Experiments were performed to clarify the relations between plant growth and light intensity.
1. A comparison was made of plant growth under Plant-Lux and R12-Y2-G4-B12. The spectral distribution of R12-Y2-G4-B12 in the visible wavelength region was similar to that of Plant-Lux. Both light sources were adjusted to provide equal energy as measured with a Moll-Gorczynski solarimeter (named Solarimeter-Intensity), but the wet and dry weights of tomato and cucumber plants under Plant-Lux were greater than those under R12-Y2-G4-B12. The energy of the spectral band in the 400-700nm range (named Effective-Intensity) and total radiation (named Total-Intensity) were then measured for both light sources. Both light sources had the same Solarimeter-Intensity, but Effective-Intensity and Total-Intensity were different. Effective-Intensity of Plant-Lux is nearly twice as high as that of R12-Y2-G4-B12, therefore it is thought that the wet and dry weights were higher under Plant-Lux than under R12-Y2-G4-B12.
2. It became clear from Experiment 1 that even if the Solarimeter-Intensity of both Plant-Lux and R12-Y2-G4-B12 was made equal, the wet and dry weights and the height of both tomato and cucumber did not show the same growth. Therefore, tomato and cucumber were irradiated by four lights; R 30, Plant-Lux+farred, Plant-Lux and R12-Y2-G4-B12. Each light source was maintained at the same Effective-Intensity and nearly the same Total-Intensity, except for the case of Plant-Lux. No significant difference was detected in the dry weight and in plant height under Plant-Lux+farred, Plant-Lux and R12-Y2-G4-B12, but strong effects on both weight and height of plants were observed under R 30.
3. The wavelength width of red light in the experiments was narrower than that of other workers used. Red lights of different wavelength widths were irradiated on both tomato and cucumber plants. The growth of tomato plants under the wide wavelength lights of red region was smaller than that under the narrow wavelength light.