Plant manufacturing method and light irradiation device

Abstract

To provide a plant manufacturing method and a light irradiation device that can suppress growth disorders and improve the commercial value of plants in a shorter period of time. [Solution] The plant manufacturing method includes an irradiation step in which light with a predetermined irradiance having a peak in a predetermined wavelength range is irradiated to the plant P for a predetermined time starting from a predetermined point in time prior to the harvest of the plant P, the predetermined wavelength range being 405 nm to 470 nm, and the predetermined irradiance being 4 mW / cm². 2 The above is the case, and the specified time is 48 hours or less.

Description

[Technical Field]

[0001] This invention relates to a method for producing plants and a light irradiation device. [Background technology]

[0002] Conventionally, techniques for cultivating plants by irradiating them with artificial light are known. Patent Document 1 is an example of this type of technique. Patent Document 1 describes a seedling cultivation method and facility for leafy vegetable seedlings, in which the seedlings are grown under illumination consisting mainly of blue light with a wavelength of 450 nm to 500 nm, thereby promoting dwarfism of the seedlings. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2013-66394 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Incidentally, there is a need to color plants to enhance their commercial value, and one method of coloring plants has been to irradiate them with light. However, conventionally, the appropriate conditions for irradiating plants with light have not been clearly defined, and there have been problems such as the plants taking a long time to color and the plants being damaged during production.

[0005] The present invention aims to provide a plant manufacturing method and a light irradiation device that can suppress growth disorders and improve the commercial value of plants in a shorter period of time. [Means for solving the problem]

[0006] (1) The plant manufacturing method according to the present invention is a plant manufacturing method comprising an irradiation step of irradiating the plant with light having a predetermined irradiance having a peak in a predetermined wavelength range for a predetermined time, starting from a predetermined time before the time of harvesting the plant, wherein the predetermined wavelength range is 405 nm to 470 nm, and the predetermined irradiance is 4 mW / cm 2 The above is the case, and the specified time is 48 hours or less.

[0007] The plant manufacturing method described in (1) can suppress growth disorders and improve the commercial value of the plants in a shorter period of time.

[0008] (2) In the method for producing plants described in (1), the predetermined wavelength range is 450 nm to 470 nm.

[0009] The plant manufacturing method described in (2) can suppress growth disorders and improve the commercial value of the plants in a shorter period of time.

[0010] (3) In the method for producing plants described in (1) or (2), the predetermined irradiance is 15 mW / cm 2 The above conditions apply, and the specified time is 24 hours or less.

[0011] The plant manufacturing method described in (3) can suppress growth disorders and improve the commercial value of the plants in a shorter period of time.

[0012] (4) In the method for producing plants described in any one of (1) to (3), the predetermined time is 12 hours or less.

[0013] The plant manufacturing method described in (4) can suppress growth disorders and further improve the commercial value of the plants in a shorter period of time.

[0014] (5) In the method for producing a plant described in any one of (1) to (4), the plant is lettuce.

[0015] The plant manufacturing method described in (5) can suppress growth disorders and improve the commercial value of the plants in a shorter period of time.

[0016] (6) The light irradiation device according to the present invention is a light irradiation device that executes the irradiation step in the method for producing a plant according to any one of (1) to (5), and emits light having a peak in the wavelength range of 405 nm to 470 nm at 4 mW / cm 2 or more to irradiate the plant, and has a switching unit capable of switching between irradiation and non-irradiation of the light by the light irradiation unit to the plant. The switching unit turns off the irradiation by the light irradiation unit within 48 hours from the start of light irradiation to the plant by the light irradiation unit.

[0017] The light irradiation device of (6) can suppress growth disorders and improve the commercial value of plants in a shorter period.

Brief Description of the Drawings

[0018] [Figure 1] It is a block diagram showing the configuration of a plant light irradiation device according to an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0019] <Method for Producing Plants> Hereinafter, a method for producing a plant according to an embodiment of the present invention will be described. The method for producing a plant according to this embodiment includes an irradiation step of irradiating a plant P with light having a predetermined irradiance having a peak in a predetermined wavelength range for a predetermined time from a predetermined time point before the harvest of the plant P (hereinafter, may be described as "irradiation light"). By the above step, the plant P is irradiated with irradiation light to color the leaves etc. of the plant P. For example, by irradiating the plant P with irradiation light, the synthesis of anthocyanin, which is a kind of polyphenol that is an antioxidant in the plant P, is effectively promoted. Anthocyanin is red and colors the leaves etc. of the plant P red. Therefore, the method for producing a plant according to an embodiment of the present invention can color the plant P to be produced, improve the appearance quality, and improve the commercial value of the plant P.

[0020] A plant manufacturing method according to one embodiment of the present invention can improve the commercial value by, for example, irradiating plants that are already of their original color with light to further color them and improve their appearance, or by differentiating them from products of other producers. Furthermore, a plant manufacturing method according to one embodiment of the present invention can improve the commercial value of plants that are manufactured in plant factories or the like and have not achieved their original color due to limited light environments, by coloring them.

[0021] Plants P produced by plant manufacturing methods include leafy vegetables such as lettuce, mizuna, and spinach, as well as sprouts such as radish and pea. Lettuce is a leafy vegetable classified in the Asteraceae family, etc., and is not particularly limited, but examples include leaf lettuce such as sunny lettuce and green leaf lettuce, crisp lettuce, salad greens, and romaine lettuce. Mizuna is a leafy vegetable classified in the Brassicaceae family, etc., and spinach is a leafy vegetable classified in the Amaranthaceae family, Chenopodiaceae subfamily, Spinach genus, etc. Radish is a biennial plant classified in the Brassicaceae family, Raphanus genus. Peas are annual or biennial plants of the Fabaceae family. Sprouts refer to seeds of grains, vegetables, legumes, etc., that are germinated by exposure to light, and the germinated shoots and stems are used as food. Radish sprouts are also called kaiware radish sprouts. Pea sprouts are also called toumyo. The plant P produced by the plant manufacturing method according to this embodiment is leaf lettuce.

[0022] Furthermore, the plant manufacturing method includes known steps for manufacturing plant P. For example, the plant manufacturing method according to this embodiment may include a sowing step, a seedling raising step, a transplanting step, and a harvesting step. In this case, the plant manufacturing method is performed in the order of sowing step, seedling raising step, transplanting step, irradiation step, and harvesting step. In the plant manufacturing method according to this embodiment, the sowing step, seedling raising step, transplanting step, and harvesting step are performed by an operator.

[0023] The sowing process is a known process of sowing seeds in a seedling growing medium such as rock wool or urethane. The seedling raising process is a known process of managing water, nutrient supply, and environmental control so that the sown seeds germinate. The transplanting process is a known process of transplanting seedlings that have germinated in the seedling raising process, and is also called the planting process. The harvesting process is a known process of harvesting plants that have grown to meet a predetermined quality standard. The plant manufacturing method only needs to include an irradiation process, and does not necessarily have to include the above processes, nor may it include processes other than those described above.

[0024] <Irradiation process> Next, the irradiation step of the plant manufacturing method according to one embodiment of the present invention will be described in more detail. The irradiation step is a step of irradiating plant P with light of a predetermined irradiance having a peak in a predetermined wavelength range for a predetermined time, starting from a predetermined point in time before the harvest of plant P, to color plant P. By coloring plant P, the appearance quality can be improved and the commercial value of plant P can be increased. In the following description, the wavelength of the peak in the predetermined wavelength range will be referred to as the peak wavelength.

[0025] The predetermined time at which the irradiation light begins on plant P is preferably 5 to 2 days before harvest. This is because if the irradiation light is applied more than 5 days before harvest using the irradiation process described later, the color of plant P will fade by the time of harvest. The period from germination to harvest of lettuce is, for example, around 4 weeks.

[0026] Furthermore, the peak wavelength is 405nm to 470nm. Preferably, the peak wavelength is 450nm to 470nm. This allows for quick and effective coloring of plant P, further improving its appearance and increasing its commercial value. If the peak wavelength is shorter than 405nm, there is a risk of plant P growth impairment, and if the peak wavelength is longer than 470nm, the color change of plant P is small and the effect of light irradiation is low.

[0027] Furthermore, when using an LED as a light source with a peak in a predetermined wavelength range, if the intensity of the LED's peak wavelength is set to 100, the light in the range with an intensity of 20 or more will be as follows: An LED panel with a peak wavelength of 405 nm will emit light in the wavelength range of 395 nm to 420 nm within the above range. An LED panel with a peak wavelength of 450 nm will emit light in the wavelength range of 430 nm to 465 nm within the above range. An LED panel with a peak wavelength of 470 nm will emit light in the wavelength range of 450 nm to 490 nm within the above range.

[0028] Furthermore, the specified irradiance is 4 mW / cm². 2 That concludes the explanation. The specified irradiance is 5 mW / cm². 2 The above is preferable. This suppresses growth disorders in plant P and improves the commercial value of the plant in a shorter period of time.

[0029] Furthermore, the specified irradiance is 15 mW / cm². 2 The above is preferable. This suppresses growth disorders in plant P and improves the commercial value of the plant in a shorter period of time.

[0030] Furthermore, the specified time is within 48 hours. This suppresses growth disorders in plant P and allows for an improvement in the commercial value of the plant in a shorter period of time.

[0031] Furthermore, the specified time is preferably within 24 hours. This suppresses growth disorders in plant P and allows for an improvement in the commercial value of the plant in a shorter period of time.

[0032] Furthermore, the specified time is preferably 12 hours or less. This allows for an improvement in the commercial value of the plants in a shorter period of time.

[0033] Furthermore, in the irradiation process, the irradiation range of the light applied to plant P may be the entire plant P or only a part of plant P.

[0034] In this case, the irradiation step, in which the irradiation range of the light applied to plant P is limited to a portion of plant P, may include a masking step in which the other parts of plant P are covered with a light-shielding sheet to mask them so that light is not irradiated to the other parts of plant P.

[0035] An irradiation process in which the irradiation range of the light applied to plant P is limited to a portion of plant P may be performed when coloring plants that have not yet achieved their original color to improve their commercial value, or when further coloring plants that have already achieved their original color to enhance their appearance or differentiate them from products of other producers and thereby improve their commercial value.

[0036] For example, in the case of improving the commercial value of a plant that does not have its natural color by coloring it, the irradiation process, in which the irradiation range of the light applied to plant P is limited to a part of plant P, may be performed by irradiating only the part of plant P that does not have its natural color. In this case, in the masking process, the light-blocking sheet may be applied to the part of plant P that has its natural color. This allows for even coloring of plant P, thereby increasing the commercial value of plant P.

[0037] Furthermore, as an example of how to improve the appearance of plants by further coloring their original color, or to differentiate them from other producers' products and enhance their commercial value, an irradiation process in which the irradiation range of the light applied to plant P is limited to a portion of plant P may be performed for the purpose of applying letters, symbols, diagrams, patterns, etc., to plant P through coloring. In this case, during the masking process, a light-blocking sheet or the like in the shape of letters, symbols, diagrams, patterns, etc., may be attached to plant P, or a light-blocking sheet or the like with holes in the shape of letters, symbols, diagrams, patterns, etc., may be attached to plant P. This makes it possible to apply letters, symbols, diagrams, patterns, etc., to plant P through coloring, improving the appearance quality and differentiating it from other products, thereby increasing the commercial value of plant P.

[0038] In this embodiment of the plant manufacturing method, the irradiation range of the light applied to the plant P during the irradiation step is the entire plant P.

[0039] The irradiation process is carried out using, for example, a light irradiation device 1 as shown in Figure 1. The light irradiation device 1, as shown in Figure 1, includes a light irradiation unit 10, a switching unit 11, and a power supply unit 12.

[0040] The light irradiation unit 10 is a device capable of irradiating plants P with irradiation light L having a peak in a predetermined wavelength range. The predetermined wavelength range is 405 to 470 nm.

[0041] The light irradiation unit 10 described above is not particularly limited, but may be, for example, an LED light irradiation device. The LED light irradiation device may be a combination of multiple LED light irradiation devices each capable of irradiating light in the above wavelength range. Alternatively, it may be an LED light irradiation device equipped with multiple LED chips of different wavelengths, capable of irradiating light of different wavelengths in combination or by switching between them.

[0042] The light irradiation unit 10 is configured to allow the irradiance to be changed (controlled). If the light irradiation unit 10 is an LED light irradiation device, the method for controlling the irradiance may be an analog method that controls the input voltage by switching the resistor connected to the LED, or it may be a PMW (Pulse Width Modulation) control method.

[0043] The switching unit 11 can, for example, switch between irradiating the plant P with light from the light irradiation unit 10 and not irradiating it. The switching unit 11 can also switch between irradiating and not irradiating the plant P with light from the light irradiation unit 10 at predetermined timings. Specifically, the switching unit 11 according to this embodiment includes a timer (not shown) and a switch that switches the power supply from the power supply unit 12 to the light irradiation unit 10 on and off based on the timer. The switching unit 11 is, for example, a known time switch. The switching unit 11 according to this embodiment switches the light irradiation by the light irradiation unit 10 to non-irradiation within 48 hours from the start of light irradiation of the plant P by the light irradiation unit 10.

[0044] The power supply unit 12 is configured to supply power to the light irradiation unit 10 via the switching unit 11. The power supply unit 12 may be, for example, a battery.

[0045] The plant manufacturing method according to the embodiment described above provides the following effects. Conventionally, there has been a need to improve the commercial value of manufactured plants by further coloring plants of normal color or by coloring plants that are lighter in color than normal, such as those produced in limited light environments like plant factories. For example, in fully artificial light plant factories, there has been a problem that red lettuce does not color due to the limited light environment.

[0046] In a plant manufacturing method according to one embodiment of the present invention, light having a peak in the wavelength range of 405 nm to 470 nm is used with an irradiance of 4 mW / cm². 2 In summary, by irradiating the plants for a period of 48 hours or less, growth disorders can be suppressed, plant coloration can be enhanced in a shorter period, and the commercial value of the plants can be improved, thus meeting the aforementioned needs for coloration.

[0047] Furthermore, the light irradiation of plants by the plant manufacturing method according to one embodiment of the present invention can also effectively sterilize bacteria, viruses, and other pathogens attached to the plants. This can improve the commercial value of the manufactured plants. [Examples]

[0048] Next, the present invention will be specifically described with reference to examples. The present invention is not limited to the following examples.

[0049] <Plant light irradiation coloration test> The following describes the tests and results for determining the optimal peak wavelength, irradiance, and irradiation time for plant coloration. Leaf lettuce (manufacturer: Nakahara Seed Co., Ltd., variety: Red Oak) was used as the plant for the tests. For leaf lettuce 28 days after the start of the sowing process, the peak wavelength was 405nm~470nm and the irradiance was 4mW / cm². 2 In summary, one leaf lettuce sample was prepared for each of the following examples (1-4), after irradiating with light under varying conditions within a range of 48 hours or less.

[0050] More specifically, in Example 1, light was irradiated on the leaf reflectors under the conditions of a peak wavelength of 405 nm, an irradiance of 5 mW / cm 2 , and an irradiation time of 24 hours. In Example 2, light was irradiated on the leaf reflectors under the conditions of a peak wavelength of 405 nm, an irradiance of 10 mW / cm 2 , and an irradiation time of 48 hours. In Example 3, light was irradiated on the leaf reflectors under the conditions of a peak wavelength of 405 nm, an irradiance of 5 mW / cm 2 , and an irradiation time of 12 hours. In Example 4, light was irradiated on the leaf reflectors under the conditions of a peak wavelength of 450 nm, an irradiance of 10 mW / cm 2 , and an irradiation time of 48 hours. In Example 5, light was irradiated on the leaf reflectors under the conditions of a peak wavelength of 470 nm, an irradiance of 10 mW / cm 2 , and an irradiation time of 48 hours.

[0051] Also, for the leaf reflectors 3 weeks and 2 days after the start of the seeding process, light was irradiated under conditions where the peak wavelength was 405 nm to 470 nm, the irradiance was 4 mW / cm 2 or more, and the irradiation time was outside the range of 48 hours or less, and one leaf reflector irradiated with light while changing the conditions was prepared as a sample after light irradiation for each of Comparative Examples 1 and 2.

[0052] More specifically, in Comparative Example 1, light was irradiated on the leaf reflectors under the conditions of a peak wavelength of 310 nm, an irradiance of 1 mW / cm 2 , and an irradiation time of 12 hours. In Comparative Example 2, light was irradiated on the leaf reflectors under the conditions of a peak wavelength of 525 nm, an irradiance of 5 mW / cm 2 , and an irradiation time of 24 hours.

[0053] For each of the samples of Examples 1 to 4 and the samples of Comparative Examples 1 and 2, measurement values in the L*a*b* color system were obtained using a spectrophotometer (model: CM-700d, manufacturer: Konica Minolta Co., Ltd.).

[0054] For each of the samples from Examples 1-4 and Comparative Examples 1 and 2, one leaf was selected from among the one or more leaves of the plant, and five measurement points were set on the surface of the leaf. Next, for each of the samples from Examples 1-4 and Comparative Examples 1 and 2, measurements were taken three times at each of the five measurement points set above, for both plants that were irradiated with light and plants that were not irradiated with light.

[0055] More specifically, measurements were taken immediately after light irradiation for each of the light-irradiated samples in Examples 1-4 and Comparative Examples 1 and 2, and these measurements were taken for the light-irradiated plants. "Immediately after irradiation" specifically refers to within 1-2 hours after the end of irradiation.

[0056] Furthermore, for Example 1 and Comparative Example 2, measurements were taken on plants before light irradiation, while for Examples 2-5 and Comparative Example 1, measurements were taken on control plants 28 days after the start of the sowing process, thus representing measurements of plants that had not been irradiated with light. The control plants were grown under the same conditions as the irradiated plants until the irradiation process. Next, for each sample from Examples 1-4 and Comparative Examples 1 and 2, the average value of 15 measurements (3 measurements at each of the 5 measurement points) was calculated and used as the measurement result.

[0057] The results are shown in Table 1. The numerical range for the coloring judgment criteria was set as follows: "3" for clearly colored, "2" for sufficiently colored, and "1" for insufficiently colored. <Coloring Evaluation Criteria> 3: The value of a* is 5 or greater, and the value of b* is less than 5. 2: The value of a* is 0 or greater and less than 5, and the value of b* is 5 or greater and less than 20. 1: The value of a* is less than 0, and the value of b* is 20 or greater.

[0058] Additionally, if the leaves wilted or became pale, indicating growth disorders, the rating was "1," and if no growth disorders were observed, the rating was "2."

[0059] [Table 1]

[0060] In Examples 1-5, the coloring rating was 2 or 3, confirming that the plant leaves were colored red. Furthermore, no growth disorders were observed in Examples 1-5. On the other hand, in Comparative Example 1, where the wavelength of light irradiated to the plants was shorter, the coloring rating was 1, confirming that the plant leaves were not colored red. Furthermore, growth disorders were observed in Comparative Example 1. Similarly, in Comparative Example 2, where the wavelength of light irradiated to the plants was longer, the coloring rating was 1, confirming that the plant leaves were not colored red. Furthermore, no growth disorders were observed in Comparative Example 2.

[0061] Examples 1-5 all have a peak wavelength of 405nm-470nm and a predetermined irradiance of 4mW / cm². 2 The above conditions and the specified time were within the range of 48 hours or less. Comparative Examples 1 and 2 were outside the range of the above-mentioned specified wavelength range, specified irradiance, or specified time. Therefore, the peak wavelength of the light irradiated to the plants was 405 nm to 470 nm, and the specified irradiance was 4 mW / cm². 2 In conclusion, it was confirmed that it is preferable for the specified time to be 48 hours or less.

[0062] Furthermore, in Examples 4 and 5, when the value of a* was 5 or greater and the value of b* was less than 5, the plant leaves were more vividly colored red, confirming that the wavelength range of the light irradiated onto the plants is preferably 450nm to 470nm. In Example 3, coloring was achieved even with a predetermined time of 12h, confirming that a predetermined time of 12h or less is more preferable.

[0063] <Other variations> In the plant manufacturing method according to the present embodiment described above, the sowing step, seedling cultivation step, transplanting step, and harvesting step are performed by an operator, but are not limited to this. For example, the plant manufacturing method may be carried out by a plant manufacturing system having the above-described light irradiation unit 10 and configured to automatically perform the sowing step, seedling cultivation step, transplanting step, and harvesting step.

[0064] More specifically, the method for producing plants is carried out by a plant factory equipped with the above-described production system. The production system may include, for example, a cultivation space such as a known greenhouse, known containers such as trays placed inside the cultivation space for planting plants, a known air conditioning unit for adjusting the temperature, humidity and carbon dioxide concentration inside the cultivation space, a known water supply unit for supplying water containing nutrients to the containers, a known measuring unit for measuring various parameters inside the cultivation space, a lighting unit for irradiating plants with light, a known transport unit capable of transporting seeds, seedlings and grown plants, and a control unit for controlling the air conditioning unit, water supply unit, lighting unit and transport unit.

[0065] The lighting unit further includes the light irradiation unit 10 described above. The control unit may be a general-purpose personal computer having a known processor and capable of performing various functions by installing various programs, or it may be a computer built into dedicated hardware. Alternatively, the control unit may be a control circuit incorporating programs for controlling the air conditioning unit, water supply unit, lighting unit, and transport unit.

[0066] Furthermore, the transport unit may include transport robots or conveyors, and the transport robots may perform tasks such as sowing seeds in the seeding process, transplanting in the transplanting process, and harvesting plants from trays in the harvesting process, while the harvested plants are transported to a designated location such as a warehouse by conveyors.

[0067] The control unit has a switching processing unit that can switch between irradiating the plant P with light from the light irradiation unit 10 and not irradiating it. The switching unit 11 can switch the irradiation by the light irradiation unit 10 to non-irradiation at a predetermined timing. For example, the switching processing unit executes a process to turn off the irradiation by the light irradiation unit 10 within 48 hours of the start of light irradiation to the plant P by the light irradiation unit 10.

[0068] Such plant factories may be fully artificial light type plant factories, sunlight-utilizing plant factories, or plant factories that combine both. If the plant factory is a sunlight-utilizing plant factory, the irradiation process may be set up as a process for improving the appearance quality before harvest. This makes it possible to color the plants more reliably, thus contributing to an improvement in the commercial value of the plants produced.

[0069] Furthermore, although the plant manufacturing method according to the above embodiment had one irradiation step, the plant manufacturing method is not limited to this and may have multiple irradiation steps. For example, the plant manufacturing method may include an irradiation step in which the irradiation range of the light applied to the plant P is the entire plant P, and an irradiation step in which the irradiation range of the light applied to the plant P is the part of the leaves of the plant P. Alternatively, it may include an irradiation step in which the irradiation range of the light applied to the plant P is the part of the leaves of the plant P, and an irradiation step in which the irradiation range of the light applied to the plant P is the part of another part of the leaves of the plant P. This makes it possible to apply more complex and sophisticated characters, symbols, figures, patterns, etc. to the plant P through coloring, thereby improving the appearance quality and differentiating it from other products, and thus increasing the commercial value of the plant.

[0070] Furthermore, the plant manufacturing method according to this embodiment may include any steps other than those described above, as long as they do not impair the effects of the present invention. Such any steps are not particularly limited and may include known steps. For example, in addition to the above steps, the method may include a step of irradiating the plant with sunlight, or a step of irradiating the plant with artificial light having any wavelength necessary for plant growth.

[0071] In the above-described embodiment, the switching unit 11 switched between irradiating the plant P with light from the light irradiation unit 10 and not irradiating it by switching the power supply to the light irradiation unit 10 on and off, but this is not limited to this. For example, the switching unit 11 may have a moving mechanism that moves at least one of the light irradiation unit 10 and the plant P, and the switching between irradiating the plant P with light from the light irradiation unit 10 and not irradiating it by moving at least one of the light irradiation unit 10 and the plant P based on a timer.

[0072] The present invention is not limited to the embodiments described above, and any modifications or improvements that can achieve the objectives of the present invention are included within the scope of the present invention. [Explanation of Symbols]

[0073] 1 Light irradiation device 10 Light-irradiating section 11 Switching section P plant

Claims

1. A method for producing plants, The process includes an irradiation step in which, starting from a predetermined point in time prior to the harvest time of the plants, light with a predetermined irradiance having a peak in a predetermined wavelength range is irradiated onto the plants for a predetermined time, and for a predetermined period of time. The specified wavelength range is 405 nm to 470 nm. The specified irradiance is 4 mW / cm². ２ That's all. A method for producing plants, wherein the specified time is 48 hours or less.

2. The method for producing plants according to claim 1, wherein the predetermined wavelength range is 450 nm to 470 nm.

3. The predetermined irradiance is 15 mW / cm². ２ That's all. The method for producing a plant according to claim 1 or 2, wherein the predetermined time is 24 hours or less.

4. The method for producing a plant according to claim 1 or 2, wherein the predetermined time is 12 hours or less.

5. The method for producing a plant according to claim 1 or 2, wherein the plant is lettuce.

6. A light irradiation device for performing the irradiation step in the method for producing a plant according to claim 1 or 2, Light with a peak in the wavelength range of 405 nm to 470 nm is used at 4 mW / cm². ２ The above describes the light irradiation unit that irradiates the plant, It has a switching unit that can switch between irradiating plants with the light from the light irradiation unit and not irradiating them, The switching unit is a light irradiation device that turns off the irradiation by the light irradiation unit within 48 hours of the start of light irradiation to the plant by the light irradiation unit.

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