Evaluation of the Effects of Artificial Light on Some Plant Characteristics in the Design and Construction of a Small-scale Plant Factory

It is predicted that the world population will grow to 9.3 billion by 2050 and the urban population will increase by 73%, growing from 3.6 billion to 6.3 billion. This huge population requires abundant food production. A plant factory with artificial light (PFAL) is a closed growing system that is insulated against heat and air. The plants grow on shelves under horizontal artificial lighting. The main goal of PFAL is commercial plant production, but mini PFALs do not have commercial goals and are used to produce plants in small domestic sizes. Plants that are less than 30 cm tall, and grow well in relatively low light conditions and at high planting densities, are suitable for the plant factory. Therefore, plants such as rice, wheat, and potatoes are not suitable for cultivation in a plant factory.The main purpose of this research is to study the proper light quality for growing radish plants. All light treatments had a significant effect on biomass, sugar, and photosynthetic pigments of radish. The results showed that the highest amount of chlorophyll a was 0.964 mg g-1 fresh leaf weight and the lowest amount was 0.318 mg g-1 fresh leaf weight. For chlorophyll b, the highest value was 0.666 mg g-1 wet weight and the lowest value was 0.229 mg g-1 wet weight. The highest and lowest carotenoid contents were 74.75 mg g-1 and 30.6 mg g-1 wet weight, respectively. The highest sugar content was 0.717 μg g-1 dry weight and the lowest was 0.02 μg g-1 dry weight. The highest fresh and dry weights of the plant were 0.27 g and 0.014 g, respectively, while the lowest values recorded were 0.155 g and 0.007 g, respectively. In this study, plant length was also examined, but no significant difference was observed between different light treatments. Based on these findings, it can be concluded that the light composition (R2, G0, B1) was the most suitable light regime for use in the designed system.

The plant studied in this investigation was radish. The place of growth was a vertically built system consisting of four floors, each divided into two sections. A controller was required in each section to regulate parameters such as light time, temperature, and moisture. The controllers were designed using Fritzing software and built with parts and sensors like DHT 11, Arduino UNO based on ATMEGA328P, Relay module Arduino, data logging shield, and driver module RC. A programming platform like Arduino was used to write codes for controlling the remaining parameters. This study tested seven different light treatments, plus sunlight as a control, to investigate their effects on radish growth. The light treatments were developed by adjusting the number of three different lights: red, green, and blue. LEDs were installed after designing and constructing the m-PFAL system. Based on previous research conducted in this field, all LED lights were positioned above the shelves to ensure that the plants received an appropriate amount of light in a vertical orientation. Additionally, light reflectors were installed beside the plants to provide proper lighting for the lower leaves. The experimental design involved a completely randomized design with eight treatments and three replications, and all data analysis was conducted through SAS software. The average comparison was performed using the Duncan method at a probability of 1% and 5%.

The results indicate that the light regime (R2, G0, B1) resulted in the highest amount of chlorophyll "a", which was significantly different from both the control and other treatments. The treatment with the lowest amount of chlorophyll "a" was (R1, G0, B0), which did not differ significantly from the control or (R1, G1, B1). The treatment with the highest amount of chlorophyll "b" was (R2, G0, B1), which differed significantly from the control but not from (R2, G1, B0) or (R1, G0, B2). Using a mixed light treatment of blue and red resulted in higher amounts of photosynthesis pigments, especially when the red light was more prevalent. The treatment with the highest wet weight was (R2, G0, B1), which did not differ significantly from natural light. The treatment with the lowest wet weight was the just red light treatment, which was much lower than the other treatments. The dry weight of the radish was 4-6 percent of its wet weight, and the treatment with the highest dry weight was (R2, G0, B1), which did not differ significantly from (R0, G1, B2) or (R1, G0, B0). The treatment with the highest amount of sugar was (R2, G0, B1), which was significantly higher than other optical regimes used and natural light. Because the production of carbohydrates and sugar is directly related to photosynthesis, it can be concluded that the state of photosynthesis was most proper in the (R2, G0, B1) treatment.

This study investigated the optimal light quality for the healthy and rapid growth of radish plants in a plant factory. LED lights can be an excellent alternative to natural light when there are limitations, such as in greenhouses or multi-floor plantings. The results show that the best light mixture was red and blue lights, with more red light than blue light, while the worst light regime was just red color, which had a negative effect on all parameters.