FIELD OF INVENTION

The present invention relates to a controlled environment agriculture lighting assembly, a PCB for use with such an assembly, and a method of assembly.

BACKGROUND

Artificial lighting is increasingly used in agricultural applications. Such lighting can be used in, for example, horticulture to extend a growing season, supplement natural light, emphasise particular growth characteristics, and many other applications.

The use of light emitting diodes (LEDs) as a basis for such artificial lights is increasing. This is due to factors such as improved energy conversion efficiencies, cooler operation, and a wider range of wavelength options.

SUMMARY

In accordance with a first aspect, there is provided a controlled environment agriculture lighting assembly comprising: a plurality of printed circuit boards (PCBs) arranged in series with each other, each PCB comprising: a PCB substrate; at least one lighting channel, the or each lighting channel comprising: a first input for receiving a drive signal; a first output for outputting a return signal; a second output for outputting a drive signal; and a second input for receiving a return signal; and one or more LEDs mounted to the substrate, the LED(s) for each channel being connected in series or parallel with each other; and a plurality of terminal pairs capable of being bridged by a resistance or a short- circuit link; the PCBs being connected such that the drive signals and return signals are passed between corresponding lighting channels on adjacent PCBs via the first input, second input, first output, and second output of the adjacent PCBs; the or each lighting channel being configured such that its LED(s) are connected for either constant current drive or constant voltage drive by an LED driver, wherein: the first output and the second input of each lighting channel of each PCB are electrically coupled to each other for passing a return signal from the second input to the first output; and for each of the lighting channel(s): if the LED(s) are connected for constant current drive, one or more short- circuit links are arranged to bridge a corresponding one or more of the terminal pairs such that the LED(s) are connected in series between the first input and the second output of each PCB; if the LED(s) are connected for constant voltage drive, one or more resistances are arranged to bridge a corresponding one or more of the terminal pairs to limit drive current through the LED(s) of each PCB.

Each lighting channel may comprise at least one LED on each of the plurality of PCBs.

Each lighting channel may extend through the plurality of PCBs, such that a single drive signal provided at the first input of a first of the PCBs in the series drives all LEDs in that lighting channel across all the PCBs.

The PCBs may be connected such that, if the LED(s) in one of the lighting channels are connected for constant current drive, the drive signal forthat channel passes serially through the LEDs across all of the PCBs.

The PCBs may be connected such that, if the LED(s) in a channel are connected for constant current drive, the return signal for that channel passes serially through each of the PCBs in a direction opposite that of the drive signal.

If the LED(s) in one of the lighting channel(s) are connected for constant current drive, the drive signal may be of a lower voltage at the first input of each PCB than it was at the first input of any preceding PCB in the series.

Each of the PCBs may comprise a drive signal bypass that, if the LED(s) in one of the lighting channel(s) are connected for constant voltage drive, provides a current path for the drive signal in parallel with the LED(s) in that lighting channel on the same PCB.

If the LED(s) in one of the lighting channel(s) are connected for constant voltage drive, the LEDs of each PCB may be configured to be driven in parallel with the LEDs of each of the other PCBs. Adjacent PCBs in the series may be connected through a connector, the connector connecting the first input and first output of one of the adjacent PCBs with the second output and second input of the other of the adjacent PCBs.

The controlled environment agriculture lighting assembly may comprise a loop-back connector connected to a sequentially last of the PCBs so as to loop back the drive signal of the corresponding lighting channel as the return signal. Optionally, the loop-back connector may electrically connect the second output of the sequentially last of the PCBs to the second input of the sequentially last of the PCBs.

The controlled environment agriculture lighting assembly may comprise a plurality of the lighting channels. Optionally, at least one of the lighting channels may be configured for constant current drive and at least one of the lighting channels is configured for constant voltage drive.

The first input and first output may be adjacent to each other at one end of each of the PCBs, and/or the second input and the second output are adjacent to each other at the other end of each of the PCBs.

Each of the lighting channel(s) may comprise a plurality of the LEDs. Optionally, for at least one of the lighting channels, at least one of the PCBs may have a different number of different LEDs and/or different LED types as compared with at least another of the PCBs.

In accordance with a second aspect, there is provided a PCB for use with the controlled environment agriculture lighting assembly of the preceding aspect, the PCB comprising: a PCB substrate; conductive traces defining: at least part of at least one lighting channel; and a plurality of terminal pairs for bridging by a resistance or a short-circuit link.

Each of the at least one lighting channel(s) may be configured for constant current drive or constant voltage drive by the bridging of at least some of the plurality of terminal pairs by one or more resistances and/or short-circuit links.

The PCB may comprise at least one LED for each of the lighting channel(s), and/or at least one resistance and/or short-circuit link bridging at least one of the terminal pairs.

In accordance with a third aspect, there is provided a method of manufacturing the PCB of the second aspect, comprising: installing one of more LEDs on the substrate for the or each of the lighting channels; for each, if any, lighting channel that is to be configured for constant current drive, bridging one or more of the terminal pairs for that channel with a short-circuit link such that the LED(s) are connected in series between the first input and the second output; and for each, if any, lighting channel that is to be configured for constant voltage drive, bridging one or more of the terminal pairs with a resistance for limiting drive current through the LED(s).

The method may comprise assembling a controlled environment agriculture lighting assembly according to the first aspect, the method comprising serially connecting a plurality of the PCBs of the second aspect to each other.

The method may comprise connecting the PCBs to each other using connectors. Optionally, each connector may be configured to connect a second output and a second input of one of the PCBs to a first input and a first output of an adjacent one of the PCBs.

The method may comprise connecting a loop-back connector to a sequentially last of the PCBs so as to loop back, in use, the drive signal of the corresponding lighting channel as the return signal.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a lighting assembly;

Figure 2 is a longitudinal section through II-II of Figure 1 ;

Figure 3 is a section through III-III of Figure 2;

Figure 4 is an underside view of the lighting assembly of Figures 1-3 with the diffuser removed;

Figure 5 is a schematic underside view of a PCB for use with the lighting assembly of Figures 1-4;

Figure 6 is a schematic underside view of the PCB of Figure 5, configured for constant current operation;

Figure 7 is a schematic underside view of several of the PCBs of Figure 6, connected in series with each other; Figure 8 is a schematic underside view of the PCB of Figure 5, configured for constant voltage operation;

Figure 9 is a schematic underside view of several of the PCBs of Figure 8, connected in series with each other;

Figure 10 is a schematic underside view of a further PCB;

Figure 11 is a schematic of LED drive circuitry for the PCB of Figure 10;

Figure 12 is a flowchart of a method of assembling a light assembly;

Figure 13 is a schematic underside view of an alternative PCB for use with a lighting assembly;

Figure 14 is a schematic underside view of PCBs for use with the lighting assembly of Figures 1-4;

Figure 15 is a schematic underside view of the PCBs of Figure 14, configured for constant current operation;

Figure 16 is a schematic underside view of the PCBs of Figure 14, configured for constant voltage operation; and

Figure 17 is a schematic underside view of the PCBs of Figure 14, configured for an alternative form of constant current operation as compared with Figure 15.

DETAILED DESCRIPTION

Referring to the drawings, Figures 1 to 4 show a controlled environment agriculture lighting assembly 100. In this implementation, lighting assembly 100 is designed for providing light in a horticultural context. Lighting assembly 100 can optionally take the form of a luminaire of the type described in patent application GB2020595.1 to Light Science Technologies Limited, the contents of which are expressly incorporated herein by cross-reference. Lighting assembly 100 comprises an elongate housing 102. In the illustrated implementation, housing 102 is formed from an aluminium extrusion. Housing 102 is generally trapezoidal in cross-section, having an open base that faces downwards when lighting assembly 100 is in use. A diffuser 104 extends across the open base.

Housing 102 includes a pair of downwardly extending clips 106 for holding one or more printed circuit boards (PCBs) as described in more detail below. Housing 102 is designed to be suspended above a crop (not shown), such that the light it emits is absorbed by the crop to improve growth in a desired manner.

At one end of housing 102, an enclosure 108 houses an LED driver in the form of drive circuitry 110. Drive circuitry 110 is connected to a source of power, such as a mains electricity supply, by a power cable 112. The operation of drive circuitry 110 is described in more detail below.

Lighting assembly 100 includes four PCBs 114, 115, 116, and 117 connected in series, as will be described in more detail below. PCBs 114-117 are retained within housing 102 by clips 106. PCB 114 is disposed closest to enclosure 108, and connected to drive circuitry 110 to be driven as described in more detail below.

PCBs 114-117 are based on the same PCB design, modified to suit the particular LEDs it carries. As best shown in Figure 5, each of PCBs 114-117 includes a PCB substrate 118 formed from a glass-reinforced epoxy material such as FR-4, although any other suitable substrate material may be used. Conductive copper traces 120 allow the defining of, in the implementation of Figure 5, a single lighting channel 122.

Lighting channel 122 includes a first input 124 for receiving a drive signal and a first output 126 for outputting a return signal. In the illustrated implementation, first input 124 and first output 126 are disposed adjacent to each other at the same end of PCB substrate 118.

Lighting channel 122 also includes a second output 128 for outputting a drive signal and a second input 130 for receiving a return signal. In the illustrated implementation, second output 128 and second input 130 are disposed adjacent to each other at the same end of PCB substrate 118, opposite the end at which first input 124 and first output 126 are disposed. Second input 130 and first output 126 are directly connected to each other.

Lighting channel 122 includes several terminal pairs for bridging by a resistance or a short-circuit link. Each terminal pair comprises a first copper pad and a second copper pad, spaced apart by a distance determined by whichever type of electronic component is intended to bridge that terminal pair.

In the implementation of Figure 5, there are four LED terminal pairs: first LED terminal pair 132, second LED terminal pair 134, third LED terminal pair 136, and fourth LED terminal pair 138, arranged in series with each other.

First LED terminal pair 132 includes a first terminal 140 connected to first input 124, and second terminal 142. Second LED terminal pair 134 includes a third terminal 144 connected to second terminal 142, and a fourth terminal 146. Third LED terminal pair 136 includes a fifth terminal 148 connected to fourth terminal 146, and a sixth terminal 150. Fourth LED terminal pair 138 includes a seventh terminal 152 connected to sixth terminal 150, and an eighth terminal 154.

Each pair of terminals in LED terminal pairs 132, 134, 136, and 138 is spaced to allow soldering of an LED to bridge the terminals. For example, if it is known that a 3030-type LED package is to be used, then the size of the terminals, and the spacing between them within each terminal pair can be selected to allow for the mounting of a 3030-type package. If a different package is to be used, then the size and spacing of the terminals can be adjusted accordingly. In at least some implementations, the size and spacing of the terminals is selected for compatibility with more than one LED package type.

Lighting channel 122 includes a first bridgeable terminal pair 156, second bridgeable terminal pair 158, and a third bridgeable terminal pair 160.

First bridgeable terminal pair 156 includes a ninth terminal 162 connected to eighth terminal 154, and a tenth terminal 164 connected to second output 128. Second bridgeable terminal pair 158 includes an eleventh terminal 166 connected to eighth terminal 154 and ninth terminal 162, and a twelfth terminal 168 connected to first output 126 and second input 130. Third bridgeable terminal pair 160 includes a thirteenth terminal 170 connected to first input 124, and a fourteenth terminal 172 connected to tenth terminal 164 and second output 128.

Each of the first, second, and third bridgeable terminal pairs 156, 158, and 160 is spaced to allow soldering of a resistor or a short-circuit link to bridge the terminals. Different combinations of resistances, short-circuit links, or open-circuits are applied to each of the first, second, and third bridgeable terminal pairs 156, 158, 160, depending upon the desired configuration of each of PCBs 114-117.

First input 124 and first output 126 terminate in a connector in the form of first connector 174, and second output 128 and second input 130 terminate in a connector in the form of a second connector 176. First connecter 174 is of a type that complementary with second connector. For example, first connector 174 can be a two-pin male connector having a pair of pins, and second connector 176 can be a two-socket female connector having a pair of sockets that are complementary to the pins of the male connector. In general, the second connector 176 of each PCB connects to the first connector 174 of the next PCB in the series. For example, the second connector 176 of first PCB 114 connects to first connector 174 of second PCB 115, and so on through third PCB 116, and fourth PCB 117. One exception to these connections is that for first PCB 114, first connector 174 connects to a complementary connector 177 (see Figures 2 and 4) connected to drive circuitry 110, as described in more detail below. The other exception to these connections is that for fourth PCB 117, second connector 176 may connect to a terminating connector. The terminating connector, if needed, may differ depending upon the intended drive configuration, as described in more detail below.

Lighting channel 122 can be configured for constant current drive or constant voltage drive by the bridging of at least some of the plurality of terminal pairs by one or more resistances and/or short-circuit links.

The skilled person will understand that LEDs operate most efficiently when operated at a particular forward current. In general, constant current drive typically involves the driver outputting a constant current at close to that optimal forward current for the string of LEDs with which the driver is intended to work. This can be achieved by varying the supply voltage. For example, the voltage required to drive a particular current through a single LED may need to be doubled to drive two LEDs in series with the same current. Dimming can be achieved by modulating the drive signal on a time basis. For example, the constant current may be pulsewidth modulated. Other dimming schemes are known to the skilled person.

In contrast, constant voltage drive involves outputting a constant voltage. Typically, a series resistance will be included to limit current through the LED(s) being driven, because current is not controlled as it is in a constant current arrangement. Again, pulse-width modulation may be used for dimming.

These descriptions of constant current and constant voltage are brief and general, and should not be considered anything more than an overview of particular implementation approaches. The skilled person will understand the different requirements for constant current drive and constant voltage drive, as well as the various ways in which they can be implemented.

An advantage of PCBs 114-117 is that they can be configured for constant current drive or constant voltage drive by the bridging of at least some of the plurality of terminal pairs by one or more resistances and/or short-circuit links. In addition, any necessary resistance value(s) can be optimised to suit the particular combination of LEDs chosen for any particular implementation.

Turning to Figure 6, there is shown an implementation of PCB 114 configured for use with a constant current driver. First LED terminal pair 132 is bridged with a first LED 178, second LED terminal pair 134 is bridged with a second LED 180, third LED terminal pair 136 is bridged with a third LED 182, and fourth LED terminal pair 138 is bridged with a fourth LED 184.

First bridgeable terminal pair 156 is bridged with a short-circuit link, in the form of a zero ohm surface mount device (SMD) resistor 186. Second bridgeable terminal pair 158 and third bridgeable terminal pair 160 are left open-circuit, and traces that do not carry current as a result are indicated by dotted lines.

The skilled person will appreciate that this arrangement results in first LED 178, second LED 180, third LED 182, and fourth LED 184 being connected in series with each other, between first input 124 and second output 128.

A constant current drive signal supplied to first input 124 will result in all of the LEDs lighting up, assuming a return signal can be passed back along the trace linking second input 130 and first output 126. One implementation for achieving this will now be described with reference to Figure 7, which shows PCBs 114-117 connected in series with each other via their respective first connectors 174 and second connectors 176. For each of PCBs 114-116, each second output 128 is connected to the first input 124 of the next PCB in series. First input 124 of first PCB 114 is connected to a drive terminal 188 of drive circuitry 110, and first output 126 of first PCB 114 is connected to a ground terminal 190 of drive circuitry 110.

A terminating connector 192 is connected to second connector 176 of fourth PCB 117. Terminating connector 192 includes an internal connection 190 that connects second output 128 to second input 130 of fourth PCB 117, thereby completing the circuit between drive terminal 188 and ground terminal 190 of drive circuitry 110.

In this implementation, drive circuitry 110 takes the form of a constant current driver configured to provide a constant current drive signal that is suitable for driving LEDs 178-184. Drive circuitry 110 is capable of providing sufficient drive voltage to ensure that all sixteen LEDs in this implementation can be driven with sufficient current. The constant current drive signal passes serially through the LEDs across all of the PCBs, being at a lower voltage at the first input of each PCB than it was at the first input of any preceding PCB in the series.

The output power of LEDs 178-184 can be controlled by pulse-width modulation of the constant current drive signal by drive circuitry 110, under the control of a lighting controller (not shown), which can be of a type known in the art.

Where different LEDs are used, drive circuitry may need to provide a different constant current output to suit the drive current requirements of those LEDs. The skilled person will appreciate that the same LED type can be used at each of the sixteen different LED terminal pairs 132-138 across PCBs 114-117. Alternatively, different types of LED can be used in any suitable combination across the sixteen LED terminal pairs 132-138, as long as they are all compatible with each other in terms of drive current. For example, the first and third LED terminal pairs 132 and 136 can include an LED having a first wavelength, while second and fourth terminal pairs 134 and 138 can include an LED having a different wavelength to the first, with both LED types having the same, or a sufficiently similar, drive current requirement.

The skilled person will also appreciate that not all LED terminal pairs 132-138 need have LEDs mounted to them. For example, where fewer than four LEDs per PCB, or fewer than sixteen LEDs across the series of PCBs, are required, one or more LEDs can be omitted, and the LED terminal pair from which it/they are omitted bridged with a short-circuit link, such as a zero-ohm SMD resistor.

Turning to Figure 8, there is shown an implementation of PCB 114 configured for use with a constant voltage driver. As with the constant current implementation of Figures 6 and 7, first LED terminal pair 132 is bridged with a first LED 178, second LED terminal pair 134 is bridged with a second LED 180, third LED terminal pair 136 is bridged with a third LED 182, and fourth LED terminal pair 138 is bridged with a fourth LED 184.

First bridgeable terminal pair 156 is left open-circuit, and traces that do not carry current as a result are indicated by dotted lines. Second bridgeable terminal pair 158 is bridged with a currentlimiting resistance in the form of a first SMD resistor 196. Third bridgeable terminal pair 160 is bridged with a short-circuit link in the form of a second SMD resistor 198 of zero-ohm resistance.

The skilled person will appreciate that this arrangement results in first LED 178, second LED 180, third LED 182, fourth LED 184, and first SMD resistor 196 being connected in series with each other, between first input 124 and first output 126. In addition, any drive signal supplied to first input 124 is fed forward via a current path provided through second SMD resistor 198 to second output 128, which is effectively in parallel with the LEDs in that lighting channel on the same PCB.

A constant voltage drive signal supplied to first input 124 will result in all of the LEDs lighting up, because current flows from first input 124, through LEDs 178-184, first SMD resistor 196, and first output 126.

Figure 9 shows PCBs 114-117 connected in series with each other via their respective first connectors 174 and second connectors 176. For each of PCBs 114-116, each second output 128 is connected to the first input 124 of the next PCB in series. First input 124 of first PCB 114 is connected to drive terminal 188 of drive circuitry 110, and first output 126 of first PCB 114 is connected to ground terminal 190 of drive circuitry 110.

Due to the way in which current is returned to the trace between second input 130 and first output 126 via second SMD resistor 196 on each of PCBs 114-117, a terminating connector 192 is not required at PCB 117 when the lighting channel of PCBs 114-117 is configured for constant voltage operation. Nevertheless, for reasons such as safety, neatness, or protection of the connector, second connector 176 on fourth PCB 117 may be terminated by a blanking plate 199 or other connector that can enclose the terminals of second connector 176, without looping back the drive signal.

In this implementation, drive circuitry 110 takes the form of a constant voltage driver configured to provide a constant voltage drive signal that is suitable for driving LEDs 178-184. Due to the drive signal supplied to first input 124 being fed forward via second SMD resistor 198 to second output 128, the LEDs of each PCB are effectively configured to be driven in parallel with the LEDs of each of the other PCBs.

Drive circuitry 110 is capable of providing current at the given drive voltage to ensure that all sixteen LEDs in this implementation can be driven with sufficient current.

The output of LEDs 178-184 can be controlled by pulse-width modulation of the constant voltage drive signal by drive circuitry 110.

The skilled person will appreciate that the same LED type can be used at each of the sixteen different LED terminal pairs 132-138 across PCBs 114-117. Alternatively, different types of LED can be used in any suitable combination across the sixteen LED terminal pairs 132-138. For example, the first and third LED terminal pairs 132 and 136 can include an LED having a first wavelength, while second and fourth terminal pairs 134 and 138 can include an LED having a different wavelength to the first, with both LED types having the same, or a sufficiently similar, drive current requirement.

Alternatively, or in addition, first SMD resistor 196 on each PCB can be selected to ensure that the series-connected LEDs 178-184 on that PCB can be driven by the constant voltage being output by drive circuitry 110. In this way, different combinations of LEDs 178-184 can be used on each PCB, offering considerable flexibility across the PCBs 114-117 as a whole. The skilled person will also appreciate that not all LED terminal pairs 132-138 need have LEDs mounted to them. For example, where fewer than four LEDs per PCB, or fewer than sixteen LEDs across the series of PCBs, are required, one or more LEDs can be omitted, and the LED terminal pair from which it/they are omitted bridged with a short-circuit link, such as a zero-ohm SMD resistor.

Where one or more LEDs are omitted, a value of first SMD resistor 196 may need to be adjusted to account for the reduced voltage drop across the smaller number of LEDs remaining. Alternatively, the LED terminal pair from which it/they are omitted can be bridged with an additional resistor (not shown) to ensure the constant voltage drive signal does not overdrive the remaining LEDs.

While Figures 1 to 9 show each PCB having a single lighting channel 122, the skilled person will appreciate that in other implementations, each PCB can have more than one lighting channel. The lighting channels can be physically and/or electrically in parallel with each other, extending from one end of the PCB to the other. For example, Figure 10 shows an alternative implementation of a PCB 114, in which subject matter in common with the previously-described implementations shares the same reference numerals.

The implementation of Figure 10 includes two parallel lighting channels 222 and 322. Prior to the addition of LEDs, resistors, and short-circuit links, each lighting channel 222 and 322 has the same schematic layout as lighting channel 122 in the implementation of Figure 5. Each lighting channel 222, 322 can be configured as either constant voltage or constant current.

Each of lighting channels 222, 322 can optionally be provided with its own LED driver of the correct type for its (constant current or constant voltage) configuration. This may be achieved in any suitable manner. For example, LED drive circuitry can include a separate LED driver for each channel, each LED driver being customisable for constant voltage or constant current operation by way of component selection. Alternatively, the LED drive circuitry can include sockets or other receptacles for receiving plug-in LED driver modules on a per-channel basis, allowing simple infield selection of drive type on a per-channel basis.

In the implementation shown in Figure 10, lighting channel 222 is configured to operate in constant current mode, and shares the same components as lighting channel 122 in Figure 6. In contrast, lighting channel 322 of Figure 10 is configured to operate in constant voltage mode, and shares the same components as lighting channel 122 in Figure 8. The skilled person will appreciate, however, that the PCB of Figure 10 can be configured in many different ways by changing which components are installed. For example, lighting channel 222 can be configured for constant voltage operation, constant current operation, or can be left without components if only lighting channel 322 is to be used. Similarly, lighting channel 322 can be configured for constant voltage operation, constant current operation, or can be left without components if only lighting channel 222 is to be used.

Figure 11 shows one example of drive circuitry 110 that can be used with the implementation of Figure 10. Drive circuitry 110 of Figure 11 includes a power supply 208, a first LED driver 210 and a second LED driver 212. To drive an assembly comprising a series of the PCBs 114 of Figure 10, first LED driver 210 is a constant current driver and second LED driver 212 is a constant voltage driver. The outputs of first LED driver 210 and second LED driver 212 terminate in a second connector 176, similar to second connector 176 of the PCBs. This allows the PCB 114 of Figure 10 to be connected to first LED driver 210 and second LED driver 212 via first connector 174 of PCB 114.

The ability to configure lighting channels for constant current and/or constant voltage operation by simply changing which pairs of terminals are short-circuited, bridged by resistances or left open-circuit renders it easier to meet complex lighting requirements that may be required in controlled environment agriculture lighting applications. For example, a particular application may require several different wavelengths of light, and it may be desirable to independently dim or otherwise control each wavelength or combination of wavelengths for optimising growth. Allowing different combinations of drive types for different lighting channels, and the ability to mix different LEDs within each channel (both electrically and in terms of physical position across a lighting assembly), may allow a supplier to maintain a relatively small stock of PCB types for a given range of lighting channels.

The number of lighting channels per PCB is limited only by space and power supply requirements. Accordingly, any desired number of channels may be provided on the PCB.

Although various implementations have been described for horticultural use, it will be appreciated that other implementations may be applied to different controlled environment agriculture lighting applications.

The skilled person will appreciate that there are other PCB layouts that offer similar functionality. For example, although Figure 5 shows that a current-limiting resistor can be mounted to second bridgeable terminal pair 158, the skilled person will appreciate that such a current-limiting resistor (when required) can be positioned anywhere in series with the LEDs on each PCB. This includes at one or more alternative and/or additional terminal pairs disposed at positions distributed before, within, and/or after the series of LEDs. Optionally, such resistance(s) can replace that at second bridgeable terminal pair 158, which can be replaced by a short-circuit link such as a zeroohm resistor, or a second bridgeable terminal pair may be omitted if not required.

In other implementations, when used for constant voltage operation, second and third bridgeable terminal pairs 158 and 160 can be left open-circuit, as described above for constant current operation, and one or more resistances included in series with the now series-connected LEDs on all the PCBs. This does require that the resistance(s) used take into account all of the LEDs across all PCBs, which may reduce the flexibility around adjusting the particular combination of PCBs at a future date.

In another implementation, the PCB traces are arranged such that the terminal pairs for each lighting channel of a PCB are disposed in series with each other. In that case, connecting multiple PCBs in series results in all LEDs in the (or each) lighting channel being connected in series with each other.

When configuring a lighting channel of this implementation for constant voltage operation, a suitable drive voltage for the LED driver is determined, along with the required total currentlimiting resistance for all of the LEDs. That resistance can then be distributed across any number of terminal pairs in series within the lighting channel. For example, the total resistance can be divided by the number of PCBs, and each PCB can have the resultant resistance installed across one of its terminal pairs. Alternatively, the required resistance can be divided across a subset of the PCBs.

An example of such an arrangement is shown in Figure 13, in which elements in common with earlier-described implementations are indicated with like reference signs. Unlike other described implementations, there is no “feed-forward” of the drive signal from PCB to PCB. Instead, the current always passes through all elements coupled across terminal pairs 132, 134, 136, 138 and 156. Each of those terminal pairs can, for example, be bridged with: an LED or a zero-ohm resistor (for constant current configuration); or an LED or a resistor (for constant voltage operation). As with the earlier-described implementations, multiple lighting channels may be provided in parallel on each PCB.

Where multiple resistors are used, it is not necessary for them to be equal in value to each other, due to all resistances and LEDs being connected in series. While the PCB is somewhat simpler in this implementation, it does require a different drive voltage depending upon the total number of PCBs to be connected in series. In all implementations, some or all of any required current-limiting resistances can be connected off-PCB. Such resistances can be, for example, collocated with the LED drive circuitry, and/or connected within one or more of the connectors or associated wiring.

An alternative implementation is shown in Figures 14 to 17, in which elements in common with earlier-described implementations are indicated with like reference signs. Only a single lighting channel is shown in Figures 14 to 17, but two or more lighting channels can be provided, for example as described in other implementations.

Figure 14 shows bare PCBs 114, 115, without any resistors or LEDs installed. Each of PCBs 114, 115 comprises two interconnected PCB substrates. PCB 114 includes a first PCB substrate 414 connected to a second PCB substrate 416, and PCB 115 includes a first PCB substrate 418 connected to a second PCB substrate 420.

Each PCB substrate includes an upper path 456, a middle path 458 and a lower path 460. The various bridgeable terminal pairs can be selectively bridged to direct current through different combinations of PCB substrates and paths. Some examples of such combinations are described below with reference to Figures 15 to 17.

Conductive connections between adjacent PCBs/substrates can be by multi-pin or multi-blade connectors, for example, or any other suitable connection method.

Each of first substrates 414, 418 includes bridgeable terminal pairs for accepting resistors (including zero-ohm resistors), such that the PCBs can be configured for serial and/or parallel driving of the LEDs. For example, each of first substrates 414, 418 includes a fourth bridgeable terminal pair 424, a fifth bridgeable terminal pair 426, and a sixth bridgeable terminal pair 428.

Each of second PCB substrates 416, 420 includes a seventh bridgeable terminal pair 430 and an eighth bridgeable terminal pair 432. Seventh bridgeable terminal pair 430 and eighth bridgeable terminal pair 432 are connected in series with first, second, third, and fourth LED terminal pairs 132, 134, 136, and 138.

Each of PCBs 114, 115 includes a first input for receiving a drive signal and a first output for outputting a return signal. Depending upon the arrangement and configuration of PCBs 114, 115 (and any LEDs and/or resistors installed on them), the first input can be considered, for example, any of terminals 434, 435, 436, 437, 438 or 439. Similarly, depending upon the arrangement and configuration of PCBs 114, 115 (and any LEDs and/or resistors installed on them), the first output can by any of terminals 434, 435, 436, 437, 438 or 439, except that which is the first input. Each of PCBs 114, 115 includes a second input for receiving a drive signal and a second output for outputting a return signal. Depending upon the arrangement and configuration of PCBs 114, 115 (and any LEDs and/or resistors installed on them), the second input can be considered, for example, any of terminals 434, 435, 436, 437, 438 or 439, except that which is the first input or the second input. Similarly, depending upon the arrangement and configuration of PCBs 114, 115 (and any LEDs and/or resistors installed on them), the second output can by any of terminals 434, 435, 436, 437, 438 or 439, except that which is the first input, the first output, or the second input.

Figure 15 shows PCBs 114, 115, along with a further PCB substrate 422 that is serially connected to second PCB substrate 420 via terminals 437, 438, 439. Further PCB substrate 422 can be used as a terminating connector, or form a first PCB substrate for a further second PCB substrate (not shown). Like first PCB substrates 414 and 418, further PCB substrate 422 includes a fourth bridgeable terminal pair 424, a fifth bridgeable terminal pair 426, and a sixth bridgeable terminal pair 428.

In Figure 15, PCBs 114, 115 and further PCB substrate 422 are configured for constant current drive. To this end, first, second, third, and fourth LEDs 178-184 are connected in series with a first resistor 440 connected across first bridgeable terminal pair 430 and a second resistor 442 connected across second bridgeable terminal pair 432. A third resistor 444 is connected across bridgeable terminal pair 426 on first PCB substrate 414, a fourth resistor 446 is connected across bridgeable terminal pair 426 on first PCB substrate 418, and a fifth resistor 448 is connected across bridgeable terminal pair 424 on further substrate 422.

In use, current flows serially from terminal 434 across upper path 456 of first PCB substrate 414, second PCB substrate 416, first PCB substrate 418, second PCB substrate 420, and further PCB substrate 422. Current then passes through fifth resistor 448, then returns back along middle current path 458, through first, second and third LEDs 178, 180, and 182, first resistor 440, fourth LED 184, and second resistor 442 on second PCB substrate 420. The current continues through fourth resistor 446, then through first, second and third LEDs 178, 180, and 182, first resistor 440, fourth LED 184, and second resistor 442 on second PCB substrate 416. Finally, the current passes through third resistor 444 and exits at terminal 435.

The values of first resistor 440, second resistor 442, third resistor 444, fourth resistor 446, and fifth resistor 448 across all of the substrates are selected such that they add together to give a total series resistance that is appropriate for all of LEDs 178-184 across all substrates. It is possible to use zero-ohm resistors across some or all of the bridgeable terminal pairs in series with the LEDs. Where any non-zero resistances are used, there can be thermal advantages to distributing the required total resistance across two or more resistors.

Optionally, all resistors can be zero-ohm, and any required resistance connected in series via one or more connectors (not shown) and/or within, or in series with, the constant current driver (not shown) used to drive the LEDs.

The skilled person will appreciate that any suitable combination of terminals 434, 435, 436, 437, 438 or 439 on any of the first, second, or further substrates can be chosen as the positive and negative terminal for the drive current, as long as the LEDs are forward-biased in use.

Figure 16 shows PCBs 114, 115, configured for constant voltage drive. As with Figure 15, first, second, third, and fourth LEDs 178-184 are connected in series with first resistor 440 connected across bridgeable terminal pair 430 and second resistor 442 connected across bridgeable terminal pair 432. Third resistor 444 is connected across bridgeable terminal pair 426 on first PCB substrate 414 and fifth resistor 448 is connected across bridgeable terminal pair 424 on further substrate 422.

A sixth resistor 450 is connected across bridgeable terminal pair 424 of first PCB substrate 418, a seventh resistor 452 is connected across bridgeable terminal pair 428 of first PCB substrate 418, and an eighth resistor 454 is connected across bridgeable terminal pair 428 of first PCB substrate 414.

In use, and in relation to the LEDs on PCB 114, current flows serially from first terminal 434 across upper path 456 of first PCB substrate 414 and second PCB substrate 416. The current then splits. Part of the current passes through sixth resistor 450 to middle path 458, and then returns to second PCB substrate 416 along middle path 458. It passes serially through first, second, and third LEDs 178, 180, 182, first resistor 440, fourth LED 184, and second resistor 442 on second PCB substrate 416, before passing to middle path 458 on first PCB substrate 414. From there, the current passes though eighth resistor 454 to lower path 460, then exits at terminal 436.

In relation to the LEDs on PCB 115, the current that does not pass through sixth resistor 450 continues along upper path 456 of first PCB substrate 418, second PCB substrate 420, and further PCB substrate 422. It then passes through fifth resistor 448 and then returns to second PCB substrate 420 along middle path 458. It passes serially through first, second, and third LEDs 178, 180, 182, first resistor 440, fourth LED 184, and second resistor 442 on second PCB substrate 420, before passing to middle path 458 on first PCB substrate 418. From there, the current passes though seventh resistor 452 to lower path 460 of first PCB substrate 418, then passes through lower path 460 of second PCB substrate 416 and first PCB substrate 414, then exits at terminal 436.

It can be seen that the string of LEDs 178-184 on PCB 114 (and its associated series resistances) are in parallel with the other string of LEDs 178-184 on PCB 115 (and its associated series resistances). A constant voltage driver can therefore be used to drive all LEDs on PCBs 114, 115.

The values of first resistor 440, second resistor 442, third resistor 444, fifth resistor 448, sixth resistor 450, seventh resistor 452, and eighth resistor 454 across all of the substrates are selected such that they add together to give a total series resistance that is appropriate for the LEDs 132-136 with which they are in series. For example, for simplicity and/or convenience, seventh resistor 452 can be the same value as eighth resistor 454, and/or fifth resistor 448 can be the same value of sixth resistor 450. However, any suitable combination of resistances can be used.

A zero-ohm resistor can be used at one or more of the bridgeable terminal pairs in series with the LEDs. Where any non-zero resistances are used, there can be thermal advantages to distributing the required total resistance across two or more of the resistors.

It may also be advantageous to use the same resistor values (optionally including one or more zero-ohm resistances) on all of the first and further PCB substrates, and/or on all of the second PCB substrates. This provides good flexibility in terms of mixing LEDs across different PCBs (and channels, where multiple channels are used) while potentially reducing the number of PCB substrates and resistor values that need to be kept in stock.

Resistors referred to by the same reference sign in the drawings need not have the same value in all drawings.

Any suitable combination of terminals 434, 435, 436, 437, 438 or 439 on any of the first, second, or further substrates can be chosen as the positive and negative terminal for the drive current, as long as the LEDs are forward-biased in use.

Turning to Figure 17, there is shown an alternative version of the implementation of Figure 15. The difference is that the current returning to the first PCB substrate on middle path 458 Is passed to lower path 460 via eighth resistor 454. Compared with the RGB described in earlier implementations, the PCB (and PCB substrates) of Figure 15 allows for more flexibility when it comes to mixing LED types across serially connected substrates. For example, because there are three paths 456, 458, and 460, different return paths can be offered for different PCBs, which can increase flexibility.

As an example, the use of three or more paths can allow a mixture of constant current and constant voltage drive within the same channel across several PCBs and/or PCB substrates. Alternatively, or in addition, one or more of the paths can be used to enable measurement of current passing through a subset of the LEDs in a channel, for example as a proxy for current passing through other LEDs in the channel.

It will be appreciated that although particular bridgeable terminal pairs are indicated as being for resistors (including zero ohm resistors) or LEDs, some or all of the terminal pairs can be bridged with either a resistor or an LED, depending upon the selected implementation.

In addition, any suitable number of bridgeable terminal pairs in any other suitable arrangement can be provided to meet the requirements of different implementations.

Also, the distribution of bridgeable terminal pairs across the first and second PCB substrates can be modified, depending upon the selected implementation. For example, a greater or lesser number of bridgeable terminal pairs can be placed on one or the other of the first, second, and further PCB substrates.

Each PCB can be split into more than two PCB substrates, which can each have any suitable combination of bridgeable terminal pairs.

Further, any suitable number of PCBs and/or PCB substrates may be provided, with any suitable distribution of the various bridgeable terminal pairs across them.

All of these factors give considerable flexibility in terms of customising both the PCB substrates, and any lighting system constructed from such PCB substrates.

Referring now to Figure 12, there is shown a method 200 of manufacturing a PCB for use in a controlled environment lighting assembly. Such a PCB can be, for example, in accordance with any of the above-described implementations, although other implementations falling within the scope of the claims will also be apparent to the skilled person.

Method 200 includes installing 202 one of more LEDs on the substrate for the or each of the lighting channels. For example, solder paste can be applied to each LED terminal pair, an LED positioned on the solder paste, and the PCB passed through a reflow oven to melt the solder paste and solder the LED(s) to the PCB.

For each, if any, lighting channel that is to be configured for constant current drive, one or more of the terminal pairs for that channel is bridged 204 with a short-circuit link such that the LED(s) are connected in series between the first input and the second output. The short-circuit links can take the form of, for example, zero-ohm resistors, such as SMD resistors.

For each, if any, lighting channel that is to be configured for constant voltage drive, one or more of the terminal pairs are bridged 206 with a resistance for limiting drive current through the LED(s). The resistance(s) can take the form of, for example, resistor(s), such as SMD resistor(s), having suitable resistance values.

Short-circuit links and resistances can be soldered to the PCB using a similar process as described for the LEDs. Optionally, a reflow or other soldering/mounting process can be performed simultaneously for the LEDs, and any resistances and/or short-circuit links.

Starting from PCBs populated with the required combination of LEDs, resistances and short- circuit links, a lighting assembly can be constructed by series-connecting several PCBs to each other using connectors. If necessary, a loop-back connector such as terminating connector 192 can be used for any lighting channel configured for constant current operation.

Although the above implementations describe the use of four LEDs per PCB, and four series- connected PCBs, the skilled person will appreciate that any suitable number of LEDs per PCB, and any suitable number of series-connected PCBs, can be selected to suit particular applications. Each channel may be configured and driven independently of the other channels.

Where two or more channels are configured to be driven in the same way, they may share an LED driver. This may be particularly convenient with constant voltage drive circuitry, as it can drive multiple channels in parallel. Using constant current drive circuitry to drive parallel strings of LEDs may result in unbalanced operation, but this may be acceptable in certain circumstances. An alternative is to configure the PCBs such that two or more constant current lighting channels are driven in series by a single constant current drive circuit, although this may increase wiring and/or connection complexity.

Although terminal pairs are shown as being discrete pairs, it is possible for pairs to share a physical terminal. This may be particularly advantageous where only one of the terminals will be in use depending upon whether the lighting channel is configured for constant current or constant voltage operation. For example, ninth terminal 162 and eleventh terminal 166 can be the same physical terminal, because only one of them is used in each configuration. Similar comments apply to tenth terminal 164 and thirteenth terminal 170.

Although the described implementations show only series-connected LEDs on each PCB, the skilled person will appreciate that one or more of the LEDs on any PCB may also be mounted in parallel (or series-parallel) with each other. The skilled person will understand what adjustments may need to be made to the schematic and any resistances required to implement such an alternative.

Any or all of the short-circuit links can take the form of a switch or jumper arrangement. This may make it easier for the PCB to be customised onsite, without the need for soldering. Although the connectors are described as connecting directly to each other, the skilled person will appreciate that they may also be connected to each other with one or more intermediate connectors. For example, one or more cables can be used to connect adjacent PCBs. Optionally, this can take the form of a ribbon connector, comprising, for example, a wire pair for each lighting channel. Although the invention has been described reference to a number of specific non-exhaustive and non-limiting embodiments, the skilled person will appreciate that the invention may be embodied in many other forms.