Light-Controlled Plant Cultivation System in Japan - Development of a Vegetable Factory Using LEDs as a Light Source for Plants

The idea of planned production of vegetables using a factory has been suggested for many years as a technology extending the application of greenhouse horticulture. However, it has not been a very long time since the world's first systematized vegetable factory appeared for commercial production. Development of vegetable factories in Japan was started in the second half of the 1970s, and subsequently many companies like manufacturers of electrical appliances, food producers, and electric power companies and so on began technology development work in this field. Currently, Japan is one of the most active countries in the world in technology development in this field. If the goals of vegetable production in factory are fully planned production and cultivation management, then in terms of lighting, a fully controlled system using artificial light only is superior to a sunlight/artificial light combined system. However, one issue with artificial lighting is the running cost, especially the cost of electricity for lighting and air conditioning. Estimates based on high pressure sodium lamps and fluorescent light indicate that lighting accounts for approximately 40% of the total running cost for vegetable production. Therefore, it is essential that electricity costs for lighting and air conditioning should be lowered in order to develop a practical vegetable factory that uses fully controlled artificial light. Light-emitting diodes (LEDs) are featured with a narrow light-emitting spectrum, enabling them to focus light on plants with just the required wavelength of light. In addition, it is possible to completely reduce thermal infrared radiation. This means the light source can be positioned very close to plants. Furthermore, the lack of infrared radiation is an important cost advantage in terms of managing the temperature of a closed vegetable cultivation system. This article will overview the history and technology development of the light-controlled plant cultivation system in Japan, especially comparing the performance and characteristics of lighting devices for vegetable cultivation.