PLANT GROWTH AND THE AERIAL ENVIRONMENT

Abstract

SummaryThe apparent efficiency of conversion of incident light energy (ɛapp/i) by whole plants of Im‐patiens parviflora in a range of natural and artificial light climates has been calculated from growth analysis data. It was found that it ranged from 1.3% in full natural daylight to 7.5% in extreme shade (metal shades transmitting 7% daylight). The corresponding figures for real efficiency, i.e. corrected for respiration losses, ɛtrue/i were 3.0% and 12.5% respectively. In the growth cabinets with light intensities roughly equivalent to 7—15% daylight a combination of two Blue/six De Luxe Warm White fluorescent tubes gave values of ɛapp/i averaging 7.4% for plants grown at 15°C, 5.9% for those at 10°C and 6.5% at 20°C. Four Daylight/four De Luxe Warm White averaged 5.8% at 20°C and Red (magnesium arsenate) at 20°C was highest with 7.7%. Blue tubes gave 6.0% apparent efficiency with plants at 15°C. In all the cabinet experiments and in the extreme shade in natural daylight the plants were small with leaves scarcely overlapping. In more open, natural daylight sites some self‐shading would have occurred. When the efficiency was expressed on a quantum basis, rather than on total energy, and correction for temperature differences applied, there was little difference between Blue, Blue‐white and Red, with Daylight‐white somewhat lower. On the basis of assimilation for a given number of lamps the combinations two Blue/six De Luxe Warm White and four Daylight/four De Luxe Warm White were the best.