WO2010046358A1

WO2010046358A1 - Greenhouse for enhanced plant growth i

Info

Publication number: WO2010046358A1
Application number: PCT/EP2009/063726
Authority: WO
Inventors: Ko Hermans; Ben Slager
Original assignee: Grow Foil B.V.
Priority date: 2008-10-21
Filing date: 2009-10-20
Publication date: 2010-04-29

Abstract

Greenhouse for growing plants comprising a sheet containing a luminescent material and which has two main surface sides, characterised in that there are on at least one of the two main surface sides irregular shaped optical structures.

Description

Greenhouse for enhanced plant growth I

Description:

The invention pertains to a greenhouse for enhanced plant growth and a method for enhancing plant growth.

Plants use light for energy and for the spectral information it carries. Although a variety of reactions are light initiated, the two dominant reactions are photosynthesis and photomorphogenesis. In photosynthesis specialized light- absorbing pigments, which are located in the leaves, convert by a complex process light energy into chemical energy. During this reaction water and carbondioxide are converted into high energy molecules, such as carbohydrates, and oxygen. In subsequent processes the high energy molecules are used as a building material or to power cellular processes. One of the main light absorbing pigments is chlorophyll. The activity of chlorophyll depends on the intensity of the light, but also on the wavelength distribution of the light source. The activity of chlorophyll is at its minimum between 470-600 nm, which corresponds to green light. This light is partially reflected, giving the plants their green appearance.

Photomorphogensis is a process in which light has a regulating effect on plant form, growth, development and differentiation of cells, tissues and organs.

Photomorphogenesis is different from photosynthesis since the former usually requires a much lower light level and is therefore more delicate with respect to changes in the light spectrum. The main proteins responsible for the occuhng reactions are phytochrome, cryptochrome, phototropins and zeaxanthin. Phytochrome is a photoreceptor which is sensitive to the red and far-red region of the visible spectrum. There are two interconvertable conformations of phytochrome with different absorption spectra refered to as P_r and Pf₁-. P_r absorbs red light (peak at ±660 nm) and converts into Pf₁-, while the Pf_r isoform absorbs far red light (peak at ±730 nm) and converts into P₁-. Pfr is considered the active form of the pigment and their responses are classically defined by their red and far-red reversibility. Phytochrome is reported to influence cardian rythms, the germination of seeds, elongation of seedlings, size, shape and number of leaves, the synthesis of chlorophylls, and the straightening of the epicotyl or hypocotyl hook of dicot seedlings. Cryptochrome, phototropins and zeaxanthin are other photoreceptor which are related to blue responses. Their influence ranges from regulating germination, elongation, photoperiodism and phototropism.

From the above it can be concluded that different processes which regulate plant growth are depended on light intensity and the spectral distribution. Therefore several methods are known to improve plant growth by altering the spectral distribution.

To improve the spectral distribution of sunlight, light absorbing dyes can be used to alter the solar spectrum. These dyes can for example be dissolved in a liquid which is applied in between hollow panels which construct the roof of a greenhouse as disclosed in document DE3913552. Changing the color of the dye, and thus liquid, during the different stages of plant development can have a positive effect on plant growth and/or quality. However, a large amount of light energy is lost due the absorption of the dyes and consequently the total light intensity, to which the plants are exposed, is reduced. Furthermore, in the case of the liquid filled hollow panels it is difficult to effectively seal the device resulting in leakage of the (toxic) liquid/dye solution.

An alternative option is to use dyes, which in addition to absorbing light also re- emit a part of the absorbed light. Said dyes convert highly energetic, short wavelength light into lower energetic, longer wavelength, light, see e.g. JP57028149. Such dyes are known to those skilled in the art as photo-luminescent dyes. Said dyes can be used in a similar approach as the above described absorbing (non luminescent) dyes. However, the total light energy that reaches the plants is even further reduced as compared to a dye which only absorbs light. Several approaches are currently used which mainly vary in the wavelengths of the absorbed and/or emitted light, types and number of different dyes.

One option is converting UV light (<400nm), which can be harmful to plants, to longer wavelength light by using organic or anorganic photo-lumiscent dyes. Since said systems target to increase mainly the total light intensity, light is emitted either in the blue (JP4141025, CN1380351 ) or red (CN1269393, JP5227849, JP4141025, CN1385490, CN1186835, JP7170865, EP0579835 A1 ) which are the peak absorption wavelengths for photosynthesis. For this purpose a single dye can be used or a mixture which causes a cascading effect by which the emission of the first dye, which absorbs UV light, is absorbed by a second dye which emits it into red light. These systems are however inefficient due to the large difference in wavelength between absorbed and emitted light and therefore require a high level of UV. This limits the use of said systems to agricultural use in equatorial countries. Another disadvantage of said systems is the dye stability due the highly energetic nature of UV light.

Yet another option is converting green light (500-600nm), which is less efficiently used by plants for photosynthesis, to red light (EP0077496, JP1160433) by using an organic or inorganic photo-lumiscent dye. Although green light is less efficiently used by plants, complete removal will result in reduced plant growth. Therefore the concentration of dye is often low and only a part of the green light can be absorbed and consquently the increase in red light intensity in the spectrum by such dyes is low.

A third option consists of a combination of the two previously discussed approaches as disclosed in CN1307070. Said system contains a combination of UV light and green light absorbing dye and it emits blue and red light, increasing the light intensity in both photosynthetically most active regions.

All previously described methods using photo-luminscence dyes, however, loose a large amount of the emitted light by trapping of said light in the polymeric or glass matrix which comprises the dyes. This trapping is caused by the total internal reflection of the emitted light at the matrix/air interface which occurs when light reaches said interface under certain angles. As a result of this trapping, light emitted by the photo-luminescent dyes is transported to the edge of the device where it is lost. It is also possible that the trapped light is re-absorbed by the luminescent dye or the matrix and the energy is dissapated as heat. As a result of this phenomenon a large amount of light emitted by photoluminescent molecules in a polymeric or glass matrix does not reach the plants.

In summary it can be concluded that the intensity of light as well as the spectral- distribution of light affects plant growth. The spectral distribution can be improved by using photo-luminescent dyes, however a large part of the light emitted by said molecules is lost.

It is thus an object of the present invention to overcome the disadvantages of the prior art.

This object is achieved by a greenhouse for growing plants comprising a sheet containing a luminescent material and which has two main surface sides, characterised in that there are on at least one of the two main surface sides irregular shaped optical structures.

The term "sheet" is to be understood as an element with small thickness relative to its length and width. The sheet may be elastic e.g. in shape of a foil or rather rigid, e.g. a glass pane, a panel, plate or polymer panel or plate. The sheet is preferably made of a transparent material. A sheet is preferable flat, but may also have a 3D shape which can be derived by modification of a flat sheet like for example: cylindrical, spherical, conical, cubical, or pyramidal. The sheet can thus be for example in the form of a film, glazing for greenhouse or tunnel covers, a film or filament for shading nets and screens, mulch films, non-woven or molded articles for the protection of young plants, a plate in front of an assimilation lamp or a tubular algae reactor.

The two main surface sides are those surface sides through which the majority of the light enters and/or leaves the device. One surface side is directed towards the light source and the other surface side directed away from the light source. Apart from the two main surface sides the sheet may have surfaces on its outer rim, e.g. in case of a rectangular plate four lateral surfaces.

The term "transparent" is to be understood as having an absorption coefficient (α) of less than 0.5mm^"1 between 400-700 nm as determined with a spectrophotometer. The absorption coefficient should be determined by measuring the absorbance (A) of the material (without luminescent dye(s) and irregular shaped optical structures or any other texture) over a distance I in millimeters. The absorption coefficient is equal to the absorbance divided by the distance (α = A/I).

The term "optical" is to be understood as being able to direct light by either refraction of diffraction.

Plants are to be considered any organism which exhibits photosynthetic abilities such as for example trees, herbs, bushes, grasses, vines, ferns, mosses, and (green) algae. The term greenhouse is to be understood as an at least partially enclosed environment in which plants are maintained. It encompasses thus also tunnels of plastic foil over agricultural crop or a tank for the growth of green algae.

In a preferred embodiment the invention relates to a tank or tubular reactor for growing algae. In an even more preferred embodiment the algae reactor has the irregular shaped optical structures inside the transparent sheet (e.g. in the shape of a box or tube) or at the outer main surface of the transparent sheet (e.g. in the shape of a box or tube), but not at the inner main surface. The outer main surface is the main surface of the sheet (or box or tube) through which the light enters the sheet and which faces away from the algae. The inner main surface is the main surface of the sheet (or box or tube) through which the light exits the sheet and which faces towards the algae.

An enhancement in plant growth can be any change in the look, taste, smell, touch or sound of at least a part of the plant. An enhanced plant growth can for example be a change in color, sweetness, bitterness, sourness, size or weight. Preferably an enhanced plant growth is an increase in biomass.

The sheet containing a luminescent material and which has on at least one of the two main surface sides an array of irregular shaped optical structures should be located in between the agricultural crop and the light source. The sheet can thus be located inside or outside the greenhouse.

The light source is preferably the sun. However, also artificial light sources are under the scope of the invention. Examples of artificial light sources are lamps like a low pressure sodium lamp, a high pressure sodium lamp, a high pressure mercury lamp, xenon lamp, fluorescent lamp or a high pressure metal halide lamp, or Light Emitting Diodes (LED's). The light source can be positioned outside or within the greenhouse. In a preferred embodiment of the invention a transparent sheet containing luminescent molecules and irregular shaped optical structures is located in a greenhouse between an artificial light source and the plants. In an even more preferred embodiment said sheet contains a luminescent material, which absorbs wavelengths between 500-650 nm and re-emits between 600-800 nm. The sheet comprising a luminescent material and which has two main surface sides, characterised in that there are on at least one of the two main surface sides irregular shaped optical elements. The sheet is positioned above the plants and is used to redirect light emitted by said luminescent material. Said luminescent material can be a mixture of one or more luminescent materials. The luminescent material can be electro-, chemo-, bio-, sono-, piezo-, cathode-, anode-, radio-, tribo-, crystallo-, cando-, thermo-, pyro-, mechano- or photo-luminescent. Preferably the luminescent material is a photo-luminescent dye. Photo- luminescent dyes absorb light at a certain wavelength and emit at another wavelength. The conversion may be a down conversion from a higher to a lower energetic state or an up conversion from a lower to a higher energetic state. There are inorganic or organic photo-luminescent dyes. In the framework of the present invention organic photo-luminescent dyes are preferred especially if the sheet is made of a polymeric material.

An example of a typical organic photo-luminescent dye which can be used is a dye which absorbs predominantly light within the range of 200nm - 400nm and emits predominantly between 300nm - 500nm or absorbs predominantly within the range of 400nm - 500nm and emits predominantly between 500nm - 700nm. An example of such a photo-luminescent dye is BASF dye violet570 and BASF yellow083. It is also possible to use a mixture of at least two organic photo-luminescent dyes e.g. a dye which absorbs predominantly light within the range of 200nm - 400nm and emits predominantly between 300nm - 500nm together with a dye which absorbs predominantly within the range of 400nm - 500nm and emits predominantly between 500nm - 700nm.

Another example of a typical organic photo-luminescent dye which can be used is a dye which absorbs predominantly light within the range of 200nm - 400nm and emits predominantly between 300nm - 500nm or absorbs predominantly within the range of 500nm - 650nm and emits predominantly between 600nm - 800nm. An example of such a photo-luminescent dye is BASF dye violet570 and BASF rot300 or rot305. It is also possible to use a mixture of at least two organic photo- luminescent dyes e.g. a dye which absorbs predominantly light within the range of 200nm - 400nm and emits predominantly between 300nm - 500nm together with a dye which absorbs predominantly within the range of 500nm - 650nm and emits predominantly between 600nm - 800nm.

An additional effect which can result from the irregular shaped optical structures is that transmitted light is redistributed. It is also possible that the structures enhance the light intensity to which the plants are exposed by redirecting light, which is reflected from the plants or their surroundings, back towards the plants. Furthermore it is possible that the irregular shaped optical structures reduce the reflection losses of the sheet, which results in an increased light intensity to which the plants are exposed. In both cases plant growth is enhanced because of additional light intensity.

The sheet comprises irregular shaped optical structures on at least one of the two main surfaces of the sheet. A single structure is characterized in that its shape is non geometrical. Excluded within the scope of this invention are thus cones, spheres, cylinders, cubes or any other geometrical structures. Preferably the shape is asymmetric and thus has no point, line or surface of symmetry. An example of irregular shaped optical structures is those obtained after sandblasting of a material. Another example of irregular shaped optical structures is those obtained after embedding particles like for example silicon oxide (SiO2), zinc oxide (ZnO), calcium carbonate or chalk (CaCO₃), barium sulfate (BaSO₄), zirconium dioxide (ZrO₂), calcium sulfate (CaSO₄), lead oxide (PbO), lead carbonate (PbCOs), powdered glass, powdered plastic, granulated plastic, crystallized plastic or titanium dioxide (TiO₂) on at least one of the two main surfaces of the sheet or in the whole sheet.

Although the optical structures according to the invention should be irregular, this does not mean that all structures should have different shapes. It is also possible that at least one of the main surfaces contains a multitude of irregular structures of similar shape. It is however preferred that the optical structures on at least one of the main surfaces are different in shape.

In a preferred embodiment the irregular shaped optical structures are covered with a second material such that the outer surface of the second material is flat. It can be set that the optical structures are "filled" with the second material.

The sheet containing a luminescent material and which has two main surface sides, characterised in that there are on at least one of the two main surface sides irregular shaped optical structures is preferable made of a transparent material, which should have an absorption coefficient of less than 0.5mm^"1 between 400-

700 nm as determined with a spectrophotometer. This material can be inorganic however preferably polymeric. Examples of polymeric materials which can be used are: polycarbonate, polymethylmethacrylate, polypropylene, polyethylene, polyamide, polyacrylamide, polyvinylchloride or copolymers or any combinations thereof. The material is preferably stabilized by UV absorbers and/or hindered amine light stabilizers. Said materials may also contain flame retarders, UV stabilizers, thermal stabilizers, anti-oxidants, plasticizers, fillers, air pockets, light scatters or titanium dioxide.

The thickness of the sheet comprising the luminescent dye and the irregular shaped optical structures is preferably less than 10 cm, more preferably less than 2 cm.

The array of optical elements can be adapted with an additional layer or coating like for example an anti-fouling coating, anti-fogging coating, anti-reflection coatings, anti-glare coatings, color reflecting/absorbing layers, infra-red filter.

The luminescent material within the sheet comprising the irregular shaped optical structures according to the invention should be soluble up to the desired concentration in the material of which the array consists. In an alternative embodiment of the invention the dye is present in an additional layer which is in close proximity to the sheet with irregular shaped optical structures. Preferably the additional layer containing the dye is in contact with the sheet comprising the irregular shaped optical structures. More preferably said layer is deposited onto the irregular shaped optical structures or vice versa.

It is another object of the present invention to provide a method for enhancing plant growth that overcomes the disadvantages of the prior art. This object is achieved by a method for enhancing plant growth in a green house, characterized in that light reaches the plants essentially by passing through a sheet containing a luminescent material and which has two main surface sides, characterized in that there are on at least one of the two main surface sides irregular shaped optical structures. The sheet may exhibit the additional features as described above.

The invention is illustrated in more detail by means of the following figures:

Figure 1 shows a schematic representation of light emitted by a luminescent material (schematically represented by the circle). Light is only partially emitted in the direction of the plants. A significant part of the light is trapped in the device by total internal reflection and lost.

Figure 2 shows schematically sheets according to prior art in comparison with a sheet according to the invention which redistributes light emitted by the luminescent materials. It is redirect such that the light in not trapped within the device.

Figure 3 shows a preferred embodiment of the sheet comprising irregular shaped optical structures, which is coated with an additional material until the outer surface of the additional material is flat.

Claims

Greenhouse for enhanced plant growthClaims:

1 . Greenhouse for growing plants comprising a sheet containing a luminescent material and which has two main surface sides, characterised in that there are on at least one of the two main surface sides irregular shaped optical structures.

2. Greenhouse according to claim 1 , characterized in that the sheet contains a combination of two optically connected materials, which have different refractive indices, and that the irregular shaped optical structures face inwards.

3. Greenhouse according to any one of claims 1 to 2, characterized in that a luminescent material is contained in a separate layer within close proximity of the sheet with the two main surface sides, characterised in that there are on at least one of the two main surface sides irregular shaped optical structures.

4. Greenhouse according to claim 1 -3, characterized in that the luminescent material is a photo-luminescent dye.

5. Greenhouse according to claim 4, characterized in that the photo- luminescent dye is a mixture of different photo-luminescent dyes.

6. Greenhouse according to claim 4 or 5, characterized in that the photo- luminescent dye predominantly absorbs light between 200-400 nm and emits between 300-500 nm.

7. Greenhouse according to claim 4 or 5, characterized in that the photo- luminescent dye predominantly absorbs light between 500-650 nm and emits between 600-800 nm.

8. Greenhouse according to claim 5, characterized in that the mixture contains a photo-luminescent dye predominantly absorbing light between 200-400 nm and emitting between 300-500 nm and a photo-luminescent dye absorbing light between 500-650 nm and emitting between 600-800 nm.

9. Greenhouse according to any one of claims 1 to 8, characterized in that the sheet containing the luminescent material is made of a polymeric material.

10. Greenhouse according to any one of claims 1 to 8, characterized in that the thickness of the sheet containing the luminescent material is less than 10 cm.

11. Greenhouse according to any one of claims 1 to 10, characterized in that the irregular shaped optical elements is adapted with one or more of the following coatings: a coating an anti-fouling coating, anti-fogging coating, anti-reflection coatings, anti-glare coatings, color reflecting/absorbing layers, infra-red filter.

12. Method for enhancing plant growth in a greenhouse characterised in that sunlight reaches the plants essentially by passing through the sheet having two main surface sides and that there are on at least one of the two main surface sides irregular shaped optical structures.

13. Method for enhancing plant growth in a green house, characterised in that artificial light reaches the plants essentially by passing through the sheet having two main surface sides and that there are on at least one of the two main surface sides irregular shaped optical structures.

14. Method for enhancing plant growth in an algae reactor characterised in that artificial light reaches the plants essentially by passing through the sheet having two main surface sides and that there are on at least one of the two main surface sides irregular shaped optical structures.