WO2005027621A1

WO2005027621A1 - Height adjustable mobile illumination apparatus for a greenhouse

Info

Publication number: WO2005027621A1
Application number: PCT/CA2003/001423
Authority: WO
Inventors: David Knelsen Dyck
Original assignee: David Knelsen Dyck
Priority date: 2003-09-19
Filing date: 2003-09-19
Publication date: 2005-03-31
Also published as: AU2003266894A1

Abstract

A height adjustable mobile illumination apparatus for a greenhouse comprising a horizontal track (1) that is longitudinally aligned with the greenhouse. The track is vertically adjustable and is suspended, from the greenhouse by a first set of cables (2). An illumination means is mounted to the underside of the track and is mobile along the length of the track by operation of a second set of cables (20). A drive system (30, 31) is used to operate the first and second sets of cables. The height of the illumination means above the plants is adjusted by raising the entire track with the first set of cables. A plurality of illumination means may be provided on a single track spaced apart along the length of the track. A system for illuminating an entire greenhouse comprises a plurality of the apparatus as previously described arranged in spaced apart relation across the width of the greenhouse.

Description

Height Adjustable Mobile Illumination Apparatus for a Greenhouse

Field of the Invention

The invention relates to illumination of plants within a greenhouse. More particularly, the invention relates to a height adjustable mobile illumination apparatus with illumination means that are mobile along the length of the greenhouse.

Background of the Invention

Greenhouses are used to provide a controlled environment for growing plants. Typically, the temperature, humidity, and amount of water provided to the plants are controlled. Greenhouses typically are transparent or translucent to sunlight; however, for certain types of plants it is beneficial to provide supplementary illumination to the plants using lamps suitable for promoting the growth of plants, for example, fluorescent, metal halide, or high pressure sodium lamps. Supplementary illumination is used to provide a greater total amount of light to the plants during the day and/or to extend the daylight portion of the day/night cycle. A number of problems are created when providing supplementary illumination using stationary lamps. Stationary lamps create a non-uniform light intensity distribution in the greenhouse characterized by regions of high light intensity under the lamps and regions of low light intensity between lamps. The non-uniform intensity distribution leads to sub-optimal growth in the greenhouse. A high temperature zone is also created directly beneath the lamps that can cause damage to the plants. It has been found that for certain plants providing supplementary illumination for a brief period followed by a period of rest is just as effective as continuously providing supplementary illumination, creating an opportunity to reduce the cost associated with supplementary illumination. Travelling lighting systems have been developed where the lamps are moved along the length of the greenhouse, providing periodic illumination to the plants contained therein. An example of such a system is provided in United States Patent 5,993,030, filed February 3, 1998 by Barton J. Barcel and issued November 30, 1999 (Barcel). Barcel discloses a travelling lighting system having a plurality of lamps supported on an elongated truss oriented across the width of the greenhouse. The truss is supported by trolleys carried in a pair of parallel spaced apart tracks extending the length of the greenhouse. The truss is advanced along the tracks so that the plurality of lamps is moved along the length of the greenhouse. This system is complicated to install and expensive to maintain. Moreover, the tracks are fixed at one height so that the distance between the lamps and the plants being illuminated is non-adjustable. As the plants grow, the distance between the plants and the lamps decreases, leading to a non- uniform light distribution that causes sub-optimal plant growth and/or excessive heating resulting in plant tissue damage.

United States Patent 6,312,139, filed November 23, 1999 by Baker, et al. and issued November 6, 2001 (Baker) discloses a vertically adjustable overhead lighting system for use in a greenhouse. The growth lights are mounted on a bar that may be raised or lowered to correlate with plant growth. However, the growth lights are not mobile along the length of the greenhouse, making the system un-economic to deploy on a large scale. The system also inherently has many of the aforementioned problems associated with stationary supplementary illumination systems. The need therefore still exists for a height adjustable mobile illumination apparatus for a greenhouse.

Summary of the Invention

According to an aspect of the invention, there is provided a mobile illumination apparatus for a greenhouse comprising: a horizontal track having a length longitudinally aligned with a length of the greenhouse and suspended by a first set of cables from the greenhouse, the first set of cables operable to vertically move the track; at least one illumination means suitable for promoting the growth of plants, the illumination means mounted to the track and connected to a second set of cables, the second set of cables operable to move the illumination means along the track; and, a drive system connected to the first set of cables and the second set of cables, the drive system for selectively operating the sets of cables.

According to another aspect of the invention, there is provided a system for illuminating plants in a greenhouse comprising: providing a plurality of the apparatus described above within a greenhouse; and, suspending each track parallel to an adjacent track spaced apart across a width of the greenhouse.

According to yet another aspect of the invention, there is provided a method of providing illumination to plants in a greenhouse comprising: providing a mobile illumination apparatus comprising a vertically movable horizontal track having an illumination means suitable for promoting the growth of plants mounted thereto, the illumination means movable along the track; vertically adjusting the track to position the illumination means a pre-determined height above the plants; and, moving the illumination means along the track at a pre-determined rate.

The horizontal track may be of any suitable shape that permits movement of an illumination means mounted thereto along the length of the track. For example, the track may comprise two C-shaped sections attached to one another with their open portions facing one another or alternatively with their open portions facing outwardly. The track may have an l-shaped, U-shaped, rectangular, or circular cross-section. The track may comprise additional members attached thereto to help stiffen the track and reduce or prevent warping or bending of the track along its length. The additional members may comprise, for example, an L-shaped member attached to the track along a top surface thereof. Alternatively, the track may form part of a structure that is used to stiffen the track and provide increased structural strength, especially when the track extends along a great length of greenhouse, for example, a webbed or truss-like structure. The track may be formed of a single continuous member or a plurality of attached members. The track may comprise a series of discrete lengths of track attached end-to-end or may comprise a single continuous length. The illumination means may be mounted to the track by means of one or more trolleys. The trolleys may be of any suitable shape or design that permits movement of the trolley along the length of the track and permits mounting of the illumination means thereto. For example, each trolley may have wheels and be mounted to the track with the wheels within complementary C-shaped sections of the track so that the trolley can roll along the length of the track. There may be two or four wheels and the wheels may be made from any suitable material, for example a dry lubricant plastic material, such as acetal plastic, commonly available under the trade name Delrin™. Alternatively, the trolley may comprise one or more ball bearings mounted within a track having a circular cross-section complementary to the bearings, thereby permitting movement of the trolley along the track. The trolley may further comprise a fixed length member for mounting the illumination means a fixed distance from the track and permitting the distance between the illumination means and the plants to be adjusted by vertically adjusting the height of the track. Any suitable number of trolleys may be used to ensure that the illumination means is stabley and securely mounted to the track.

The track may be suspended from the greenhouse by means of a first set of cables. The cables may be suspended from any suitable part of the greenhouse, for example, the trusses of the greenhouse, by means of a pulley or pulleys mounted to the trusses. The cables may be attached to the track by any suitable means, for example a track hanger passing over the track in a manner that does not interfere with passage of a trolley past the track hanger. It is understood by a person of skill in the art that any suitable flexible tension transmitting member, for example ropes, chains, or cords, may be substituted for cables as described herein.

The first set of cables may comprise a plurality of individual cables, each of the individual cables attached to the track at spaced apart intervals along its length. Each individual cable may pass over a pulley and then be connected to one or more of the other cables to thereby form the first set of cables. Retracting the first set of cables causes a tension to be applied to each of the individual cables, causing the track to be raised uniformly along its length and maintaining its horizontal orientation. This reduces the likelihood of damage being caused to the track and the likelihood of warping the track, which could lead to binding of the trolleys as they travel along the length of the track. The illumination means may be moved along the track by means of a second set of cables. The second set of cables may be parallel with the track and may comprise a single cable or a plurality of cables. The second set of cables may form a continuous loop that may be moved in either a clockwise or counter-clockwise direction. This allows the illumination means to be moved either in a first forward direction or a second rearward direction along the length of the track. The loop may pass over a drive pulley at one end of the track and over an idler pulley at the opposite end of the track, the drive pulley being used to cause movement of the loop. Alternatively, the second set of cables may be wound about a pair of spools, one spool located at each end of the track, so that as the cable is un-wound from one spool it is wound on to the spool at the opposite end of the track. Any suitable cable arrangement may be used that causes movement of the illumination means along the track. The illumination means is generally oriented downwardly to illuminate plants beneath the illumination means. It is preferable that the illumination means be mounted to the track in a manner that reduces or prevents shadows from being cast on to the plants below. The illumination means may be located adjacent any surface of the track, for example, the illumination means may be located on the underside of the track. The trolleys may then extend downwardly from the track and may be mounted to the top of the illumination means to help reduce or prevent shadow formation. The second set of cables may be located on the underside of the track as well, between the illumination means and the track, in a further effort to avoid shadow formation. The second set of cables may be attached to one or more trolleys and/or the illumination means itself.

The illumination means may comprise an electrical power supply and an illumination element. The illumination element may be adjacent the electrical power supply or separated therefrom. Generally, the distance between the electrical power supply and the illumination element is minimized, however, the electrical power supply may be located remotely from the illumination element and need not necessarily be located on the underside of the track. The illumination means may further comprise a pair of electrical power supplies and a pair of illumination elements. The electrical power supplies may be located adjacent one another. Shielding may be employed to limit electromagnetic interference between the power supplies. A single electrical power supply may be used to power a plurality of illumination elements.

The illumination element comprises at least one lamp suitable for promoting plant growth and may comprise a reflector and/or a lens. Lamps suitable for promoting plant growth are generally known to persons skilled in the art and typically emit visible light in the red and/or blue spectrum. Examples of lamps that may be suitable for use include fluorescent, metal halide, or high pressure sodium lamps. However, persons skilled in the art may select any suitable lamp employing the latest in lamp technology. A reflector may be used to direct the lamp output downwardly towards the plants in the greenhouse. The reflector may be of any suitable shape, for example parabolic, and a lens may be used to aid in focusing the lamp output. Various types of electrical power supplies are known and an appropriate electrical power supply may be selected for the type of lamp used. An electrical power supply may also be referred to in the art as a ballast or a transformer. Electrical power supplies generally include means to control the power supply, start the lamp, maintain an output from the lamp, shut down the power supply in the event of unacceptably high temperatures, etc. Heat dissipation means may also be installed with the power supply. These may be in the form of fins on the exterior of the power supply and/or supplementary cooling means. These variations are well known to persons skilled in the art.

The electrical power supply is connected to an electrical power source by means of an electrical cable. The cable may be suspended from the underside of the track by means of a plurality of cable trolleys. The cable may be looped over the cable trolleys such that a serpentine path is created by the cable between the power supply and the power source. As the illumination means moves along the track, tension is applied to the cable and the serpentine path straightens, thereby causing the cable trolleys to move along the track in response to movement of the illumination means. The cable trolleys may be similar in design to the trolleys used to support the illumination means, but generally include a cable hanger that is suitable for supporting a loop of cable without chaffing the cable during movement along the track.

A drive system is used to operate the first and second sets of cables. The drive system may comprise any number of motors, for example, one, two, three, etc. In the case of a pair of motors, each motor could operate one of the sets of cables. The drive system may include means to centrally control the motors. A first motor may be connected to a winch used for operating the first set of cables and may be activated to cause vertical adjustment of the height of the track. A second motor may be connected to the drive pulley used for operating the second set of cables and may be activated to cause the illumination means to move along the track. At least one of the motors may be operated at two or more speeds; for example, the second motor connected to the drive pulley may be operated at two or more speeds. The motors may be connected to a variable speed drive so that the speed may be infinitely adjusted. The motors may be electrically powered or fluid powered. When the motors are fluid powered, the drive system may include an electrically powered pump for supplying fluid to the fluid powered motors and valve means to control the speed at which the motors are operated. A clutch and/or gear box may also be used to adjust the speed at which the cables are operated, regardless of whether the motors are electrically powered or fluid powered. In use, the illumination means moves along the length of the track in a forward direction at a first speed. This speed is generally selected so that the illumination means moves slowly. The illumination means travels in the forward direction a certain distance along the track and then reverses direction. The illumination means may then travel in the reverse direction at a second speed. The second speed may be greater than the first speed so that the illumination means rapidly returns to the front of the track. This ensures that the plants at either end of the track do not receive an excessive amount of heat and/or light from the illumination means, which could result in damage to the plant and/or sub-optimal plant growth. A plurality of illumination means may be mounted on a single track at spaced apart intervals along the track. Each illumination means is separated from the next adjacent illumination means by a first distance and travels a second distance, less than the first distance, along the track before reversing direction. The second distance may be chosen so that the difference between the first distance and the second distance is sufficient to permit cable trolleys associated with the first illumination means of the plurality of illumination means to accumulate along the track.

The rate of movement of the illumination means is the second distance divided by the total time the illumination means travels in the forward and reverse directions. The rate at which the illumination means moves may be selected based on: the type of plants; the amount of light to be received by the plants; the amount of heat that can be tolerated by the plants; the desired illumination cycle to be received by the plants; or, a combination thereof. For example, certain plants require a great amount of light, but cannot tolerate heat; the rate at which the illumination means moves could be selected so that the illumination means moves quickly along the track and makes a greater number of trips along the track in a given period of time. The illumination cycle is the ratio of the amount of time that the plant is illuminated to the amount of time that the plant is not illuminated in a given period. The illumination cycle can be adjusted by increasing the rate of travel of the illumination means and/or by adjusting the total amount of time that supplementary illumination is provided in a given day. For example, for pepper plants, it has been found that an illumination cycle of between 10% and 40%, preferably 20%, produces optimal results.

The track may be vertically adjusted to position the illumination means a predetermined height above the plants. The height may be selected based on: the type of plants; the light intensity to be received by the plants; the amount of heat that can be tolerated by the plants; the greenhouse area to be covered by the illumination means; or, a combination thereof. The height of the track may be vertically adjusted as the plants grow to preserve a desired distance between the illumination means and the plants. Alternatively, the distance between the illumination means and the plants may be less when the plants are small, providing more heat to the plants, and may be increased as the plants grow and become less heat tolerant. The light intensity received by the plants decreases as the illumination means is moved further away from the plants. The illumination means covers a greater area of greenhouse when positioned further away from the plants; however, this can lead to non-uniformity of illumination at the periphery of coverage. The total amount of light received by the plants is the product of the light intensity and the exposure time of the plants to the light and is affected both by the height of the illumination means, the rate of travel of the illumination means, and the illumination cycle. An entire greenhouse^' may be illuminated by providing a plurality of the apparatus according to the present invention arranged in parallel side-by-side relation across the width of the greenhouse. Each apparatus may be spaced apart from an adjacent apparatus by a certain interval determined by the desired uniformity of coverage of the illumination means. Decreasing the separation interval between each apparatus leads to greater uniformity of illumination at the periphery of coverage of each illumination means; however, this requires a greater number of the apparatus for a given width of greenhouse, thereby increasing the cost of illuminating the greenhouse. An economic trade-off exists between uniformity of illumination and the spacing interval and an acceptable number of the apparatus may therefore be determined for a given greenhouse and type of plant grown based on economic considerations.

Brief Description of the Drawings

Having described the invention, preferred embodiments thereof will now be described with reference to the accompanying drawings, in which:

Fig. 1 is a perspective view of an apparatus according to the present invention; Fig. 2 is a side view of the apparatus of Fig. 1 ;

Fig. 3 is a side view of a drive system according to the present invention; Fig. 4 is a perspective view of the drive system of Fig. 3; Fig. 5 is a perspective view of a trolley according to the present invention;

Fig. 6 is a perspective view of a track according to the present invention with the trolley of Fig. 5; Fig. 7 is a side view of an illumination means according to the present invention;

Fig. 8 is a perspective view of the illumination means of Fig. 7; and,

Fig. 9 is a perspective view of a system according to the present invention.

Detailed Description of Embodiments

Referring to Figs. 1 and 2, an apparatus according to the present invention comprises a track 1 suspended from a greenhouse by a first set of cables 2. The first set of cables 2 passes over a pulley 3 attached to a truss 4 of the greenhouse. A second set of cables

20 is provided on the underside of the track 1 and is operable to move an illumination means 50 along the length of the track. The illumination means 50 is mounted to the underside of the track 1 by means of two trolleys 51. A drive system 30 comprises a pair of motors, the first motor 31 connected to the first set of cables 2 and the second motor 32 connected to the second set of cables 20. An electrical cable 70 is suspended from the underside of the track 1 by means of a plurality of cable trolleys 71 and forms a serpentine path between adjacent cable trolleys. Limit switches 90, 91 are spaced apart along the track 1 a pre-determined distance to provide a signal to the drive system 30 indicating when the illumination means 50 has traveled along the track the pre-determined distance.

The first set of cables 2 is comprised of a plurality of individual cables 5 attached to the track 1 at spaced apart locations along its length by means of track hangers 8 that will be discussed in greater detail hereinafter. The first set of cables 2 is coiled about a spool (not shown) of a winch that is operated by the drive system. When the first set of cables 2 is retracted, a tension is applied to each of the individual cables 5 and the track 1 is raised uniformly along its length. The first set of cables 2 is thereby used to vertically adjust the height of the track 1 , thereby adjusting the height of the illumination means 50 mounted thereto with respect to the plants below. The first set of cables 2 is attached to the track 1 by means of a plurality of track hangers 8 positioned along the length of the track. Each track hanger 8 passes over the outside of the track 1 and has a lower inwardly bent portion for supporting the track 1 from the underside thereof. The inwardly bent portion is sized to permit movement of the trolleys 51 and cable trolleys 71 past the track hanger 8 along the length of the track 1. If the track 1 comprises a series of discrete lengths of track attached end-to-end, the track hanger 8 can be positioned over the joint between adjacent sections of track to provide support at the joint.

Turning to Figs. 3 and 4, the second motor 32 is electrically powered and connected to a gearbox 33. The gearbox 33 has a gear shaft 34 extending outwardly therefrom with a first sprocket 35 concentrically mounted thereon. In the embodiment shown, the second motor 32 is capable of operating at two speeds and the gearbox 33 permits manual adjustment of the gear ratio, allowing a desired rotational speed of the first sprocket 35 to be selected. A chain 36 operatively connects the first sprocket 35 to a second sprocket 37 that is concentrically mounted on a sprocket shaft 38. The sprocket shaft 38 is journaled within a bearing mounted to the underside of the track 1 by means of a bracket 40. A drive pulley 41 (not shown in Fig. 3) for operating the second set of cables 20 is also concentrically mounted on the sprocket shaft 38. The second set of cables 20 forms a continuous loop passing over the drive pulley 41 at one end of the track 1 and over an idler pulley (not shown) at the opposite end of the track. A guide pulley 42 is used to support the underside of the loop and reduce the distance between the underside of the loop and the track 1. The loop is under tension between the two pulleys and frictionally engaged with the drive pulley 41. Operation of the second motor 32 causes rotation of the first sprocket 35, producing a corresponding rotation of the second sprocket 37 by virtue of the chain 36. This rotates the sprocket shaft 38 and the drive pulley 41 mounted thereon, creating a bi-directional movement of the second set of cables 20 along the length of the track 1 due to the continuous loop formed between the two pulleys.

The electrical cable 70 is suspended from the underside of the track 1 by a plurality of cable trolleys 71. Each cable trolley 71 includes a cable hanger 72 suspended from the underside of the cable trolley. Each cable hanger 72 has a rounded profile with a resilient surface to reduce chaffing of the electrical cable 70. The electrical cable 70 passes over each cable hanger 72 and forms a serpentine path between adjacent cable trolleys 71. The electrical cable 70 is connected at one end to the illumination means 50 (not shown in Fig. 4) and as the illumination means moves along the track 1 , a tension is applied to the electrical cable, causing a corresponding movement of the cable trolleys 71 and a straightening of the serpentine path between adjacent cable trolleys. As the illumination means 50 approaches the limit of its travel in the forward direction along the length of the track 1, the electrical cable 70 is nearly straightened between adjacent cable trolleys 71. When the illumination means 50 begins to travel in the reverse direction the tension in the electrical cable 70 is reduced, permitting the cable trolleys 71 to also move in the reverse direction due to sagging of the electrical cable between adjacent cable trolleys. The length of the electrical cable 70 between adjacent cable trolleys 71 is selected so as to minimize excessive sagging of the cable that could interfere with plants, people, or equipment within the greenhouse.

Referring to Figs 5 and 6, a trolley 51 is shown. The trolley 51 has two pairs of wheels 52 positioned on either side of a mounting flange 53. The pairs of wheels 52 are made of a durable dry lubricant plastic material available, for example, an acetal plastic such as Delrin™. Hanging brackets 54 are attached to the mounting flange 53 and depend downwardly therefrom. Each hanging bracket 54 is L-shaped, having an outwardly bent portion at its lower end for mounting the illumination means (not shown) thereto. The second set of cables 20 forms a continuous loop that passes between the hanging brackets 54 and is in contact with the upper surface of a trolley pulley 56 mounted between the hanging brackets. The second set of cables 20 is attached to the hanging brackets 54 of at least one of the trolleys 51 by means of a clamp 57 that frictionally engages the second set of cables so that the trolley 51 moves with the second set of cables.

With reference specifically to Fig. 6, the track 1 has an inverted U-shaped cross-section with lower inwardly bent portions 58 at the extremities of the U. The pairs of wheels 52 are positioned on the interior of the track 1 and ride along the upper surface of the inwardly bent portions 58. The distance between the center of each pair of wheels 52 and the overall width of each pair of wheels is selected to reduce binding of the trolley as it travels along the length of the track due to misalignment of the wheels. The overall width of each pair of wheels 52 closely corresponds to the interior dimensions of the track 1.

Figs. 7 and 8 show an illumination means 50 suspended from the underside of the track 1 by means of two trolleys 51. The second set of cables 20 forms a continuous loop that passes between the brackets 54 of the trolleys 51 , the upper part of the loop riding over trolley pulley 56 and the lower part of the loop attached to at least one of the trolleys 51 by means of a clamp (not shown). The second set of cables 20 is operable to bi-directionally move in a continuous fashion about the loop, thereby causing movement of the illumination means 50 along the length of the track 1 by virtue of the attachment of the second set of cables to the trolleys 51. The illumination means 50 comprises a support member 60 to which are mounted two electrical power supplies

61. Each electrical power supply 61 is electrically connected to a power source by means of the electrical cable 70. Each electrical power supply 61 is also electrically connected to an illumination element 62. Referring specifically to Fig. 8, the illumination element comprises a housing 63 that contains a reflector 64 and a lamp 65. The housing 63 has on its underside a lens 66 and the reflector 64 directs the output of the lamp 65 through the lens on to the plants below.

Fig. 9 shows a system according to the present invention comprising a plurality of the apparatus as previously described spaced apart across a width of the greenhouse. The track 1 of each apparatus is parallel to an adjacent track and spaced apart across the width of the greenhouse by a spacing interval s. The spacing interval s is determined based on the coverage of the illumination means 50 and the desired uniformity of illumination across the width of the greenhouse. The track 1 of each apparatus may be set at the same height or a different height, depending on the size and type of plants being illuminated. This allows the greenhouse grower greater flexibility in the illumination delivered across the width of the greenhouse than previously available.

In operation, the track 1 is vertically adjusted to position the illumination means 50 a pre-determined height above the plants. The height is selected based on: the type of plants; the light intensity to be received by the plants; the amount of heat that can be tolerated by the plants; the greenhouse area to be covered by the illumination means; or, a combination thereof. Typically, the track 1 is vertically adjusted in response to plant growth, thereby changing the height of the illumination means 50 to a new height selected based on the foregoing criteria. The illumination means 50 is then moved along the track 1 at a pre-determined rate. The rate is selected based on: the type of plants; the amount of light to be received by the plants; the amount of heat that can be tolerated by the plants; the illumination cycle to be received by the plants; or, a combination thereof. For example, the illumination cycle may provide between 10% and 40% illumination to the plants, preferably 20% for plants such as peppers. As shown in Fig. 9, a plurality of illumination means 50a, 50b, 50c may be provided along the length of each track 1. The illumination means 50a, 50b, 50c are spaced apart by a first distance along the length of the track 1 and move together, thereby preserving the first distance. Each of the illumination means 50a, 50b, 50c travels along the length of the track 1 a second distance that is less than the first distance. The second distance is selected to provide sufficient space along the track 1 for accumulation of the cable trolleys 71 and electrical cable 70 associated with the illumination means 50a. For the illumination means 50a, the second distance is demarcated by limit switches 90, 91. Each illumination means 50a, 50b, 50c moves in a forward direction at a first pre-determined speed until the illumination means 50a reaches the limit switch 91. The limit switch 91 then sends a signal to the control unit of the drive system 30, which signals the second motor 32 to reverse direction. Each illumination means 50a, 50b, 50c then moves in a reverse direction along the track 1 at a second pre-determined speed. When the illumination means 50a reaches the limit switch 90, a signal is again sent to the control unit of the drive system 30, causing each illumination means 50a, 50b, 50c to resume moving in the forward direction at the first pre-determined speed.

The second pre-determined speed is typically faster than the first pre-determined speed. This is so that each illumination means 50a, 50b, 50c moves quickly back to its starting position to commence the next illumination cycle, ensuring that illumination is applied evenly across the plants with a constant interval between periods of illumination. Also, tissue damage caused by receiving a double dose of light and heat from sequential periods of illumination is prevented for plants near either of the limit switches 90, 91.

Claims

1. A mobile illumination apparatus for a greenhouse comprising: a) a horizontal track having a length longitudinally aligned with a length of the greenhouse and suspended by a first set of cables from the greenhouse, the first set of cables operable to vertically move the track; b) at least one illumination means suitable for promoting the growth of plants, the illumination means mounted to the track and connected to a second set of cables, the second set of cables operable to move the illumination means along the track; and, c) a drive system connected to the first set of cables and the second set of cables, the drive system for selectively operating the sets of cables.

2. The illumination apparatus of claim 1 , wherein the illumination means is located on an underside of the track.

3. The illumination apparatus of claim 1 or 2, wherein the illumination means is mounted at a fixed distance from the track.

4. The illumination apparatus of any one of claims 1 to 3, wherein retracting the first set of cables raises the track and extending the first set of cables lowers the track, thereby raising and lowering the illumination means.

5. The illumination apparatus of any one of claims 1 to 4, wherein the first set of cables is suspended from a truss of the greenhouse by a pulley.

6. The illumination apparatus of any one of claims 1 to 5, wherein the second set of cables is parallel with the length of the track and located on an underside of the track.

7. The illumination apparatus of any one of claims 1 to 6, wherein the second set of cables forms a continuous loop.

8. The illumination apparatus of any one of claims 1 to 7, wherein the illumination means is mounted to the track by means of one or more trolleys that are mobile along the length of the track.

9. The illumination apparatus of claim 8, wherein the second set of cables is attached to the one or more trolleys, the second set of cables operable to move the one or more trolleys, thereby moving the illumination means along the track.

10. The illumination apparatus of any one of claims 1 to 9, wherein the illumination means comprises at least one electrical power supply and at least one illumination element, the electrical power supply located adjacent the illumination element.

11. The illumination apparatus of any one of claims 1 to 10, wherein the illumination means comprises two electrical power supplies and two illumination elements, each electrical power supply located adjacent an illumination element, the electrical power supplies adjacent one another.

12. The illumination apparatus of claims 10 or 11 , wherein each electrical power supply is connected to a source of electrical power by means of an electrical cable that is suspended from the underside of the track.

13. The illumination apparatus of claim 12, wherein the electrical cable is suspended from the underside of the track by means of a plurality of cable trolleys that are mobile along the length of the track, the electrical cable able to move in response to movement of the illumination means along the length of the track.

14. The illumination apparatus of any one of claims 1 to 13, wherein there are a plurality of illumination means on the track.

15. The illumination apparatus of claim 14, wherein the plurality of illumination means are spaced apart by a first distance along the length of the track.

16. The illumination apparatus of claims 15, wherein each illumination means travels along the length of the track a second distance that is less than the first distance.

17. The illumination apparatus of any one of claims 1 to 16, wherein the illumination means moves along the length of the track at a first pre-determined speed in a forward direction and a second pre-determined speed in a reverse direction.

18. The illumination apparatus of claim 17, wherein the second pre-determined speed is faster than the first pre-determined speed.

19. The illumination apparatus of any one of claims 1 to 18, wherein the drive system comprises a first and second motor, the first motor for operating a winch connected to the first set of cables, the second motor for operating a drive pulley connected to the second set of cables.

20. The illumination apparatus of claim 19, wherein at least one motor may be operated at two or more speeds.

21. The illumination apparatus of claims 19 or 20, wherein the second motor may be operated at two or more speeds.

22. The illumination apparatus of any one of claims 19 to 21 , wherein the motors are fluid powered and the drive system comprises a pump for delivering fluid to the motors.

23. The illumination apparatus of any one of claims 1 to 22, wherein the drive system comprises a clutch and gear box for varying the speed at which the first and/or second set of cables is operated.

24. A system for illuminating plants in a greenhouse comprising: a) providing a plurality of the apparatus according to any one of claims 1 to 23 within a greenhouse; and, b) suspending each track parallel to an adjacent track spaced apart across a width of the greenhouse.

25. A method of providing illumination to plants in a greenhouse comprising: a) providing a mobile illumination apparatus comprising a vertically movable horizontal track having an illumination means suitable for promoting the growth of plants mounted thereto, the illumination means movable along the track; b) vertically adjusting the track to position the illumination means a pre-determined height above the plants; and, c) moving the illumination means along the track at a pre-determined rate.

26. The method of claim 25, wherein the height is selected based on: the type of plants; the light intensity to be received by the plants; the amount of heat that can be tolerated by the plants; the greenhouse area to be covered by the illumination means; or, a combination thereof.

27. The method of claims 25 or 26, wherein the track is vertically adjusted in response to plant growth, thereby changing the height of the illumination means.

28. The method of any one of claims 25 to 27, wherein the rate is selected based on: the type of plants; the amount of light to be received by the plants; the amount of heat that can be tolerated by the plants; the illumination cycle to be received by the plants; or, a combination thereof.

29. The method of claim 28, wherein the illumination cycle provides between 10% and 40% illumination to the plants.

30. The method of claims 28 or 29, wherein the illumination cycle provides 20% illumination to the plants.