Abstract:
A method for using LEDs to supplement natural light in a greenhouse and a support structure for attaching LEDs in a greenhouse so that the plants receive substantially even light distribution from the LEDs and minimal natural light is blocked by the lighting system. A narrow attachment rail is used to suspend a strip of LEDs from the frame structure of the greenhouse.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application 60/472,869, filed May 23, 2003. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to a method and apparatus for using light emitting diodes in a greenhouse setting. More particularly, it relates to a method of using LEDs to supplement natural light and a support structure for using LEDs in a greenhouse setting.  
         DESCRIPTION OF RELATED ART  
         [0003]    Sunlight is made up of a variety of wavelengths. The energy of light is inversely proportional to its wavelength. In other words, the longer the wavelength the less energy the light has. Sunlight can be separated into different wavelengths or colors by passing it through a prism. Similarly, when the sun is at an angle to the earth&#39;s atmosphere, the light is reflected and spread by the atmosphere. This is why sunrises and sunsets are so colorful. Another less desirable result of this phenomenon is that a portion of blue light is not transmitted through the atmosphere during the winter.  
           [0004]    The light humans see is in the visible spectrum. Visible light ranges from approximately 400 nm to approximately 700 nm. Violet light is the shortest wavelength; highest energy light of the visible spectrum and red light is the longest wavelength, lowest energy light of the visible light. The longer the wavelength of visible light the more red its color. Ultraviolet light has a shorter wavelength and has more energy than visible light. X-rays are the highest energy, shortest wavelength light. Infra red light is a low energy light, having a wavelength longer than that of red light. A large portion of sunlight is in the infrared range.  
           [0005]    Photosynthesis is the process that converts energy from sunlight or other light to chemical forms of energy that can be used by biological systems. Energy for photosynthesis is provided by light, which is absorbed by the pigments of the plant. The color and intensity of light are used in different photosynthesis reactions. For example, blue light plus water plus carbon dioxide produces oxygen and sugar while red light plus water plus sugar produces plant cells. The brighter or more intense the light, the more energy the plant receives. Red light promotes height and blue light promotes growth in girth. Thus, plants grown in red light will be tall and spindly and plants grown in blue light will have a thick, strong stem, but will not be especially tall.  
           [0006]    In greenhouses, it is often desirable to control a plant&#39;s growth. For example, due to conditions, customer or seasonal demands, transportation issues, etc. it may be desirable to promote or inhibit budding, promote or inhibit flowering, promote germination, promote the leafiness of the plant, encourage a strong and/or lengthy stem, have a stronger plant, have a bigger harvest, and/or promote or inhibit ripening of a fruit or vegetable.  
           [0007]    Commonly, greenhouses will use lights to encourage or discourage plant growth. Common types of lighting for landscapes and greenhouses include incandescent lights, florescent lights, high-pressure sodium lights, medal halide lights, and mercury vapor lights. Incandescent lights produce all wavelengths of light and are closest to natural sunlight. Thus, they are commonly used to promote vegetative growth. The amount of intensity of particular wavelengths of light may be adjusted with the type of lights used to control growth mode. In addition to controlling growth modes with light, growth modes can also be controlled by adjusting or changing the fertilizer, stressing the plant such as with cold, shorter or longer lighted periods or by adding a lighted period at night.  
           [0008]    In the winter the sun is lower on the horizon. When sunlight passes through the ozone layer about 50% of the blue light is reflected off the ozone layer rather than being transmitted. Incandescent lights, while mimicking natural light tend to be comprised of a higher percentage of low energy light than natural light. Thus, a plant grown under incandescent light or under natural winter light tends to get less blue light than is optimal. There is a need for a system which can be used to supplement the natural light in the winter by providing the high frequency wavelengths reflected by the ozone layer to the plants with minimal interference with the amount of natural light.  
           [0009]    Flower producers may wish to grow leafy, strong plants, but discourage flowering until it is the season for the plant. A greenhouse vegetable producer may wish to encourage germination growth, budding and fruiting of plants but then inhibit ripening of the vegetable so that is not overly ripe at the time it reaches the food market. Thus, there is a need for a plant illumination system which allows the grower to supplement natural light to adjust the growth mode of plant without interring with the amount of natural light received.  
           [0010]    Light Emitting Diodes (LED) consists of a layer of two different semi-conductors. They can be used to provide a source for light with a specific wavelength.  
           [0011]    Currently, light emitting diodes LEDs have been used for low light, small size greenhouse environments. There is a need for an LED plant illumination system, which allows for the use of LEDs on a large scale, such as a commercial greenhouse.  
           [0012]    There is a need for a plant illumination system, which makes use of LEDs to provide the desired light intensity and/or wavelength to promote or discourage specific growth modes without interfering with the natural light. There is also a need for a system that can be used with natural light, artificial light or a combination of artificial and natural light without blocking a significant amount of the light.  
           [0013]    Prior art lighting systems for greenhouses are about 18 cm wide and, thus, block a portion of the natural light. There is a need for a system that reduces the amount of blocked natural light.  
           [0014]    Prior art lighting systems are heavy. A single sodium vapor lamp can weigh 40 pounds. There is a need for a lightweight lighting system.  
           [0015]    The lamps of prior art lighting systems must be placed far above the plants. There is a need for a lighting system which can be located close to the plants allowing for a shorter greenhouse.  
         SUMMARY OF THE INVENTION  
         [0016]    The present invention relates to an illumination system for plants to supplement natural light without substantially interfering with the amount of natural light. The present invention uses a strip of high brightness LEDs that deliver uniform illumination. The LED strip reduces energy and maintenance costs. The strip system may be installed in a commercial greenhouse. Because of its narrow width, the strip is useful to supplement natural light because it allows a maximum amount of natural light to reach the plants.  
           [0017]    In one embodiment of the present invention, LEDs with specific wavelengths are used in the system for a specific effect. For example, blue LEDs to supplement the winter sunlight.  
           [0018]    In another embodiment of the present invention the plants are exposed to sunlight and/or artificial lights, preferably, natural light or sunlight and LEDs are used to supplement the light. For example, in winter high frequency light is reflected off the ozone layer. Blue LEDs are used to supplement the natural light to compensate for the high frequency light that is not transmitted by the ozone layer. In addition, when specific wavelengths are needed for a desired effect, additional LEDs may be provided which emit light at the desired wavelengths. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 is a cross section of a prior art lighting assembly.  
         [0020]    [0020]FIG. 2 is an overhead view of a prior art lighting system.  
         [0021]    [0021]FIG. 3 is an overhead view of detail  3  of FIG. 2.  
         [0022]    [0022]FIG. 4 is a side view of a prior art lighting system.  
         [0023]    [0023]FIG. 5 is a view of the inventive lighting assembly.  
         [0024]    [0024]FIG. 6 is a cross section of the inventive lighting assembly.  
         [0025]    [0025]FIG. 7 is a cross section of the support structure of the inventive lighting assembly.  
         [0026]    [0026]FIG. 8 is an overhead view of the inventive lighting system.  
         [0027]    [0027]FIG. 9 is an overhead view of detail  9  of FIG. 8.  
         [0028]    [0028]FIG. 10 is a side view of the inventive lighting system.  
         [0029]    [0029]FIG. 11 shows the spectral distribution of sunlight at mid-day during the summer, at sunset during the summer and of an incandescent lamp.  
         [0030]    [0030]FIG. 12 shows the spectral distribution of a high-pressure sodium vapor lamp and a 455 nm blue LED.  
         [0031]    [0031]FIG. 13 shows the ideal phototropic curve and the photosynthesis curve.  
         [0032]    [0032]FIG. 14 shows the photosynthesis curve of the high-pressure sodium vapor lamp and the 455 nm blue LED of FIG. 12. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]    Plants grow due to photosynthesis. Plants use water, carbon dioxide and light to create energy and oxygen. Different wavelengths of light affect plants differently. Most plants reflect green light. Thus, the best light for most plant growth is in the red and blue wavelengths. Red light tends to make plants grow tall. Blue light tends to make plants with strong stems. As can be seen in FIG. 13, photosynthesis is maximized at about 440 nm and about 680 nm. In contrast, humans see best if the light is between about 500 and 650 nm. FIG. 13 also shows the phototropic curve. This shows the wavelengths of light that humans see best.  
         [0034]    The maximum transmission of blue light occurs about midday. Because of the angle of the sun, the high-energy blue light tends to be reflected off the ozone layer in the morning and evening. Thus, there is less blue in the light. Similarly, there is less blue light in the winter because the earth is at an angle to the sun. In the winter about 50% of the high-energy blue light is reflected by the ozone layer and the light that is transmitted consists primarily of lower-energy light. As a result, plants may not get sufficient amounts of blue light.  
         [0035]    Plants grown under artificial light may also be deficient in blue light. For example, high intensity sodium lamps, which are often used in greenhouses, maximize the light that can be seen by humans. Incandescent lights, which are often used in home plant growing situations, also have less blue light than the amount needed for optimal plant growth. A grower may want to supplement the amount of blue light. In some situations, the grower may wish to encourage or discourage particular plant growth modes with specific wavelengths of light. Thus, it is often necessary or desirable to supplement natural or artificial light with specific wavelengths of light.  
         [0036]    Prior art lighting systems block a portion of the natural light entering the greenhouse. As can be seen in FIGS. 1-3, prior art systems utilize bulky lights  10  that block 10% or even more of the footprint of the lighted area  20  of the greenhouse. This undesirable effect is worsened by shadows that are cast by the frame and/or lights  10 . The prior art system uses a plurality of lights. For example, in a typical system using high-pressure sodium (HPS) lamps, the reflector  16  of the lamp is 35 cm wide by 35 cm long, the power supply  14  of the lamp is about 18 cm wide by 38 cm long, and the attachment supports  12  are about 4 cm wide. The greenhouse support frame  22  is about 3 cm wide.  
         [0037]    Another disadvantage of prior art systems is uneven lighting. As can be in FIG. 4 some plants  24  are illuminated by two lamps  10  while others are illuminated by three. As a result, the plants may not grow and mature at the same rate. Some plants may mature slowly or will not grow as large as others.  
         [0038]    Prior art lighting systems are heavy, a single sodium vapor lamp can weigh 40 pounds. Thus, the greenhouse frame needs to be strong enough to support the lighting system. Further, prior art lighting systems have lamps that must be kept away from the plants. This requires the greenhouse structures be of sufficient height to keep the lights away from the plants.  
         [0039]    Turning now to FIGS. 5 and 6, the inventive lighting structure is shown. The structure comprises a support rail  30 , preferably made of aluminum. Preferably, the support rail  30  has a channel  34  for receiving the light engine and at least two pair of external ribs  40  defining a mounting slot  42 . The external ribs also dissipate heat. More preferably, the support rail  30  has a base  32 , a channel  34  for receiving the light engine, a pair of ears  36 , a pair of internal grooves  38 , at least two pair of external ribs  40  that define at least one mounting slot  42 .  
         [0040]    The light engine comprises a printed circuit board (PCB)  52 , preferably a metal core PCB with a plurality of LEDs  54  mounted thereon. The PCB  52  is in the form of a strip that slides into the channel  34  and is held in the internal grooves  38 . Preferably, the LEDs  54  is power package LEDs  54 . Preferably, the LEDs are spaced equally along the strip. A shim is used to secure the PCB  52  to the rail  30  and ensure a snug fit. Preferably, the shim is a collar  56  that surrounds at least one LED  54 . The LEDs  54  are powered by a power supply  60 . Preferably, the PCB  52  is connected to the power supply  60  by wires  62  and the power supply  60  is remote from the light engine. For example, the power supply  60  could be placed under the plants  24  to prevent it from blocking any of the natural sunlight. The power supply can power more than one light engine.  
         [0041]    An attachment hook  44  or other mechanical attachment means is used to attach the rail  34  to the greenhouse frame  22 . The attachment hook  44  is attached to the rail  30  at the mounting slots  42 . The attachment hook  44  is attached to the roof of the greenhouse or to an existing support frame  22 .  
         [0042]    The light engines are relatively light. Thus, the greenhouse can be built so the frame can support the greenhouse. Extra weight of the lamps does not need to be a consideration when determining the frame strength and/or design.  
         [0043]    Further, the LEDs can be located close to or away from the plants. Thus, the light engines can be retrofit on an existing greenhouse frame. In addition, because the LEDs do not have to be kept away from the plants, the greenhouse can be built lower to the ground. This saves materials and may allow lighter weight frames to be used. It may also allow for reduced heating and/or cooling costs since the area to be heated or cooled may be smaller than in conventional greenhouses.  
         [0044]    In one embodiment, the rails and light engines are approximately the same length and a plurality of rails  30  each with a light engine are used for each row where each light engine can either have a separate power supply  60 , or preferably several light engines are electronically connected to a single power supply  60 . In the preferred embodiment, the rails  30  are longer than the light engines. Pluralities of light engines are slid into the channel  34 . The light engines are electronically interconnected. Preferably, one power supply  60  powers several light engines.  
         [0045]    In one embodiment, each rail  30  is separated from the next rail  30  in the row. In an alternative embodiment, several rails  30  are interconnected. In another embodiment, each row comprises a single rail.  
         [0046]    As can be seen by FIGS. 8-10, the LED strip system provides even light to the plants without substantially affecting the amount of natural light received by the plants. In one embodiment, the rail  30  is about 1½ times as wide as a standard frame  22  for a commercial greenhouse. In another embodiment, the rail  30  is approximately the same size as a standard frame  22 . In yet another embodiment, the rail  30  is narrower than the frame  22 . Preferably, the rails  30  are 4.5 cm wide and 240 cm long. Preferably, the light engine is 60 cm long and 3 cm wide. In the preferred embodiment, the LEDs  54  are mounted on narrow rails  30 .  
         [0047]    The rails  30  are mounted on the existing frame  22  of the greenhouse between the rows of plants. The frame  22  acts as a cooling structure for the LEDs  54 .  
         [0048]    In the preferred embodiment the LEDs  54  and the attachment rail  30  take up less than 25% of the lighted area  20  of the greenhouse.  
         [0049]    In an alternative embodiment, the LEDs  54  and the rail  30  take up less than 15% of the lighted area  20  of the greenhouse.  
         [0050]    In an alternative embodiment, the LEDs  54  and the rail  30  take up less than 10% of the lighted area  20  of the greenhouse.  
         [0051]    In an alternative embodiment, the LEDs  54  and the rail  30  take up less than 5% of the lighted area  20  of the greenhouse.  
         [0052]    In an alternative embodiment, the LEDs  54  and the rail  30  take up less than 3% of the lighted area  20  of the greenhouse.  
         [0053]    High-energy LEDs  54  can be used to supplement natural or artificial light. Preferably, light between approximately 400 and 500 nm is used. This light is almost invisible to humans. In one embodiment, LEDs  54  with a peak emission of 435 nm are used. In another embodiment, LEDs with a peak emission of 455 nm are used. In another embodiment, some or all of the LEDs are of a desired wavelength to supplement the light or to obtain a desired growth characteristic.