Patent Publication Number: US-2018042186-A1

Title: A system for indoor cultivation of plants with  simulated natural lighting conditions

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of a plant cultivating system. More particularly, the invention relates to an indoor soilless plant cultivation system, for cultivating plants in a nutrient-rich solution. 
     BACKGROUND OF THE INVENTION 
     Many people are attracted to living in urban settings by virtue of the economic progress that may be realized. Cities bring together diverse groups of people and companies in ways that increase productivity and create the networks, clusters, and chance interactions that lead to the discovery of new innovations and the creations of new entrepreneurial businesses. Other advantages of living in urban settings include the large number of cultural activities that are available and the relative ease in commuting to work. 
     While 60% of the human population now lives in cities and are protected against the outdoor elements, food-bearing plants are subjected to the rigors of the outdoors. People hope for a good weather year in order to ensure that the food supply will be readily available. Many times due to a rapidly changing climate regime, however, massive floods, protracted droughts, class 4-5 hurricanes, and severe monsoons take their toll each year, destroying millions of tons of valuable crops. 
     By the year 2050, nearly 80% of the earth&#39;s population will reside in urban centers. Applying the most conservative estimates to current demographic trends, the Earth&#39;s population will increase by about 3 billion people during this period. An estimated 10.9 million square km of new land (about 20% more land than all of Brazil) will be needed to grow enough food to feed them, if traditional farming practices continue as today. At present, throughout the world, over 80% of the land that is suitable for raising crops is in use. Historically, some 15% of that agriculturally suitable land has been laid waste by poor management practices. Indeed, much land has become despoiled, such that natural eco-zones have been converted into semi-arid deserts. 
     The traditional agricultural practice of growing food-bearing plants outdoors, or within greenhouses located at agricultural areas, is problematic in terms of weather related or pest related crop failure, the cost of transporting the grown crops to food distribution centers, the ecological damage due to fossil fuel emissions from the vehicles that transport the crops and that are used for performing agricultural activities such as plowing, the cost for fertilizers and pesticides, the occurrence of infectious diseases acquired at an agricultural interface, and ecological damage due to agricultural runoff. 
     In order to sustain the Earth&#39;s growing population, it would be desirable to learn how to safely grow food within city-located, environmentally controlled multistory facilities, in order to maintain a readily available food supply while overcoming the problems associated with traditional agricultural practices. 
     Some indoor hydroponic system are known from the prior art wherein plant growth units are stacked one on top of another, a solution of water and plant nutrient is introduced to the plants, and panels comprising artificial light sources that eliminate the need for natural sunlight and enable light cycles of varied duration are provided on top of each plant growth unit. 
     Photoperiodic flowering plants flower in response to a sensed change in night length, and therefore require a continuous period of darkness before floral development can begin. However, the prior art light panels for simulating such light cycles are costly due to the need of a light panel at each level of a growth unit and of a dedicated control system for each panel. Additionally, the light panels are self-heating, and expensive to operate cooling systems are needed to remove the generated heat. 
     Light-emitting diodes (LEDs) have been found to be ideal light sources for crop production by virtue of their small size, durability, long operating lifetime, wavelength specificity, relatively cool emitting surfaces and linear photon output with electrical input current. Work at NASA&#39;s Kennedy Space Center has focused on the proportion of blue light required for normal plant growth as well as the optimum wavelength of red and the red/far-red ratio. The addition of green wavelengths for improved plant growth has also been addressed. [“Plant Productivity in Response to LED Lighting”, G. Massa et al, HortScience, December 2008, vol. 43, no. 7, 1951-1956] However, the inability of such prior art lighting systems to provide substantially equal light distribution limits implementation thereof for an indoor plant growth unit of large vertical dimensions. 
     Another drawback of prior art systems for cultivating plants is the safety of workers, when pest control is needed, in which case the entire cultivating space is sprayed by pesticide. This implies using a greater amount of pesticide. However, some pesticides may cause cancer and other health problems, as well as harming the environment. 
     It is an object of the present invention to provide an indoor soilless cultivating system for the sustainable crop production of a safe and varied food supply. 
     It is an additional object of the present invention to provide an indoor soilless cultivating system with a lighting system that maintains a substantially equal light distribution to facilitate photosynthesis at an indoor plant growth unit of relatively large vertical dimensions. 
     It is an additional object of the present invention to provide an indoor soilless cultivating system by which the operating and capital costs of light sources used to simulate the light cycles required by photoperiodic flowering plants are significantly reduced relative to those of the prior art. 
     It is yet an additional object of the present invention to provide an indoor soilless cultivating system by which the operating and capital costs of cooling systems for removing the heat generated by light sources that simulate the cyclical nature of natural sunlight are significantly reduced relative to those of the prior art. 
     It is yet another object of the present invention to provide an indoor soilless cultivating system which saves a substantial amount of the required pesticide to be sprayed, to thereby reduce the exposure of workers and the environment to harmful effects. 
     Other objects and advantages of the invention will become apparent as the description proceeds. 
     SUMMARY OF THE INVENTION 
     The present invention provides an indoor soilless plant cultivating system, comprising a plurality of stationary light posts, each of which adapted to illuminate a predetermined sector of an indoor facility in accordance with a predetermined illumination signature; a plurality of plant growth towers that are rotatable about a substantially vertical axis in accordance with a predetermined timing sequence so as to be exposable to the light generated at any given time by one or more of the light posts and that are arranged by at least one module defining a module darkened interior region within which plants being instantaneously positioned receive a sensation of nighttime; and irrigation means for supplying the plants being cultivated in each of said towers with a nutrient-rich solution. 
     The system further comprises a drive unit for cyclically rotating each of the towers so as to be sequentially exposed to morning light conditions, noon light conditions, afternoon light conditions and nighttime conditions in accordance with the illumination signature emitted by the light posts of the at least one module. The drive unit may be configured to cause a complete tower rotation once every 24-hour period. 
     Each of the towers is preferably configured with a plurality of mounting elements by each of which a corresponding plant is mountable at a different tower peripheral portion and is urged to grow outwardly from said peripheral portion, groups of said mounting elements being defined at different height levels of the tower. 
     Leaves of all of the plants being grown on one of the towers are exposed to a substantially uniform distribution of light emitted from light elements mounted on an adjacent one of the light posts for a given emulated time period despite a height differential between the plants. 
     To achieve the substantially uniform distribution of light, the light elements may be sufficiently small such that they have a density of no less than 40 light elements within a light post height of 50 cm and are mounted on each of the light posts in such a way that only one light element is mounted at any given height. A segment of the light elements has a predetermined number and sequence of light elements arranged such that constituent beams emitted from the light elements of said segment are mixed within a conical distribution angle to provide a photosynthetic photon flux density at the tower peripheral portion upon which the mixed beam impinges that stimulates photosynthesis for a given plant being grown. Thus the photosynthetic photon flux density at another tower peripheral portion being illuminated at the given emulated time period is substantially equal. 
     The predetermined number and sequence of light elements are preferably repeated along the height of the light post for all other segments. 
     In one aspect, each of the light elements is provided with a directional lens configured to produce a light emitting angle whose angular boundaries are incident on the tower periphery, causing propagation of the emitted light to an internal region of the module between two adjacent towers to be blocked as a result of its incidence on the tower periphery, to thereby ensure that said internal region will be darkened to a radiation level less than a predetermined photosynthetically active radiation level for the plant being cultivated. 
     The plant cultivating system provides at least the following advantages:
         A modular scalable system that is simple to ship, build and maintain.   The system can be deployed in any existing building with any geometrical shape regardless of its original purpose.   Dynamic allocation of the number of towers inside the same facility, or on different floors of the same facility, for different crops depending on seasonal demand or opportunities.   The facility is isolated from outdoor conditions to support plant cultivation every hour and every day of the year regardless of the outdoor weather conditions and climate.   Substantial shortening of the growth cycle of each plant, for extremely fast growth of high quality products.   The number of plants able to be grown in the system for a given area is 7 times greater as compared to traditional hydroponic growth.   Operation of the system approaches an optimum point in combining usage of light, air, water which are the most critical elements conducive to plant growth.   The plants being grown are not subject to damage due to extreme meteorological conditions and natural disasters.   Crops have maximum nutritional values, superior taste and freshness.   Reduced refrigerated transportation time and cost.   As the cultivating system is soilless, 95% less water is required to grow the crops than prior art systems.   No greenhouse gas emissions.   Easy and relatively inexpensive closed perimeter security and surveillance systems, preventing agricultural theft losses that are on the rise worldwide.   No soil pollutants.   Solution of land shortage problem.   Airflow system by which plant-released carbon dioxide is transported to a daytime region for an improved photosynthesis process.   Artificial pollination.       

     The present invention is also directed to an indoor plant cultivating system, comprising a plant growth apparatus on which one or more plants are mountable; a stationary light post adapted to illuminate said one or more plants in accordance with a predetermined illumination signature; and irrigation means for supplying said one or more plants with a nutrient-rich solution, wherein each of one or more segments of light elements mounted on said light post has a predetermined number and sequence of light elements arranged such that constituent beams emitted from the light elements of said segment are mixed within a conical distribution angle to provide a photosynthetic photon flux density at a peripheral portion of said plant growth apparatus upon which the mixed beam impinges that stimulates photosynthesis for said one or more plants being grown. 
     The present invention is also directed to an artificial pollination system, comprising a post on which are mounted an air discharge nozzle; a plant growth apparatus on which one or more pollen bearing plants are mountable; a sensor for detecting an instantaneous position of said one or more plants; an air receiver tank for storage of compressed air; a conduit extending from said air tank and in fluid communication with said nozzle; a control valve operatively connected with said conduit; and a controller in data communication with said sensor and said control valve, wherein said controller is operable to command opening of said control valve for a predetermined time, when a signal transmitted by said sensor is indicative that at least one of said plants is in pollen releasable proximity to said nozzle, so that a pulsed supply of the compressed air at a sufficiently high pressure to induce release of pollen from its anther and airborne transport of said released pollen to a carpel of the same or of an adjacent plant will be directed to said plant in pollen releasable proximity to said nozzle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a plan view of a plant cultivating system, according to one embodiment of the present invention; 
         FIG. 2  is a plan view of a plant cultivating system, according to another embodiment of the invention; 
         FIGS. 3A and 3B  are a schematic side view of two light posts, respectively, showing the relative arrangement of the light elements mounted thereon; 
         FIG. 3C  is a schematic illustration of the conical distribution angle of light that is emitted from a light element segment of a light post and that impinges upon a peripheral tower portion; 
         FIG. 4  is a schematic illustration in elevation view of one embodiment of irrigation means for irrigating plants being hydroponically cultivated; 
         FIG. 5  is a schematic illustration in elevation view of one embodiment of irrigation means for irrigating plants being aeroponically cultivated; 
         FIGS. 6A and 6B  are schematic illustrations in elevation view of another embodiment of irrigation means for irrigating plants being aeroponically cultivated; 
         FIG. 7  is a front view from within the interior of a portion of an outer wall of a tower used in conjunction with the irrigation means of  FIG. 1 ; 
         FIG. 8  is a schematic illustration of a recycling system for efficiently utilizing the irrigation fluid used in conjunction with the plant cultivating system; 
         FIG. 9  is a schematic illustration in side view of a temperature of a closed-loop liquid circulation system air to control the temperature of air in the vicinity of a tower; 
         FIG. 10  is a schematic illustration of an air circulation arrangement used in conjunction with the plant cultivating system for facilitating an increase in plant growth; 
         FIG. 11  is a schematic illustration of an artificial pollination system used in conjunction with the plant cultivating system; 
         FIG. 12  is a perspective view from the side of structural elements for use in conjunction with a module of towers; 
         FIG. 13  is a perspective view from the top of the structural elements of  FIG. 12 , showing an upper frame and a centrally positioned ceiling fan; 
         FIG. 14  is an enlarged perspective view from the side of the upper frame of  FIG. 13 , showing one embodiment of a drive unit for rotating a tower; 
         FIG. 15  is an enlarged perspective view from the side of a tower wall of  FIG. 13 , showing a removable plant supporter; 
         FIG. 16  is a perspective view of a multidirectional spraying column; 
         FIG. 17  is a plan view of a module of towers, showing the relative position of the multidirectional spraying column of  FIG. 16 ; and 
         FIG. 18  is a schematic illustration of a control system used in conjunction with the plant cultivating system for modulating the light energy directed to the plants. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention is an energy efficient, indoor soilless plant cultivating system which employs a plurality of stationary light posts, each of which illuminates a predetermined sector of an indoor facility in accordance with a predetermined illumination signature. The plants to be cultivated are mounted on a plant growth unit provided with irrigation means (hereinafter “tower”) of a large vertical dimension similar to that of each light post, for efficiently utilizing the inner dimensions of the facility, which may be an abandoned building in an urban setting or a building in an industrial park dedicated to be used by the cultivating system. The system operates in conjunction with a module that includes a predetermined number of towers, such that each tower of a module is rotated by a drive unit about a vertical axis in accordance with a predetermined timing sequence so as to be exposable to the light generated at any given time by one or more of the light posts. An interior region of the module is not exposed to the light generated by any of the module related light posts, and the plants instantaneously positioned within the darkened interior region receive the sensation of nighttime. 
     The indoor facility is preferably isolated from the outdoor conditions, including light, humidity and temperature conditions, present outwardly from the facility. The plant cultivating system is able to emulate optimal outdoor growing conditions that are different from the instantaneous outdoor conditions, so that the leaves of all plants subjected to a controlled environment will be exposed to a substantially uniform light distribution for the given emulated time period despite a height differential between therebetween. Even though the plants are isolated from the outdoors, the production of fruit and seed crops is made possible by virtue of an artificial pollination system. 
       FIG. 1  schematically illustrates a plant cultivating system  10  in plan view, according to one embodiment of the present invention. Plant cultivating system  10  comprises a plurality of modules, and for purposes of brevity, one of the modules  5  will be described. 
     Module  5  includes four circular towers  2   a - d  arranged in a symmetrical square-like configuration. Eight evenly spaced light posts  6   a - h  are deployed adjacent to the imaginary perimeter  7  of module  5 , such that first row light posts  6   a - c  are positioned adjacent to adjoining service pass  11   a , third row light posts  6   f - h  are positioned adjacent to adjoining service pass  11   b  which is opposite to service pass  11   a , and second row light posts  6   d - e  are positioned at the two sides, respectively, of perimeter  7  according to the illustrated orientation, while being positioned at an intermediate region of module  5  and interposed between a first row and third row light post. 
     Service passes  11   a  and  11   b , to be used for accessing the towers for maintenance, plant treatment and harvesting purposes, may have a width of 70 cm. Harvesting may be carried out with manual carts that are advanceable along rails. The carts may have a hydrologic raising capability to permit comfortable access to an upper tower region. For use during extreme cold weather conditions, a rail may be configured as a series of interconnected round hollow pipes through which warm water is flowable, to support heat dispersion as a part of the ambient control system of the facility. These pipes may have a unique mechanical profile, for example funnel-shaped, to assist in uniformly spreading the heat. 
     Each of the light posts may operate continually, to emit light in accordance with a predetermined post-specific illumination signature, along a predetermined angular sector S, e.g. 60 degrees. The setting of the predetermined angular sector may be obtained by means of a directional lens  9  provided with each light element mounted on a post and by a selected spacing between a light element and a corresponding lens. Each light element also has a designed illumination range. 
     In the exemplary deployment of the light posts, the illumination signature of posts  6   a ,  6   c ,  6   f  and  6   h  simulates the lighting conditions of noontime at a region N. The instantaneous illumination signature of posts  6   b ,  6   d ,  6   e  and  6   g  simulates the lighting conditions of morning at a region M, and afternoon or evening at a region A, with respect to light intensity and/or wavelength. Darkened interior region D is located beyond the limited illumination range of the lighting elements mounted on each of light posts  6   a - h , and therefore plants instantaneously positioned within darkened region D receive the sensation of nighttime. A distance between the towers at a darkened region D may be 80 cm for towers having a diameter of 60 cm. 
     Each of towers  2   a - d  has mounting means  17  by which each corresponding plant  19  is retained on the periphery of a tower while being exposed to the light posts. The various plants are arranged in layers, so that plants  19  are found throughout the height and circumference of a tower, for maximum utilization of the volume within the facility. Plants  19  may also be arranged in an inclined disposition, so that will be urged to grow outwardly from the tower without interfering with an adjacent plant. 
     The plant cultivating system of the present invention is conducive to the growth of many different types of crops, particularly high quality crops that are not necessarily indigenous to the surroundings of the given facility by virtue of the optimal environment in which they are grown, including leafy vegetables such as lettuce, chicory, tomato, cucumber, chili, pepper and spinach, berries such as strawberries, cranberries, blueberries and raspberries, and herbs such as herbs for flavoring, food, medicine and cosmetics, for example medical  cannabis.    
     The circular configuration of the towers promotes trellising of climbing plants such as cherry tomatoes and grave vines around the tower periphery to advantageously minimize usage of the module surface area. Removable supporters  211  ( FIG. 15 ) may be plugged into vacant holes  208  around the tower periphery to support the weight of the crop if the load on the tower is anticipated to be excessive. 
     Directional lens  9  may be configured to produce a light emitting angle whose angular boundaries, when taking into account the given tower diameter and the given distance from a light post to a tower, are tangential with, or are otherwise incident on, the periphery of the tower. The propagation of the emitted light to an internal region of module  5  is blocked as a result of its incidence on the tower periphery, to thereby ensure that the internal region between two adjacent towers will be darkened to a radiation level less than a predetermined photosynthetically active radiation level for the plant being cultivated, for example darkness levels of up to 90% or more. The darkness level is also assisted by the ongoing growth of the leaves or branches of the plants which help to block the penetration of light into the inner region. 
     The rotation of each of towers  2   a - d  by means of a central vertical shaft and a drive unit allows each plant  19  to be cyclically exposed to morning light conditions, noon light conditions, afternoon light conditions and nighttime conditions by completing a full rotation about its vertical axis once every 24-hour period, thus simulating a daily day/night cycle. The drive unit may be an electric motor, or a hydraulically or pneumatically actuated drive unit. 
     It will be appreciated that a tower need not rotate at a constant rate. If a selected plant flourishes when exposed to certain light conditions, the relative dwelling time of the plant in those optimum lighting conditions may be increased. 
       FIG. 2  illustrates a module  25  comprising three rotatable towers  2   a - c , providing darkened interior region D, to which the mounted plants are cyclically exposed, as described above. 
     The definition of the darkened interior regions by the aforementioned module configurations advantageously contributes to the safety of workers and other bystanders by deploying a multidirectional spraying column  231  illustrated in  FIGS. 16 and 17  within a darkened region D. 
     Multidirectional spraying column  231 , which may have a rectilinear or curvilinear configuration, has a plurality of nozzles  234  that protrude in different directions. When pesticide is delivered through conduit  237 , for example in response to a controlled duty cycle via an underground conduit, to spraying column  231 , a spray is issued from each nozzle  234  and is directed at each of towers  2   a - d . The extending direction and the spray pattern of each nozzle  234  are carefully selected to avoid pesticide wastage as a result of unnecessary spraying in a region R between towers. 
     Since towers  2   a - d  are continuously rotated, all plants will be exposed to the sprayed pesticide. However, workers are generally located within service passes  11   a - b  ( FIG. 1 ) which are outwardly separated from the modules, and will therefore not be exposed to the sprayed pesticide. This spraying arrangement will increase the safety of workers and will significantly reduce, or substantially eliminate harm, to the environment by minimizing discharge of harmful pesticide. Also, the amount of pesticide needed for effective pest control will be significantly reduced. 
     Even though the plants are grown in a soilless environment and are therefore not susceptible to damage by soil dwelling pests, nevertheless Small plantings that were germinated outside the facility and were already infected by pests or bacteria before being mounted in a tower, and therefore need to be treated with pesticide. 
       FIGS. 12-15  illustrate exemplary structural features for use with the plant cultivating system. 
     As shown in  FIG. 12 , the vertical shaft of each of the four towers  2   a - d  of module  5  is rotatably mounted from above in a corresponding seat or bearing provided in an upper square or rectangular frame  191  and from below in a corresponding seat or bearing provided in a bottom bar  197 . Upper frame  191  may be embedded in a roof or ceiling portion  189 , or may be internally open and positioned below roof or ceiling portion  189 . 
     The eight stationary light posts  6   a - h  are attached to upper frame  191  and are in fixed contact with the underlying ground surface, light posts  6   a ,  6   c ,  6   f  and  6   b  extending downwardly from a corresponding corner of the upper frame and the remaining light posts being connected to a corresponding cross member  194  extending outwardly from a central region of an upper frame side element. Each of the light posts is thus positioned at a relatively short and defined distance from the periphery of a tower, for example a minimal distance between the light post and tower periphery of 30 cm, although this distance is generally reduced due to the presence of the growing leaves. While the tower rotates, the actual distance from a plant to the light post varies. The four bottom bars  197  extend inwardly from a bottom portion of each of the light posts underlying a corresponding corner of upper frame  191  and are connected together. 
     The central opening of upper frame  191  facilitates the positioning of ceiling fan  162  ( FIG. 13 ), the purpose of which will be described hereinafter. Ceiling fan  162  may be suspended by a hangar attached to an overlying ceiling region, so as to be positioned within the central opening, whether at, above or below the height of upper frame  191 . Alternatively, the grille  164  of fan  162  may be connected to two or more side elements  193  of upper frame  191 . 
     Each tower  2   a - d  may be configured with one or more access hatches  199  that cover a corresponding opening formed in the periphery of a tower. The hatches  199  enable maintenance workers to access the hollow core of a tower, in order to clean or repair the tower periphery and the irrigation elements, for example, or for harvesting purposes. The hollow core also facilitates the growth of plants with large sized tubers and bulbs. 
     As shown in  FIG. 13 , each tower may be configured with a polygonal periphery that is substantially circular, such that each vertically extending and planar wall  192  defines a wall of the polygon. A plurality of vertically spaced planting holes  208  by which a plant is mounted on the tower are formed within each wall  192 . If a plant has a size which is not compatible with the opening of a planting hole  208 , a supporter  211  shown in  FIG. 15 , e.g. configured as an elbow made of molded rubber or plastic, may be removably inserted in one of the planting holes to assist in securely mounting a differently sized plant. 
     For example, a tower configured with a height of 240 cm and a diameter of 57 cm was formed with  11  planting holes  208  in each wall  192 , when each planting hole was spaced by 20 cm center to center from an adjacent planting hole on the same wall. 
     Walls  192  may be made of an opaque or black material for optimal light absorption. The inner surface of a wall  192  may be provided with grooved drainage channels, e.g. vertically extending, by which irrigation fluid is directed towards the roots of the plants, to thereby maximize usage thereof. 
     One embodiment of the drive unit is shown in  FIGS. 13 and 14 . A serrated wheel  196  is fixed to the upper surface  197  of each of the towers, so as to be coaxial therewith. The longitudinal axis of serrated wheel  196  is rotatably mounted at the corresponding junction  200  between upper frame side element  193  and cross member  194 , to facilitate rotation of the tower. 
     A terminal end  201  of a substantially horizontally disposed reciprocating piston rod assembly  202 , which may be hydraulically, pneumatically or electrically actuated, is connected, e.g. pivotally connected, to bracket  207  extending downwardly from side element  193 . Piston rod assembly  202  has a bifurcated head  206  that is adapted to receive within its interior a tooth  198  radially extending from the periphery of serrated wheel  196 , when the piston rod is extended, and to apply a force to a side edge of tooth  198 , causing serrated wheel  196  and the tower connected thereto to rotate about its vertically oriented longitudinal axis for a discrete angle depending on the predetermined stroke of the piston rod. The piston rod is then retracted, in anticipation of an additional rotation initiating operation. 
     In order to ensure substantially homogeneous distribution of the light emitted by the elongated light posts onto vertically spaced plants, which may be spaced along a common tower by a large difference in height of as much as 3 meters or more, the light elements are densely mounted on each light post, for example 50 light elements are mounted within a distance of 50 cm such that only one light element is mounted at any given height. A number and sequence of light elements may be pinpointed in order to generate a plant-specific light signature that will optimize plant growth. 
       FIGS. 3A and 3B  schematically illustrates an exemplary sequence of the light elements, which are shown in exaggerated size for clarity and are mounted on light posts  6   a  and  6   b  for generating an illumination signature that emulates the lighting conditions of noontime and of reduced light intensity conditions, respectively. The light elements, which are vertically spaced and vertically aligned, are preferably LED elements, although other light elements are also in the scope of the invention. Each light post is preferably tubular, to maximize heat dissipation from the continually operating light elements. If so desired, the light elements may be operated according to a selected duty cycle or time sequence, in order to generate a desired waveform. 
     Light elements for emitting the following five colors are illustrated: blue (B) at a wavelength of 440-460 nm for use mainly during noon conditions, green (G) at a wavelength of 505-530 nm, red (R) at a wavelength of 620-650 nm for use mainly during morning/afternoon conditions, deep red (DR) at a wavelength of 650-680 nm, and cool white (CW) at a color temperature, or the temperature of an ideal black-body radiator that radiates light of a comparable hue, of 5000° K. These colors were selected as they constitute the basic spectral components of sunlight needed by plants, although other colors are also in the scope of the invention. 
     The sequence of the light elements is carefully selected so as to generate a desired plant-specific light signature as a result of the interaction of the light beams emitted from adjacent light elements and of the vertical wavelength distribution throughout the length of the light post. The light signature generated by two adjacent light posts is also able to interact. 
     A segment  31  of light elements  33  having a height J is shown in  FIG. 3C . Segment  31  includes a predetermined number of vertically spaced light elements  33 , for example 30 elements. Each light element  33  of segment  31  emits a corresponding beam that impinges upon a peripheral portion  27  of tower  2 , which is spaced by a distance K from light post  6 . Within the conical distribution angle  36  of light that is emitted from segment  31 , being bounded by equal sides L to define an isosceles triangle in cross section, the constituent beams emitted from each light element  33  are mixed to provide a photosynthetic photon flux density (PPFD) at peripheral portion  27  that optimally stimulates photosynthesis for the given plant being grown. Likewise the PPFD at any other peripheral portion  27 , or at any leaf of the plant being cultivated which is adapted to absorb the emitted light, included within conical angle  36  is substantially equal. The light element sequence of segment  31  is repeated along the height of light post  6  for all other segments, for example segment  32  adjacent to segment  31 . This light element arrangement thus promotes substantially equal light distribution to all plants being grown throughout the height of tower  2 . 
     Morning and afternoon lighting conditions may be emulated, for example, by generating the following percentage of relative light energy corresponding to spectral components of light emitted from a light element segment: (1) dark blue at a wavelength of approximately 450 nm, 12%, (2) red at a wavelength of approximately 660 nm, 62%, (3) infrared at a wavelength of approximately 730 nm, 7%, and (4) white at a color temperature of 4000° K, 19%. Plants are generally exposed to these morning and afternoon lighting conditions for two quarters of a 24-hour period. 
     Noon lighting conditions may be emulated, for example, by generating the following percentage of relative light energy corresponding to spectral components of light emitted from a light element segment: (1) dark blue at a wavelength of approximately 450 nm, 34%, (2) red at a wavelength of approximately 660 nm, 31%, (3) infrared at a wavelength of approximately 730 nm, 7%, and (4) white at a color temperature of 4000° K, 28%. Plants are generally exposed to these noon lighting conditions for one quarter of a 24-hour period. 
     The tubular configuration of the light posts may also be utilized to enable circulation through their interior of an irrigation fluid. The irrigation fluid flowing through the sealed interior of a light post cools the continually operating light elements, and in turn becomes heated to plant growth inductive temperature of approximately 30° C. The heated irrigation fluid in turn is directed to the plants, for fostering their growth. The normally unexploited energy source of heat dissipated from light sources is therefore utilized to improve the plants&#39; growth. 
       FIG. 4  illustrates one embodiment of irrigation means  30  for watering the plants which are being hydroponically cultivated. Cold irrigation fluid  34   a  is injected into the interior  37  of light post  6  and is progressively heated as it rises within the light post interior. The warm irrigation fluid  34   b  is discharged from the top of light post interior via emitter  39  to reservoir  46  located at the top of tower  2 , for example at a rate of 1 L/min. 
     Each plant  19  being cultivated is retained in a basket  41  that allows the roots to be exposed to the irrigation fluid. Basket  41  is turn is mounted in a corresponding inclined hollow holder  43 , e.g. cylindrical, which is secured to, or integrally formed with, the vertical outer wall  45  of tower  2 , allowing each plant  19  to suitably grow while being exposed to the light emitted from elements  9 . 
     A corresponding conduit  49  extends downwardly, for example at an incline, from reservoir  46  to a holder  43 , or from a first holder to a second holder therebelow, to introduce the irrigation fluid to each holder. As each holder  43  is disposed at an incline with respect to vertical wall  45 , the accumulation  52  of the introduced irrigation fluid is collected at the bottom of the holder at a height suitable for the immersion therein of the roots of plant  19  so as to supply nutrients to the plant, and then overflows in cascaded fashion to the holder therebelow. The spent overflow eventually flows to reservoir  54  at the bottom of tower  2 . Each conduit  49  may be semicircular so as to simulate oxidation within the cascading irrigation fluid while being exposed to the surrounding air. 
     The effluent from bottom reservoir  54  flows through standpipe  56  to a secondary catchment tank  58  and then to main catchment tank  59  by gravity, to which fresh water is added via inlet  61 . A blend tank  63  receives the discharge from main catchment tank  59 , Additives, such as nitrogen, phosphorus, potassium, and other essential nutrients normally found in soil, are added, in optimum concentrations and in correct balance, are added. An aeration pump  67  delivers the produced irrigation fluid  34  to the inlet of the light post interior  37 . 
     A sound emitter  51 , e.g. a loudspeaker, may be mounted on the outer wall of light post  6 , for generating acoustical signals that may be conducive for the plant growth. 
     Irrigation means  70  illustrated in  FIG. 5  may be used for watering plants  19  which are being aeroponically cultivated. Irrigation fluid is introduced from blend tank  63  to pipe  72  formed within the interior of vertical shaft  74  by which tower  2  rotates. The blending of the irrigation fluid is similar to that described in  FIG. 4 . A plurality of vertically spaced foggers  76  mounted on vertical shaft  74  and in fluid communication with pipe  72  eject a mist  79  directed to the roots  81  of plants  19  for providing a plentifully supply of oxygen. Each plant  19  being cultivated is retained in a basket  41  which is fitted within an aperture formed in vertical wall  45  of tower  2 , and is mounted at an incline by means of a corresponding oblique brace  77 , thereby allowing roots  81  to be exposed to the irrigation fluid. 
     An exemplary arrangement of apertures  89  formed in outer tower wall  45  is shown in  FIGS. 6A and 6B . 
     At the same time, rotation of shaft  74  according to a predetermined timing sequence causes plants  19  to be exposed to the light generated at any given time by one or more of light posts  6 . The interior of each light post interior is cooled by injected cold water  84   a  that is progressively heated as it rises. The heated water  84   b  is discharged through top plate  83  of tower  2  and is collected at bottom reservoir  54 . 
       FIG. 7  illustrates a configuration of an outer wall  95  of the plant growth tower by which water conservation is considerably increased. Outer wall  95  is formed with a plurality of narrow slots  91 , each of which is preferably recessed in order to receive liquid discharge from a fogger that has impacted the outer wall and would normally flow downwardly into the bottom reservoir of the tower without irrigating a plant. Each slot  91  extends for example from upper edge  92  of outer wall  95  to the periphery of an aperture  89  into which a plant growing basket is fitted, thereby providing another source of irrigation in addition to the fogger discharge. A slot  91  need not be straight as shown, but rather may be curved, or assume any other desired shape or disposition. 
       FIG. 8  schematically illustrates an open-loop recycling system  110  for efficiently utilizing the irrigation fluid. In system  110 , the roots  81  of plants  19  retained within the interior of tower are aeroponically irrigated by means of the irrigation fluid that is delivered by high pressure feed pump  115  through central vertical pipe  72  of tower  2  and to vertically spaced foggers  76 , to produce a mist environment. 
     The irrigation fluid is fed to feed pump  115  from second mixing chamber  121 , into which is introduced the discharge of both first mixing chamber  117  and ozone generator  126 , the latter serving to inject an oxidizing agent in the form of O2 or O3 into irrigation fluid for the purpose of disinfecting waterborne organisms and thereby enriching the fluid. In first mixing chamber  117  are mixed fresh water flowing through valve  106 , e.g. a control valve, and the discharge of dosage pump  124 , e.g. a peristaltic dosing pump, which delivers a predetermined amount of nutrients, such as nitrogen, phosphorus, potassium, and acid, needed by the type of crop being cultivated. 
     Controller  135  is in data communication with feed pump  115 , dosage pump  124 , and ozone generator  126 , in order to regulate the conductivity and pH of the irrigation solution and to deliver it to foggers  76  at predetermined times. Ozone generator  126  is generally commanded to operate shortly before the activation of feed pump  115 , to ensure suitable oxygenation of the irrigation fluid. Controller  135  may also be in data communication with air conditioning system  137  and local dehumidifier  139  for maintaining a predetermined air quality, including a desired degree of humidity, in the vicinity of each tower  2 . 
     The surplus irrigation fluid not consumed by the plant roots  81  is collected in a reservoir  101  at the bottom of tower  2 . A condensate pump, upon being commanded by controller  135  at a predetermined time, delivers the collected irrigation fluid via conduit  146  to used fluid storage tank  142 , which also receives condensate delivered from dehumidifier  139  via conduit  147 . A recirculation pump in data communication with controller  135  delivers the reused fluid to first mixing chamber  117  via conduit  148  and valve  138 , which may be a control valve commanded by controller  135 . 
     In addition to air conditioning system  137  and dehumidifier  139  ( FIG. 8 ), the temperature of air in the vicinity of each tower may be controlled by means of the closed-loop liquid circulation system  155  shown in  FIG. 9 . Pump  151  delivers the cooling liquid upwardly through the interior of light post  6  to become progressively heated while the continually operating light elements mounted on the light post become cooled. The heated irrigation fluid discharged from the top of light post interior is pressurized by pump  153 , and consequently flows at a sufficiently high rate through liquid-air heat exchanger, e.g. a radiator, to cause the surrounding air  159  to become heated. The heat depleted liquid is then introduced to pump  151 . The increase in temperature of the surrounding air  159  may be controlled by the flowrate of the circulating liquid. 
       FIG. 10  illustrates an air circulation arrangement that facilitates an increase in plant growth. A ceiling fan  162  is installed so as to be centrally positioned within, and above, darkened interior region D of module  5 . Since plants  19  release carbon dioxide during respiration at night, darkened interior region D is characterized by an increased concentration of carbon dioxide relative to other regions of the module. During operation of ceiling fan  162 , the plant-released carbon dioxide, or air saturated with the plant-released carbon dioxide, is subjected to suction by ceiling fan  162 , and is accordingly caused to be transported to outer noontime regions N of module  5 , or alternatively to morning or afternoon regions. Plants  19  require a significant amount of carbon dioxide in order to conduct photosynthesis. By being able to direct the normally unexploited source of plant-released carbon dioxide to a daytime region, plants  19  are advantageously able to undergo an increased rate of growth while producing a larger amount of sugars and carbohydrates during the photosynthesis process as a result of absorbing a corresponding increased amount of carbon dioxide. Ceiling fan  162  may be deactivated when it overlies a region that is instantaneously illuminated with daytime light conditions. 
     The photosynthesis process is accompanied by loss of water as a result of evaporation from the stomates, or microscopic openings in the leaves of a plant through which incoming and outgoing gases such as carbon dioxide and oxygen and water vapor are released. The transport of plant-released carbon dioxide to a daytime region, resulting in a larger degree of photosynthesis, thus contributes to an even greater rate of water evaporation, inducing the plant in response to absorb a correspondingly increased amount of water through its roots to maintain an optimal water balance. The plant may also be induced to absorb an increased amount of water through its roots by commanding dehumidifier  139  ( FIG. 8 ) to maintain a relatively low moisture level in the plant growing space surrounding a tower relative to the high moisture level within the core of a tower. 
     The intake of water through the roots of a plant is a major driving force for the movement of minerals from the roots and the transport of photosynthesis derived sugars throughout the plant. The plants grow in an optimal soilless environment at a controlled temperature and humidity, and consume a very small amount of water relative to their outdoor cultivated counterparts. As the roots do not have to expend the plant&#39;s energy to penetrate soil in quest for water and nutrients, the unused energy can be utilized by the plant&#39;s metabolic processes in other ways. For example, fruits tend to be sweeter, while leafy vegetables achieve a crispy leaf texture since the plant utilizes the unused energy to produce more minerals. 
     It will be appreciated that the plant-released carbon dioxide may also be transported through ducts, for example connected to upper frame  191  ( FIG. 13 ), to a daytime region. 
     The temperature of the transported carbon dioxide, as well as fresh air, if desired to be mixed therewith, may be controlled by air conditioning system  137  as commanded by controller  135 . 
     In another embodiment, the apparatus of the present invention may be used in conjunction with artificial pollination system  170  shown in  FIG. 11 . 
     Light post  176  carries a plurality of vertically spaced air discharge nozzles  173  which receive a pulsed supply of compressed air in parallel from air receiver tank  177 . Air receiver tank  177  for storage of compressed air in turn is in fluid communication with compressor  174 , positioned at a region of low humidity and possibly positioned on the floor of the facility. Compressor  174  is activated when the pressure within tank  177  is less than a predetermined low value, and is deactivated when the pressure within tank  177  is greater than a predetermined high value. A conduit  172  external to light post  176  extends from tank  177  and is in fluid communication with each nozzle  173 , and a control valve  179  may be operatively connected with conduit  172 , adjacent to the outlet port of tank  177 . Each nozzle  173  may have a diverging outlet to direct the discharged compressed air in a conical pattern, to ensure impingement of the compressed air onto the stamen of plant  19 , for example a strawberry plant, to induce the release of pollen  182  from its anther and the airborne transport of pollen  182  to the carpel of the same or of an adjacent plant. 
     Artificial pollination system  170  of course is capable of inducing the release of pollen from its anther only when the pollen bearing plant is reliably positioned in close proximity to a nozzle  173  at substantially the same height. Repeated and reliable rotational displacement of tower  2  about its longitudinal axis  184  may be made possible by a step motor  187 , which is adapted to rotate tower  2  in discrete predetermined step increments in response to a command pulse received by the driver circuit. Alignment of a plant with a corresponding nozzle  173  may be achieved by knowing the angular displacement of each step, the diameter of the tower and the number of plants that are mounted around the circumference of the tower. 
     The efficacy of artificial pollination system  170  may be enhanced by a controlled change in the local humidity. Controller  135  is therefore operable to perform the five stage process of (1) commanding dehumidifier  139  to significantly reduce the local humidity in the vicinity of tower  2 , for example to a level of 20% for strawberries, to reduce the adhesiveness of the pollen and to thereby support release of the pollen bearing anther from the stamen filament, (2) receiving information from the driver circuit of motor  187  as to when, or as to how many steps are made, until a given plant  19  will be positioned in pollen releasable proximity to nozzle  173 , (3) commanding opening of control valve  179  for a predetermined time so that the compressed air will be directed to a given plant, (4) commanding dehumidifier  139  to significantly increase the local humidity in the vicinity of tower  2  following the anther release, for example to a level of 50% for strawberries, to ensure viability of the pollen and the adhesiveness of the stigma on which the pollen is to be deposited, and (5) closing control valve  179  at the conclusion of the pollination cycle. 
     The duration of the control valve opening may be regulated by controller  135  in response to the instantaneous air pressure within air receiver tank  177 , to ensure a sufficiently high air flowrate to induce the release of pollen from its anther. For example, each nozzle  173  may be spaced 30 cm from the tower periphery, and the pressure of air when being discharged from the nozzle is about 6 bar, regardless of the number of nozzles. 
       FIG. 18  illustrates another embodiment of the invention wherein the light emitted to the plants is modulated. 
     Several studies conducted by Dr. T. C. Singh, head of the Botany Department at Anamalia University, India and others confirmed that the music affects plant growth. Plants feel the vibration of the generated sound waves, and will speed the protoplasmic movement in the cells, to stimulate the manufacture of more nutrients that will give a stronger and better plant. [http://hubpages.com/living/the-effect-of-music-on-plant-growth, updated on Nov. 12, 2015, Oct. 3, 2016] 
     Control system  240  directs modulated light energy to the plants to stimulate an improvement in metabolic processes similarly to a plant reaction to modulated acoustic waves. The modulated light energy is generated by a digital signal processing (DSP) module  245  configured with a suitable transfer function, which may be housed in controller  135  ( FIG. 10 ) or in any other suitable hardware component. In response to the input of an audio file  241  transmitted by player  242 , DSP module  245  transfers the audio signal to discrete frequency components, and then these frequency components are sequentially transferred to modulated voltage components and modulated light wavelength components to generate a corresponding light waveform. DSP module  245  also controls the light intensity of the light waveform, depending on the daylight region to which the plants are presently exposed, and filters the light waveform. The output light waveform is transmitted to the programmable power supply  247  of the LEDs  249  mounted on a light post to generate the desired modulated light beam  251 . 
     In another embodiment, all planting holes formed in the tower walls are assigned a unique identifier which is stored in a system database. The following information related to each plant being grown is associated with the identifier and is also stored in the database: time of planting, growing protocol parameters, geographical location at any given time, and time of harvesting. The precise real-time geolocation of every plant with respect to a service passage facilitates the use of robotics for plant harvesting. 
     While some embodiments of the invention have been described by way of illustration, it will be apparent that the invention can be carried out with many modifications, variations and adaptations, and with the use of numerous equivalents or alternative solutions that are within the scope of persons skilled in the art, without exceeding the scope of the claims.