Field of the invention

The invention relates to a liquid cooled solid state lighting assembly and to a growing system having a plurality of such lighting assemblies.

Background of the invention

From US 8,651,704 a system and method for solid-state (LED) light source heat management is known in which a cooling fluid is circulated through the enclosure of the light source. In particular in greenhouses and in growing chambers in which no daylight is admitted (so- called "plant factories") the problem of providing sufficient lighting levels while at the same time controlling the temperature to remain within the optimal growing range, is particularly challenging.

It therefore is an object of the present invention to provide a liquid cooled solid state lighting assembly which is of compact shape, which can be easily manufactured and which allows a high output power. It is a further object to provide a lighting assembly that can be easily mounted and that provides accurate control of lighting and temperature conditions in a growing chamber. Summary of the invention

Hereto a liquid cooled solid state lighting assembly according to the invention having a metal fixture carrying a solid state light source and at least one cooling channel for passing a cooling liquid, is characterized in that the fixture comprises a rectangular parallelepiped- shaped cooling body having an emission surface, an opposed back surface and four side surfaces having a height H, the emission surface carrying a solid state light source, the cooling body and having on a side surface a cooling liquid inlet and a cooling liquid outlet, connected by the cooling channel in the cooling body, which cooling channel has at least four cooling channel sections extending from near one side surface to near an opposite side surface.

The cooling body effectively removes the heat generated by the solid state light source such that high powers, for instance 500 W and more, can be utilized. Multiple cooling bodies according to the invention can be connected to cooling fluid ducts of a growing chamber in a modular way such that a versatile system is obtained. By providing a number of cooling channels in the relatively flat cooling body, which may for instance measure about 25 cmx 25 cmx 4 cm, a compact construction having good cooling properties is obtained.

In a preferred embodiment, the light source is covered by a lens. Because of effective removal of the heat that is generated by the light source via the cooling channels, the outwardly facing surface of the light source can be covered by a lens. The reduction in heat transfer from the light source caused hereby is compensated by the effective cooling in the cooling body, allowing high power light sources to be used in combination with a lens to obtain a directionally controlled and homogenous light output.

The cooling channels may be provided by drilling in the side surface of the cooling body. This results in a cooling body which is easily manufactured from a single piece of metal, having good heat transfer properties and providing a liquid-tight enclosure.

In an alternative embodiment, an upper part and a lower part are releasably interconnected along an interface plane that is parallel to the emission surface and the back surface, in which the cooling channels extend from the interface plane downward into at least one of the upper and lower parts.

The cooling channels may be provided by milling or casting in the freely accessible interface, which is sealed after forming of the cooling channels by interconnection of the upper and lower parts by welding or soldering or by bolting including for instance an elastomeric seal between the parts.

The back surface of the cooling body may comprise a cooling liquid inlet and/or a cooling liquid outlet opening in fluid connection with the cooling channel. In this way the cooling body may be connected to cooling fluid duct either via the side surfaces or via the back surface such that flexibility in installation in a growing system is provided.

An alternative embodiment of a liquid-cooled solid state lighting assembly according to the invention has a fixture of elongated shape and comprises a metal tubular channel situated on top of a U-shaped receiving section in which a strip of solid state lighting elements is received, the tubular channel and the U-shaped receiving section being formed in one piece by extrusion. The strip of solid state lighting elements is well-protected against mechanical impact by being enclosed by the U-shaped receiving section while the extruded cooling channel on top warrants direct and effective heat transfer from the light source. The construction is of compact height and is light-weight so that it can be suspended from a lightweight support structure in a growing chamber.

The width of the receiving section may be wider than an outside diameter of the cooling channel, the receiving section having a transverse section with longitudinal sides, which transverse section is wider than the distance between the legs of the U-shaped section. The transverse section prevents the light source from radiating upwards and forms a flange for engaging with U-shaped support brackets for mounting. The U-shaped support brackets may be flexible and are provided with a connection member for connection to a support structure, a distance between the legs of the support brackets corresponding with the width of the transverse part of the receiving section and comprising a receiving slot for resiliently engaging with the longitudinal sides of the transverse section.

The invention also relates to a growing system comprising a number of lighting assemblies and having a cooling fluid supply duct and parallel thereto a cooling fluid discharge duct, extending in a length direction, the lighting assemblies extending along the fluid supply and discharge ducts and being with their inlet and outlets connected to a respective duct, each lighting assembly comprising control electronics at a distance from the cooling body, and a temperature sensor in the cooling body, wherein the control electronics and the temperature sensor of the lighting assemblies are connected to a control unit for control of the power supplied to each lighting assembly or each group of lighting assemblies.

The lighting assemblies may be controlled individually and/or in groups to provide optimal lighting conditions and may be reduced in power or switched off when the temperature of a lighting assembly rises above a predetermined threshold value.

The growing system may comprise an enclosed growing chamber having growing chamber walls, wherein the control electronics of the lighting assemblies and the control unit are situated outside of the growing chamber. In this way the control electronics can be maintained at a stable, low temperature condition which is independent of the conditions inside the growing chamber.

The fluid supply duct and the fluid discharge duct may be connected to a heat exchanger situated outside of the growing chamber. Brief description of the drawings

Some embodiments of a lighting assembly will by way of non-limiting example be explained in detail with reference to the accompanying drawings. In the drawings:

Fig. 1 shows an exploded view of a first embodiment of a lighting assembly according to the invention comprising a lens,

Fig. 2 shows the lighting assembly of fig 1 in its assembled state,

Fig. 3 shows a plan view of an embodiment of a one-part cooling body having drilled cooling channels,

Fig. 4 shows a perspective view of an embodiment comprising a two-part cooling body, Fig. 5 shows a schematic overview of a growing system according to the present invention comprising a plurality of lighting assemblies,

Fig. 6 shows an embodiment of a growing system comprising a plurality of lighting assemblies according to the invention wherein control electronics and a heat exchanger are situated outside of the growing chamber,

Fig. 7 shows a further embodiment of an extruded elongate fixture in a lighting assembly according to the invention, and

Fig. 8 shows a detail on an enlarged scale of the extruded lighting assembly of fig. 7.

Detailed description of the invention

Fig 1 shows a lighting assembly 1 comprising a metal fixture 2 and a solid state light source 3. The metal fixture 2 has a rectangular tile-shaped cooling body 4 having an emission surface 5, a back surface 6 and side surfaces 7,8,9, 10. The length of the sides 7-10 may for instance be 20 cm, the height H may be about 4 cm. The metal of the fixture may for instance comprise aluminium or copper. The light source 3 is attached to the emission surface 5. A reflector 11 is placed over the light source 5. Via ring 12 a lens 13, having a diameter of for instance 12 cm is placed on top of the light source 5.

Cooling channels 15, 15', 15" are drilled from side surface 8 towards the opposite side surface 9 and end in proximity of the side surface 9. After forming of the cooling channels 15-15", these cooling channels are closed off via a plug 17. A fluid inlet channel 16 extends from side surface 7 towards opposite side surface 10, along the side 8. A fluid outlet channel extends parallel to the inlet channel 16 from the side surface 10 towards the side surface 7 along the side 9. The inlet channel 16 and the outlet channel in interconnect the cooling channels 15- 15" and can be connected via couplings 19, 20 to respectively a fluid inlet duct and a fluid discharge duct. Control electronics 21 are connected to the light source 3 and are situated outside the cooling body 4.

Fig. 3 shows the cooling channels 25,26, 27,28,29 and 30 inside the cooling body 4. An additional fluid inlet opening 32 and fluid outlet opening 31 may be provided in the back surface 6 of the cooling body 4.

Fig 4. Shows a cooling body 4 which is comprised of two parts 35, 36. In the interface plane 38, a single cooling channel 37 is provided in the lower part 35 extending from inlet 40 to outlet 41. A sealing ring 39 extends in the interface plane 38 along the periphery of the cooling body. The upper and lower parts 35,36 may be interconnected using a bolted connection or alternatively via soldering or welding.

Fig. 5 shows a number of interconnected lighting assemblies 50, 50' each connected to a fluid supply duct 51 and a fluid discharge duct 52. A temperature sensor 53,53 'and control electronics 54,54'are connected to each assembly 50,50'and to a control unit 55 such as a PLC.

Fig. 6 shows an embodiment in which the assemblies 50,50'are situated in an enclosed growing chamber 56 in which no daylight is present. The control electronics 54,54'and a control unit 55 are placed outside of the enclosure of the growing chamber 56.

Fig. 7 shows a lighting assembly 59 with an extruded elongate cooling body 60 having a tubular cooling channel 61 and a U-shaped receiving section 62. In the receiving section 62, a strip shaped PCB 63 carrying the lighting elements is placed. Flexible U-shaped support brackets 64,64' connect the cooling body 60 to a support in the growing chamber.

As can be seen from fig. 8, a transverse section 65 below the cooling channel 61 is wider than the outside diameter of the cooling channel 61 and forms longitudinal sides 66 of the cooling body 60. The flexible legs 66 of the support brackets 64,64' comprise a slot 67 which resiliently engages with the longitudinal sides for snapping the cooling body 60 into the brackets 64,64' . Via a bolt 69, the brackets 64, 64' are connected to a support structure of the growing chamber.