Plant Growth Characteristics under All Direction Illumination

I. Effects of Light Intensity, CO₂ Concentration and Air Temperature on Growth Rate of Lettuce

Abstract

The optimization of illumination conditions with fluorescent lamps was studied to collect basic data for the reduction of light power consumption in a plant factory.
1. A cylindrical growth chamber with higher light reception was developed which houses on its periphery a vertically arranged array of fluorescent lamps.
2. A semi-logarithmic plot of the fresh weight of lettuce (Lactuca sativaL. cv. Okayama saradana) against cultural time gave a straight line with a correlation coefficient of 0.99.
3. The lettuce grew acceleratedly at a CO₂concentration of 350 ppm under a light intensity of 250 μE·m^-2·s^-1: the fresh weight was doubled in two days.
4. The effect of CO₂concentration on the growth rate was hardly appreciable over a range of 350-4, 000 ppm at high light intensity of 250μE·m^-2·s^-1but remarkable at a low light intensity of 85μE·m^-2·s^-1.
5. The growth rate seemed to be saturated at light intensity of 85μE·m^-2·s^-1which is about a quarter of the saturation light intensity observed with the conventional, downward illumination. The optimum temperature under illumination from all direction was higher than that of the downward illumination.
6. The ratio of fresh weight of leaves to that of roots was higher under lower light intensity.