Seven dimensions of light in regulating plant growth

Abstract

Light is one of the most important factors for plant growth and development, regulating plants' photosynthesis, morphogenesis, metabolism, gene expression, and other physiological responses. The characteristics of light in influencing plant growth are generally attributed to three dimensions, i.e., the intensity, quality, and duration of light. The real situation could, however, be more complicated and may not be fully realized and revealed in the natural environment. As plants are moved into artificially controlled environment agriculture, more dimensions of light must be considered. Based on our observations and experiments, a model of seven dimensions of light in regulating plant growth is proposed, which includes intensity, quality, pattern, uniformity, direction, polarization, and coherence. Preliminary experiments have also been conducted to demonstrate these characteristics. Light intensity, which is quantified as µmol photons m-2 s-1, is a measure of the photosynthetic photon flux density (PPFD) in the range of photosynthetically active radiation (PAR). Light quality refers to the composition and distribution of the illumination's spectrum. The pattern of illumination, much more complicated than the duration of illumination, is defined as the possible combinations of illumination modes. The uniformity of illumination includes that of light intensity and quality. Direction of light will cause phototropic response of plants. Polarization is the property of light with all light waves oscillating in the same transverse direction and the influence of the polarized light on plants is still unknown. Coherence of light can be intuitively viewed as the length a light wave can extend. It is a unique property of the laser that the ordinary light generally does not have. Comparison of the effects of coherent and non-coherent lights on plants has not yet been conducted.