Led-based lighting device

Abstract

The present disclosure describes a LED-based horticultural lighting device. The light- ing device comprises an elongated, strip-like circuit board (30), a plurality of LEDs (32) mounted on the circuit board (30), a transparent or semi-transparent sheath (36) covering the circuit board, and a heat sink (4) in the form of a metal profile on to which the circuit board is mounted. The LEDs (32) produce a spectrum having a spectral peak in blue wavelength range and a peak in red wavelength range. The sheath (36) is made of heat-shrinkable material and the sheath-covered circuit board (30) is positioned in a channel formed by opposite flanks of the profile of the heat sink (4).

Description

[0001] LED-BASED LIGHTING DEVICE

[0002] FIELD

[0003] The present invention relates to LED-based lighting, and in particular LED-based horticultural lighting fixtures.

[0004] BACKGROUND

[0005] LED-based lighting has many ways proven to be more energy efficient and cost-efficient that older lighting technologies. For these reasons alone, it may be desirable to use LEDs in various special applications, such as in plant cultivation applications.

[0006] However, cultivation spaces, such as greenhouses and vertical farms, are a very challenging environment for artificial lighting. The climatic conditions, such as the temperature and the humidity, in cultivation spaces are typically much harsher than in living spaces, for example. Lighting in cultivation spaces may also be exposed to other harmful environmental conditions, such as dirt, dust, and insects. Therefore, artificial lighting for horticultural use typically requires a high level of protection.

[0007] Maximizing crop yield may is also typically important, especially when cultivation is done for commercial purposes. Further, ease of maintenance is an important aspect of horticultural lighting. The number of lighting devices in a cultivation facility may be in hundreds or thousands, meaning that it is desirable to time spent on maintaining an individual lighting device.

[0008] At the same time, the lighting devices should have as high energy efficiency as possible. The high number of lighting devices means that any improvement in energy efficiency may have a significant impact on electricity costs. Also, a high energy efficiency reduces a need for cooling in the lighting devices.

[0009] SUMMARY

[0010] The objective of the invention is to alleviate the afore-mentioned challenges. The object of the disclosure is achieved by a lighting device and a manufacturing method that are characterized by what is stated in the independent claims. The preferred embodiments of the disclosure are disclosed in the dependent claims.

[0011] Many of the above-discussed challenges can be addressed with a LED-based horticultural lighting device that has a sealed light-emitting module attached to a heat sink. The light-emitting module may comprise an elongated circuit board with a plurality of LEDs. The circuit board may be sealed within a transparent or semi-transparent sheath made of heat-shrinkable material. The heat sink may be in the form of a metal profile with a channel and the light-emitting module may be secured in the channel. The LEDs and the spectrum they produce may selected based on the application.

[0012] An advantage of this kind of lighting device is that its vulnerable parts, such as the circuit board and its components, are well protected against climatic and environmental conditions. Further, the above-described is rugged, easy to maintain and easy to manufacture.

[0013] BRIEF DESCRIPTIONS OF THE DRAWINGS

[0014] In order to best describe the manner in which embodiments of the lighting device and its manufacturing method are implemented, as well as define other advantages and features of the disclosure, a more particular description is provided below and is illustrated in the appended drawings. Understanding that these drawings depict only exemplary embodiments of the invention and are not therefore to be considered limiting in scope, the examples will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

[0015] Figures 1A to IE show examples of spectrums suitable for various horticultural applications;

[0016] Figure 2 shows and embodiment of a lighting device according to the present disclosure;

[0017] Figures 3A to 3D show exemplary stages manufacturing a light-emitting module; and

[0018] Figures 4A to 4C show simplified details for one embodiment where an aluminium rail with a C-profile is being used as the heat sink. DETAILED DESCRIPTION

[0019] The present disclosure introduces a LED-based lighting device that is rugged, simple, and well protected against environmental hazards. In particular, a lighting device according to the present disclosure is well suited to be used in plant cultivation spaces.

[0020] In the context of present application, a cultivation space is intended to be understood as a space dedicated to cultivation of plants. A cultivation space is typically a closed space where climatic conditions, such as temperature and humidity, can be controlled. A greenhouse is one example of a cultivation spaces. A greenhouse is a structure that allows people to temperature and humidity while letting the plants utilize natural light from the sun. Another example of a cultivation space is a vertical farm. Similar to a greenhouse, a vertical farm is a structure that allows regulation of climatic conditions. However, a vertical farm may be partially or completely devoid of sunlight. Light emissions the plants need for photosynthesis may be mostly or completely generated with artificial lighting.

[0021] While lighting devices according to the present disclosure are mostly discussed in relation to horticultural applications, the lighting devices may be used also for other purposes. For example, some of the features of the lighting devices according to the present disclosure, such as ruggedness and high protection level, may be highly advantageous in industrial applications, such as in construction industry.

[0022] Spectrums for horticultural applications

[0023] Regardless of the application, an important aspect of a lighting device is the spectrum it produces. For example, horticultural applications define special requirements for the desired spectrum as plants need suitable lighting for their photosynthesis. Thus, artificial lighting for horticultural applications may be configured to generate light that supports photosynthesis. In some applications, the artificial lighting may merely supplement natural light received by the plant. In other applications, such as in vertical farms, the artificial lighting may be the sole source of light.

[0024] In broad terms, photosynthesis in plants can be supported by emitting light in Photosynthetically Active Radiation (PAR) wavelength range. PAR designates a spectral wavelength range of solar radiation from 400 to 700 nm that photosynthetic organisms are able to use in the process of photosynthesis. However, plants do not utilize all emissions equally well within this range. Plants absorb the received light primarily using pigments such as chlorophyll and carotenoids. The pigments utilize only some wavelength regions well, the main regions being in the blue wavelength band (i.e., wavelength range 400 - 500 nm) and in the red wavelength band (i.e., wavelength range 600 - 700 nm). Two important absorption peaks of photosynthetic photoreceptors are located in regions from 625 to 675 nm and from 425 to 475 nm. However, there are also other localized absorption peaks in the near ultraviolet (near-UV) region (300 - 400 nm) and in the far-red region (700 - 800 nm).

[0025] To maximize the energy efficiency of artificial lighting, it may be desirable to maximize the emissions at wavelengths best utilized by plants. For this reason, the LEDs of a lighting device according to the present disclosure may be configured to produce a spectrum comprising a peak in the blue wavelength range and a peak in the red wavelength range. At the same time, it may be desirable to minimize emissions at wavelengths utilized by poorly by plants. The green part of the light spectrum is not absorbed well by plants. Typically, it is reflected which is the reason that most plants have a green colour.

[0026] In addition to enabling / enhancing photosynthesis, the spectrum of horticultural lighting may have other functions. For example, plants may have photomorphogenetic photoreceptors with sensitivity peaks in the red wavelength band (e.g., at 660 nm) and in the far-red wavelength band (e.g., at 730 nm). These photoreceptors may cause photomorphogenetic responses, such as leaf expansion, neighbour perception, shade avoidance, stem elongation, seed germination, and flowering induction. In some cases, the photomorphogenetic responses may relate to the sensing of the light quality in the form of the red (R) to far-red (FR) ratio (R / FR).

[0027] Horticultural lighting devices may be used to produce different spectrums with different characteristics in order to achieve desired effects in plants. The characteristics are defined by spectral features present in the spectrum. In the context of the present disclosure, a spectral feature is a feature observable in the parameters of the spectrum. For example, a spectral peak, i.e., a peak in emission intensity, is one example of a spectral feature. Similarly, valleys and slopes in the in the intensity of the spectrum can be seen as spectral features. Further, relations between intensities (or their peak maximums) can be seen as spectral features. Widths of spectral peaks (and the relations between the widths) can be seen as spectral features. The following paragraphs describe some exemplary spectrums that can be produced with the lighting device according to the present disclosure.

[0028] Figure 1A shows an example simple of a spectrum with a red spectral peak (peak maximum at 650 nm) and a blue peak (peak maximum at 460 nm). In the context of the present disclosure, a red spectral peak (or simply, a red peak) is a spectral peak having its maximum peak value at the red wavelength range (600 - 700 nm), and a blue spectral peak (or simply, a blue peak) is a spectral peak having its maximum peak value at the blue wavelength range (400 - 500 nm). Throughout the present disclosure, various spectral features are referred to in a similar manner, i.e., by naming them by the colour of the wavelength band in question.

[0029] In Figure 1A, the red peak and the blue peak correspond well to the two main absorption peaks of photosynthetic photoreceptors mentioned earlier. The read peak in Figure 1A is broader than the blue peak. The blue peak has FWHM (Full Width at Half Maximum) of less than 50 nm, whereas the FWHM of the red peak is more than 50 nm. In some embodiments, the red peak may also be narrow. For example, both the blue and red peak may have FWHM of 50 nm or less. Figure IB shows such an embodiment.

[0030] In Figures 1A and IB, the highest peak of the spectrum is located in the red wavelength range. However, spectrums of lighting devices according to the present disclosure are not limited to the above-discussed embodiments with spectrums that comprise a red peak and a blue peak, where the red peak is higher than the blue peak. Requirements for the spectrum depend on the application, and a lighting device according to the present disclosure may be designed to produce a spectrum according to the requirements.

[0031] In Figures 1A and IB, the green emissions (i.e., emissions in the green wavelength range 500 - 600 nm) are almost non-existent, or are at least well below the adjacent wavelength ranges, i.e., the blue and red wavelength ranges. In this manner, emissions at wavelengths utilized by poorly by plants are minimised. However, in some cases, it may be preferable to have at least some emissions in the green wavelength range. Figure 1C shows an example of such an embodiment. In Figure 1C, the spectrum comprises a blue peak (preferably in a specific range 425 - 475 nm), and a spectral red peak (preferably in a specific range 625 - 675 nm). The spectrum has a spectral valley with a base value in the wavelength range of 475 - 500 nm and a broad-band spectral feature extending throughout the green wavelength range (500 - 600 nm). The red peak has the highest relative emission intensity within the spectrum in Figure 1C. The blue peak has a relative emission intensity that is non-zero but less than the maximum relative emission intensity of the red peak. Similarly, the broadband spectral feature in the green wavelength range has a relative emission intensity that is non-zero but less than the relative emission intensity of the red peak. The base value of spectral valley in the wavelength range 475 - 500 nm is below all relative intensities of the broadband spectral feature in the green wavelength range. The spectrum of Figure 1C also has a spectral feature in the far-red wavelength range (700-800 nm). This spectral feature has a non-zero relative intensity that is below the maximum relative intensity of the spectrum and is in the form of a constantly falling slope in the direction of increase of the wavelength. One advantage of the spectrum presented in Figure 1C is that it increases overall biomass due to its ability to stimulate leaf expansion. An additional benefit is that it has the potential to accelerate plant maturity and ripening.

[0032] The examples of Figures 1A to 1C show examples where there are fairly few spectral features. However, in some embodiments, the spectrum may be a more complex combination of spectral features. For example, there may be a plurality of spectral peaks clustered within a wavelength band. Figure ID shows one example of such spectrum. The embodiment of Figure ID is similar to the embodiment of Figure 1C in that it has at least some emissions at green wavelength range and that there is one main peak in the red region. However, in the blue region, there are three local peaks (having local maximum peaks at wavelengths of about 410 nm, 450 nm, and 470 nm). The spectrum presented in Figure ID has broadband characteristics and resembles natural sun light. It can be used in research and biotech applications, for example.

[0033] In the examples of spectrums above, the spectral features have mostly been within the PAR region (400 - 700 nm). However, the spectrum produced with a lighting device according to the present disclosure may also comprise spectral features outside the PAR region. Figure IE shows one example of such an embodiment. Similar to the spectrums in Figures 1C and ID, the spectrum in Figure IE has a blue peak, a red peak, a spectral valley with a base value in the wavelength range of 475 - 500 nm and a broad-band spectral feature extending throughout the green wavelength range (500 - 600 nm). In addition, the spectrum has a peak in the near-UV range (300 - 400 nm) and a peak in the far-red wavelength range (700 - 800 nm). Preferably, said peaks are within ranges 370 - 400 nm and 700 - 750 nm, respectively. In Figure IE, the peak in near-UV area is located at 390 nm and the peak in the fare red range is at 740 nm. The spectrum of Figure IE is especially well suited for controlled environment agriculture and research throughout all growth stages. The spectrum is highly effective and is well suited to act as a sole source of light in plant cultivation.

[0034] Lighting fixtures for horticultural applications

[0035] Another important aspect of horticultural lighting is efficient positioning of the lighting. To maximize yield received from a cultivation space, plants grown in the cultivation space may be arranged into tight rows. In greenhouses, the rows may be in one horizontal plane so that the plants all also have access to natural light. In vertical farms, however, the rows of plants may be arranged into horizontal rows that are stacked vertically. To accommodate this row-based arrangement of plants, the lighting devices may be in the form of lighting fixtures where a plurality of light sources are integrated to a single frame. The horticultural lighting fixtures can be in the form of elongated light bars, for example. Figure 2 shows an example of such a light bar. In Figure 2, a light bar 2 has an elongated frame 22 and a plurality of light sources 24. Power is supplied to the light bar 2 via a power cable 26 at one end of the light bar 2. The length of a lighting fixture according to the present disclosure is larger than its width. In Figure 2, the length is shown as dimension L and the width is shown as dimension W. The length may be ten or more times the width of the lighting fixture, for example. The thickness (i.e., the dimension perpendicular to the length and the width) of the lighting fixture is preferably less than the width. The thickness maybe a half or less than a half of the width, for example.

[0036] This kind of elongated lighting fixture can be easily mounted to illuminate a row (or a portion of a row) of plants. The light-emitting side of the light bar 2 is facing up in Figure 2. However, during use the light-emitting side is oriented to face the plants, e.g., from above or from a side. In order to maximize mounting options, it is preferable to keep the weight of the lighting fixture as small as possible. Further, the lighting fixture preferably has a mounting interface that allows different mounting positions and orientations.

[0037] In the following, various aspects of lighting fixtures according to the present disclosure are discussed in more detail in relation to Figures 3A to 3D and 4A to 4C.

[0038] Light-emitting diodes

[0039] The above-discussed spectral characteristics can be implemented with light-emitting diodes (LEDs). A lighting fixture according to the present disclosure may comprise one or more types of LEDs. In some embodiments, only one type of LEDs is used. This may be desirable in order to reduce costs, or to minimize distortion of emitted spectrum over time due to different aging of different types of LEDs, for example. In some embodiments, the one type of LEDs may be used to produce a plurality of spectral features. For example, a primary emission this one type of LED may produce a first spectral feature at one wavelength range while a conversion material provided in the LED may convert a part of the first spectral feature into a second spectral feature. In this context, the term "conversion material" refers to a material that converts incoming light emission to a lower-energy light emission, i.e., to a higher wavelength emission. This kind of materials are also referred to as "phosphors".

[0040] The embodiment of Figure 1A can serve as an example of a spectrum that can be produced with only one type of LEDs. The blue peak in Figure 1A may be in the form of a primary emission from a LED chip of a blue LED, since LED chips typically produce narrow spectral peaks. The broader red peak may be produced by using conversion material or materials in the proximity of the blue LED. Conversion materials typically produce broader peaks.

[0041] In addition to using only one kind of LEDs, a lighting fixture according to the present disclosure may comprise a plurality of types of LEDs. Each LED type may have its own spectral characteristics, and the total spectrum produced by the lighting fixture may be a composite of these spectral characteristics. It may in some cases be easier to produce a desired spectrum of the lighting fixture by using a plurality of different types of LEDs. The different types of LEDs may include LEDs without conversion material and LEDs provided with conversion material. In addition, the use of different types of LEDs can be used to enable adjustability of the produced spectrum. The lighting fixture may comprise a control device (e.g., a switch, dial, or an electrical controller) for adjusting the spectrum prior to and / or during use, for example.

[0042] Figure IB can serve as a simple example of using a plurality of LED types in the lighting fixture. One type of LEDs (blue LEDs in Figure IB) is used to produce one peak and another type of LEDs (red LEDs in Figure IB) to produce another peak. Similarly, the spectrum of Figure 1C can be produced with a combination of different types of LEDs, for example. Some of LEDs may be provided with one or more conversion materials. In Figure 1C, for example, the broad red peak and the broadband spectral feature in the green wavelength range may in some embodiments be produced by utilizing conversion materials. Similar approach may also be taken in the embodiments of Figures ID and IE.

[0043] The number of LEDs in a lighting fixture according to the present disclosure may be in tens, hundreds, or even thousands. As a result, the nominal power of the lighting fixture may be in tens of watts to hundreds of watts, for example. With surface-mount (SMD) or chip-on-board (COB) LEDs, high component and energy density can be achieved. The LEDs can be arranged into a row or rows of LEDs extending along the length of the lighting fixture. As a result, high-intensity light emissions can be produced from a compact-sized light source. In this manner, crop yield from the cultivated plants can be improved.

[0044] Circuit Board

[0045] In a lighting fixture according to the present disclosure, the plurality of LEDs may be mounted on circuit board. The circuit board may in the form of an elongated striplike or plate-like structure that extends for the whole length of the lighting fixture. The LEDs may be mounted on one side (i.e., a light-emitting side) of the circuit board. Figure 3A shows a simplified example of an elongated circuit board 30. A plurality of components, including a plurality of LEDs 32 in a row and a connector 34, have been mounted on the circuit board 30. The dash-dotted line in Figure 3A (and in the other Figures) represents a separation, indicating that the length of the lighting fixture is not limited to any specific value.

[0046] Since the LEDs may induce a large amount of heat, it is preferable that the circuit board has good thermal conductivity. To achieve this, the circuit board may have a metal core. For example, the circuit board may be in the form of a MCPCB (Metal Core Printed Circuit Board). The material of the metal core may be aluminium, for example. The metal core may be coated with an electrically insulating layer, and conducting traces and solder pads for the components may be formed on top of the insulating layer, for example.

[0047] Dimensions of the circuit board may depend on the application. In horticultural applications, a length of over 50 cm may be preferable. For example, a length of 100 cm or more may be used. Similarly, the width of the circuit board and the positioning and pattern of the LEDs on the circuit board may vary depending on the application. For example, in some embodiments, LEDs may be arranged into a single row on the circuit board. In such cases, width of 3 cm or even less may suffice. However, if LEDs are arranged into a plurality of rows, a greater width may be appropriate. Similarly, thickness of the circuit board depends on the intended application of the lighting fixture. A greater thickness (of the core material in particular) may provide additional rigidness for the elongated circuit board which may help in the soldering process when mounting components to the circuit board. On the other hand, it may be desirable to have some flexibility in the direction of its thickness. When the circuit board is able to flex laterally at least a small amount, mounting of the circuit board to a heat sink may become easier.

[0048] In the paragraphs above, various parameters of the circuit board are discussed mostly in view of one particular embodiment of the circuit board. However, implementations of a circuit board of a lighting unit according to the present disclosure is not limited to said embodiment. Materials and dimensions of the circuit board can be modified to best suit the intended application.

[0049] Protecting sheath

[0050] As mentioned earlier, sufficient protection against harsh climatic and environmental conditions, such as high temperature and humidity, accumulation of dust and dirt, and / or presence of insects, is important in horticultural applications. The sheath should preferably also act as an electrical insulator. At the same time, however, the sheath preferably should obstruct the light emitted by the LEDs as little as possible.

[0051] To protect the LEDs and circuit board, the lighting fixture according to the present disclosure comprises a transparent or semi-transparent sheath that covers the circuit board and the LEDs. For example, the LEDs and circuit board may be enveloped within a transparent or semi-transparent sheath made of a heat-shrinkable material. This sheath, in some cases originally in the shape of straight, loose tube / sleeve, forms a tight cover around the circuit board and its components once treated with heat. For reference, Figure 3A shows a sleeve 35 inside which the circuit board is inserted. The sleeve may then be shrunk into the sheath by applying heat.

[0052] In order to further improve the protection, both ends of the sheath may be sealed. On a first end of the sheath, a seal in the form of a flat, planar structure may be formed out of the sheath. This structure is preferably shaped such that the whole sheath-covered circuit board can be inserted to a heat sink. For example, the first end of the heat-shrunk sleeve may be heat sealed and / or folded. The sheath may be folded on top of the sheath-covered circuit board or itself. In this manner, the first end is shaped into a flat, rectangular piece that may act as a guide that helps when the sheath-covered circuit board is being mounted in or on a heat sink. Figure 3B shows one example of the above-described first end of the sheath. In Figure 3B, the circuit board 30 and components 32 mounted on it are encased within a transparent sheath 36. Parts (e.g., LEDs 32 and the circuit board 30) covered with the sheath 36 are illustrated with dashed lines in the present disclosure. The first end of the sheath 36 has been folded into a fold 36.1. The fold has been further sealed with a heat seal 36.2. The embodiment of Figure 3B is just one example of implementation of sealing the first end of the sheath. In other embodiments, the seal can be formed in different manner, with or without folding.

[0053] A second end of the sheath may be sealed similarly or in a different manner than the seal at the first end. For example, in some embodiments, the second end of the sheath acts as an access point for a power cable and may therefore have a different structure than the first end. Figure 3C shows simplified details for an exemplary embodiment of the second end of the sheath 36. In this embodiment, the second end of the sheath 36 may remain unsealed during the heat-shrinking operation. As a result, the second end may form into an opening 36.3 with a cross section shaped like a flattened circle or an obround. Through the opening 36.3, a power cable 38 may be attached to the circuit board. As mentioned earlier, the circuit board 30 may comprise at least one connector 34. The connector 34 may be comprise one or more wire inputs configured to receive conductor wires 38.1 of the power cable 38. In some embodiments, the connector 34 may be in the form of a push-type quick wire terminal that has actuators (e.g., levers or push-buttons) which, when pushed down (e.g., through the sheath 36), allow the wires 38.1 to be inserted to the wire inputs. In some embodiments, the circuit board 30 may also comprise a power switch that can be in similar manner operated through the sheath 36.

[0054] Once the power cable 38 has been attached to the circuit board, the opening 36.3 at the second end of the sheath 36 with an elastic plug 39 (through which the cable 38 extends). The plug 39 may be a ring-shaped element made of rubber, for example. Once in place, the plug 39 seals the circuit board 30 and its components (including the LEDs 32 and the connector 34) inside a sealed cavity formed by the sheath 36 and the plug 39.

[0055] With both ends of the sheath being sealed, the circuit board and its components are completely encased within the sheath. The sheath-covered circuit board forms a lightemitting module that can be used as a part of a lighting fixture according to the present disclosure. Figure 3D shows an example of such a lighting module. In Figure 3D, a light-emitting module 3 comprises a circuit board 30 is sealed within the sheath 36. The first end of the sheath is sealed with a fold 36.1 and a heat seal 36.2. At the second end of the sheath 36, a power cable 38 connects to the circuit board 30 through a plug 39 that seals the opening 36.3 at the second end.

[0056] Figures 3A to 3D show only one example of the structure of the sheath and the seals at its ends. The sheaths of lighting fixture according to the present disclosure are not limited only to this example. The sheath and the seals can be implemented in a different way, as long as their implementations allow the lighting module to be attached to a heat sink.

[0057] FEP as the heat-shrinkable material of the sheath

[0058] The protective functionalities of the sheath may set quite demanding requirements for the material of the sheath. The inventors have found out that fluorinated ethylene propylene (FEP) fulfils these requirements very well. FEP is transparent, heat-shrink- able, and has a very large working temperature range (from about -200 C° to about 200 C°). It has a low dielectric constant, so it acts as an electrical insulator. FEP itself chemically inert so it suits for horticultural applications where contamination of the plants grown is not desirable. In addition, FEP is transparent to ultraviolet (UV) light and does not degrade when exposed to it. Spectrums of lighting fixtures intended for horticultural applications may comprise some UV light. Even in embodiments of the lighting fixture according to the present disclosure where the lighting fixture does not emit light at UV range, it may be preferable that the lighting fixture is tolerant to UV. The lighting fixture may be exposed to UV light present in natural sunlight or in the light generated by other artificial light sources.

[0059] Further, FEP is hardwearing and has non-stick surface that repels water and dirt. This improves robustness and maintainability (e.g., ease of cleaning) of the lighting fixture. In addition, a sheath formed out of FEP has a low-friction surface which eases the insertion of the sheath-covered circuit board to the heat sink.

[0060] While thermal conductivity of FEP is low, heat flow through it (from the printed circuit board to the heat sink) can be maintained sufficient by keeping the thickness of the FEP-based sheath sufficiently small. For this reason, the thickness of the sheath (in heat-shrunk stage) is preferably less than 0.35 mm. However, appropriate maximum thickness depends on the nominal power of the LEDs and their cooling requirements.

[0061] While FEP is presented as a preferable material for the sheath, possible materials for the sheath of lighting fixture according to the present disclosure are not limited only to it. For example, depending on the application, other fluoropolymers with similar characteristics, such as ethylene tetrafluoroethylene (ETFE), perfluoroalkoxy alkanes (PFA), and polytetrafluoroethylene (PTFE) may be used. Further, other materials than fluoropolymers may also be used.

[0062] Heat Sink

[0063] As mentioned earlier, LEDs of lighting fixture according to the present disclosure may produce a high amount of heat. To provide sufficient cooling for the LEDs, the lighting fixture according to present disclosure comprises a heat sink on to which the circuit board is mounted. The heat sink may comprise a channel in which the light-emitting module is positioned.

[0064] In some embodiments, the heat sink may be an aluminium rail with a C-profile. The opposite flanks (i.e., the sides extending between the light-emitting side and its opposite side) of the profile form a channel in which the circuit board can be positioned. In this context, a C-profile refers to a rail-like structure that has a C-shaped crosssection with hook-like ends facing each other on opposite flanks of the cross-section.

[0065] Figures 4A to 4C show simplified details for one embodiment where an aluminium rail with a C-profile is being used as the heat sink. Figure 4A shows a perspective view of the light-emitting module 3 positioned within the channel formed by the opposite flanks of the heat sink 4. The light-emitting module may comprise LEDs 32 mounted on a circuit board 30. The circuit board 30 and the components (e.g., the LEDs 32) mounted thereon may be encased within a sheath 36. The light-emitting module 3 may be the same as or similar to that presented in Figure 3D, for example. Figure 4B shows a cross-sectional view of the same setup. In Figures 4A and 4B, the profile of the heat sink 4 has hook-like loops 41 on both flanks. The loops 41 have empty cavities 41.1 in their centres. In this manner, heat-dissipating surface area of the heat sink 4 can be maximized with minimal material usage. At the same time, the flat centre portion of the profile of the heat sink 4 is attached to a second side (opposite to the light-emitting side) of the circuit board 30, thereby providing a large surface area for heat transfer between the circuit board 30 and the heat sink 4 (via the sheath 36). Heat transfer from the heat sink 4 to ambient air occurs largely on the side of the lighting fixture facing away from the plants. In some embodiments, the outer surface of the loops 41 can be provided with extrusions forming fins extending along the length of the profile. However, in order to maximize the ease of cleaning, it may be desirable to keep the surfaces smooth, as shown in Figures 4A to 4C.

[0066] In addition to improving heat transfer, the heat sink may have other functions. For example, it can act as a frame module for the lighting fixture. In the case of the embodiment of Figures 4A to 4C, the loops 41 of the C-shaped profile provide additional structural durability, stability and rigidness for the heat sink, and thus, to the whole lighting fixture.

[0067] Further, the heat sink may act as a main mounting interface for the lighting fixture. Various mounting elements, such as mounting holes and brackets may be formed directly to the second side of the heat sink. For example, if the heat sink is made of an aluminium profile, mounting elements may be drilled or milled directly to it. Alternatively, or in addition, mounting elements may be attached to the heat sink. In this manner, any forces (including gravitational force) influencing the lighting fixture during use are directed to the heat sink instead of more vulnerable elements such as the circuit board. The heat sink may also be provided with a strain relief element for the power cable. The strain relief element may clamp the power cable to the heat sink (e.g., with screw-fastened or by crimping) so that pulling or tugging the power cable does not damage the connector or the circuit board.

[0068] The heat sink may be provided with end caps that close the open ends of the profile. Figure 4C shows a simplified example of one end cap for a heat sink of a lighting fixture according to the present disclosure. In Figure 4C, the end cap 5 has a base 52 that abuts the end of the head sink 4 when attached to its final position. A planar cover 54 element extends from the base 52. The cover element 54 shields components the ends of the sheath-covered circuit board at the ends of the heat sink 4. In addition, mounting pins 56 (only one visible in Figure 4C) extend from the base 52 in Figure 4C. The mounting pins 56 may be configured such that they fit snugly to the cavities 41 of the C-profile of the heat sink 4, thereby securing the end caps 5 to their places. Additionally, the mounting pins 56 may act as positioning elements for the light-emitting module 3. The mounting pins 56 may be configured to have wedge-like shapes so that they force the light-emitting module 3 to the centre of the heat sink 4 in width-wise direction. In this manner, correct positioning of the light-emitting module 3 can be ensured.

[0069] Together, the light-emitting module and the heat sink acting as a frame module form a modular lighting fixture implementation that can be easily adjusted to suit different requirements. A heat sink that is formed out of a straight, continuous profile is simple and cost-effective. It is also very easily scalable to different lengths of lighting fixtures.

[0070] While the heat sink has been mostly discussed in view of an embodiment where the heat sink is in the form of a simple metal profile, other implementations of the heat sink are also possible in the context of the lighting fixture according to the present disclosure. For example, the heat sink may be made of a different material than aluminium. For example, the heat sink may in some embodiments be made out of rolled or stamped sheet metal. Further, in some embodiments, the heat sink may be in the form of a metal U-profile and it may be provided with retaining elements (such as retaining bands or hold-down clips) that hold the light-emitting module in place. The heat sink may also be formed out of a plurality of parts that, when attached together, keep the light-emitting module in place. The above-described lighting fixture can be used to produce any of the above-described spectrums and is therefore not limited to any specific spectrum. Further, the different variants of the above-discussed aspects of the lighting fixture according to the present disclosure can be freely combined as desired.

[0071] Manufacturinq method

[0072] In addition to a lighting device, the present disclosure introduces a method of manufacturing such a device. The method may be considered to comprise two stages: first, preparation of a light-emitting module and, second, assembling of the lighting device.

[0073] The first stage of the method comprises providing a circuit board with LEDs mounted thereon, inserting the circuit board in a sleeve of heat-shrinkable material, and applying heat to the sleeve to form a tight sheath around the circuit board.

[0074] In some embodiments of the method, once the sheath has been formed by applying heat, one end of the sheath has been sealed by heat sealing and / or by closing one end by folding. Said end may be folded on top of itself and / or on top of the circuit board, for example. Figure 3B shows an example of an end of the sheath having been folded on top of itself and then being heat sealed.

[0075] The other end of the sheath may temporarily remain open after the heat-shrink operation. This open end may be used for connecting power cables to the circuit board. For example, as explained earlier in relation to Figure 3C, the circuit board may comprise a connector into which exposed end of conductor wires of the power cable can be attached. The connector may be in the form of a push-type quick wire terminal, that has actuators which, when pushed down, allow wires to be inserted. The method may comprise pushing down the actuators through the surface of the sheath, inserting the end of the power cable in the opening in the sheath, inserting the exposed ends of the wires of the power cable in the terminals of the connector and releasing the actuators of the connector to secure the ends of the wires in the terminals of the connector.

[0076] Once the power cable has been attached to the circuit board, the open end of the sheath is sealed with an elastic plug (through which the cable runs). As a result, a sealed, sheath-covered circuit board is produced (e.g., as shown in Figure 3D). This circuit board can be used as light-emitting module in a lighting device according to the present disclosure. In the second stage, a light-emitting module as described above is attached to a heat sink. This can provide additional rigidity for the lighting device. For example, the heat sink may have a C-profile, so that a channel is formed by the opposite flanks of the C-profile. The sheath-covered circuit board may be slid to the channel of the heat sink and secured therein to form the lighting fixture. In some embodiments of the method, the method may further comprise adding end caps to the ends of the heat sink. The end caps may be similar to or the same as described in Figure 4C, for example.

[0077] The above paragraphs discuss the manufacturing method according to the present disclosure in view of one particular embodiment. The method is not limited to said embodiment. For example, some steps of the method may occur in different order.

[0078] Just as one example, the attachment of a power cable may occur before or after the circuit board is inserted to the heat sink.

Claims

CLAIMS1. A LED-based horticultural lighting fixture, wherein the lighting fixture comprises:- an elongated circuit board (30) with a plurality of LEDs (32) mounted thereon, wherein the LEDs (32) are configured to produce a spectrum having a spectral peak in blue wavelength range and a peak in red wavelength range,- a transparent or semi-transparent sheath (36) that forms a tight cover around the circuit board (30) and is made of a heat-shrinkable sleeve that has been shrunk around the circuit board (30), and- a heat sink (4) comprising a channel in which the sheath-covered circuit board (30) has been positioned, wherein the heat sink (4) has a form of a C-profile, the opposite flanks of the C-profile defining the channel, and wherein a first end of the sheath (36) has been sealed by folding the first end on top of itself or the sheath-covered circuit board (30), the first end being in a form of a flat, planar structure that fits inside the channel.

2. A horticultural lighting fixture according to claim 1, wherein the spectral peak in the red wavelength range exceeds the peak in the blue wavelength range.

3. A lighting fixture according to claim 1 or 2, wherein the sheath is made of fluorinated ethylene propylene (FEP).

4. A lighting fixture according to any one of claims 1 - 3, wherein the first end of the sheath has been further sealed by a heat seal.

5. A lighting fixture according to any one of claims 1 - 4, wherein- a second end of the sheath (36) has been sealed by an elastic plug (39), and- a power cable (38) extends through the plug (39) and is connected to the circuit board (30).

6. A lighting fixture according to claim 5, wherein- the circuit board comprises a push-type quick wire terminal, and conductor wires of the power cable are connected to wire inputs of the wire terminal.

7. A lighting fixture according to any one of claims 1 - 6, wherein- the circuit board is a metal core printed circuit board (MCPCB), the material of the core being aluminium.

8. A lighting fixture according to any one of claims 1 - 7, wherein the heat sink is in the form of an aluminium rail having the C-profile.

9. A lighting device according to claim 8, wherein- the profile of the heat sink has hook-like loops on both flanks, the loops having empty cavities in their centres,- the lighting device further comprises at least one end cap, the end cap having at least one mounting pin that is positioned within at least one one of said empty cavities.

10. A lighting fixture according to any one of claims 1 - 9, wherein- at least one of the LEDs is provided with a conversion material converting at least portion of the primary emission of the LED into a longer-wavelength emission.

11. A lighting fixture according to any one of claims 1 - 10, wherein nominal power of the lighting fixture is in tens of watts to hundreds of watts.

12. A lighting fixture according to any one of claims 1 - 11, wherein the peak in blue wavelength range has its peak value in range 425 - 475 nm and the peak in red wavelength range has its peak value in range 625 - 675 nm.

13. A lighting fixture according to any one of claims 1 - 12, wherein the spectrum has a spectral valley with a base value in the wavelength range of 475 - 500 nm and a broad-band spectral feature extending throughout the green wavelength range.

14. A method of manufacturing a LED-based horticultural lighting fixture, wherein the method comprises:- providing a circuit board (30) with LEDs (32) mounted thereon,- inserting the circuit board (30) in a sleeve (35) of heat-shrinkable material,- applying heat to the sleeve (35) to form a tight sheath (36) around the circuit board (30),- providing a heat sink (4) having a C-profile, a channel being formed by the opposite flanks of the C-profile, and- sliding the sheath-covered circuit board (30) to the channel, the first end having been closed by folding the first end on top of itself or the sheath-covered circuit board, such that the first end forms of a flat, planar structure fitting inside the channel.

15. A method according to claim 14, wherein the method comprises:- attaching a power cable (38) to the circuit board (30) via a second, open end of the sheath (36), and- plugging the second end with a plug (39) through which the power cable (38) runs.

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