System and method for irradiating a plurality of plants

Abstract

System and method are disclosed for irradiating a plurality of plants (11)​. The system (3) comprises one or more luminaires (5) having a controllable power level and a controller (100) communicatively connected to the one or more luminaires (5)​. The one or more luminaires (5) are adapted to generate radiation with a controllable spectral distribution. The controller (100) comprises an input interface (6) for receiving a first control signal representing a target power level. The controller (100) is configured to determine a target spectral distribution for the one or more luminaires (5) in dependence on the target power level, and to send a second control signal to the one or more luminaires (5) to cause the one or more luminaires (5) to generate radiation with the target power level and with the target spectral distribution.

Description

[0001] SYSTEM AND METHOD FOR IRRADIATING A PLURALITY OF PLANTS

[0002] FIELD OF THE INVENTION

[0003] This disclosure relates to a system and method for irradiating a plurality of plants, in particular to such system wherein a controller is configured to determine a target spectral distribution for one or more luminaires in dependence on a received target power level. This disclosure further relates to a computer-implemented method for irradiating a plurality of plants and to a computer program and computer-readable storage medium for performing such method.

[0004] BACKGROUND OF THE INVENTION

[0005] To allow for year-round production of crops in greenhouses, such as tomato, many growers nowadays use supplemental lighting, such as LED lighting, especially during the autumn, winter, and spring, when daylight levels are in general insufficient for crop growth (in northern countries) and crop prices are high. The supplemental lighting, also more generally referred to as artificial lighting, can be applied above the canopy of plants (so- called top-lighting) or from within the canopy of plants (so-called inter-lighting).

[0006] Plants use light as the energy source for assimilating CO2 from the ambient air and converting it into biomass. This process is called photosynthesis. Part of the biomass is partitioned to the fruits (such as tomatoes). Light is therefore essential for plant and fruit growth. In modern greenhouses, environmental parameters such as climate and irrigation are well under control, meaning that the availability of light is the factor limiting growth.

[0007] Supplemental lighting based on LEDs is overtaking lighting based on HPS technology. Compared to HPS, LED lighting is almost a factor of two more energy efficient. Moreover, LED lighting can easily be dimmed (fast), allowing to tune the light level to the most optimal level at all times during a day. Soon, most LED installations sold will have dimming capability.

[0008] Supplemental LED lighting in horticulture consumes energy, resulting in an operational cost that is substantial and resulting in a non-negligible carbon footprint in case electricity generated from fossil fuels is used. It is therefore desired to reduce the energy consumption by adapting the light level to the changing circumstances (such as changing daylight levels) such as to maximize the light use efficiency (LUE, expressed in g / mol, i.e., the ratio of grams of harvested biomass to mols of light photons used to produce that biomass).

[0009] The process of photosynthesis occurs primarily under conditions of light within a range of wavelengths. This range is roughly from 400 - 700 nm. The radiation within this range is called photosynthetically-active-radiation (PAR). Typically, a luminaire for horticulture has different color channels to cover various parts of the PAR spectrum, e.g., red, blue, and green or white. Although the different color channels are often individually dimmable, many greenhouse / vertical farm / climate cell control systems only specify an overall light level. When changing (e.g., dimming) the overall light level, the light outputs of the individual channels are all changed (e.g., dimmed) by the same percentage as the overall light level. However, a different dimming behavior may be more efficient, for example, because the energy efficacies of the different color channels may differ substantially, and the crop may not use the light from the different color channels equally efficient.

[0010] US 2016 / 0088802 Al discloses individually dimming up / down the blue, red and far-red color channels in dependence on the composition of the daylight and the desired settings from a light recipe.

[0011] In light of the above, there is a need in the art for a system and method for irradiating a plurality of plants that further increases the light use efficiency.

[0012] SUMMARY OF THE INVENTION

[0013] To that end, an irradiation system for irradiating a plurality of plants is disclosed. The irradiation system comprises one or more luminaires having a controllable power level and a controller communicatively connected to the one or more luminaires. The one or more luminaires are adapted to generate radiation with a controllable spectral distribution. The controller comprises an input interface for receiving a first control signal representing a target power level. The controller is configured to determine a target spectral distribution for the one or more luminaires in dependence on the target power level, and to send a second control signal to the one or more luminaires to cause the one or more luminaires to generate radiation with the target power level and with the target spectral distribution. The irradiation system is used for growing the plurality of plants.

[0014] The controllable power level of the one or more luminaires may comprise at least one of: a controllable radiant power and a controllable energy consumption. Radiant power may be defined in terms of, e.g., radiant flux or Photosynthetic Photon Flux (PPF) expressed in pmol / s, irradiance or Photosynthetic Photon Flux Density (PPFD) expressed in pmol / (s • m2), irradiance expressed in W / m2, or any other suitable terms. Conversion between these units may depend on, e.g., spectral composition of the radiation, distance between the luminaire and a reference surface, shape of the radiation field created by the luminaire, et cetera. Energy consumption refers to the amount of (electric) energy consumed by the luminaire, and is typically expressed in watts.

[0015] The target power level is a non-spectrally resolved value. The target power level can be an absolute power level or a relative power level, e.g., relative to the maximum power level of the luminaire(s) or relative to the actual operating power level of the luminaire(s). A power level may also be referred to as a dimming value.

[0016] The radiant power and the energy consumption of the luminaire typically have a known relation, which may be non-linear. For example, depending on the configuration, a relative target power level of 0.5 may configure the irradiation system to consume half of its maximum energy consumption, or to output half of its maximum radiant power, which itself may be measured, e.g., in photons or in watts. For a typical irradiation system, these are three different power levels. In practice, the meaning of the target power level often depends on the output of the (greenhouse / vertical farm / climate cell control) computer providing the target power level.

[0017] As used herein, a relative power target level of 1 refers to the irradiation system outputting a maximum amount of radiation and consuming a maximum amount of energy, and a relative power level of 0 refers to the irradiation system outputting no radiation and consuming a minimum amount of energy.

[0018] In many situations, the (overall) power level for the irradiation system is determined by a greenhouse / vertical farm / climate cell control computer that also controls, e.g., climate and / or irrigation in a greenhouse. However, many greenhouse / vertical farm / climate cell control computers are not configured to control the spectrum of the irradiation system, e.g., to control individual color channels, but only provide an overall power level. The embodiments described herein take care of that lack of control by the greenhouse / vertical farm / climate cell control computer by, effectively, translating a single, non-spectrally resolved power level into a spectrally resolved control value (e.g., a plurality of control values for a plurality of color channels).

[0019] In an embodiment, the one or more luminaires comprise a first group of radiation sources having a first radiation spectrum and a second group of radiation sources having a second radiation spectrum, different from the first radiation spectrum. The first group of radiation sources is independently controllable from the second group of radiation sources. In such an embodiment, determining the target spectral distribution may comprise determining a first power level for the first group of radiation sources and a second power level, different from the first power level, for the second group of radiation sources.

[0020] For example, the groups of radiation sources may define color channels. The groups of radiation sources may be distributed over the luminaires (in embodiments with more than one luminaire); e.g., each luminaire may comprise part of the first group of radiation sources and part of the second group of radiation sources. Alternatively, each luminaire may comprise (part of) a single group of radiation sources.

[0021] For example, the second group of radiation sources may comprise (mainly) red light radiation sources, while the first group of radiation sources comprises white, blue, and / or green radiation sources.

[0022] It is noted that other embodiments than (LED-based) luminaires with separate controllable color channels are also envisaged. For example, it is known that for incandescent bulbs, the emitted spectrum is typically dependent on the light intensity. Consequently, there is a difference in emitted spectrum between reducing the number of burning bulbs to reduce the overall power level and reducing the power of each individual bulb to reduce the overall power level. Hence the controller may be configured to distribute an allotted amount of power over a plurality of radiation sources in different ways, leading to different spectral distributions.

[0023] In an embodiment, the first group of radiation sources has a lower efficacy than the second group of radiation sources, and wherein a ratio between the first power level and the second power level decreases with decreasing target power level.

[0024] For example, red radiation sources typically have the highest efficacy, while white radiation sources typically have the lowest efficacy. Efficacy can be defined as the relation between the output of the irradiation system on the one hand and the electrical energy consumption of the irradiation system on the other hand and is a measure of the efficiency of a radiation system. Phrased differently, it can be defined as a measure, e.g. a quantitative value, of the optical output per unit of electrical (power) input of the radiation system. The efficacy can be different for different light sources, e.g., different type of LEDs and / or different wavelengths (e.g., blue versus red LEDs). Thus, the efficacy can be defined in terms of, e.g., photosynthetically active photons output per second in pmol / s, optical output in lumens, radiant power in watts, et cetera, per watt of (electrical) power consumed by the respective group of radiation sources. In an embodiment, a proportion of red light in the target spectral distribution increases with a decreasing power level, for at least the first range of target power level values. For example, the proportion of red light in the target spectral distribution may increase with decreasing target power level for the first range of target power level values and may be constant for a second range of target power level values.

[0025] For example, the one or more luminaires may comprise a red channel and at least one other channel, the at least one other channel preferably being one of: a blue channel, a green channel, or a white channel. In that case, determining the target spectral distribution may comprise determining a first power level for the red channel and at least one second power level, different from the first power level, for the at least one other channel. Specifically, the system may be configured such that the proportion of red light in the target spectral distribution increases with a decreasing target power level for at least a first range of target power level values.

[0026] In an embodiment, the target spectral distribution is based on or takes into account a spectral distribution of natural light. For example, the target spectral distribution may reflect the spectral distribution of natural light, or supplement the natural light with missing spectral contributions, e.g., to achieve an overall spectral distribution optimized for crop growth. In the following the terms “natural light” and “daylight” will be used interchangeably.

[0027] The spectral distribution of the natural light can be a fixed reference spectral distribution, e.g., a single reference spectral distribution based on an average spectral distribution measured at noon over a certain time period, such as over a couple of days, a week or a month, e.g., in summer, or a time-dependent spectral distribution based on measurements at various times of the day and / or the year. The spectral distribution of the natural light can also be based on a current measurement of the spectral distribution. Depending on the implementation, the system may be configured to receive or determine a time of the day and / or a time of the year, and / or to receive or determine a spectral distribution of the natural light for that time of the day and / or time of the year.

[0028] For example, if the natural light already provides a sufficient amount of blue light (or at least, can be expected to provide a sufficient amount of blue light, for example based on a measured natural light level or a time of the day and year), the blue light fraction in the output of the irradiation system may be reduced without affecting crop growth.

[0029] In an embodiment, the controller is further configured to receive a signal indicative of a measured natural light level, and wherein the target spectral distribution is based on the measured natural light level. The natural light level typically refers to a light intensity and may be expressed using the same kind of quantities as the radiant power (e.g., PPF, PPFD, . . .), or using a different suitable quantity (e.g., lumen, lux, . . .). The natural light level can be a non-spectrally resolved value. The natural light level may be measured at one or more wavelengths or one or more wavelength bands, such as the visible wavelength range, the PAR wavelength range, the red wavelength range, etc.

[0030] In an embodiment, a ratio between blue light and red light is larger than or equal to a predefined threshold for all non-zero target power levels, preferably the predefined threshold being at least 1%, at least 2%, at least 3%, at least 4%, at least 5%, or at least 10%. For example, the target spectral distribution may comprise at least 5% blue light, which has been found to benefit plant health of the irradiated plants, as a certain fraction of blue light may be needed for, e.g., the opening of the stromata. The ratio is typically determined based on relative photon counts but may also be determined using a different suitable output measure as described above.

[0031] In an embodiment, the controller is configured to store a relationship between power levels and spectral distributions, and wherein the controller is configured to determine the target spectral distribution based on the first control signal and the stored relationship. The relationship can take the form of, e.g., a functional relationship, a look-up table, et cetera. In some embodiments, the controller is furthermore configured to receive a (new) relationship. This way, the relationship between the received target power level and the target spectral distribution can be adjusted, e.g., by the grower.

[0032] In an embodiment, the controller is configured to store a plurality of relationships between power levels and spectral distributions, to receive a further signal configuring the controller to select one relationship, and to determine the target spectral distribution based on the first control signal and the selected relationship.

[0033] For example, the controller may store a plurality of relationships between power levels and spectral distributions corresponding to (e.g., optimized for) different crops, or a plurality of relationships optimized for different greenhouse / vertical farm / climate cell zones, or a plurality of relationships optimized for different growth stages of crops, et cetera.

[0034] In an aspect, this disclosure relates to a horticulture arrangement comprising such an irradiation 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, and a controller that controls the (horticulture) radiation. 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.

[0035] Radiation for growth typically comprises a mixture of at least red and blue radiation. Red radiation may be understood as radiation having a wavelength between 600- 700 nm, whereas far-red radiation may be understood as radiation having a wavelength between 700-780 nm. Blue radiation may be understood as radiation having a wavelength between 400-500 nm. Green radiation may be understood as radiation having a wavelength between 500-600 nm. Radiation with a wavelength shorter than 400 nm, in particular radiation with a wavelength between 10-400 nm, may be referred to as ultraviolet radiation. Radiation with a wavelength longer than 780 nm, may be referred to as infrared radiation; in particular, radiation with a wavelength between 780-2500 nm may be referred to as near infrared radiation.

[0036] In particular, the term “horticulture radiation” especially refers to radiation having one or more wavelengths in one or more of a first wavelength range of 625-675 nm and a second wavelength range of 400-475 nm. Additionally, green or white light may be added. The relative energies (expressed in, e.g., W / m2) that are provided in these wavelength ranges may depend upon the type of plant and / or the growth phase. Especially, the term “horticulture radiation” may refer to the PAR range (the photosynthetically active range 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 range 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, i.e., 700-780 nm and near-infrared, e.g., 780- 850 nm. In general, plants may be sensitive both to absolute intensities of wavelengths and to relative intensities of wavelengths.

[0037] 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 controller may be configured inside or external from the climate cell. Especially, a plant farm may comprise a climate cell.

[0038] 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 quality parameters or air composition, air flow, etc. The radiation intensity as received by the plurality of plants may refer to, e.g., the physical quantity “irradiance” (typically expressed in W / m2) or “photon flux density” (typically expressed in pmol / (m2• s)). 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, and / or environment-related conditions to which the plant is subjected (such as natural radiation, temperature, relative humidity, CO2 level, irrigation, nutrient supply, etc.).

[0039] 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, the horticulture irradiation system may comprise racks with each rack having two or more plant supports, with each plant support having a corresponding radiation system overarching the plant support. Hence, the term “irradiation system” may also refer to a plurality of (individually controlled) irradiation systems.

[0040] The controller is configured to control both 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 operation 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 operation 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. The controllable radiation sources can be, e.g., LED radiation sources, HID radiation sources, incandescent radiation sources, or other suitable radiation sources. The one or more controllable radiation sources may include means for controlled radiant power to the plants, e.g., through filtering and / or concentrating the generated radiation.

[0041] In a further aspect, embodiments in this disclosure relate to a computer- implemented method for controlling an irradiation system, the irradiation system comprising one or more luminaires for generating radiation having a controllable spectral distribution and a controllable power, the method comprising: receiving a first control signal from an external signal source, the first control signal representing a target power level; determining a target spectral distribution for the one or more luminaires in dependence on the received first control signal; and sending a second control signal to the one or more luminaires to cause the one or more luminaires to generate radiation with the received target power level and with the determined target spectral distribution.

[0042] As above, the target power level can be, e.g., a set radiation intensity or a set (electrical) energy consumption.

[0043] Thus, a system as described above may be controlled using this method. The method may be executed, for example, by the controller described above.

[0044] One aspect of this disclosure relates to a computer, e.g., a greenhouse / vertical farm / climate cell control 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.

[0045] 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, such as a greenhouse / vertical farm / climate cell control computer system, being configured for executing any of the methods disclosed herein.

[0046] 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, such as a greenhouse / vertical farm / climate cell control computer, is configured to perform any of the methods disclosed herein.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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).

[0051] 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.

[0052] 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.

[0053] 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.

[0054] The flowchart and diagrams 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.

[0055] 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 controllers) or be stored upon manufacturing of these systems.

[0056] 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.

[0057] BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Aspects of the invention will be explained in greater detail by reference to exemplary embodiments shown in the drawings, in which:

[0059] FIG. 1 schematically illustrates a system for irradiating a plurality of plants according to a first embodiment;

[0060] FIG. 2 is a flow chart illustrating a first embodiment of a method for irradiating a plurality of plants;

[0061] FIG. 3 is a flow chart illustrating a second embodiment of a method for irradiating a plurality of plants;

[0062] FIG. 4 is a flow chart illustrating a third embodiment of a method for irradiating a plurality of plants; FIG. 5 schematically illustrates a system for irradiating a plurality of plants according to a second embodiment;

[0063] FIG. 6 is an example of a relation between a spectrally unresolved target power level and a plurality of spectrum-dependent power levels;

[0064] FIG. 7 is a schematic graph depicting an example of a supplemental light profile over a day; and

[0065] FIG. 8 illustrates a data processing system according to an embodiment.

[0066] DETAILED DESCRIPTION OF THE DRAWINGS

[0067] In the figures, identical reference numbers indicate identical or similar elements.

[0068] Fig. 1 schematically illustrates a system for irradiating a plurality of plants according to a first embodiment. The system 1 comprises an irradiation system 3 that is configured to irradiate the plurality of plants 11. The irradiation system 3 comprises one or more luminaires 5 and a driver 7 configured to drive the one or more luminaires 5. The one or more luminaires 5 may comprise, e.g., a plurality of individually or group-wise controllable LEDs. The one or more luminaires 5 may be configured to provide growth or horticulture radiation. The one or more luminaires 5 are adapted to generate radiation with a controllable spectral distribution.

[0069] The irradiation system 3 furthers comprise a controller 100. The controller 100 comprises an input interface 6 for receiving a first control signal from data processing system 99. Data processing system 99 can be, e.g., a greenhouse / vertical farm / climate cell control computer. The controller 100 may further comprise a processor 102 and a memory 104 communicatively coupled to the processor. The controller 100 is configured to control the one or more luminaires 5 to generate radiation with a set power level, e.g., a radiant power level and / or an energy consumption level, and with a set target spectral distribution. The controller 100 may comprise an output interface 8 for sending the second control signals to the one or more luminaires, either directly or indirectly.

[0070] For example, in the embodiment of Fig. 1, the controller 100 sends the second control signal to the driver 7, which then converts the second control signal (e.g., a 0-10V signal, a DALI signal, a power line communication PWC signal) into a drive signal (e.g., a current or PWM signal) for the one or more luminaires 5. In other embodiments, the driver may be integrated into the one or more luminaires. Yet other embodiments may not comprise a driver. The first control signal represents a target power level, which target power level defines at least one of a target radiant power or a target energy consumption. The controller 100 is configured to determine a target spectral distribution for the one or more luminaires 5 in dependence on the target power level, and to send a second control signal to the one or more luminaires 5 to cause the one or more luminaires to generate radiation with the target power level and with the target spectral distribution.

[0071] Each luminaire 5 may comprise at least one radiation source. In a typical embodiment, each luminaire comprises a plurality of controllable radiation sources for generating artificial radiation. The controllable radiation sources can be, e.g., LED radiation sources, HID radiation sources, or other suitable radiation sources. In some embodiments, each luminaire or group of luminaires has its own driver 7, which may be integrated in the luminaire. In the depicted example, only a single controller 100 is shown; however, in other embodiments, each luminaire or group of luminaires may have its own controller. Although shown separately, the controller and the driver may be integrated into a single device, which may or may not be integrated into one or more of the one or more luminaires.

[0072] The system 1 may also comprise the data processing system 99, e.g., a greenhouse control computer. Although the following focuses on implementation in a greenhouse, similar implementations are envisioned for, e.g., vertical farms or climate cells. The data processing system 99 is communicatively connected to the controller 100 of the irradiation system 3. In particular, the data processing system 99 may be configured to generate and transmit control signals, e.g., first control signals, to the controller 100, which controller may be configured to receive said control signals and control the radiation sources 5 accordingly.

[0073] In greenhouses, settings such as temperature, CO2 level, irrigation, vents, heating, as well as supplemental lighting are controlled by an algorithm running on the greenhouse control computer 99. Often, the lighting is controlled by sending an overall target power level signal to the irradiation system 3, e.g., a request to establish a supplemental lighting level between 0% and 100%. The target power level signal may also be referred to as a dimming signal.

[0074] This overall target power level signal may be translated into a target power level per luminaire or per channel within a luminaire by an algorithm running on the controller 100. In this case, this algorithm takes care of the dimming relations between the different channels according to the embodiments described herein. User input and / or channel efficacy and / or crop light recipe input and / or natural light level input can be included to establish the desired control value relations between the different channels. An example of a translation of an overall target power level into three target power levels for three light channels is provided below with reference to Fig. 6.

[0075] The controller 100 may be implemented as a (second) data processing system, for example as discussed in more detail below with reference to Fig. 8.

[0076] Fig. 2 is a flow chart illustrating a first embodiment of a method for irradiating a plurality of plants. The method may be executed, for example, by a controller 100 of an irradiation system 3 comprising one or more luminaires 5 for generating radiation having a controllable spectral distribution and a controllable power level. For example, the irradiation system as described above with reference to Fig. 1.

[0077] A first step 13 comprises receiving a first control signal from an external signal source, e.g., a greenhouse control computer. The first control signal represents a target power level, e.g., a set radiation intensity or a set energy consumption. The first control signal is not spectrally resolved; in a typical embodiment, it is just a single number. The first control signal may represent a relative target power level (typically between 0 and 1), but it can also be an absolute power level (expressed in, e.g., moles of photons produced, or Watts of electricity consumed).

[0078] A step 21 comprises determining a target spectral distribution for the one or more luminaires in dependence on the received first control signal in step 13. The determination can be based on, e.g., a function or look-up table stored in a memory of the controller. For example, the controller may be configured to store a relationship between power levels and spectral distributions, so that the controller may be configured to determine the target spectral distribution based on the first control signal and the stored relationship. An example of a function for converting a single target power level into several power levels for several color channels is illustrated in Fig. 6.

[0079] A further step 15 comprises sending one or more second control signals to the one or more luminaires to cause the one or more luminaires to generate radiation with the received target power level and the determined spectral distribution, as illustrated in steps 231-n.

[0080] There may be a further translation step performed by the driver to determine one or more control values for the radiation sources in the luminaires, based on the one or more second control signals.

[0081] Fig. 3 is a flow chart illustrating a second embodiment of a method for irradiating a plurality of plants. In this embodiment, the controller is configured to receive, in a step 17, a signal indicative of a measured natural light level. The measured natural light level is typically a non-spectrally resolved value. The measured natural light level can be an instantaneous value.

[0082] A step 22 comprises determining a target spectral distribution for the one or more luminaires in dependence on the first control signal received in step 13 and based on the measured natural light level received in step 17. For example, if there is a relatively high (instantaneous) measured natural light level, this can imply that the plants already receive a sufficient amount of blue light, so that the fraction of blue light in the determined target spectral distribution and to be provided by the luminaires can be lowered. This leads to a higher LUE. On the other hand, if the measured natural light level is relatively low, a higher fraction of blue light in the determined target spectral distribution may be used to warrant sufficient amounts of blue light.

[0083] Thus, by receiving, in step 17, the signal indicative of the measured natural light level, the system may effectively distinguish between various reasons for reducing the supplemental light level.

[0084] Fig. 4 is a flow chart illustrating a third embodiment of a method for irradiating a plurality of plants. In this embodiment, the steps 17, 25, and 19 are performed by a data processing system 99 as described above in connection to Fig. 1. In the embodiment, the controller is configured to receive, in step 13, a first control signal from the data processing system, e.g., a greenhouse control computer. The data processing system is configured to receive, in step 17, a signal indicative of a measured natural light level. As shown by the dashed line, optionally, the signal may also be received by the controller directly, as described above.

[0085] The measured natural light level may be an instantaneous value. The measured natural light level may also be an integrated value, e.g., a measured (partial) daily light integral. In some embodiments, an integrated value may be determined based on a plurality of instantaneous values. Based on the (instantaneous and / or integrated) natural light level, in a step 25, the data processing system determines the first control signal to be sent to the controller. For example, the data processing system may determine that a certain amount of supplemental light is needed to meet a certain total amount of light, either instantaneously or integrated over the entire day. Fig. 7 illustrates an exemplary relation between measured natural light level and determined supplemental light level. In the current example, the data processing system is further configured to receive, in step 19, a user input. The user input may specify, e.g., a minimum daily light integral, a minimum instantaneous light level, et cetera.

[0086] Thus, in the example shown in Fig. 4, the greenhouse control computer may control greenhouse settings such as temperature, CO2 level, irrigation, vents, heating, as well as supplemental lighting based on an algorithm and potentially user input. For example, the settings may depend on the crop currently being grown in the greenhouse. The lighting is controlled by sending the first control signal representing an overall target power level to the irradiation system (e.g., a request to establish a supplemental light level between 0% and 100%).

[0087] This overall target power level is translated, in step 15, into one or more second control signals, e.g., a control signal per color channel, by an algorithm running on e.g., a controller of an irradiation system (sometimes referred to as a lighting control computer). In this case, this algorithm takes care of the power level relations between the different color channels according to the present disclosure. User input and / or crop light recipe input and / or natural light level input can be included to establish the desired power level relations between the different color channels.

[0088] Alternatively, the translation of an overall power level to control values per color channel may also be done by the drivers of the luminaires (every luminaire or group of luminaires can have such as driver), which in that case can effectively be considered controllers for the purposes of the current disclosure.

[0089] Fig. 5 schematically illustrates a system for irradiating a plurality of plants according to a second embodiment. The supplemental-light system 3 comprises one or more luminaires 5 with, in this case, three independently controllable light channels 81-3. In an example, these may refer to a red channel 83, a blue channel 81, and a white or green channel 82. In this example, each luminaire comprises a driver (not shown). In other embodiments, a single driver may drive multiple luminaires. In some embodiments, the driver may be integrated into the lighting control computer 100.

[0090] In greenhouses, settings such as temperature, CO2 level, irrigation, vents, heating, as well as supplemental lighting are typically controlled by an algorithm running on a greenhouse control computer 99. The lighting is controlled by sending an overall dimming signal 33 to the supplemental lighting system 3; e.g., a request to establish a supplemental light level between 0% and 100%. A lighting control computer 100 translates this overall dimming signal (the target power level) to a dimming signal (target power level) 351-3 for each channel, which may similarly be expressed as a percentage. Optionally, external input, such as natural light level input 37and / or user input can be included to establish the desired dimming relations between the different color channels. The use of natural light level input has been described above with reference to Fig. 3. User input may be used to ensure specific user preferences are met.

[0091] As an example, the irradiation system 3 may have 3 dimmable color channels: channel 1, corresponding to first radiation sources 81; channel 2, corresponding to second radiation sources 82; and channel 3, corresponding to third radiation sources 83. In the depicted example, the irradiation system 3 is based on a single type of luminaire 5, having 3 different color channels, but in other embodiments, the irradiation system 3 can be based on 3 different types of luminaires with each type considered to be a separate color channel, or a combination of these options.

[0092] In this example, channel 1 produces blue light, channel 2 produces white light, and channel 3 produces red light (see Table 1). White light typically consists of a combination of blue (B), green (G), red (R), and a small fraction of far red (FR).

[0093] Typically, the efficacy (or energy efficiency) of these channels will be different. In general, to produce 1 mole of photons, the red channel (channel 3) will be the channel with the highest efficacy. A white channel typically has the lowest efficacy.

[0094] Table 1 Lamp channels and channel efficacies as typically used in supplemental lighting for horticulture.

[0095] Channel Colour Efficacy(pmol / J)

[0096] 1 Blue(450 nm) 2.8

[0097] 2 White 2.4

[0098] 3 Red (660 nm) 4.0

[0099] Fig. 6 is an example of a relation between a spectrally unresolved target power level (horizontal axis) and a plurality of spectrum-dependent power levels (vertical axis). The shown example has two different regimes, one for 0 % < P < 50 %, and one for 50 % < P < 100 %, where P is the spectrally unresolved target power level: for 0 % < P < 50 % :3= 0.9 , Pi = 0, i = 0.1 for 50 % < P < 100 % : P3= 0.5 P + 0.2,2= 0.3 P - 0.15, i = 0.2 P ~ 0.05

[0100] Here, 1-3 are the respective relative power levels for color channels 1-3. The sum of the power levels for the individual color channels should equal the received spectrally unresolved power level. Thus, the parameters P1-3 are subject to the constraint P + P2 + P3= P to ensure that the determined power level is indeed equal to the received power level. Here, the power level may refer either to the energy consumption of the system or to the light output of the system, possibly with some offset.

[0101] Thus, in this example, for power levels below 50%, predominantly light of the third channel (red) is used with a small amount of light of the first channel (blue), whereas for higher power levels, a gradually more equal mix of the three channels is used (albeit with still a relatively large contribution of the third channel). In a typical embodiment, channel 1 may refer to blue light, channel 3 to red light, and channel 2 to green light or white light. For example, in the embodiment of Fig. 5, spectral contribution 32 may represent the output of the third channel, spectral contribution 34 may represent the output of the second channel, and spectral contribution 36 may represent the output of the first channel. The total output power level 38 equals the received power level.

[0102] Fig. 7 is a schematic graph depicting an example of a supplemental light profile (solid line) over a day at the availability of a daylight profile (dotted line) over the day. Time is depicted on the horizontal axis and light intensity is depicted on the vertical axis. In this example, the grower expects that a dimming level of 80% suffices to reach a desired daily light integral (DLI). Hence, the supplemental light is switched on, at 04:00 h, at a dimming level of 80%. When the daylight level increases, the supplemental light level is gradually dimmed down between 7:30 and 10:30. During (or towards the end) of the daylight period, it might become clear that a dimming level of 80% is insufficient to reach the desired DLI. Consequently, the supplemental light level is gradually increased to 100% at the end of the daylight period, and maintained at that level until the supplemental lighting is switched off at 22:00 to ensure the plants receive a period of darkness of sufficient duration.

[0103] In the case of supplemental lighting for greenhouse horticulture, the supplemental lighting is preferably provided at times when the daylight level is low. For low light levels, the process of photosynthesis shows a linear relation with light level. At higher light levels, however, increasing the light level will (at some point) lead to a saturation of photosynthesis. As a result, the light use efficiency (LUE) goes down, which is undesirable. Therefore, the optimal supplemental light level is related to the daylight level: the lower the daylight level, the higher the supplemental light level can be, and vice versa, for example with the purpose of keeping the photosynthesis process running just below the saturation level.

[0104] Additionally, there is an optimal integral amount of light for any crop (the so- called daily light integral (DLI)), being the best compromise between biomass or fruit production versus LUE (for instance, for tomato, the desired DLI typically is 15 mol / m2 / day). Thus, the amount of supplemental lighting per day that is desired depends on the DLI of the daylight received during that day.

[0105] Most crops need a (usually contiguous) period of darkness. This limits the amount of time available for supplemental lighting, especially during seasons with long daylight periods. For instance, for tomato, this period of darkness should be at least 6 hours per day. Crop deficiencies will occur in case this rule is not obeyed.

[0106] Most crops require a certain minimum and / or maximum fraction of certain colors in the light irradiating the crop to initiate or maintain certain photobiological processes. These fractions may refer to an absolute radiant power of that color (expressed in, e.g., pmol / (m2• s)) or may refer to a relative radiant power of that color in the total radiant power. For example, most plants require a minimum fraction of blue light in the spectrum of light offered, to ensure opening of the stomata for CO2 uptake, while too much blue light limits growth. This may further depend on the developmental stage of the crop.

[0107] Based on the above considerations, a supplemental light profile as depicted in Fig. 7 can be further split in supplement light profiles for each of the available color channels as described herein.

[0108] As stated before, the optimal supplemental light level can be related to the daylight level. At times when the supplemental light level is comparable to or lower than the daylight level, the spectral composition of the supplemental radiation is typically of subordinate importance as far as the effect on the crop is considered. The reason is that in such cases the daylight spectrum in the combination of supplemental light and daylight tends to already contain sufficiently high fractions of, e.g., blue light and green light to make up for blue and green light that may be lacking in the supplemental light.

[0109] Consequently, when dimming the overall supplemental light level because of an increase in the available daylight level, the blue and green part of the supplemental light spectrum may be dimmed more than the red part. Thus, a proportion of red light in the target spectral distribution increases with decreasing target power level, and vice versa. As just mentioned, when the daylight level increases, the daylight tends to provide sufficient amounts of blue and / or green light, and hence, having blue and / or green light in the supplemental light may not be necessary anymore. And in that case, from a light use efficiency and an energy consumption point of view, it is typically better to exchange this blue and / or green light by red light.

[0110] This results in a power level behavior as exemplified in Fig. 6. Upon dimming the overall supplemental light level (e.g., following an increase in daylight level), the blue and white channels (channels 1 and 2, respectively, represented by contributions 34 and 36) are dimmed more than the red channel (channel 3, represented by contribution 32).

[0111] While the systems and methods for irradiating a plurality of plants described above refer to different color channels, such as a blue, white or geen, and red channel, these systems and methods may also be used in cases where the one or more luminaires comprise individually controllable channels of the same color.

[0112] Fig. 8 depicts a block diagram illustrating a controller as claimed in an embodiment. The controller may be implemented as a specifically configured, but otherwise well-known data processing system.

[0113] As shown in Fig. 8, the controller 100 may include at least one processor 102 coupled to memory elements 104 through a system bus 106. As such, the controller 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 controller 100 may be implemented as a computer that is suitable for storing and / or executing program code. It should be appreciated, however, that the controller 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.

[0114] 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.

[0115] Input / output (VO) devices depicted as an input device 112 and an output device 114 optionally can be coupled to the controller 100. 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 controller 100 either directly or through intervening I / O controllers. For example, input device 112 may be used to receive user input, or to receive a signal indicative of a measured natural light level.

[0116] In an embodiment, the input and the output devices may be implemented as a combined input / output device (illustrated in Fig. 8 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.

[0117] A network adapter 116 may also be coupled to the controller 100 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 116 may comprise a data receiver for receiving data that is transmitted by said systems, devices and / or networks to the controller 100, and a data transmitter for transmitting data from the controller 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 controller 100. The data receiver may also be referred to as an input interface. The data transmitter may also be referred to as an output interface. Other embodiments may use different kinds of input interfaces and / or output interfaces.

[0118] As pictured in Fig. 8, 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 controller 100 may further execute an operating system (not shown in Fig. 8) 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 controller 100, e.g., by the processor 102. Responsive to executing the application, the controller 100 may be configured to perform one or more operations or method steps described herein.

[0119] In one aspect of the present invention, the controller 100 may represent a controller for a LED driver as described herein. In another aspect, the controller 100 may represent a client controller. In that case, the application 118 may represent a client application that, when executed, configures the controller 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.

[0120] In yet another aspect, the controller 100 may represent a server. For example, the controller may represent an (HTTP) server, in which case the application 118, when executed, may configure the controller to perform (HTTP) server operations.

[0121] 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.

[0122] 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.

[0123] 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 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

CLAIMS:

1. An irradiation system (3) for irradiating a plurality of plants (11), the irradiation system (3) comprising: one or more luminaires (5) having a controllable power level, the one or more luminaires being adapted to generate radiation with a controllable spectral distribution; and a controller (100) communicatively connected to the one or more luminaires, the controller comprising an input interface for receiving a first control signal, the first control signal representing a target power level, the target power level defining at least one of: a target radiant power or a target energy consumption; wherein the controller (100) is configured to determine a target spectral distribution for the one or more luminaires (5) in dependence on the target power level, and to send a second control signal to the one or more luminaires (5) to cause the one or more luminaires (5) to generate radiation with the target power level and with the target spectral distribution.

2. The irradiation system (3) as claimed in claim 1, wherein the one or more luminaires (5) comprise a first group of radiation sources having a first radiation spectrum and a second group of radiation sources having a second radiation spectrum, different from the first radiation spectrum, the first group of radiation sources being independently controllable from the second group of radiation sources; and wherein determining the target spectral distribution comprises determining a first power level for the first group of radiation sources and a second power level, different from the first power level, for the second group of radiation sources.

3. The irradiation system (3) as claimed in claim 2, wherein the first group of radiation sources has a lower efficacy than the second group of radiation sources, and wherein a ratio between the first power level and the second power level decreases with decreasing target power level, wherein an efficacy of a group of radiation sources is defined as a measure of an optical output from the group of radiations sources per unit of electrical input to the group of radiation sources.

4. The system as claimed in any one of the preceding claims, wherein a proportion of red light in the target spectral distribution increases with decreasing target power level.

5. The system as claimed in any one of the preceding claims, wherein the target spectral distribution is based on or takes into account a spectral distribution of daylight.

6. The system as claimed in any one of the preceding claims, wherein the controller is further configured to receive a signal indicative of a measured daylight level, and wherein the target spectral distribution is based on the measured daylight level.

7. The system as claimed in any one of the preceding claims, wherein a ratio between blue light and red light is larger than or equal to a predefined threshold for all nonzero target power levels, preferably the predefined threshold being at least 1%, at least 2%, at least 3%, at least 4%, or at least 5%.

8. The system as claimed in any one of the preceding claims, wherein the controller (100) is configured to store a relationship between power levels and spectral distributions, and wherein the controller (100) is configured to determine the target spectral distribution based on the first control signal and the stored relationship.

9. The system as claimed in any one of claims 1-7, wherein the controller (100) is configured to store a plurality of relationships between power levels and spectral distributions, to receive a further signal configuring the controller (100) to select one relationship, and to determine the target spectral distribution based on the first control signal and the selected relationship.

10. A computer-implemented method for controlling an irradiation system (3), the irradiation system (3) comprising one or more luminaires (5) for generating radiation having a controllable spectral distribution and a controllable power, the method comprising: receiving a first control signal from an external signal source (99), the first control signal representing a target power level;determining a target spectral distribution for the one or more luminaires (5) in dependence on the received first control signal; and sending a second control signal to the one or more luminaires (5) to cause the one or more luminaires (5) to generate radiation with the received radiation intensity or energy uptake and with the target spectral distribution.

11. A computer program comprising instructions which, when executed by the controller of the system as claimed in one of claims 1 to 9, causes the system to perform the method as claimed in claim 10.

12. A computer-readable signal medium or non-transitory computer-readable storage medium having stored thereon a computer program as claimed in claim 11.

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