Plant factory is expected as one of the manufacturing methods in agriculture. It produces vegetables in a full artificial environmental system which is comprised of LED light, air-conditioner, hydroponics, various sensors and controllers etc. The prospects of plant factory are discussed by reviewing recent progress.

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In this paper we propose two types of scanning laser illumination systems. Red (R), green (G), and blue (B) laser diodes (LD) were combined as a scanning type light source for plant cultivation in plant factories. Our results showed that the plants were sensitive to 20-ns-pulse width LD light, and photosynthesis was done with high-speed modulated optical signals. We performed plant growth experiments with another scanning type of laser illumination system combined with an image processing camera. The growth states of the plants were detected by the image recognition function. We also confirmed the selective photosynthesis promotions of plants by spatially selective laser illumination.

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Microalgae are drawing keen attention as alternative sources of sustainable energy or functional materials. Photobioreactors are suitable for the production of high-value-added materials by microalgae because those systems can minimize such uncertain factors as weather fluctuations that negatively affect production. On the other hand, the utilization of artificial light sources in the photobioreactors increase cost. Recently, light-emitting diodes (LEDs) and laser diodes (LDs) are expected to be effective light sources for plant production in closed systems: “plant factories”. Even though LEDs and LDs can be adopted for photobioreactors, relatively few studies have compared the effects of LED or LD irradiation on the growth and productivity of microalgae with plants. This review summarizes the recent trials of the utilization of LEDs or LDs for algal culture.

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Optical sensing, being non-destructively and rapid, has been used in agriculture, forestry, livestock, and fisheries industries for the last two decades to aid in the production and quality control of food and biological materials. In particular, machine vision and photo-optical devices have been widely deployed in fruit grading systems, becoming an integral part of these systems. Moreover, much wider applications of optical sensing to biological materials and their properties in more diversified settings is expected in the near future. In this paper, innovative optical sensing technologies utilizing the spectral reflectance and surface structural properties of primary industry products that are currently being developed are introduced. Such sensing systems have the potential to ameliorate the trade-off between food production and environmental conservation imperatives.

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Expectations for energy source shift from fossil fuels to renewable biofuels continue to grow. Renewable bioproducts are also being developed for sustainable societies. Microalgae are ideal biomass producers because their excellent characteristics surpass land plants; they grow much faster, can be cultivated at unused hydrospheres, and accumulate a large quantity of such valuable compounds as lipids and carotenoids. Many studies have been carried out to commercialize biomass production using microalgae. To achieve sufficient cost-effectiveness, more useful microalgal strains must be obtained and their cultivation conditions must be optimized. The recent development of various light-emitting diodes (LEDs) has accelerated the understanding of the light effects of specific wavelengths on microalgae. This review introduces the recent progress in the production of biofuels and carotenoids using microalgae as well as discoveries about microalgal responses to light revealed by LEDs.

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Plant growth is significantly affected by such environmental parameters as light, water, atmosphericcomposition and pressure, temperature, humidity, and nutrients. A higher growth rate for plants might be attained by modulating such environmental parameters, which also affect the plant’s physiological responses and quality and quantity of metabolites. In this study, we designed and fabricated an environment-controlled chamber called a plant growing chamber (PGC) to offer a variety of growth conditions for plants. Our PGC modulates temperature, humidity, light intensity, light wavelength, air pressure, etc. Using it, we focused on atmospheric pressure to examine its effects on plant growth. We used an aquatic plant, Spirodela polyrrhiza, as a test plant and evaluated its growth rate under elevatedatmospheric pressure varying from 0.1 to 0.4 MPa. The effects of elevated pressure on the growth rate were analyzed by an imaging processor. The growth rate increased up to 1.25 times under 0.2 MPa, suggesting that photosynthesis can be improved under conditions of elevated pressure.

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Current status and future prospect of red broad area laser diodes (BA-LDs) are reviewed with emphasis on output power and photo conversion efficiency. The LDs have been developed mainly for lighting and display application, therefore the lasing wavelength is around 638 nm. Artificial plant cultivation with lighting devices has been gathered attentions because it would be another application of the visible LDs and LEDs. For the photosynthesis, most energy effective wavelength is 660-670 nm, 20-30 nm longer than that for lighting/display. 660 nm BA-LDs with the same structure as the 638 nm one except the active layer showed better output power characteristics, indicating the 660 nm LDs would be suitable light source for plant factories.

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The effect of elevated ambient pressure on the CO2 exchange rate of aseptic medium-cultured plants (Arabidopsis thaliana) is experimentally investigated. The total pressure and the partial pressure of CO2 are varied under the constant temperature of 24°C. As a result, the rate of gross photosynthesis increases significantly and the rate of dark respiration slightly increases with the increase of CO2 partial pressure proportional to the total pressure increase. On the contrary, when the CO2 partial pressure is kept constant with the increased total pressure, the rate of net photosynthesis decreases and the rate of dark respiration increases. The results suggest the possibility of gaining oxidation tolerance under a high pressure environment. This tendency can be effective to achieve high yield production system of biomass.

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Since laser headlamps are expected to increase distance visibility during night-time driving, we investigated distance visibility in dynamic conditions and legibility under reflected light on road signs due to high luminous intensity. We evaluated discomfort glare and the appearance of road-sign colors due to characteristic spectral distribution of laser headlamps. For their performance of high luminous intensity, our results assumed an obstacle (20×20 cm and 10% reflectance) on the road and indicated that its visibility was approximately 1.5 times greater than high-beam lamps using mass-produced LEDs. We also identified the required upper limit luminance value that ensures road-sign legibility. Regarding laser headlamp performance of spectral distribution characteristics, discomfort glare was not affected. Laser headlamps also tend to clarify and sharpen road-sign colors more than other light sources. Our results suggest that laser headlamps can contribute to night-time traffic safety by improving distance visibility without focusing on characteristic spectral distribution.

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