WO2014115009A1

WO2014115009A1 - Light source and illumination system for aquaculture application.

Info

Publication number: WO2014115009A1
Application number: PCT/IB2013/061415
Authority: WO
Inventors: Cristina Tanase; Ivo Wilhelmus Johannes Marie Rutten; Eugen Jacob De Mol; Rob Franciscus Maria Van Elmpt
Original assignee: Koninklijke Philips N.V.
Priority date: 2013-01-22
Filing date: 2013-12-30
Publication date: 2014-07-31

Abstract

An illumination system is disclosed that contains a light source. The light source comprises a plurality of light emitting diodes. The light source also comprises a power input configured for receiving a power signal from a power source to enable the light emitting diodes to emit light at a light intensity selected from a light intensity range. In addition, the light source contains at least a first current source and a second current source to provide a first current and a second current, respectively. The first current source and the second current source are arranged such that the first current is provided to at least one of the light emitting diodes when a light intensity is selected in a first portion of the light intensity range and the second current is provided to at least one of the light emitting diodes when a light intensity is selected in a second portion of the light intensity range. The first portion and the second portion of the light intensity range correspond to different portions of the light intensity range.

Description

source and illumination system for aquaculture application

FIELD OF THE INVENTION

The present invention relates to the field of light sources and illumination systems comprising such light sources. More particularly, the invention relates to the field of light sources and illumination systems for aquaculture applications wherein the light intensity of the light source can be controlled accurately, particularly at low light intensities.

BACKGROUND OF THE INVENTION

Aquaculture is the marine counterpart of agriculture wherein aquatic animals, such a fish, are bred under controlled conditions. Examples of fish bred under these circumstances include salmon, tilapia, catfish, sea bass, bream and trout. Aquaculture is a fastly developping area that has undergone several major changes in the past decades.

A typical breeding cyclus for atlantic salmon is as follows. First, juveniles experience no / little light while in alevin stage followed by a continous 24 hour low lighting regime for a certain period of time. Then, a photoperiodic regime follows for a period of 6-8 weeks follows in order to induce smoltification, during which the fish are exposed to alternating periods of darkness and light of low intensity within 24 hours. After the period of 6-8 weeks, the fish are moved in a transfer tank wherein the fish is kept continously under artificial low light level to complete smoltification and prepare for sea transfer. The last step in this process is moving the fish to a sea cage for further growth.

It has been found that light plays an important role in farming fish, both in indoor fresh water and in outdoor fresh or marine water. Prior art illumination systems for such applications apply conventional artificial light sources, such as metal halide lamps. These lamps are switched on when artificial light is to be applied. There are no or only limited possibilities for controlling the light intensity of such sources.

More recently, it has been proposed to apply light sources comprising light emitting diodes (LEDs). The main advantage of LED systems is that such systems allow better control of the light intensity and colour of the emitted light. For example, US

2009/309515 discloses a method and apparatus for illuminating a marine habitat for growth utilizing an LED light system. The light system includes an LED light source, a power supply for such light source and a controller for controlling the activation status and the intensity of the LED light source.

The conventional lighting systems applied for aquaculture applications typically use high power metal halide light sources, e.g. light sources with an electrical power starting from 250W up to 2000 W. The conventional metal halide lighting has no control over the light intensity, the light turns on and off instantaneous. For such light sources, even when LEDs are applied, a problem exists in controlling the light intensity from such sources, especially at low light intensities where e.g. a very low light intensity between 0-10% of the maximum light intensity is desired. Prior art drivers for light emitting diodes are generally only suitable for controlling the light intensity at intensities higher than 10% of the maximum light intensity. This is caused by the lack of controllability of the drivers for the LED light sources when low light intensity is required.

SUMMARY OF THE INVENTION

In view of the above it is desirable to provide a light source for aquaculture applications wherein the light intensity of the light source is controllable.

In view of the above, it is further desirable to provide such a light source wherein the intensity of the light emitted from the light source is controllable in the range between 0-10 % of maximum light intensity and preferably in the full light intensity range between 0-100 %.

To that end, in a first aspect of the invention, a light source is disclosed that comprises a plurality of light emitting diodes. The light source is adapted to emit light at a light intensity within a light intensity range. The light source also comprises a power input configured for receiving a power signal from a power source to operate the light emitting diodes. In addition, the light source contains at least a first current source and a second current source to provide a first current and a second current, respectively. The first current source and the second current source are arranged such that the first current is provided to at least one of the light emitting diodes when a light intensity is selected in a first portion of the light intensity range and the second current is provided to at least one of the light emitting diodes when a light intensity is selected in a second portion of the light intensity range. The first portion and the second portion of the light intensity range correspond to different portions of the light intensity range.

In a second aspect of the invention, an illumination system is disclosed for illuminating a volume of water containing aquatic animals. The illumination system comprises at least one light source as defined in the previous paragraph and a controller. The controller is configured for controlling the at least one light source for selectively providing the first current and the second current to emit light in the first portion and the second portion of the light intensity range, respectively.

Still further, in a third aspect of the invention, a method for reducing stress experienced by aquatic animals in a volume of water using such an illumination system is disclosed.

The inventors have found that the application of artificial light causes stress to the fish, particularly when the light sources instantaneously emit light at full intensity or are switched off at once. It has e.g. been observed with juvenile fish that when, in a 6-8 weeks photoperiodic regime, the light sources immediately apply light at full light intensity , the fish start moving around fastly in the tank and the oxygen level in the tank drops, indicating an increased level of stress. The observed stress experienced by the fish results in a decrease in appetite (which results in smaller fish), a decrease in well-being and a higher chance of diseases and mortality.

The disclosed light source and illumination system allow for a gradual increase and decrease of the light intensity, especially in the low light intensity range, such that the eyes of the fish can slowly adapt to the light. A 100% level of the light intensity is only reached after a certain period of time, e.g. 30 minutes, an hour or two hours. As a consequence, the stress level of the fish is reduced.

The use of two separate current sources enables splitting up the control range for providing current to light emitting diode(s) into several subranges. At least one of these subranges may be selected such that appropriate control is obtained in a portion of the light intensity range between 0-10 % of the maximum light intensity. By appropriately selecting the current sources and taking into account that the output power of an individual current source is typically only controllable down to approximately 10% of its maximum output power, an appropriate arrangement of at least two current sources and a plurality of light emitting diodes can be configured such that the light intensity can be accurately controlled in at least the low range of light intensity and preferably across the full light intensity range. It should be noted however, that the controllability of the output power of typical current sources below about 10% is primarily a matter of accuracy of control. Controlling current sources down to lower power levels may also be applied if accurate control in the lower light intensities of the light source is not mandatory. It should be appreciated that the first and second portions of the light intensity range may be succesive portions of the light intensity range. The first and second portions preferably do not overlap and in embodiments they do not overlap. It should also be appreciated that more than two current sources may be part of the arrangement, resulting in further splitting up the light intensity control range in further portions of the light intensity range from which a light intensity can be selected. It should also be appreciated that the light emitting diode(s) to which the first and second currents are provided may or may not be the same light emitting diode(s). The current sources may be arranged to drive their own light emitting diode(s) or they may be arranged to selectively drive common light emitting diode(s).

Furthermore, it is noted that the light source, or more specifically, the current(s) provided to the light emitting diodes, can be controlled using a single control channel. Thus, in an embodiment of the light source, the light source comprises a control input for receiving a control signal for selectively providing the first current to at least one light emitting diode and the second current to at least one light emitting diode, to select emitting light in the first portion and the second portion of the light intensity range, respectively.

It is also noted that the light emitting diodes and the first and second current sources would normally be integrated in a single housing of the light source. However, the first and second current sources may also be contained in a housing separate from the light emitting diodes.

The maximum output powers of the current sources may be selected to be different in order to optimally control the total light intensity of the plurality of light emtting diodes over a full range between 0 -100% of the maximum light intensity of the light source.

It should be noted that, in a specific arrangement, the current sources may each comprise a controllable switch and an inductor for controlling the time during which a voltage source is connected or disconnected to the current source and for controlling the increase and decrease of the current supplied to the light emitting diodes. The inductor is connected in series with the light emitting diodes, such that for example a decreasing current is still fed to the light emitting diodes after disconnection from the voltage source.

In an embodiment of the light source, the first current source and the second current source are arranged in parallel and the light source comprises a switch arranged for selectively providing either the first current from the first current source or the second current from the second current source to the plurality of light emitting diodes. In this embodiment, the light emitting diodes may all be arranged in series and the switch determines whether the first or second current source provides a current to the series arrangement of light emitting diodes.

In another embodiment of the light source, the light emitting diodes are arranged such that a first set of light emitting diodes is connected to the first current source and a second set of light emitting diodes is connected to the second current source. In this embodiment, each current source provides a current to a dedicated set of light emitting diodes, thereby avoiding the need of a switch for switching a particular current sources to the light emitting diodes. The number of diodes may be different in each set, dependent e.g. on the maximum output power of the current source supplying the current for the set. The sets of diodes may be sets of diodes capable of emitting light of different colours. This enables spectral control by using a combination of different colours in different time periods, for example to provide sun rise and sun set light effects.

In an embodiment of the light source, at least the first current source and the second current source are arranged to receive a dc voltage signal from a common dc voltage source. Conventionally, drivers for LED light sources each contain an AC/DC voltage converter. By using a common voltage converter for the current sources, a cost effective solution is obtained. More particularly, the AC/DC voltage converter may comprise a power factor controller (PFC) that may be common to the current sources. A PFC ensures that the AC current waveform follows the AC voltage waveform as closely as possible such that power loss is reduced.

The light source may be used in an illumination system for illumination of a volume of water containing aquatic animals and in a method for reducing stress experienced by aquatic animals in the volume of water.

In further embodiments, the light sources may be adapted to, in addition to switching the first current source and the second current source for applying a first current respectively a second current to the at least one light emitting diode, further control the first current provided by the first current source and the second current provided by the second current source. In particular, the illumination system may comprise a controller adapted to provide control signals to control the light source such that the first current is varied to vary the light intensity of the light emitted from the at least one light emitting diode over the first portion of the light intensity range over a time period between 1 minute and 2 hours, preferably between 1 minute and 30 minutes, wherein the first portion of the light intensity range corresponds to a range from 0 to 10 % of the maximum light intensity range. The gradual increase and/or decrease of the light intensity of the light source may follow a linear or non-linear characteristic and reduces the stress experienced by the aquatic animals.

In an embodiment of the illumination system and method, the controller is adapted to control the light source such that the first current is varied to vary the light intensity over the first portion of the light intensity range and the second current is varied to vary the light intensity over the second portion of the light intensity range, wherein the first current is varied at a lower rate than the second current. Varying the rate at which the light intensity is changed enables taking the sensitivity of the fish eye photoreceptors into account. The light intensity may be varied slowly until the maximum eye sensitivity of the fish is reached, followed by a faster increase of the light intensity afterwards.

It is noted that the invention relates to all possible combinations of features recited in the claims. Thus, all features and advantages of the first aspect likewise apply to the second and third aspects, respectively. BRIEF DESCRIPTION OF THE DRAWINGS

The various aspects of the invention, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which:

Fig. 1 is a schematic illustration of an illumination system according to an embodiment of the invention;

Figs. 2A and 2B are schematic illustrations of a light source and a corresponding control characteristic of the light source for use in the illumination system of Fig. 1;

Fig. 2C is a schematic illustration of a particular embodiment of a current source for use in the light source of Fig. 2 A;

Figs. 3A-3C depict a light source and a corresponding control intensity - time characteristic according to a first embodiment of the invention and an application characteristic for illuminating a volume of water containing aquatic animals;

Figs. 4B and 4B depict a light source and a corresponding intensity - time characteristic according to a second embodiment of the invention;

Fig. 5 depicts a light source according to a third embodiment of the invention;

Fig. 6 is an exemplary light intensity vs. time characteristic for providing light to a volume of water using the illumination system of Fig. 1; and Fig. 7 is a flow chart illustrating steps of a method according to an

embodiment of the invention.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and to fully convey the scope of the invention to the skilled addressee. Like reference characters refer to like elements throughout the description.

Fig. 1 is a schematic view of an illumination system 100 comprising a light source 110. Fig. 2A is a schematic illustration of such a light source. The light source 110 comprises a plurality of light emitting diodes (LEDs) 200. The light source 110 is thereby arranged to emit light. The light source 110 is preferably arranged to be immersible in a volume of water.

The light source 110 comprises a first curent source 21 OA and a second current source 210B for respectively providing a first current II and a second current 12 to one or more of the light emitting diodes (LEDs) 200. As will become apparent from the further embodiments described in further detail below, different implementations for the arrangement of the electrical connections between the current sources 21 OA and 210B and the LEDs 200 have been envisaged. Therefore, these electrical connections are not drawn in the general embodiment of Fig. 2 A.

The first and second current sources 210A, 210B are operatively connected to a common DC voltage source 220. The common DC voltage source 220 comprises a power input for receiving a power signal e.g. from mains. As mentioned previously, the common DC voltage source 220 may comprise a power factor controller (PFC) that is common to the current sources driving the one or more LEDs. A PFC ensures that the AC current waveform follows the AC voltage waveform from the mains as closely as possible such that power loss is reduced.

The first and second current sources 21 OA, 210B and the DC voltage source 220 may be considered components of the driver for driving the light source and may be integrated in a single housing 120 of the light source 110. The housing 120 may optionally contain a plurality of light sources 110, which then integrated the driver and the light source into one housing.

The illumination system 100 further comprises a controller 130 which is adapted to provide control signals to the light source 110. The controller 130 is configured, as depicted in Fig. 2A, for controlling the light source 110 to selectively provide the first current II to at least one LED of the plurality of LEDs 200 and the second current 12 to at least one LED of the plurality of LEDs 200 so as to emit light in a first portion PI

respectively in a second portion P2 of the light intensity range of the light source 110 as is shown in general in Fig. 2B and as will be described in further detail with reference to Figs. 3-6. There are various implementations of how the controller 130 may influence which current source is providing current to one or more of the LEDs, as will be described below in more detail. Therefore, the control signal CTRL from controller 130 is shown to be applied to the light source 110 in general and not to a specific component thereof.

Optionally, the controller 130 may be operatively connected to an input device 140. The input device 140 is configured to receive values for e.g. the timing of control signals for applying the first and/or second current to the light source to control the rate at which the light intensity of the light emitted from the light source 110 is varied. These values may be set depending on factors such as type of species of animals, development stage of the animals and other factors. The values may be preset by the manufacturer or be set by a user, e.g. the operator of the fish hatchery.

The controller 130, or a different control means, is also configured for controlling the amount of current from the first and/or second current sources 21 OA, 210B to be fed to the LEDs 200 in order to affect the light intensity from these LEDs 200. A suitable control signal for such a purpose comprises a pulse width modulated signal to control the duty cycle of a current provided to the LEDs 200.

A particular embodiment of a current source 21 OA, 210B is schematically illustrated in Fig. 2C, wherein the value dT is controlled by pulse width modulation. The LEDs 200 are arranged in series with an inductor L and a switch S that connects to DC voltage of the PFC 220. Switch S is succesively opened and closed under control of a pulse width modulated control signal CTRL. During time intervals dT, switch S is closed and an increasing current flows from the voltage source through inductor L and LEDs 200 back to the voltage source. After time interval dT, switch S is opened and, as a result of opening switch S and the response to that by inductor L, a decreasing current flows through the LEDs for the remainder of the time interval T, namely T-dT. During this time interval T-dT, the current flows through the inductor L, the LEDs 200 and the current director arranged in parallel with the LEDs 200.

In the particular setup of Fig. 2C the current obtained through the LEDs 200 has a triangular waveform. The inductance of the inductor L determines the maximum current that can be obtained. In other words, the inductance of inductor L for current source 21 OA is different from the inductance of inductor L for current source 210B. In this manner, realistic values for dT can be maintained while making available a wide range of output currents. The peak of the waveform divided by 2 is the average current through the LEDs 200. The value of the current can be changed by changing the time period dT during which the switch S is closed.

Such a current source may be applied both for the current source 21 OA for obtaining the first portion PI and for the current source 210B for obtaining the second portion P2 of the light intensity range.

The illumination system 100 may further comprise at least one position actuator 160. The position actuator 160 is arranged to adjust the depth of immersion of the at least one light source 110 in the volume of water. The depth of immersion represents a vertical distance between a surface of the volume of water and the at least one light source 110. The controller 130 may further be adapted to receive a desired position setpoint for the at least one light source 110. The illumination system 100 may also be arranged above the surface of the volume of water for illumination of the body of water.

Methods of using the illumination system 100 for slowly increasing the light intensity over a period of time will now be described in more detail.

Fig. 3 A depicts a more detailed embodiment of a light source 110. The light source 110 comprises a power factor controller PFC and means 220 for converting an AC voltage into a DC voltage. The AC power may be provided from mains.

The light source 110 contains two current sources 210A and 210B having different maximum output powers of 30 W and 300 W respectively.

A switch 300 is provided for either connecting the first current source 21 OA or the second current source 210B to a series arrangement of LEDs 200. In a first state of the switch 300, the 30 W current source 21 OA is connected to the series of LEDs 200. In a second state of the switch 300, the 300 W current source 210B is connected to the series of LEDs 200. It should be noted that in light sources with more than two current sources, the switch 300 may be able to assume a corresponding number of states. Since current sources 21 OA and 21 OB feed their current to the same series of LEDs 200, both current sources 21 OA, 210B observe the same LED forward voltage and the current from the current sources determines the power provided to the LEDs 200. The current differences, i.e. the power differences, can be obtained by applying inductors of different inductances as has been illustrated with reference to Fig. 2C.

The CTRL signal in Fig. 3 A determines the pulse width modulation (PWM) of the current sources. Applying inductors with different inductances results in different currents when the same value for dT is used as was shown in Fig. 2C. In this manner, by using current sources with different output powers, a wider range of output currents can be obtained without putting extreme requirements on values for dT.

As shown in Fig. 3B, when switching on the light source 1 10, switch 300 is in the first state wherein a small current is provided to the series arrangement of LEDs 200 from the 30 W current source 21 OA and the current output is gradually increased until the 30W maximum output power is reached. Then, as soon as the maximum output power is reached, controller 130 switches switch 300 to the second state so that the second current 12 is now solely provided to the series arrangement of LEDs 200. Again, the output current is then gradually increased until the maximum output power of 300 W is reached.

Current source 21 OA is accurately controllable in a range of 10%- 100% of its maximum output power using the CTRL input, corresponding to a variation in the output power between 3 and 30 W. Similarly, current source 210B is accurately controllable in a range of 10%- 100% of its maximum output power using the CTRL input, corresponding to a variation in the output power between 30 and 300 W. It is assumed that the light emission intensity from the LEDs 200 is 100% when current is provided at 300 W. Thus, the combination of the current sources 21 OA, 210B, provides for an accuratly controllablerange between 3W and 300 W corresponding to a variation in the light intensity between 1% and 100%), wherein the first current source 21 OA provides for a variation in current II during which the light intensity varies between 1%> and 10%> of the total light intensity of the LEDs 200 and the second current source 210B provides for a variation in the current 12 during which the light intenstiy varies between 10%> and 100% of the total light intensity of the LEDs 200. In other words, whereas neither of the the current sources 21 OA, 210B alone are able to accurately control the light intensity LI of the LEDs 200 between 1%> and 100%>, the combination of the current sources is able to cover that this range.

Fig. 3C provides an application characteristic for an illumination system 100 applied to a tank with juvenile salmon. The light intensity LI is first slowly increased using only current source 210A starting from 1% until 10 % over a period of e.g. 5-15 minutes. After this period, a control signal is provided to the light source 1 10 such that the state of switch 300 switches to the second state wherein the second current source 210B provides current 12 to the LEDs 200. The light intensity is then brought to 100% of the maximum light intensity within further 15-25 minutes.

The controlled increase of the light intensity from 1% to 100% using the light source 1 10 results in a reduced stress level for the juvenile salmon in the tank.

The light intensity may then be maintained at 100% for a longer period of e.g. 1 1 hours. Thereafter, the light intensity LI is reduced slowly by again controlling the switch 300 from the controller 130. First the light intensity is reduced from 100% to 10% using the second current source for providing current 12 to the LEDs 200. Then switch 300 is switched such that first current II can be provided to the LEDs 200 and the light intensity can be controllably reduced from 10% to 1% of the total light intensity. After having obtained the 1%) light intensity, the light source 1 10 may be switched off completely.

The light and dark cycles as described above may be repeated. They may use different times if need be. The cycles may be programmed in controller 130 using e.g. user input 140.

Figs. 4A and 4B are schematic illustrations of a further embodiment of a light source 1 10. In the embodiment of Fig. 4A, the light source 1 10 contains three current sources 21 OA, 210B and 2 IOC. The current sources 21 OA, 210B and 2 IOC receive a DC voltage from a common DC voltage source 220, indicated as PFC. Each of the current sources 210A, 210B and 210C is assigned to a separate string of LEDs 200A, 200B and 200C, respectively. The number of LEDs is different for each of the strings. Alternatively or in addition, the colour of the light emitted from the LEDs may differ between the strings.

A single control input is provided to determine which of the current sources

21 OA, 210B and 2 IOC provides respective currents II, 12 and 13 to the corresponding string of LEDs 200A, 200B and 200C. The string with LEDs 200A may e.g. contain 1 LED. The string with LEDs 200B may e.g. contain 10 LEDs. The string with LEDs 200C may e.g. contain 100 LEDs.

In the embodiment of Fig. 4 A, each of the current sources 21 OA, 210B, 2 IOC provides a current to a separate string of LEDs. In contrast to the embodiment of Fig. 3 A, therefore, the LED forward voltage observed by the current sources may be selected to be different per current source, e.g. by providing different numbers of LEDs for each of the strings. As a result, the embodiment of Fig. 4A provides for wider dynamic range. In the embodiment of Fig. 4A, the current sources may be configured (e.g. by selecting appropriate inductances for inductors L) such that the same value for dT (see Fig. 2C) may result in the same output current from the current sources. However, since the LED voltage differs between the LED strings, the light output of the different strings is different despite the same current value being applied to these strings.

From the control characteristic depicted in Fig. 4B, it can be observed that the light intensity LI can now be controlled between 0.1% and 100% of the total light intensity that can be emitted from the light source 110. In a first portion of the light intensity range, the first current source 21 OA varies the current between 10% of its maximum output power and 100% of its maximum output power, i.e. between 0.3W and 3W. This corresponds to a change of the light intensity over portion PI . Similary, the output power of the second current source 210B can be varied between 3W and 30W and the output power of the third current source 210C can be varied between 30W and 300W. This corresponds to a variation in the light intensity over portions P2 and P3, respectively. In combination, this results in a variation of the light intensity between 0.1% and 100% of the total light intensity using the combination of current sources 21 OA, 210B and 2 IOC. Accordingly, the light source 110 of Fig. 4A can be used for aquaculture applications wherein the light intensity needs to be controlled carefully, particularly at low light intensity ranges below 10% of the total light intensity range.

Fig. 5 is a schematic illustration of a third embodiment according to the invention. In this embodiment, a dedicated driver I, II, ... n is provided for each of the strings of LEDs 200A, 200B, ... 200n. A driver includes both a current source and a DC voltage source for converting the AC voltage provided by the mains to a DC voltage for the current source. Therefore, the embodiment of Fig. 5 is a less preferable embodiment from a cost perspective in view of e.g. the need for complete drivers for each of the individual LED strings. The current provided by each driver is controlled via a control input CTRLn for each driver, using e.g. a DALI control interface. In this system, controller 130 may have stored an address of each of the drivers and control the current provided by the drivers from a single controller using these addresses.

The colour of the light emitted by the LEDs 200 A, 200B, ... 200n may be different.

In an example, the light source 110 may be a 750 W light source containing six drivers and six corresponding LED strings 200A...n. Two of the drivers may be drivers with a maximum output power of 75W and four drivers may have a maximum output power of 150 W. In order to emit low intensity light in a controllable fashion, first driver I is used to ramp up the power from 7.5W (1% of the total lamp power) to 75W (10% of the total lamp power). Then the second 75W driver II may be activated in addition to the first 75W driver to further increase the total light intensity using now a second string of LEDs 200B. It should be noted that the output power of the first driver I may be reduced a bit to avoid emission of a light spike when the second driver II is activated, as driver II may at switching on already start at 10% of its control range i.e. at 7.5W which then may be compensated for by temporally reducing the output power of driver I with a similar amount. When all drivers operate at maximum output power, the 750 W light source emits light at 100% of the total light intensity.

As described above, the strings of LEDs may emit light of different colours. This enables addressing spectral dimming control using a single control channel. This also enables using a combination of different colours during different time periods, for example to provide a spectrum that is linked to dusk and dawn effects.

Fig. 6 depicts a diagram showing that the rate at which the light intensity is varied may change, e.g. between the different portions PI, P2, P3 of the light intensity range.

The time for ramping up and dimming down the light between 0% and 100% of the maximum light intensity LI may be between 1 min and 2 hours. The rate at which the light intensity is changed is not necessarily a linear function but may depend on the sensitivity or adaptability of the fish eye photoreceptors. The change is indicated by ALI/At (where LI represents the light intensity and t represents the time).

The ramp up and dim down behavior can be defined by at least 2 zones: one in which the intensity of light increases very slowly in time (ALLAt)i which is related to very slow adaptation of fish to light and a second zone (ALI/At)₂ which is related to linear or more than linear (exponential, etc) ramp up or dim down of the light when a certain light intensity level LI is already reached, this light intensity being related to a certain level of adaptation of the eye sensitivity of fish. One might consider also an additional zone in which the daylight intensity is very high and above the threshold of eye sensitivity, when the fish does not so much perceive a further increase in light intensity (ALI/At)₃.

An indication regarding absolute light intensity (which is correlated in most of the cases to spectral sensitivity) and eye sensitivity of fish is present in the literature. An extensive study of the structure of the eye in response to different light levels was conducted in Ali MA. 1959. The ocular structure, retinomotor and photo-behavioral responses of juvenile Pacific salmon. Canadian Journal of Zoology 37:965-996. As an example, for juvenile salmon the time to adapt to a minimum light level is from 1 min up to 10 min and the minimum light intensity to be considered as a threshold in the zone 1 is 1 lux which equates to the light produced by moonlight, including dawn and dusk, leading to a (ALI/At)i of maximum 1 lux/hour as a suitable value in zone 1;

(ALI/At)₂ is related to daylight sensitivity for which the value to be considered are 400 lux minimum for sunrise or sunset conditions on a clear day.and 25,000 lux maximum in a typical overcast day and to which light adaptation takes place between 1 and 30 min, leading to a (ALI/At)₂ of 10³ up to 10⁵. As juvenile salmon is not yet used to open see light conditions such as changes between overcast daylight and bright sunlight, zone 3 may not apply in this case. The total time claimed for 0% to 100% ramp up or dim down of light is between 1 min and 2 hours.

Finally, Fig. 7 is a schematic illustration of a few steps of a method for reducing stress for aquatic animals in a volume of water using the illumination system 100 depicted in Fig. 1.

In a first step, the light intensity of the light source 110 or light sources 110 is increased slowly as described e.g. with reference to Fig. 3C. The light intensity from the applied light sources 110 can be controlled accurately, particularly at light intensities below 10% of the maximum light intensity. The light intensity is increased during a period tl from a very low light intensity level to the maximum light intensity level, wherein the light intensity can be controlled over the full range. In a second step, the light intensity is maintain at 100%) during a particular period of time t2. Then, after period t2 has expired, the light intensity level is slowly decreased during a period of time t3.

Claims

CLAIMS:

1. A light source (110) for providing light of a light intensity within a light intensity range, the light source comprising:

a plurality of light emitting diodes (200);

at least a first current source (21 OA) and at least a second current source (210B) for providing a first current (II) and a second current (12), respectively;

a power input (220) configured for receiving a power signal from a power source and providing power to at least the first current source (21 OA) and the second current source (210B);

wherein the first current source (21 OA) and the second current source (210B) are arranged such that

the first current (II) is provided to at least one of the light emitting diodes (200; 200A) when the light intensity is selected in a first portion (PI) of the light intensity range, and

the second current (12) is provided to at least one of the light emitting diodes (200; 200B) when the light intensity is selected in a second portion (P2) of the light intensity range,

wherein the first portion (PI) and the second portion (P2) of the light intensity range correspond to different portions of the light intensity range.

2. The light source (110) according to claim 1, wherein the first current source

(21 OA) is configured for providing the first current (II) to the at least one light emitting diode (200; 200A) for emitting light from the at least one light emitting diode at a light intensity selected in the first portion (PI) of the light intensity range, wherein the first portion (PI) of the light intensity range corresponds to a portion from 0 to 10 % of the light intensity range.

3. The light source (110) according to claim 1 or 2, wherein the first current source (21 OA) is configured to provide a first maximum output power and the second current source (21 OB) is configured to provide a second maximum output power, wherein the first maximum output power is different from the second maximum output power.

4. The light source (110) according to any one of the preceding claims, wherein the first current source (21 OA) and the second current source (21 OB) are arranged in parallel and the light source (110) comprises a switch (300) arranged for selectively providing either the first current (II) or the second current (12) to the plurality of light emitting diodes (200).

5. The light source (110) according to any one of the preceding claims 1-3, wherein the light emitting diodes (200) are arranged such that a first set of light emitting diodes (200 A) is connected to the first current source (21 OA) and a second set of light emitting diodes (210B) is connected to the second current source (210B).

6. The light source (110) according to claim 5, wherein the first set of light emitting diodes (200A) is configured for emitting light at a first wavelength and the second set of light emitting diodes (200B) is configured for emitting light at a second wavelength, wherein the first wavelength and the second wavelength are different wavelengths.

7. The light source (110) according to any one of the preceding claims, wherein the first current source (21 OA) and the second current source (210B) are arranged to receive a dc voltage signal from a common dc voltage source (220), wherein the common dc voltage source preferably comprises a power factor controller.

8. The light source (110) according to any one of the preceding claims, comprising a control input for receiving a control signal (CTRL) for controlling the providing of the first current (II) to the at least one light emitting diode and the second current (12) to the at least one light emitting diode.

9. An illumination system (100) configured for illumination of a volume of water for containing aquatic animals, the illumination system comprising:

at least one light source (110) according to one or more of the preceding claims, and

a controller (130) configured for controlling the at least one light source (110) so as to selectively provide the first current (II) to the at least one light emitting diode (200; 200 A) and the second current (12) to the at least one light emitting diode (200: 200B) for emitting light in the first portion (PI) and the second portion (P2) of the light intensity range, respectively.

10. The illumination system (100) according to claim 9, wherein

the light source (110) is configured for emitting light at a light intensity in a light intensity range, and

the controller (130) is adapted to control the light source such that the first current (II) is varied to vary the light intensity of the light emitted from the light source over the first portion (PI) of the light intensity range over a time period between 1 minute and 2 hours, preferably between 1 minute and 30 minutes, wherein the first portion of the light intensity range corresponds to a portion from 0 to 10 % of the light intensity range.

11. The illumination system (100) according to claim 9 or 10, wherein the controller (130) is adapted to control the light source (110) such that the first current (II) is varied to vary the light intensity over the first portion (PI) of the light intensity range and the second current (12) is varied to vary the light intensity over the second portion (P2) of the light intensity range, wherein a rate of variation of the first current (II) is lower than a rate of variation of the second current (12).

12. The illumination system (100) according to claim 11, wherein the first current

(II) and the second current (12) are varied such that the light intensity of the light source is varied according an exponential function, across the light intensity range.

13. The illumination system (100) according to any one of the claims 9 to 12, wherein the illumination system comprises a plurality of light sources (110) according to any one of the claims 1-8, wherein the light sources are immersed or immersible in the volume of water.

14. A method for reducing stress experienced by aquatic animals contained in a volume of water, the volume of water being illuminated with an illumination system according to the any of the claims 9 to 13, the method comprising the steps of:

selectively providing a first current (II) to at least one light emitting diode (200; 200A) of a light source (110) of the illumination system (100);

varying the first current (II) to vary a light intensity of light emitted from the at least one light emitting diode (200; 200 A) over a first portion (PI) of a light intensity range of the light source (110), over a time period between 1 minute and 2 hours, preferably between 1 minute and 30 minutes,

wherein the first portion (PI) of the light intensity range corresponds to a range from 0 to 10% of the light intensity range of the light source.

15. The method according to claim 14, further comprising the steps of:

varying the first current (II) to vary the light intensity over the first portion

(PI) of the light intensity range;

varying a second current (12) to vary the light intensity over a second portion

(P2) of the light intensity range;

wherein the first current (II) is varied at a lower rate than the second current

(12).