Mirai Co Ltd built a vegetable plant that uses only LED lamps for supplying light to grow vegetables in Tagajo City, Miyagi Prefecture, Japan.
It is one of the largest all-LED vegetable plants in the world, the company said. At the plant, it is possible to ship 10,000 heads of lettuce per day.
The building of the vegetable plant used to be part of Sony Sendai Technology Center. Mirai has been conducting verification tests for the development of technologies to control cultivation environments and LED lamps suited for vegetable plants in collaboration with General Electric Japan Ltd as one of the projects funded by Tohoku Bureau of Economy, Trade and Industry. Kajima Corp designed and constructed the entire plant and developed a rack for cultivation.
The most distinguished feature of the plant is the LED lamp that General Electric Japan developed for vegetable plants. It evenly disperses LED light, which has a high directivity. Also, the company introduced a technology to apply lights with different wavelengths in accordance with the growth stage of a vegetable.
For example, at an early stage when a vegetable has just been taken out of a room that grows seedlings, a whitish light generated by combining white and red LEDs is applied to the vegetable to facilitate photosynthesis. Then, a reddish light generated by using red and blue LEDs is applied to facilitate the growth of leaves and roots. When the harvest time approaches, the whitish light is applied again to facilitate photosynthesis.
As a result, power consumption was reduced by 40% while yield per unit area increased by 50%, compared with a vegetable plant using only fluorescent lamps. However, Mirai did not disclose the specific wavelengths of the LED lamps, saying that they are its know-how.
Also, to make use of the building whose ceiling is as high as 7m, a 6m-high 15-level rack was developed. While lighting equipment, nutrient solution circulation system, etc were integrated and made highly functional, costs were reduced by, for example, using general-purpose rack materials.
In addition, Kajima Corp introduced technologies to simulate cultivation environments. The technologies were developed based on the know-how built up by constructing vegetable plants. The position of the air-conditioning and other equipment was decided by repeatedly performing calculations to make sure that the multiple levels of the rack do not cause large differences in temperature, air flow, illuminance, etc.