Nabesei Co Ltd, a company specializing in electronic parts, exhibited plants grown under LED lights in three different colors at an exhibition that took place from April 15 to 17, 2009, in Tokyo.
Plants of the same size were continuously irradiated with light from a lighting device equipped with 630nm red LEDs, a device with 430nm blue LEDs and a pink-colored LED light composed of half red LEDs and half blue LEDs.
After three weeks of irradiation, the growths of the plants were compared with one another. As a result, it was discovered that the pink LED light most effectively promotes the growth of plants, the company said.
According to Nabesei, plants do not need all wavelengths in the visible light range for their growth, but they absorb light with certain wavelengths to grow. For example, when they perform photosynthesis or come into bloom, red light around a wavelength of 660nm, which is the absorption peak for chlorophyll, promotes the growth. Meanwhile, when the plants form flower buds, blue light around a wavelength of 450nm promotes the growth.
When comparing the plants under the three kinds of light, those under the red LED light grew slower than others and were smaller as a whole. The plants under the blue LED light had fewer leaves and were spindly on the whole. On the other hand, the plants under the pink LED light had larger leaves and had generally grown in a more balanced way.
However, the wavelength ranges that affect the growth of plants are slightly different depending on the plant type. Therefore, field tests to evaluate the irradiation time and other issues should be conducted at agricultural experiment stations from now on, Nabesei said.
In line with the ban on the sale of incandescent bulbs in 2012, the company plans to focus on the application of LEDs to illumination equipment for growing chrysanthemums. The irradiation of red LED light can delay the formation of buds on chrysanthemums. Moreover, LED light keeps bugs away because the LED emission spectrum is deviated from the bugs' visibility curve.
In addition, Nabesei exhibited a completely watertight LED light in a tank. The product is also available in a bendable type, which is suitable for interior lighting and plant cultivation requiring water sprinkling, the company said.