance values for the plurality of second spectral bands and / or vice versa.

[0016] Each channel of the multi-channel lighting system may be configured to emit radiation at a controllable radiant flux. In particular, each channel of the multi-channel lighting system may be configured to emit radiation at an (at least to some extent) individually controllable radiant flux. Consequently, the control value may be implemented as an (expected) absolute or relative radiant flux value. Alternatively, the control value can be representative of an absolute or relative power consumption, or any other suitable parameter.

[0017] The irradiance value may be expressed, for example, in pmol / s / m2, W / m2, lm / m2, or any other suitable quantity.

[0018] Compared to previous calibration methods, the calibration method described herein is better equipped to handle the entirety of the different spectral ranges involved in a multi-channel, multi-spectrum luminaire. In general, two main sources of errors can arise from existing calibration methods.

[0019] First, existing calibration methods do not consider the variability of the LED chips in the LED channels. Certain LED chips, mainly white LED and far-red LED have a wide spectral distribution that overlaps multiple spectral ranges. Depending on the LED manufacturer batch, these LEDs can have spectral deviation in the order of up to 10%. The current method addresses this problem by using only measurement data, instead of a combination of measurement data and technical specification data (which, moreover, may not always be available to the one performing the calibration).

[0020] Second, existing calibration methods do not consider the variability of the spectral measurements. A single spectral measurement can have uncertainty errors in the order of 5% and repeatability errors in the order of 2%, which can significantly reduce the quality and accuracy of the calibration.

[0021] The current method allows for an arbitrary number of measurements / calibration settings (provided the minimum number of the number of channels of the luminaire is observed), and automatically provides a calibration matrix that is an optimal fit to the possibly mutually inconsistent measurements (due to variability in the spectral measurements). As an accurate light recipe can make a significant difference in the yield quality, a high accuracy of the calibration can be required. The calibration methods described herein can be adapted to provide the desired accuracy by including additional calibration settings.

[0022] The calibration method described herein takes advantage of the fact that the same type of measurement device typically used for existing calibration methods, makes it possible to retrieve not only the total measured PPFD, but also the partial PPFDs per spectral range (i.e., the plurality of second spectral ranges). In an embodiment, the control value is a radiant flux value representing an expected radiant flux output by a respective channel of the multi-channel lighting system. The radiant flux may comprise photosynthetic radiation. Photosynthetic radiation or photosynthetically active radiation is typically defined as the wavelength range substantially corresponding to 400-700 nm (blue, green, and red light).

[0023] In an embodiment, the plurality of second spectral bands includes one or more of: a UV-B spectral band substantially corresponding to wavelengths in a range of 280- 315 nm, a UV-A spectral band substantially corresponding to wavelengths in a range of 315- 400 nm, a blue spectral band substantially corresponding to wavelengths in a range of 400- 500 nm or a range of 420-490 nm, a green spectral band substantially corresponding to wavelengths in a range of 500-600 nm or a range of 500-570 nm, a red spectral band substantially corresponding to wavelengths in a range of 600-700 nm or a range of 620-680 nm, and a far-red spectral band substantially corresponding to wavelengths in a range of 700- 800 nm or a range of 700-750 nm.

[0024] As used herein, the blue range substantially corresponding to the range of 400-500 nm may be understood as the blue range corresponding to the range 400-499 nm, the range 401-500 nm, the range 400.0-500.0 nm, the range 399.5-500.4 nm, the range (400-500] nm, the range [400-500) nm, et cetera, depending on the specific context; the other ranges may be understood analogously. Growers are currently used to provide growing recipes in relatively broad spectral bands conventionally referred to as blue, green, red, and far-red.

[0025] It is noted that the plurality of first spectral bands typically is different from the plurality of second spectral bands. For example, a blue LED typically only has a non- negligible emission in only a relatively narrow part of the blue spectral band. Additionally, the plurality of first spectral bands may comprise spectral bands covering several color bands, such as white LEDs covering at least part of the blue, green, and red spectral bands. For example, a multi-channel luminaire may comprise blue, white, deep-red, and far-red LEDs, whilst the grower specifies a light recipe in terms of blue, green, red, and far-red light.

[0026] In this application, the term ‘color’ is used in a general sense and includes, e.g., ultraviolet such as UV-A, UV-B and UV-C, and infrared, in particular near infrared (NIR). Similarly, the term Tight’ is used in a general sense and refers to electromagnetic radiation of the visible, ultraviolet, and infrared parts of the spectrum.

[0027] In an embodiment, the calibration matrix K corresponds to

[0028] K = fTc( Tc)-i or an inverse thereof, wherein <PCis a settings matrix wherein an zthrow represents an zthcalibration setting of the set of calibration settings and each column represents a spectral band from the plurality of first spectral bands, and Icis a measurement matrix wherein an zthrow represents the measured irradiance associated with the zthcalibration setting and each column represents a spectral band from the plurality of second spectral bands.

[0029] Such a calibration matrix may be considered to comprise two pieces of information:

[0030] 1. a conversion constant c that converts “first spectral band irradiance” to “first spectral band radiant flux”; and

[0031] 2. a spectral calibration matrix S’ that converts “first spectral bands radiant flux” to “second spectral bands radiant flux”.

[0032] Thus, the calibration matrix K may be written as K = c • S.

[0033] The conversion constant c can be calculated as: whereinctis a total settings vector representing a row sum of the settings matrix <PCand / ctis a total measurement vector representing a row sum of the measurement matrix Ic. Thus, an zthrow of the total settings vector ctrepresents an zthtotal calibration setting of the set of calibration settings, and an zthrow of the total measurement vector Ictrepresents the total measured irradiance associated with the zthcalibration setting. The row sum of a matrix is a vector of which each element equals the sum of the elements in the corresponding row of the matrix, i.e.,ct=C• [1, 1, 1]Tand Ici= Ic■ [1, 1, 1]T, wherein [1, 1, 1]Tis an all- ones vector with a number of elements (all equal to 1) equal to the number of first and second spectral bands, respectively (and hence, equal to the number of columns ofCand / c, respectively).

[0034] The spectral calibration matrix S can be calculated based on c and K as:

[0035] S = c-1K.

[0036] This way, the effect of the distance between the measurement position and the radiation source (luminaire) may be separated from the intrinsic properties of the luminaire. Assuming there are no significant influences of environmental properties such as light reflection and light absorption, the radiant flux spectral calibration matrix S’ depends only on the luminaire, whereas the factor c can be adjusted based on the position relative to the luminaire; for example, the factor c could be extrapolated as a function of the inverse squared distance between the area of interest and the luminaires. By keeping the radiant flux spectral calibration constant, the need to perform a new calibration procedure for different distances can be avoided, since this matrix depends only on the spectral distribution of the luminaire’s first spectral bands (hence, the luminaire’s intrinsic properties) and on the spectral distribution of the controller’s second spectral bands.

[0037] In an embodiment, the number of calibration settings is larger than the number of channels of the multi-channel lighting system. This allows to increase the accuracy of the calibration by reducing the effects of random measurement errors.

[0038] In an embodiment, the set of calibration settings comprises at least one calibration setting that defines a non-zero radiant flux value for a particular channel and a zero radiant flux value for all other channels of the multi-channel lighting system.

[0039] In an embodiment, at least two of the channels of the multi-channel lighting system are configured to emit substantially equal spectra. It is noted that other known calibration methods are often not compatible with substantially equal channels, for example because a matrix describing such a system would have no (pseudo)inverse.

[0040] In an embodiment, the set of calibration settings comprises at least two calibration settings defining a different, positive radiant flux values for at least one channel of the multi-channel lighting system.

[0041] In a further aspect, this disclosure relates to a data processing system comprising at least one processor, at least one memory storing executable instructions, the at least one memory being communicatively connected to the at least one processor, and at least one communication interface communicatively connected to the at least one processor. Execution of the executable instructions configures the at least one processor to: receive or determine a set of calibration settings, each calibration setting defining a respective radiant flux value for each channel of a multi-channel lighting device having a plurality of channels, each channel of the plurality of channels being configured to emit radiation at a respective radiant flux in a respective spectral band from a plurality of first spectral bands, the set of calibration settings comprising a number of linearly independent calibration settings equal to a number of channels of the multi-channel lighting device; for each calibration setting in the set of calibration settings: select a calibration setting from the set of calibration settings; generate and transmit, via the at least one communication interface, control signals to the multi-channel lighting device to configure the multi-channel lighting device to emit radiation according to the selected calibration setting; and receive, via the at least one communication interface, for each spectral band in a plurality of second spectral bands different from the plurality of first spectral bands, an irradiance value at a specified position relative to the multi-channel lighting device; and determine a calibration matrix based on the set of calibration settings and the measured irradiance values.

[0042] In an embodiment, the control signals are transmitted to a controller of the multi-channel lighting device, wherein the controller is adapted to configure the multichannel lighting device to emit radiation according to the selected calibration setting.

[0043] In a further aspect, this disclosure relates to a multi-channel lighting system comprising a multi-channel lighting device having a plurality of channels, each channel of the plurality of channels being configured to emit radiation at a respective radiant flux in a respective spectral band from a plurality of first spectral bands, at least one processor, at least one memory storing executable instructions, the at least one memory being communicatively connected to the at least one processor, and at least one communication interface communicatively connected to the at least one processor, wherein execution of the executable instructions configures the at least one processor to: receive or determine a set of calibration settings, each calibration setting defining a respective radiant flux value for each channel of the multi-channel lighting device, the set of calibration settings comprising a number of linearly independent calibration settings equal to a number of channels of the multi-channel lighting device; for each calibration setting in the set of calibration settings: select a calibration setting from the set of calibration settings; configure the multi-channel lighting device to emit radiation according to the selected calibration setting; and receive, via the at least one communication interface, for each spectral band in a plurality of second spectral bands different from the plurality of first spectral bands, an irradiance value associated with the selected calibration setting at an area of interest; determine a calibration matrix based on the set of calibration settings and the measured irradiance values; and store the determined calibration matrix in the at least one memory. The term ‘area of interest’ as used with respect to a multi-channel lighting system described herein may be considered equivalent to the term ‘specified location’ as used with respect to the calibration method and data processing system described herein.

[0044] The determined calibration matrix may be stored in a memory of the data processing system as described herein or, alternatively, in a memory of the multi-channel lighting device, e.g., the memory of a controller of the multi-channel lighting device as described herein. When the calibration matrix is stored in the multi-channel lighting system, the calibration matrix may be transmitted from the data processing system to the multichannel lighting device via the at least one communication interface described herein. In an embodiment, the at least one processor is further configured to receive, via the at least one communication interface, a desired irradiance value for at least one second spectral band of the plurality of second spectral bands at the area of interest, determine a radiant flux value for each channel of the multi-channel lighting device using the calibration matrix and the desired irradiance value for the at least one second spectral band, and configure the multi-channel lighting device to emit the corresponding radiation; and / or to receive, via the at least one communication interface, a desired radiant flux value for at least one channel of the multi-channel lighting device and determine a corresponding irradiance value for each of one or more spectral bands of the plurality of second spectral bands.

[0045] In an embodiment, the multi-channel lighting system is a horticultural lighting system and the area of interest comprises a plant canopy and / or a plant tray.

[0046] In another embodiment, the multi-channel lighting system is an animal farming lighting system and the area of interest comprises one or more animals and / or a living area for one or more animals.

[0047] In the context of the present disclosure, the multi-channel lighting device may also be referred to as an irradiation system and may comprise one or more controllable radiation sources, and / or one or more controllable radiation filters and / or radiation concentrators (possibly in combination with a ‘fixed’ radiation source, i.e., a radiation source providing radiation with fixed radiation properties).

[0048] In an aspect, this disclosure relates to a horticulture arrangement comprising such a system. The term “horticulture arrangement” especially refers to an arrangement including a plant support wherein or whereon plants may grow, an irradiation system that is configured to direct (horticulture) radiation to the plant support wherein or whereon the plants may grow (or grow), and a control system that controls the (horticulture) radiation. The control system may comprise or be communicatively connected to the data processing system.

[0049] In use, the horticulture arrangement may include a plant support with a plant, or a plant support with a seed, or a plant support with a seedling, etc. Herein, the term “plant” is used for essentially all stages of plant development.

[0050] The term “horticulture radiation” especially refers to radiation having one or more wavelengths in one or more of a first wavelength region of 625-675 nm (i.e., red light) and a second wavelength region of 400-475 nm (i.e., blue light). Additionally, green or white light may be added. The relative energies (expressed in, e.g., W / m2) that are provided in these regions may depend upon the type of plant and / or the growth phase. Hence, a recipe may define the ratio, optionally as a function of time, for one or more types of plants. Especially, the term “horticulture radiation” may refer to the PAR region (the photosynthetically active region from 400-700 nm, i.e., red+green+blue). The term “horticulture radiation” may also be used for radiation that is applied to plants in hydroponic applications. As known in the art, in the PAR region the reflection coefficient of leaves is very low (5-10% for red and blue light, 15-25% for green light). Towards the far-red and near infrared, beyond 700 nm, the reflection coefficient increases. Hence, in specific embodiments, the horticulture radiation, may in addition to PAR radiation also include a small fraction (e.g., <25 % of the power, especially about at maximum 10 % of the power) far-red and / or near-infrared, e.g., 800- 1000 nm.

[0051] When pre-harvest radiation is offered, this is generally meant to stress the plants such that the plants will respond by producing some compound of interest (e.g., nutritional content, colorants, taste compounds, et cetera). Such pre-harvest radiation typically contains a large fraction of blue radiation (e.g., about 450 nm), and / or UV-A radiation (e.g., 385-400 nm) and / or radiation levels in excess of 50 pmol m2s '. In some cases, UV-B radiation can also be applied beneficially. In general, plants may be sensitive both to absolute intensities of certain wavelengths and to relative intensities of different wavelengths.

[0052] The term “horticulture arrangement” may also refer to a plant farm or climate cell, wherein the plants are grown under controlled conditions, and wherein the plants substantially do not receive natural radiation (daylight). Further, such plant farm may be climatized, such as in the case of a climate cell. Hence, in embodiments, the horticulture arrangement includes such plant farm or climate cell. In other embodiments, the plant farm or climate cell includes at least part of the horticulture arrangement. For instance, a climate cell may comprise the plant support and the irradiation system, and the control system may be configured inside or external from the climate cell. Especially, a plant farm may comprise a climate cell.

[0053] The control system of such horticulture arrangement may control one or more of temperature, humidity, CO2 level, irrigation, nutrient supply, radiation intensity (irradiance) of the horticulture radiation, air conditions including one or more of air temperature, air composition, air flow, etc. Such horticulture system may be configured to control one or more of these conditions at different locations in the arrangement. Hence, the irradiation with the horticulture radiation may in embodiments be done in response to, e.g., one or more of time of the day, season of the year, (local) irradiation conditions, age of plant, condition of the plant, planting period, etc. Hence, the irradiation with the horticulture radiation may in embodiments be done in response to plant related data, time related parameters, conditions to which the plant is subjected (such as natural radiation, temperature, relative humidity, CO2 level, irrigation, nutrient supply, etc.).

[0054] The horticulture irradiation system is especially configured to provide horticulture radiation to plants. This may especially imply that the horticulture irradiation system is configured to provide horticulture radiation in a direction of a plant support wherein or whereon plants may grow. Such plant support may be a tray. Especially, the term “plant support” may also refer to a plurality of plant supports, as the plants may be grown in layers one over the other (“multi-layer system”). Hence, racks with each two or more plant supports, with over each plant support a radiation system. Hence, the term “irradiation system” may also refer to a plurality of (individually controlled) irradiation systems.

[0055] Further, the control system is configured to control one or more of a radiation intensity and a spectral distribution of the horticulture radiation. The term “controlling” and similar terms especially refer at least to determining the behavior or supervising the running of an element. Hence, herein “controlling” and similar terms may, e.g., refer to imposing behavior to the element (determining the behavior or supervising the running of an element), etc., such as e.g. measuring, displaying, actuating, opening, shifting, changing temperature, etc. Beyond that, the term “controlling” and similar terms may additionally include monitoring. Hence, the term “controlling” and similar terms may include imposing behavior.

[0056] The phrase “one or more of a radiation intensity and a spectral distribution of the horticulture radiation” may refer to the total spectral distribution of the horticulture radiation, i.e. the power, especially in the visible, near-UV and near-IR parts of the electromagnetic spectrum, provided by the irradiation system. However, in specific embodiments the control system may also be configured to control the spectral distribution, e.g. reducing or increasing parts of the spectral distribution relative to other parts of the spectral distribution. Hence, in embodiments the control system may be configured to control one or more of the intensity and the spectral distribution of the horticulture radiation, for instance in dependence of the one or more optical sensor signals.

[0057] As indicated above, the control system is configured to control one or more of a radiation intensity and a spectral distribution of horticulture radiation in dependence of the canopy being closed in at least part of the horticulture arrangement.

[0058] The controllable radiation sources can be, e.g., LED radiation sources, HID radiation sources, laser radiation sources, or other suitable radiation sources. One aspect of this disclosure relates to a computer comprising a computer readable storage medium having computer readable program code embodied therewith, and a processor, preferably a microprocessor, coupled to the computer readable storage medium, wherein responsive to executing the computer readable program code, the processor is configured to perform any of the methods disclosed herein.

[0059] One aspect of this disclosure relates to a computer program or suite of computer programs comprising at least one software code portion or a computer program product storing at least one software code portion, the software code portion, when run on a computer system, being configured for executing any of the methods disclosed herein.

[0060] One aspect of this disclosure relates to a non-transitory computer-readable storage medium storing at least one software code portion, the software code portion, when executed or processed by a computer, is configured to perform any of the methods disclosed herein.

[0061] As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, a method or a computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, microcode, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Functions described in this disclosure may be implemented as an algorithm executed by a processor / microprocessor of a computer. Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied, e.g., stored, thereon.

[0062] Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of a computer readable storage medium may include, but are not limited to, the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of the present invention, a computer readable storage medium may be any tangible medium that can contain, or store, a program for use by or in connection with an instruction execution system, apparatus, or device.

[0063] A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device.

[0064] Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber, cable, RF, etc., or any suitable combination of the foregoing. Computer program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java™, Smalltalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user’s computer, partly on the user’s computer, as a stand-alone software package, partly on the user’s computer and partly on a remote computer, or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user’s computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

[0065] Aspects of the present invention are described below with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products as claimed in embodiments of the present invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor, in particular a microprocessor or a central processing unit (CPU), of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer, other programmable data processing apparatus, or other devices create means for implementing the functions / acts specified in the flowchart and / or block diagram block or blocks.

[0066] These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function / act specified in the flowchart and / or block diagram block or blocks.

[0067] The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions / acts specified in the flowchart and / or block diagram block or blocks.

[0068] The flowcharts in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products as claimed in various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the blocks may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and / or flowchart illustrations, and combinations of blocks in the block diagrams and / or flowchart illustrations, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

[0069] Moreover, a computer program for carrying out the methods described herein, as well as a non-transitory computer readable storage-medium storing the computer program are provided. A computer program may, for example, be downloaded (updated) to the existing systems (e.g., to the existing control systems) or be stored upon manufacturing of these systems.

[0070] Elements and aspects discussed for or in relation with a particular embodiment may be suitably combined with elements and aspects of other embodiments, unless explicitly stated otherwise. Embodiments of the present invention will be further illustrated with reference to the attached drawings, which schematically will show embodiments as claimed in the invention. It will be understood that the present invention is not in any way restricted to these specific embodiments.

[0071] BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Aspects of the invention will be explained in greater detail by reference to exemplary embodiments shown in the drawings, in which:

[0073] FIG. 1 schematically illustrates a system for calibrating a multi-channel lighting system according to an embodiment;

[0074] FIG. 2 is a flow chart illustrating an embodiment of a method for calibrating a multi-channel lighting system; and

[0075] FIG. 3 illustrates a data processing system according to an embodiment.

[0076] DETAILED DESCRIPTION OF THE DRAWINGS

[0077] In the figures, identical reference numbers indicate identical or similar elements.

[0078] Fig. 1 schematically illustrates a multi-channel lighting system and a calibration system according to a first embodiment. The multi-channel lighting system 1 comprises a multi-channel lighting device 3 having a plurality of channels. Each channel of the plurality of channels is configured to emit radiation at a respective (controllable) radiant flux in a respective spectral band from a plurality of first spectral bands. In this context, a channel refers to one or more light sources that are controlled together. The channels are independently controllable over at least part of their output range.

[0079] In the depicted example, the multi-channel lighting device 3 comprises a plurality of controllable radiation sources 5. The controllable radiation sources may comprise, e.g., a plurality of individually or group-wise controllable LEDs. In this example, the radiation sources 5 are controlled by controller 7. The radiation sources may be configured to provide, e.g., growth or horticulture radiation. The controller can control the radiative flux of each of the channels, thus controlling a radiation intensity and a spectral distribution of the emitted radiation.

[0080] In the depicted example, the lighting system is a system for irradiating a plurality of plants 11. In such horticultural irradiating system, the channels may correspond to, e.g., blue, white, deep-red, and far-red. The system may comprise multiple channels with the same nominal color (e.g., two red channels); however, due to manufacturing differences, the actual output of two nominally identical channels may be different. The system may also comprise partially overlapping channels, e.g., a red channel and a red + far-red channel. Other systems may comprise different channels. For example, a Hue light may comprise a red LED, a green LED, a blue LED, a high-CCT white LED (e.g., T= 4000 K) and a low- CCT white LED (e.g., T= 2200 K). In this context, CCT refers to a correlated color temperature.

[0081] The calibration system comprises a data processing system 100, that during a calibration procedure may be communicatively connected to the multi-channel lighting device 3. The data processing system comprises a processor, a memory, an input interface, and an output interface. The memory is communicatively connected to the processor, The input and output interfaces are also communicatively connected to the processor. The memory may store executable instructions that, when executed by the processor, configure the processor to perform method steps as described herein, e.g., the method steps described with reference to Fig. 2. The input interface and output interface may be combined in a single I / O interface, e.g., a (general) communication interface. In particular, the data processing system may be configured to generate and transmit control signals, via the output interface, to the controller 7, which controller may be configured to receive said control signals and control the radiation sources 5 accordingly. An example of a data processing system is described in more detail below with reference to Fig. 3.

[0082] The processor of the data processing system 100 may be configured to receive (e.g., via the input interface or from the memory) a set of calibration settings. Alternatively, the processor may be configured to determine a set of calibration settings, e.g., based on properties of the multi-channel lighting device such as number of channels, spectral properties of the channels, radiant power of the channels, et cetera. Each calibration setting defines a respective radiant flux value for each channel of the multi-channel lighting system. The set of calibration settings comprises a number of linearly independent calibration settings equal to a number of channels of the multi-channel lighting system. The set of calibration settings may comprise additional calibration settings, so that the number of calibration settings is larger than the number of channels.

[0083] The set of calibration settings may comprise at least one calibration setting that defines a non-zero radiant flux value for a particular channel and a zero radiant flux value for all other channels of the multi-channel lighting system. This causes the channels to be activated individually, which is a straightforward way of ensuring linearly independent calibration settings. The set of calibration settings may be defined by a matrix <PC, also referred to as a settings matrix, wherein an zthrow represents an zthcalibration setting of the set of calibration settings and each column represents a channel (or a spectral band from the plurality of first spectral bands).

[0084] The data processing system 100 is configured to select a calibration setting from the set of calibration settings and to cause the multi-channel lighting device 3 to emit radiation according to the selected calibration setting.

[0085] The data processing system 100 is configured to receive a set of measurement values representing irradiance values for each spectral band in a plurality of second spectral bands different from the plurality of first spectral bands. The irradiance values are measured at a specified position 13 relative to the multi-channel lighting system. For example, in a horticultural application, the irradiance may be measured at the top of the canopy of the plants being irradiated. In an aquacultural setting, the irradiance values may be determined, e.g., at a surface of the water or at a predetermined distance (e.g., depth) from the surface.

[0086] In the depicted example, the measurements are obtained from a measurement device 9. The measurement device measure an irradiance value for each spectral band in a plurality of second spectral bands, which is different from the plurality of first spectral bands. For example, the first spectral bands may include, e.g., a white spectrum which overlaps with several second spectral bands. In practice, it is not uncommon for identical words being used to denote different (but potentially overlapping) first and second spectral bands; e.g., a ‘blue’ light source may emit light with wavelengths between 430-480 nm (first spectral band), whereas ‘blue’ light in a light recipe may refer to any light with a wavelength between 400- 500 nm (second spectral band).

[0087] The plurality of second spectral bands usually comprises the spectral bands that a user wishes to specify irradiance values for, e.g., in a so-called light recipe. The measurement device may measure an irradiance value for a number of wavelength bands over a predefined wavelength range that covers at least the spectral bands in the plurality of second spectral bands. The spectral resolution of the measurement device may be larger than that of the plurality of second spectral bands; for example, the measurement device may measure irradiance values with a resolution of 1 nm, and the irradiance value for a spectral band may be obtained by summing (or integrating) the irradiance value for all wavelengths or wavelength bands within the spectral band. The summing may be performed, e.g., by the measurement device, by the processor of the data processing device, or by a different device. The measurement values may define a measurement matrix Icwherein an zthrow represents the measured irradiance associated with the zthcalibration setting and each column represents a spectral band from the plurality of second spectral bands. Thus, the matricesCand Ichave the same number of rows (corresponding to the number of calibration settings), but may have different numbers of columns (corresponding to the pluralities of first and second spectral bands, respectively).

[0088] In some embodiments, the plurality of second spectral bands includes one or more of a UV-B spectral band substantially corresponding to wavelengths in a range of 280- 315 nm, a UV-A spectral band substantially corresponding to wavelengths in a range of 315- 400 nm, a blue spectral band substantially corresponding to wavelengths in a range of 400- 500 nm or a range of 420-490 nm, a green spectral band substantially corresponding to wavelengths in a range of 500-600 nm or a range of 500-570 nm, a red spectral band substantially corresponding to wavelengths in a range of 600-700 nm or a range of 620-680 nm, and a far-red spectral band substantially corresponding to wavelengths in a range of 700- 800 nm or a range of 700-750 nm.

[0089] The boundaries of the second spectral bands may be selected in part based on the properties of the measurement device.

[0090] The processor is further configured to determine a calibration matrix K based on the set of calibration settings and the measured irradiance values. The calibration matrix K may be determined based on the settings matrix and the measurement matrix, e.g., by computing:

[0091] K = / Tc( Tc)-i

[0092] The productc( jc)-1may also be referred to as a transpose of a right pseudoinverse of the calibration matrix <PCFunctionally equivalent calibration matrices may be constructed using, e.g., a left pseudoinverse, et cetera. Such alternatives can be readily constructed using known linear algebra techniques.

[0093] The calibration matrix K may be written as K = c • S, wherein c is a conversion constant that converts “first spectral band irradiance” to “first spectral band radiant flux” which typically depends on the specified position relative to the multi-channel lighting system, and wherein S’ is a spectral calibration matrix that converts “first spectral bands radiant flux” to “second spectral bands radiant flux”. In general, the scaling factor c can be estimated based on geometrical considerations, such as the inverse-square law. Alternatively, the scaling factor c may be measured separately, based on, e.g., a single wavelength or a full spectrum light intensity, which can be done much quicker than a complete spectral analysis used for the determination of S. The spectral calibration matrix S typically depends on the characteristics of the luminaire(s), and may change slowly over time. Consequently, a periodic calibration service may comprise updating the scaling factor c with a first frequency (e.g., monthly) and updating the spectral calibration matrix S’ with a second, lower frequency (e.g., yearly).

[0094] The calibration matrix allows to convert a set of radiant flux values for the plurality of channels into a set of irradiance values for the plurality of second spectral bands and / or vice versa, for example:

[0095] I = K or = K11 where I is a vector representing the set of irradiance values for the plurality of second spectral bands at the specified location and is a vector representing a set of radiant flux values for the plurality of first spectral bands (or the plurality of channels). Typically, the vector I is the output that a user wants to specify, or at least know, and which may be defined in a typical light recipe, while the vector <t> is the input that the user or the controller specifies to operate the multi-channel lighting device.

[0096] The multi-channel lighting device 3 may comprise at least one radiation source 5. In a typical embodiment, the multi-channel lighting device comprises a plurality of controllable radiation sources 5, typically LEDs, for generating artificial radiation.

[0097] Alternatively or additionally, the controllable radiation sources may comprise HID radiation sources, laser sources, or other suitable radiation sources.

[0098] The multi-channel lighting device may further comprise a controller 7. The controller 7 may comprise a processor and a memory communicatively coupled to the processor. The multi-channel lighting device 3 may comprise an interface to enable communication with data processing system 100. The multi-channel lighting device3 is configurable to emit radiation according to a radiation recipe to the plurality of plants 11.

[0099] A calibration system for calibrating a multi-channel lighting system according to an embodiment may comprise a data processing system 100 as described above. Optionally, the calibration system may also comprise the measurement device 9.

[0100] Fig. 2 is a flow chart illustrating an embodiment of a method for calibrating a multi-channel lighting system. Each channel of the multi-channel lighting system may be configured to emit radiation at a respective radiant flux in a respective spectral band from a plurality of first spectral bands. At least two of the channels of the multi-channel lighting system may be configured to emit substantially equal spectra. This method may be performed by a calibration system as described above, e.g., data processing system 100. A step 21 comprises receiving or determining a set of calibration settings. Each calibration setting defines a respective radiant flux value for each channel of the multichannel lighting system. The set of calibration settings comprises a number of linearly independent calibration settings equal to a number of channels of the multi-channel lighting system.

[0101] For example, the set of calibration settings may be represented by a settings matrixC, wherein an zthrow represents an zthcalibration setting of the set of calibration settings and each column represents a spectral band from the plurality of first spectral bands. The rank of the matrix <PCis equal to the number of columns of the matrix <PCIn some embodiments, the number of calibration settings is larger than the number of channels of the multi-channel lighting system. In that case, the settings matrix <PChas more rows than columns.

[0102] A step 23 comprises selecting a calibration setting from the set of calibration settings. A step 25 comprises configuring the multi-channel lighting system to emit radiation according to the selected calibration setting.

[0103] A step 27 comprises receiving a set of measurement values representing irradiance values for each spectral band in a plurality of second spectral bands different from the plurality of first spectral bands. The irradiance values are measured at a specified position relative to the multi-channel lighting system.

[0104] Steps 23-27 are repeated for each calibration setting in the set of calibration settings. Hence, a step 28 may comprise determining whether a set of measurement values has been received for each calibration setting, and if not, repeating steps 23-27 until the criterion is met.

[0105] For example, the set of measurement values may be represented by a measurement matrix Ic, wherein an zthrow represents the measured irradiance associated with the zthcalibration setting and each column represents a spectral band from the plurality of second spectral bands. Because the number of calibration settings is at least equal to the number of channels of the multi-channel lighting system, the measurement matrix has a rank equal to the number of columns of the measurement matrix (if this would not be the case, this may be an indication that at least one of the channels of the multi-channel lighting system is malfunctioning).

[0106] A step 29 comprises determining a calibration matrix based on the set of calibration settings and the measured irradiance values. The calibration matrix allows to convert a set radiant flux values for the plurality of channels into a set of irradiance values for the plurality of second spectral bands and / or vice versa. For example, the calibration matrix K may be defined as

[0107] K = fTc( Tc)-i or an inverse and / or transpose thereof.

[0108] As an example, a user may desire to use luminaire comprising a plurality of LED-chips to irradiate a target area according to a certain light recipe. To create light according to the light recipe, mixing light colors with a specific light intensity per light color is possible by powering the LED-chips used in a luminaire in a variety of ways. To realize the desired light recipe with the luminaire, the following aspects are important (1) the combination of LED-chips used in the luminaire; (2) the maximum power that the luminaire can handle; and (3) the spectra (also referred to as colors, expressed as, e.g., a nanometer range) that are being radiated by the various LED-chips; these spectra may be disjoint or completely or partially overlapping.

[0109] In general, the combination of these aspects (i.e., the LED-chips used in the luminaire, the maximum power of the luminaire, and the multi-color radiation), make it challenging for a typical user to create a desired or valid light recipe. Two examples to demonstrate this are provided:

[0110] 1. Turning on a ‘white’ LED-chip (which may be necessary to achieve the desired intensity) will automatically have an impact on the blue, green, and red spectra in the light recipe.

[0111] 2. Maximizing the green light spectrum may imply a minimum intensity for other colors (such as blue, red and far-red) due to the activation of the white LED. In other words, in the current example, it is not possible to have zero blue spectrum and some green spectrum for instance.

[0112] Therefore, the methods disclosed herein result in a calibration matrix K that converts non-calibrated spectral values (PPFs) that are provided as input into calibrated spectral distribution values (PPFDs) that are received by the crop. The inverse K-1of the calibration matrix K — or in case of a non-square matrix, the left inverse given by K-1= (KJK'1Kr— can be used to convert desired PPFD values in the crop into luminaire PPF (control) values to be set in the luminaires. In principle, the calibration procedure can be used for all current and future color-controlled luminaires with multiple channels, as well as one-channel dimmable luminaires by providing an accurate spectral composition of the LED PPF output. In the following, a concrete example is given to elucidate the calibration procedure. The method may be generalized as described above.

[0113] In this example, a user would like to calibrate the light levels on the crop coming from four-channel luminaires (e.g., as provided by Signify). The exact spectrum of each color channel is unknown (e.g., due to manufacturing uncertainties), and is indicated by a descriptive label, in this example: blue, white, deep-red, and far-red. In principle, no a priori knowledge of the channels is needed. In the current example, the control value is the nominal (absolute) radiant flux in pmol / s of each channel.

[0114] In this example, the set of calibration settingsCis provided in Table 1. The set of calibration settings comprises six calibration settings to calibrate four channels of the multi-channel lighting system, so that the number of calibration settings is larger than the number of channels. The set of calibration settings comprises, for each respective channel, a calibration setting wherein the respective channel has a non-zero radiant flux value and the other channels have a zero radiant flux value. Thus, the rank of the calibration settings matrix C is equal to the number of channels. Consequently, settings 5 and 6 may be considered to be included primarily to improve the accuracy of the calibration method.

[0115] Table 1. List of predefined PPF levels for calibration: <PC

[0116] A spectral-measurement device is set up (e.g., by an application engineer) at a specified position relative to the multi-channel lighting system, for instance in the crop at the canopy level. The multi-channel lighting system is configured to emit light according to the set of calibration settings, and the spectral-measurement device is configured to measure the associated irradiance value, in this case a photosynthetic photon flux density (PPFD) in pmol s1m2, for each of a plurality of second spectral bands. In this example, the second spectral bands are defined as blue (401-500 nm), green (501-600 nm), red (601-700 nm), and far-red (701-800 nm). The spectral -measurement device may make several measurements in each second spectral band, e.g., with a resolution of 1 nm, and the measurements may be summed according to the defined second spectral bands. The measurement data may be provided to a data processing system, which upon receiving the measurement data may construct a measurements matrix Icas shown in Table 2. Due to measurement variations, the measurement in setting 5 is not necessarily equal to the sum of those in settings 1-4, and similarly, setting 6 does not necessarily result in exactly twice the values of setting 5, even though the input in setting 5 is equal to the sum of settings 1-4 and the input in setting 6 is twice that of setting 5.

[0117] Table 2. Measurement values Icassociated with the calibration settings <PC

[0118] Using the calibration matrix <PCand the measurement matrix Ic, the calibration matrix K that converts uncalibrated control values (in this case, PPF) into calibrated output values (in this case, PPFD) is obtained as:

[0119] K = / Tc( Tc)-i

[0120] The elements of the resulting matrix are provided in Table 3.

[0121] Table 3. Resulting calibration matrix. The user can now calculate the real PPFD in the crop based on a luminaire channel setting of 200 pmol / s deep-red and 100 pmol / s white by multiplying a control vector = [200, 0, 100, 0]T(denoting PPF in pmol / s) with the calibration matrix K.

[0122] The (dimensionless) spectral calibration matrix S’ can then be computed by dividing all elements in the calibration matrix by the conversion constant c: Fig. 3 depicts a block diagram illustrating a data processing system as claimed in an embodiment.

[0123] As shown in Fig. 3, the data processing system 100 may include at least one processor 102 coupled to memory elements 104 through a system bus 106. As such, the data processing system may store program code within memory elements 104. Further, the processor 102 may execute the program code accessed from the memory elements 104 via a system bus 106. In one aspect, the data processing system may be implemented as a computer that is suitable for storing and / or executing program code. It should be appreciated, however, that the data processing system 100 may be implemented in the form of any system including a processor and a memory that is capable of performing the functions described within this specification.

[0124] The memory elements 104 may include one or more physical memory devices such as, for example, local memory 108 and one or more bulk storage devices 110. The local memory may refer to random access memory or other non-persistent memory device(s) generally used during actual execution of the program code. A bulk storage device may be implemented as a hard drive or other persistent data storage device. The processing system 100 may also include one or more cache memories (not shown) that provide temporary storage of at least some program code in order to reduce the number of times program code must be retrieved from the bulk storage device 110 during execution.

[0125] Input / output (VO) devices depicted as an input device 112 and an output device 114 optionally can be coupled to the data processing system. Examples of input devices may include, but are not limited to, a keyboard, a pointing device such as a mouse, a touch-sensitive display, an external control system referred to herein, or the like. Examples of output devices may include, but are not limited to, a monitor or a display, speakers, the LED driver, or the like. Input and / or output devices may be coupled to the data processing system either directly or through intervening I / O controllers.

[0126] In an embodiment, the input and the output devices may be implemented as a combined input / output device (illustrated in Fig. 3 with a dashed line surrounding the input device 112 and the output device 114). An example of such a combined device is a touch sensitive display, also sometimes referred to as a “touch screen display” or simply “touch screen”. In such an embodiment, input to the device may be provided by a movement of a physical object, such as, e.g., a stylus or a finger of a user, on or near the touch screen display. A network adapter 116 may also be coupled to the data processing system to enable it to become coupled to other systems, computer systems, remote network devices, and / or remote storage devices through intervening private or public networks. The network adapter may comprise a data receiver for receiving data that is transmitted by said systems, devices and / or networks to the data processing system 100, and a data transmitter for transmitting data from the data processing system 100 to said systems, devices and / or networks. Modems, cable modems, and Ethernet cards are examples of different types of network adapter that may be used with the data processing system 100.

[0127] As pictured in Fig. 3, the memory elements 104 may store an application 118. In various embodiments, the application 118 may be stored in the local memory 108, the one or more bulk storage devices 110, or apart from the local memory and the bulk storage devices. It should be appreciated that the data processing system 100 may further execute an operating system (not shown in Fig. 3) that can facilitate execution of the application 118. The application 118, being implemented in the form of executable program code, can be executed by the data processing system 100, e.g., by the processor 102. Responsive to executing the application, the data processing system 100 may be configured to perform one or more operations or method steps described herein.

[0128] In one aspect of the present invention, the data processing system 100 may represent a calibration system as described herein.

[0129] In another aspect, the data processing system 100 may represent a client data processing system. In that case, the application 118 may represent a client application that, when executed, configures the data processing system 100 to perform the various functions described herein with reference to a “client”. Examples of a client can include, but are not limited to, a personal computer, a portable computer, a mobile phone, or the like.

[0130] In yet another aspect, the data processing system 100 may represent a server. For example, the data processing system may represent an (HTTP) server, in which case the application 118, when executed, may configure the data processing system to perform (HTTP) server operations.

[0131] Various embodiments of the invention may be implemented as a program product for use with a computer system, where the program(s) of the program product define functions of the embodiments (including the methods described herein). In one embodiment, the program(s) can be contained on a variety of non-transitory computer-readable storage media, where, as used herein, the expression “non-transitory computer readable storage media” comprises all computer-readable media, with the sole exception being a transitory, propagating signal. In another embodiment, the program(s) can be contained on a variety of transitory computer-readable storage media. Illustrative computer-readable storage media include, but are not limited to: (i) non-writable storage media (e.g., read-only memory devices within a computer such as CD-ROM disks readable by a CD-ROM drive, ROM chips or any type of solid-state non-volatile semiconductor memory) on which information is permanently stored; and (ii) writable storage media (e.g., flash memory, floppy disks within a diskette drive or hard-disk drive or any type of solid-state random-access semiconductor memory) on which alterable information is stored. The computer program may be run on the processor 102 described herein.

[0132] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and / or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0133] The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of embodiments of the present invention has been presented for purposes of illustration but is not intended to be exhaustive or limited to the implementations in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the present invention. The embodiments were chosen and described in order to best explain the principles and some practical applications of the present invention, and to enable others of ordinary skill in the art to understand the present invention for various embodiments with various modifications as are suited to the particular use contemplated.

Claims

CLAIMS1. A method for calibrating a multi-channel lighting system having a plurality of channels, each channel of the plurality of channels being configured to emit radiation at a respective radiant flux in a respective spectral band from a plurality of first spectral bands, the method comprising: receiving or determining a set of calibration settings, each calibration setting defining a respective control value for each channel of the multi-channel lighting system, the set of calibration settings comprising a number of linearly independent calibration settings equal to a number of channels of the multi-channel lighting system; for each calibration setting in the set of calibration settings:— selecting a calibration setting from the set of calibration settings;— configuring the multi-channel lighting system to emit radiation according to the selected calibration setting; and— receiving, for each spectral band in a plurality of second spectral bands different from the plurality of first spectral bands, a measurement value representing an irradiance value at a specified position relative to the multi-channel lighting system; and determining a calibration matrix based on the set of calibration settings and the measured irradiance values, the calibration matrix allowing to convert a set of control values for the plurality of channels into a set of irradiance values for the plurality of second spectral bands and / or vice versa.

2. The method as claimed in claim 1, wherein the control value is a radiant flux value representing an expected radiant flux output by a respective channel of the multichannel lighting system, preferably the radiant flux comprising photosynthetic radiation.

3. The method as claimed in claim 1 or 2, wherein the plurality of second spectral bands includes one or more of: a UV-B spectral band substantially corresponding to wavelengths in a range of 280-315 nm, a UV-A spectral band substantially corresponding to wavelengths in a range of 315-400 nm, a blue spectral band substantially corresponding towavelengths in a range of 400-500 nm or a range of 420-490 nm, a green spectral band substantially corresponding to wavelengths in a range of 500-600 nm or a range of 500- 570 nm, a red spectral band substantially corresponding to wavelengths in a range of 600- 700 nm or a range of 620-680 nm, and a far-red spectral band substantially corresponding to wavelengths in a range of 700-800 nm or a range of 700-750 nm.

4. The method as claimed in any one of the preceding claims, wherein the calibration matrix K corresponds toK = fTc( Tc)-i or an inverse and / or transpose thereof, wherein <PCis a settings matrix wherein an zthrow represents an zthcalibration setting of the set of calibration settings and each column represents a spectral band from the plurality of first spectral bands, and Icis a measurement matrix wherein an zthrow represents the measured irradiance associated with the zthcalibration setting and each column represents a spectral band from the plurality of second spectral bands.

5. The method as claimed in any one of the preceding claims, wherein the number of calibration settings is larger than the number of channels of the multi-channel lighting system.

6. The method as claimed in any one of the preceding claims, wherein the set of calibration settings comprises at least one calibration setting that defines a non-zero control value for a particular channel and a zero control value for all other channels of the multichannel lighting system.

7. The method as claimed in any one of the preceding claims, wherein at least two of the channels of the multi-channel lighting system are configured to emit substantially equal spectra.

8. The method as claimed in any one of the preceding claims, wherein the set of calibration settings comprises at least two calibration settings defining different, positive control values for at least one channel of the multi-channel lighting system.

9. A data processing system comprising at least one processor, at least one memory storing executable instructions, the at least one memory being communicatively connected to the at least one processor, and at least one communication interface communicatively connected to the at least one processor, wherein execution of the executable instructions configures the at least one processor to: receive or determine a set of calibration settings, each calibration setting defining a respective control value for each channel of a multi-channel lighting device having a plurality of channels, each channel of the plurality of channels being configured to emit radiation at a respective radiant flux in a respective spectral band from a plurality of first spectral bands, the set of calibration settings comprising a number of linearly independent calibration settings equal to a number of channels of the multi-channel lighting device; for each calibration setting in the set of calibration settings:— select a calibration setting from the set of calibration settings;— generate and transmit, via the at least one communication interface, control signals to the multi-channel lighting device to configure the multi-channel lighting device to emit radiation according to the selected calibration setting; and— receive, via the at least one communication interface, for each spectral band in a plurality of second spectral bands different from the plurality of first spectral bands, an irradiance value at a specified position relative to the multi-channel lighting device; and determine a calibration matrix based on the set of calibration settings and the measured irradiance values.

10. A multi-channel lighting system comprising: a multi-channel lighting device having a plurality of channels, each channel of the plurality of channels being configured to emit radiation at a respective radiant flux in a respective spectral band from a plurality of first spectral bands; and the data processing system of claim 9, wherein the specified position relative to the multi-channel lighting device is an area of interest and wherein the data processing system is further configured to store the determined calibration matrix in the at least one memory.

11. The multi-channel lighting system as claimed in claim 10, wherein the at least one processor is further configured to: receive, via the at least one communication interface, a desired irradiance value for at least one second spectral band of the plurality of second spectral bands at the area of interest, determine a control value for each channel of the multi-channel lighting device using the calibration matrix and the desired irradiance value for the at least one second spectral band, and generate and transmit control signals to the multi-channel lighting device to configure the multi-channel lighting device to emit the corresponding radiation; and / or receive, via the at least one communication interface, a desired control value for at least one channel of the multi-channel lighting device and determine a corresponding irradiance value for each of one or more spectral bands of the plurality of second spectral bands.

12. The multi-channel lighting system as claimed in claim 10 or 11, wherein the multi-channel lighting system is a horticultural lighting system and the area of interest comprises a plant canopy and / or a plant tray.

13. The multi-channel lighting system as claimed in claim 10 or 11, wherein the multi-channel lighting system is an animal farming lighting system and the area of interest comprises one or more animals and / or a living area for one or more animals.

14. A computer program comprising instructions which, when executed by a data processing system as claimed in claim 9, causes the data processing system to perform the method as claimed in any one of claims 1-8.

15. A computer-readable storage medium having stored thereon a computer program as claimed in claim 14.

Images