Development of Plant Factory Using Fluorescent Lamps: Reduction of Lighting Power Consumption by Close Illumination

We developed a pilot scale plant of a plant factory equipped with fluorescent lamps to closely illuminate plants, and painted the inside white to effectively use the reflected light (close illumination method). In this paper, the light-energy saving effect of the close illumination method on lettuce cultivation was investigated experimentally and theoretically by employing this pilot scale system. (1) The mean light intensity on the cultivation panel (area of 12 m2) was as high as 650 μE/m2/s (45 klx), when 42 fluorescent lamps (110 w) were placed 30 cm above the cultivation panel and illuminated. The coefficient of utilization (U), which indicates the light utilization efficiency in the growth room, was about 1. 7. The measured value of U agreed well with the value calculated by Moon's equation, and was nearly 3 times higher than high pressure sodium lamps placed about 100 cm above the cultivation panel. (2) One hundred and twenty stocks of lettuce/day (75 g fresh weight/plant) were produced in a cultivation area of 24 m2 (12 m2/bed × 2 layers), 29 days from the germination. Also, the fresh weight of seedlings weighing about 0.2 g increased by about 40 times in 9 days. (3) The lighting power consumption and total power consumption for the production of lettuce (75 g/plant) was about 1.1 kwh/plant and 2. 5 kwh/plant, respectively. Thus, the lighting power consumption was about half that of conventional high pressure sodium lamps. On the other hand, the lighting power consumption for the production of seedlings weighing about 10 g/plant and 0.2 g/plant was about 0.3 kwh/plant and 0.06 kwh/plant, respectively. (4) Utilizing close illumination with fluorescent lamps, 3 layers of planting beds were vertically stacked for seedling cultivation, and 2 layers for growth. Thus, a compact cultivation system was achieved using the close illumination method.