Method and system for inhibiting plant growth

Abstract

To provide a method and system for inhibiting plant growth that places minimal burden on the environment and ecosystems. [Solution] The present invention provides a method for inhibiting plant growth, comprising the step of irradiating a plant with left-circularly polarized inhibiting light during a second hour of the day, which is different from the first hour during which the plant is irradiated with growth light. The photon flux density of the inhibiting light is less than the light compensation point of the plant.

Description

[Technical Field]

[0001] This invention relates to a method for inhibiting plant growth and a system for inhibiting plant growth. [Background technology]

[0002] One method of removing weeds that has been conventionally known is to spray liquid or granular herbicides on the land where weeds are growing. However, when using herbicides, there are problems as described in Non-Patent Document 1 below. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Naruhisa Hatakeyama, "Ecological Impact Assessment of Herbicides on Algae and Aquatic Plants," Journal of the Japanese Society of Environmental Toxicology (Jpn.J.Environ.Toxicol.), 9(2), pp. 51-60, 2006. [Overview of the project] [Problems that the invention aims to solve]

[0004] As described in Non-Patent Document 1, the use of herbicides may have a significant impact on the environment and ecosystems, such as rivers and soil. [Means for solving the problem]

[0005] To solve the above problems, a method for inhibiting plant growth according to one aspect of the present invention comprises the step of irradiating the plant with left-circularly polarized inhibiting light during a second hour of the day, which is different from the first hour during which the plant is irradiated with growth light. The photon flux density of the inhibiting light is less than the light compensation point of the plant.

[0006] A method for inhibiting plant growth according to one aspect of the present invention comprises: a light source device that emits light; an illuminance uniformizing optical device that uniformizes the illuminance of the light emitted from the light source device; a projection optical device capable of adjusting the size of the irradiation area of ​​the light emitted from the illuminance uniformizing optical system; a polarization conversion device that converts the light emitted from the light source device into left-hand circular polarization; and a control device that controls the intensity of the light emitted from the light source device. [Brief explanation of the drawing]

[0007] [Figure 1] This is a photograph showing the initial morphology of the tomato in the first embodiment. [Figure 2] This is a photograph showing a tomato being illuminated with two types of circularly polarized light. [Figure 3] This photograph shows the morphology of the right-hand stem before irradiation with right-circularly polarized light. [Figure 4] This photograph shows the morphology of the central stem before irradiation with right-circularly polarized and left-circularly polarized light. [Figure 5] This photograph shows the morphology of the left stem before irradiation with left-circularly polarized light. [Figure 6] These are photographs showing the overall shape of a tomato after being irradiated with various types of circularly polarized light. [Figure 7] This is a photograph showing the morphology of the left stem under left-circular polarized light, taken on the same day as Figure 6. [Figure 8] This photograph shows the morphology of the left stem when illuminated with left-circularly polarized light, taken on a later date than Figure 7. [Figure 9] Figure 8 is another photograph showing the morphology of the left stem when illuminated with left-circularly polarized light, taken on the same day as the original photograph. [Figure 10] This is a photograph showing the initial morphology of horsetail in the second example. [Figure 11] This is a photograph showing horsetail being illuminated with left-circularly polarized light. [Figure 12] This is a photograph showing the morphology of horsetail after irradiation with left-circularly polarized light. [Figure 13] This is a photograph showing the morphology of horsetail the year after Figure 12. [Figure 14]It is a photograph showing the form of shepherd's purse on a shooting date after that of FIG. 13. [Figure 15] It is a photograph showing the ground condition of the land where the experiment of the third embodiment was conducted. [Figure 16] It is a photograph showing a state where the left circularly polarized light is irradiated onto the Japanese butterbur. [Figure 17] It is a photograph showing the form of the Japanese butterbur after irradiation with the left circularly polarized light. [Figure 18] It is a photograph showing the form of the Japanese butterbur on a shooting date after that of FIG. 17. [Figure 19] It is a photograph from another angle showing the form of the Japanese butterbur on the shooting date same as that of FIG. 18. [Figure 20] It is a photograph showing the form of the Japanese butterbur on a shooting date after that of FIG. 19. [Figure 21] It is a photograph showing the form of the Japanese butterbur on a shooting date after that of FIG. 20. [Figure 22] In the fourth embodiment, it is a photograph showing the form of the sweet potato before irradiation of light at the start of the experiment. [Figure 23] It is a photograph showing the form of the sweet potato scheduled to be irradiated with the right circularly polarized light before the start of the experiment. [Figure 24] It is a photograph showing the form of the sweet potato scheduled to be irradiated with the left circularly polarized light before the start of the experiment. [Figure 25] It is a photograph showing the form of the sweet potato without irradiation of light after the start of the experiment. [Figure 26] It is a photograph showing the form of the sweet potato after irradiation with the right circularly polarized light. [Figure 27] It is a photograph showing the form of the sweet potato after irradiation with the left circularly polarized light. [Figure 28] It is a photograph comparing three types of sweet potatoes. [Figure 29] It is a schematic configuration diagram of the plant growth inhibition system. [Figure 30] [[ID=​​​​

[0008] [Methods for inhibiting plant growth] The following describes an example of a method for suppressing plant growth according to this embodiment. The plant growth inhibition method of this embodiment includes the step of irradiating plants whose growth is to be inhibited with weak left-circularly polarized inhibiting light at a predetermined time during the night, different from the daytime when plants are exposed to sunlight. As will be described in detail later, the intensity of the inhibiting light is set to be sufficiently low. Specifically, if the intensity of the inhibiting light is expressed in terms of photon flux density, the photon flux density of the inhibiting light is a value less than the light compensation point of the plant whose growth is to be inhibited. Left-circular polarization is circular polarization in which the rotation direction of the plane of polarization of the light is counterclockwise, as viewed from an observer positioned opposite the direction of light propagation.

[0009] In this specification, light necessary for plant growth is referred to as growth light, and light irradiated for the purpose of inhibiting plant growth is referred to as inhibiting light. In this embodiment, sunlight corresponds to the growth light in the claims. Therefore, in this embodiment, the time during which sunlight irradiates the plants during the day corresponds to the first hour in the claims. The time during which the plants are irradiated with inhibiting light consisting of left-circular polarization corresponds to the second hour in the claims.

[0010] In this specification, the term "photon flux density" specifically refers to the photosynthetically effective photon flux density. That is, photon flux density is an indicator of light intensity, expressed as the number of photons in the wavelength range of 400 nm to 700 nm that are effective for plant photosynthesis, passing through a unit area per unit time. The unit of photon flux density is, for example, μmol / m³. 2 The value is / s. The light compensation point is the photon flux density at which the photosynthetic rate becomes zero, when the difference between the carbon dioxide absorption rate in photosynthesis and the carbon dioxide release rate in respiration is defined as the photosynthetic rate. Therefore, when light with a photon flux density exceeding the light compensation point is shone on a plant, the plant's photosynthetic reaction occurs. On the other hand, if light with a photon flux density below the light compensation point is shone on a plant, the plant's photosynthetic reaction does not occur.

[0011] Three types of photoreceptors are known in plants: phytochrome, cryptochrome, and phototropin. Phytochrome responds to red and far-red light, cryptochrome responds to blue light, and phototropin responds to blue light. Of these photoreceptors, phytochrome and phototropin are unique to plants. Given the characteristics of these photoreceptors, it is desirable that the wavelength range of the suppression light includes both the blue and red wavelength ranges.

[0012] The photon flux density of the suppressing light should preferably be below the light compensation point of the plant, and above the minimum value at which a signaling effect is expressed in the above-mentioned photoreceptors when the suppressing light is irradiated. For light irradiation to plants to elicit photosynthesis, a photon flux density of approximately 10 W / m² is required under natural daylight (approximately 6500 K as the total sun radiation during the day). 2 Radiation intensity (approximately 40 μmol / m³) 2 While a photon flux density of 1 / s is required, for light irradiation to plants to exert a signaling effect on photoreceptors, a radiant intensity much lower than that which elicits photosynthesis is sufficient. In other words, the suppression light in this embodiment only needs to have an intensity that is weak enough not to cause photosynthesis, but is sufficient to exert a signaling effect on photoreceptors.

[0013] [First Embodiment] The following describes a first embodiment of the present invention. In the first embodiment, we will describe a growth inhibition experiment conducted by the inventors using tomatoes.

[0014] Figure 1 is a photograph showing the initial state of a tomato. As a sample for this experiment, we prepared a tomato plant with three stems (1L, 1C, and 1R) branching from a single plant, as shown in Figure 1. The tomato was grown in a planter, which was placed outdoors and received sunlight during the day. As a result, the tomato was growing well. Figure 1 was taken on November 19, 2022.

[0015] In this specification, daytime is defined as the time from sunrise to sunset, and is synonymous with the daytime as defined in the claims. The sunlight in this embodiment corresponds to the growth light as defined in the claims. Therefore, the time during daytime when sunlight is irradiating the tomato corresponds to the first hour as defined in the claims.

[0016] Figure 2 is a photograph showing tomatoes being illuminated with two different types of light. Next, two types of circularly polarized light were simultaneously shone on the tomato plants at a specific time during the night. Specifically, as shown in Figure 2, left-handed circularly polarized light was shone on region A1, which included the leaves attached to the leftmost stem 1L and the leaves attached to the central stem 1C. Right-handed circularly polarized light was shone on region A2, which included the leaves attached to the rightmost stem 1R and the leaves attached to the central stem 1C. Therefore, the leaves attached to the central stem 1C were shone with both left-handed and right-handed circularly polarized light.

[0017] The illumination conditions were set to a 4-hour period from 7 PM to 11 PM. The illumination period was 27 days, from November 19, 2022 to December 14, 2022. The photon flux density for both left-circularly polarized and right-circularly polarized light was approximately 3 μmol / m³. 2 The concentration was set to / s. Therefore, the leaves attached to the right stem 1R and the leaves attached to the left stem 1L each contained approximately 3 μmol / m³. 2 When light at / s is shone, approximately 6 μmol / m³ is detected in the leaves attached to the central stem 1C. 2 Light with a wavelength of / s was irradiated. The wavelength band of each circularly polarized light included the red and blue wavelength bands. The light compensation point for tomatoes is approximately 50 μmol / m². 2 It is / s.

[0018] Figure 3 is a photograph showing the morphology of the right stem 1R before irradiation with right-circularly polarized light. Figure 4 is a photograph showing the morphology of the central stem 1C before irradiation with both right-circularly polarized and left-circularly polarized light. Figure 5 is a photograph showing the morphology of the left stem 1L before irradiation with left-circularly polarized light. These images were taken on November 19, 2022. As shown in Figures 3 to 5, before irradiation with each circularly polarized light, the three stems 1R, 1C, and 1L, and the leaves attached to each stem, were all growing normally, and no difference in growth status was observed.

[0019] Figure 6 is a photograph of the entire tomato plant taken on the day after being irradiated with each type of circularly polarized light for a certain period of time. Figure 7 is a photograph of the left stem 1L irradiated with left-circularly polarized light, taken on the same day as Figure 6. The dates of photographs 6 and 7 are December 10, 2022. Figure 8 is a photograph of the left stem 1L irradiated with left-circularly polarized light, taken on a later date than Figure 7. Figure 9 is a photograph taken from a different angle than Figure 8. The dates of photographs 8 and 9 are December 14, 2022.

[0020] Although difficult to see in the photograph in Figure 6, the leaves on the left stem 1L, which were irradiated with left-circular polarized light, were in a worse state of growth compared to the leaves on the right stem 1R, which were irradiated with right-circular polarized light, and the leaves on the central stem 1C, which were irradiated with both types of circular polarized light. Specifically, the leaves on the right stem 1R and the central stem 1C were dark green and firm. On the other hand, the leaves on the left stem 1L, as shown in Figure 7, were yellowed and wilted overall. Figures 8 and 9 are photographs taken four days after the date of Figure 7, and the yellowing and wilting of the leaves are even more pronounced.

[0021] [Discussion regarding the first embodiment] In this example, a tomato plant with three branched stems was used, so individual plant differences did not affect the experimental results. Nevertheless, it was found that the growth of the stems and leaves irradiated with left-circular polarized light was inferior to that of the other stems and leaves.

[0022] [Second Example] A second embodiment of the present invention will be described below. In the second embodiment, we will describe the growth inhibition experiment conducted by the inventors using horsetail.

[0023] Figure 10 is a photograph showing the initial stage of horsetail. As shown in Fig. 10, the experiment was conducted in a part of a garden where many mustard plants were thriving. The rectangular area indicated by reference sign A is the area irradiated with left - circularly polarized light. The shooting date of Fig. 10 is May 16, 2023.

[0024] Fig. 11 is a photograph showing the state of mustard plants being irradiated with left - circularly polarized light. As shown in Fig. 11, at a certain time at night, the area A shown in Fig. 10 was irradiated with left - circularly polarized light. As the irradiation conditions of the left - circularly polarized light, the irradiation time was set to 4 hours from 19:00 to 23:00 at night. The irradiation period was set to every day for 22 days from May 16, 2023 to June 6, 2023. The left - circularly polarized light was irradiated obliquely downward with respect to the ground using the growth - suppression system 10 installed at a predetermined height from the ground. Therefore, among the rectangular area A, the light intensity at the location close to the growth - suppression system 10 was relatively high, and the light intensity at the location far from the growth - suppression system 10 was relatively low. Specifically, the photon flux density of the left - circularly polarized light was about 18 μmol / m 2 / s at the front - side location close to the growth - suppression system 10, and about 5 μmol / m 2 / s at the back - side location far from the growth - suppression system 10. The wavelength band of the left - circularly polarized light was set to a wavelength band including the red wavelength band and the blue wavelength band.

[0025] Fig. 12 is a photograph showing the state of mustard plants on the shooting date 10 days after the start of the experiment. The shooting date of Fig. 12 is May 25, 2023. As shown in Fig. 12, the mustard plants remained thriving, and the growth state of the mustard plants was almost unchanged from the start of the experiment. Since no suppression of the growth of the mustard plants was observed at this point, the experiment of irradiating with left - circularly polarized light was temporarily terminated.

[0026] Fig. 13 is a photograph showing the state of mustard plants on the shooting date about one year after the shooting date of Fig. 12. The shooting date of Fig. 13 is May 21, 2024. As a result of the present inventor observing the area A where the mustard plants were irradiated with left - circularly polarized light the previous year again, as shown in Fig. 13, it was discovered that almost no mustard plants had germinated.

[0027] Figure 14 is a photograph showing the state of horsetail (Equisetum arvense) at a later date than that of Figure 13. The photograph in Figure 14 was taken on June 10, 2024. As shown in Figure 14, even after approximately three weeks had passed since the date of the photograph in Figure 13, the situation in area A remained largely unchanged, indicating that horsetails hardly germinated.

[0028] [Discussion regarding the second embodiment] Horsetail (Equisetum arvense) is a perennial plant with rhizomes. It stores nutrients obtained through photosynthesis in its rhizomes to survive the winter, and then uses these stored nutrients to germinate in the spring of the following year. Considering this characteristic, the reason why horsetail did not grow the year after being exposed to left-circular polarized light is presumed to be that some effect occurred due to the exposure to left-circular polarized light, preventing the storage of nutrients necessary for the horsetail's germination the following year in its rhizomes. Horsetail is generally considered a highly prolific and difficult-to-remove weed. However, as described above, it has been found that irradiating horsetail with left-circular polarized light can suppress its germination the following year.

[0029] [Third Embodiment] A third embodiment of the present invention will be described below. In the third embodiment, we will describe a growth inhibition experiment conducted by the inventors using foxtail grass.

[0030] Figure 15 is a photograph showing the condition of the ground in the garden where the experiment was conducted. The experiment involved weeding a portion of the garden to create a weed-free area B, as shown in Figure 15. The area of ​​area B used in the experiment was 1 m². 2 The date of the photograph in Figure 15 is June 8, 2023.

[0031] Figure 16 is a photograph showing the condition of foxtail grass being illuminated with left-circularly polarized light. As shown in Figure 16, during a certain period of time at night, the experimental area B was measured at 0.5 m 2The area was divided into two regions, and left-circularly polarized light was irradiated only into one region, B1. The irradiation conditions for left-circularly polarized light were set to a 4-hour period from 7 PM to 11 PM. The irradiation period was daily for two months, from June 7, 2023 to August 7, 2023. Similar to the second example, left-circularly polarized light was irradiated obliquely to the ground using a growth suppression system. The photon flux density of left-circularly polarized light was approximately 18 μmol / m³ at the front of the area close to the growth suppression system. 2 The rate is / s, and in the innermost area far from the growth inhibition system, it is approximately 5 μmol / m³. 2 The value was / s. The wavelength band for left circular polarization was defined as the wavelength band including the red wavelength band and the blue wavelength band. In the following explanation, the region irradiated with left circular polarization will be referred to as the irradiated region B1, and the region not irradiated with left circular polarization will be referred to as the unirradiated region B2.

[0032] Figure 17 is a photograph showing the state of foxtail grass 26 days after the start of the experiment. The photograph in Figure 17 was taken on July 2, 2023. As shown in Figure 17, foxtail grass began to grow in area B, where no weeds had initially grown. However, at this point, it is still difficult to discern any difference in the growth state of foxtail grass between the irradiated area B1 and the unirradiated area B2.

[0033] Figure 18 is a photograph showing the state of foxtail grass 10 days after the date of the photograph in Figure 17. The date of the photograph in Figure 18 was July 12, 2023. Although it is a little difficult to see in Figure 18, at this point, a difference in the growth state of foxtail grass was confirmed between the irradiated area B1 and the unirradiated area B2.

[0034] Figure 19 is a photograph taken on the same day as the photograph in Figure 18, but taken from a closer angle to the ground than the photograph in Figure 18. As shown in Figure 19, multiple foxtail grass plants with flower spikes were found in the non-irradiated area B2 (part of photograph E1), whereas no foxtail grass plants with flower spikes were found in the irradiated area B1.

[0035] Figure 20 is a photograph taken on August 4, 2023, 24 days after the date of the photograph in Figure 19, and was taken from the same angle as the photograph in Figure 19. As shown in Figure 20, in the unirradiated area B2, the foxtail grass was generally taller, and the foxtail grass with flower spikes grew particularly large (part of photograph E2). On the other hand, in the irradiated area B1, there was very little foxtail grass with flower spikes (part of photograph E3), and the foxtail grass was generally shorter.

[0036] Figure 21 is a photograph taken on August 7, 2023, three days after the date of the photograph in Figure 20, and was taken from the same angle as the photograph in Figure 20. As shown in Figure 21, the difference in the growth state of foxtail grass between the unirradiated area B2 and the irradiated area B1 is even more pronounced.

[0037] [Discussion regarding the third embodiment] Foxtail grass (Setaria viridis) is an annual plant that reproduces by the dropping of seeds from its flower spikes to the ground, and is known for its strong reproductive capacity. However, this experiment revealed that irradiating foxtail grass with left-circular polarized light can suppress its growth. The inventors compared the growth status of foxtail grass in unirradiated area B2 and irradiated area B1. In unirradiated area B2, the average height of foxtail grass was approximately 70-80 cm, while in irradiated area B1, the average height was approximately 30-40 cm. Furthermore, in unirradiated area B2, the number of flower spikes was 0.5 m 2 While there were 34 in total, in the irradiated area B1, the number of flower spikes was 0.5 m 2 There were three per plant. In this way, by reducing the number of foxtail grass flower spikes, it is possible to reduce the germination of foxtail grass in the next season.

[0038] [Fourth embodiment] A fourth embodiment of the present invention will be described below. In the fourth embodiment, we will describe a growth inhibition experiment conducted by the inventors using sweet potatoes.

[0039] Figures 22 to 24 are photographs showing the initial stage of sweet potatoes. As samples used in the experiment, sweet potatoes grown in planters were used, as shown in Figures 22 to 24. The sweet potatoes were exposed to sunlight during the day and were growing well. Figures 22 to 24 were taken on August 9, 2024. Sweet potato S1 in Figure 22 was a sample that was not irradiated with any circularly polarized light. Sweet potato S2 in Figure 23 was a sample that was irradiated with right-circularly polarized light. Sweet potato S3 in Figure 24 was a sample that was irradiated with left-circularly polarized light.

[0040] Next, sweet potato S2 in Figure 23 was irradiated with right-circularly polarized light, and sweet potato S3 in Figure 24 was irradiated with left-circularly polarized light for a certain period of time at night. The irradiation conditions for each circular polarization were set to a 4-hour period from 19:00 to 23:00 at night. The irradiation period was 38 days, from August 10, 2024 to September 16, 2024. Regarding the intensity of each circular polarization, the photon flux density of the right-circularly polarized light was approximately 10 μmol / m³. 2 Assuming a speed of / s, the photon flux density of left-circularly polarized light is approximately 1 μmol / m³. 2 The value was set to / s. The wavelength range for each circularly polarized light was defined as the wavelength range including the red wavelength band and the blue wavelength band.

[0041] Figure 25 is a photograph showing the state of sweet potato S1 30 days after the start of the experiment, without any circularly polarized light irradiation. The photograph in Figure 25 was taken on September 8, 2024. Comparing Figure 25 with Figure 22, we can see that the number of leaves has increased, indicating that sweet potato S1 is growing well.

[0042] Figure 26 is a photograph showing the state of sweet potato S2 irradiated with right-circularly polarized light 30 days after the start of the experiment. The photograph in Figure 26 was taken on September 8, 2024. Comparing Figure 26 with Figure 23, we can see that the number of leaves has increased, indicating that sweet potato S2 is growing well.

[0043] Figure 27 is a photograph showing the state of sweet potato S3 30 days after the start of the experiment, when irradiated with left-circularly polarized light. The photograph in Figure 27 was taken on September 8, 2024. As shown in Figure 27, the appearance of sweet potato S1, which was not irradiated with the light shown in Figure 25, and sweet potato S2, which was irradiated with right-circularly polarized light shown in Figure 26, is completely different, and sweet potato S3, which was irradiated with left-circularly polarized light, withered away.

[0044] Figure 28 shows photographs comparing the appearance of three different types of sweet potatoes after they were removed from their planters. The photographs in Figure 28 were taken on September 16, 2024. As shown in Figure 28, sweet potato S1, which was not irradiated with circularly polarized light, and sweet potato S2, which was irradiated with right-hand circularly polarized light, grew normally, while sweet potato S3, which was irradiated with left-hand circularly polarized light, withered.

[0045] [Discussion regarding the fourth embodiment] In this example, sweet potatoes irradiated with left-circular polarized light withered and died within about a month, unlike other sweet potatoes, indicating that a significant growth-inhibiting effect can be obtained.

[0046] [Summary of Examples] Through the four examples described above, although the form and degree of change differ depending on the type of plant, it was found that the growth of various plants can be suppressed by irradiating them with left-circularly polarized light for a predetermined period of time at night. Therefore, this growth suppression method may be applicable to uses such as removing weeds, keeping plant height low, and thinning out densely growing leaves and stems. This method does not use herbicides or other chemicals, thus reducing the burden on the environment and ecosystems. Furthermore, since this method requires a low intensity of left-circularly polarized light, the energy required to implement this method can be reduced. As in the examples above, irradiating with left-circularly polarized light including the red and blue wavelength bands, i.e., magenta-colored left-circularly polarized light, at night may cause nuisance to the lives of people in the vicinity of the irradiated area. However, since this method requires a sufficiently low light intensity, the impact on nearby lives can be kept to a minimum.

[0047] [Plant growth inhibition system] The following describes an example of a plant growth inhibition system according to this embodiment. Figure 29 is a schematic diagram of the growth suppression system 10 of this embodiment. As shown in Figure 29, the growth suppression system 10 of this embodiment comprises a light source device 20, a control device 30, an illumination uniformity optical device 40, a color separation optical device 50, an optical modulation device 60R, an optical modulation device 60G, an optical modulation device 60B, a synthesis optical device 70, a projection optical device 80, and a polarization conversion device 90.

[0048] The light source device 20 consists of a high-pressure mercury lamp that emits white light LW. The light source device 20 may also consist of other components besides the ultra-high-pressure mercury lamp, such as a light-emitting diode, a laser diode, or a phosphor that emits fluorescence upon irradiation with excitation light. It is desirable that the light source device 20 emits light containing at least a blue light component and a red light component.

[0049] The control device 30 controls the intensity of the white light LW emitted from the light source device 20 to below the light compensation point of the plant whose growth is to be suppressed. The control device 30 consists of a CPU built into the system.

[0050] The illuminance uniformizing optical device 40 uniformizes the illuminance of the white light LW emitted from the light source device 20 in the irradiated area. The illuminance uniformizing optical device 40 includes a first lens array 41, a second lens array 42, a polarization conversion element 43, and a superimposed lens 44. By equipping the growth suppression system 10 with the illuminance uniformizing optical device 40, illuminance unevenness in the light irradiated area can be reduced, and a uniform growth suppression effect can be obtained.

[0051] The first lens array 41 has a plurality of first lenses 41a for dividing the white light LW emitted from the light source device 20 into a plurality of partial luminous beams. The plurality of first lenses 41a are arranged in a matrix in a plane perpendicular to the illumination optical axis 20ax. The illumination optical axis 20ax is defined as the central axis of the white light LW emitted from the light source device 20.

[0052] The second lens array 42 has a plurality of second lenses 42a corresponding to a plurality of first lenses 41a of the first lens array 41. The plurality of second lenses 42a are arranged in a matrix in a plane perpendicular to the illumination optical axis 20ax. Together with the superimposed lens 44, the second lens array 42 images the images of each first lens 41a of the first lens array 41 near the optical modulators 60R, 60G, and 60B, respectively.

[0053] The polarization conversion element 43 converts the white light LW emitted from the second lens array 42 into linearly polarized light having a predetermined polarization direction. The polarization conversion element 43 includes a polarization separation film and a phase difference plate (not shown).

[0054] The superimposing lens 44 focuses each partial light beam emitted from the polarization conversion element 43 and superimposes it near the optical modulator 60R, optical modulator 60G, and optical modulator 60B, respectively.

[0055] The color separation optical device 50 separates the white light LW emitted from the light source device 20 into red light LR, green light LG, and blue light LB. The color separation optical device 50 includes a first dichroic mirror 51, a second dichroic mirror 52, a first reflective mirror 53, a second reflective mirror 54, a third reflective mirror 55, a first relay lens 56, and a second relay lens 57.

[0056] The first dichroic mirror 51 transmits red light LR and reflects light containing green light LG and blue light LB. Thus, the first dichroic mirror 51 separates the white light LW emitted from the light source device 20 into red light LR and light containing green light LG and blue light LB. The second dichroic mirror 52 reflects green light LG and transmits blue light LB. Thus, the second dichroic mirror 52 separates the light containing green light LG and blue light LB emitted from the first dichroic mirror 51 into green light LG and blue light LB.

[0057] The first reflective mirror 53 is positioned in the optical path of red light LR and reflects the red light LR that has passed through the first dichroic mirror 51 toward the optical modulator 60R. The second reflective mirror 54 and the third reflective mirror 55 are positioned in the optical path of blue light LB and guide the blue light LB that has passed through the second dichroic mirror 52 toward the optical modulator 60B. The green light LG is reflected from the second dichroic mirror 52 toward the optical modulator 60G.

[0058] The first relay lens 56 is positioned between the second dichroic mirror 52 and the second reflective mirror 54 in the optical path of the blue light LB. The second relay lens 57 is positioned between the second reflective mirror 54 and the third reflective mirror 55 in the optical path of the blue light LB. The first relay lens 56 and the second relay lens 57 compensate for the optical loss of the blue light LB, which is caused by the blue light LB having a longer optical path length than the red light LR and green light LG.

[0059] Optical modulator 60R modulates red light LR. Optical modulator 60G modulates green light LG. Optical modulator 60B modulates blue light LB. Optical modulators 60R, 60G, and 60B each use, for example, a transmissive liquid crystal panel. Polarizing plates (not shown) are also placed on the incident and exit sides of each liquid crystal panel.

[0060] A field lens 65R is positioned on the incident side of the optical modulator 60R. The field lens 65R parallelizes the red light LR incident on the optical modulator 60R. A field lens 65G is positioned on the incident side of the optical modulator 60G. The field lens 65G parallelizes the green light LG incident on the optical modulator 60G. A field lens 65B is positioned on the incident side of the optical modulator 60B. The field lens 65B parallelizes the blue light LB incident on the optical modulator 60B.

[0061] The composite optical device 70 receives light of each color emitted from the optical modulators 60R, 60G, and 60B. The composite optical device 70 combines red light LR, green light LG, and blue light LB, and emits the combined light toward the projection optical device 80. A cross dichroic prism is used in the composite optical device 70.

[0062] The projection optical device 80 has multiple projection lenses. The projection optical device 80 magnifies and illuminates the composite light emitted from the composite optical device 70 toward the illumination area. The projection optical device 80 may have a zoom function. This allows the size of the light illumination area to be adjusted.

[0063] The polarization converter 90 is located on the light emission side of the projection optical device 80. The polarization converter 90 converts linearly polarized light emitted from the projection optical device 80 into left-hand circularly polarized light (LP). The polarization converter 90 is composed of a quarter-wave plate. The lagging or leading axis of the quarter-wave plate is positioned at a 45-degree angle with respect to the polarization axis of the linearly polarized light emitted from the projection optical device 80.

[0064] Figure 30 shows the spectrum of left-circularly polarized LP emitted from the growth suppression system 10. As shown in Figure 30, left-circularly polarized light (LP) contains a blue light component peaking at 450 nm and a yellow to red light component peaking at 600 nm, with almost no green light component. The wavelength range of such left-circularly polarized light (LP) can be adjusted by controlling the light transmission amount of optical modulators 400R, 400G, and 400B.

[0065] The growth suppression system 10 of this embodiment can efficiently suppress the growth of plants present in any location.

[0066] It should be noted that the technical scope of the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention. For example, in the embodiment of the growth inhibition method described above, sunlight that naturally irradiates plants during the day was used as growth light. However, instead of this configuration, artificial lighting, such as that used in plant factories, may be used as growth light. When using artificial lighting as growth light, the time during which the inhibiting light is irradiated does not necessarily have to be at night; it can be at a different time from the time when the growth light is irradiated.

[0067] In the above embodiment of the growth suppression system, the growth suppression system comprises a color separation optical device, three light modulation devices, and a synthesis optical device. However, these components are not required, and the system may be configured to directly incident light emitted from an illumination uniformization optical device onto a projection optical device. The growth suppression system may also comprise a light source device including a red LED, a blue LED, and a dichroic mirror that combines red and blue light. With this configuration, it is possible to emit only one type of light by turning on either the red LED or the blue LED and turning off the other.

[0068] Furthermore, the specific numerical values ​​such as the irradiation time of the suppression light and the photon flux density mentioned in the above embodiments are merely examples and can be changed as appropriate.

[0069] [Summary of this disclosure] A summary of this disclosure is provided below.

[0070] (Note 1) The process includes irradiating the plant with left-circularly polarized suppression light during a second hour of the day, which is different from the first hour during which the plant is irradiated with growth light. A method for inhibiting plant growth, wherein the photon flux density of the suppressing light is less than the light compensation point of the plant.

[0071] According to the configuration described in Appendix 1, it is possible to provide a method for suppressing plant growth that reduces the energy required to implement this method while minimizing the burden on the environment and ecosystems.

[0072] (Note 2) The aforementioned first time is a time within the illumination period, The method for suppressing plant growth as described in Appendix 1, wherein the second time is the time outside of the time when sunlight is available.

[0073] According to the configuration described in Appendix 2, sunlight can be used as growth light, and suppressive light can be irradiated at night.

[0074] (Note 3) The method for inhibiting plant growth as described in Appendix 1 or Appendix 2, wherein the second time is 4 hours or more.

[0075] According to the configuration described in Appendix 3, plant growth can be reliably suppressed.

[0076] (Note 4) The aforementioned photon quantum flux density is 3 μmol / m³ 2 A method for inhibiting plant growth described in any one of the appendices 1 to 3, wherein the value is 1 / s or greater.

[0077] According to the configuration described in Appendix 4, plant growth can be reliably suppressed.

[0078] (Note 5) The aforementioned photon quantum flux density is 15 μmol / m³. 2 A method for inhibiting plant growth as described in Appendix 4, wherein the duration is 1 / s or greater.

[0079] According to the configuration described in Appendix 5, plant growth can be suppressed more effectively.

[0080] (Note 6) A method for inhibiting plant growth according to any one of the appendices 1 to 5, wherein the inhibiting light is irradiated onto the chlorophyll-containing parts of the plant in the above step.

[0081] According to the configuration described in Appendix 6, the photoreceptors present in plants can detect the irradiation of inhibitory light, thus effectively suppressing plant growth.

[0082] (Note 7) The method for inhibiting plant growth according to any one of the appendices 1 to 6, wherein the photon flux density of the inhibiting light is greater than or equal to the minimum value at which a signaling effect occurs in the photoreceptors of the plant when the inhibiting light is irradiated.

[0083] According to the configuration described in Appendix 7, the photoreceptor can detect the irradiation of inhibitory light as a signal, thus reliably suppressing plant growth.

[0084] (Note 8) The method for suppressing plant growth as described in any one of the appendices 1 to 7, wherein the wavelength band of the suppressing light includes the blue wavelength band and the red wavelength band.

[0085] According to the configuration described in Appendix 8, plant growth can be reliably suppressed using light in wavelengths at least necessary for growth inhibition.

[0086] (Note 9) A light source device that emits light, An illuminance uniformizing optical device for uniformizing the illuminance of the light emitted from the light source device, A projection optical device capable of adjusting the size of the irradiation area of ​​the light emitted from the illumination uniformization optical device, A polarization conversion device that converts the light emitted from the light source device into left-hand circularly polarized light, A control device for controlling the amount of light emitted from the light source device, A plant growth suppression system equipped with [a specific feature].

[0087] According to the configuration described in Appendix 9, it is possible to provide a plant growth suppression system that reduces energy consumption while minimizing the burden on the environment and ecosystems. [Explanation of symbols]

[0088] 10...Growth suppression system, 20...Light source device, 30...Control device, 40...Illumination uniformity optical device, 80...Projection optical device.

Claims

1. The process includes a step of irradiating the plant with left-circularly polarized suppression light during a second hour of the day, which is different from the first hour during which the plant is irradiated with growth light. A method for inhibiting plant growth, wherein the photon flux density of the suppressing light is less than the light compensation point of the plant.

2. The aforementioned first time is a time within the illumination period, The method for suppressing plant growth according to claim 1, wherein the second time is the time outside of the time when sunlight is available.

3. The method for suppressing plant growth according to claim 1 or claim 2, wherein the second time is 4 hours or more.

4. The aforementioned photon flux density is 3 μmol / m³ ２ A method for suppressing plant growth according to claim 1 or claim 2, wherein the value is 1 / s or greater.

5. The aforementioned photon quantum flux density is 15 μmol / m³. ２ A method for suppressing plant growth according to claim 4, wherein the value is 1 / s or greater.

6. The method for inhibiting plant growth according to claim 1 or claim 2, wherein in the above step, the inhibiting light is irradiated onto the part of the plant that contains chlorophyll.

7. The method for suppressing plant growth according to claim 1 or claim 2, wherein the photon flux density of the suppressing light is greater than or equal to the minimum value at which a signaling effect occurs in the photoreceptors of the plant when the suppressing light is irradiated.

8. The method for suppressing plant growth according to claim 1 or claim 2, wherein the wavelength band of the suppression light includes the blue wavelength band and the red wavelength band.

9. A light source device that emits light, An illuminance uniformizing optical device for uniformizing the illuminance of the light emitted from the light source device, A projection optical device capable of adjusting the size of the irradiation area of ​​the light emitted from the illumination uniformization optical device, A polarization conversion device that converts the light emitted from the light source device into left-hand circularly polarized light, A control device for controlling the intensity of the light emitted from the light source device, A plant growth suppression system equipped with [a specific feature].

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