“Gradient” Experiment in Horticulture Lighting

Abstract

Introduction. A characteristic feature of most experimental research works on horticulture lighting is the need to vary the main parameters of the light regime while maintaining other environmental factors at the same level throughout the experiment. The approach to creating the requisite variety of variations of light regime parameters in one cycle of plant cultivation, considered in this work, may be acceptable for reducing the time of experiments or for exploratory works. The aim of the work is to show the possibility of using the illuminance gradient as a source of variation in its value in experimental works on horticulture lighting. Materials and Methods. We used an LED lamp with a cosine light spatial distribution, placed above the work surface, on which containers with sweet pepper plants were placed. The optical density of the leaves in various spectral ranges was used as a biometric parameter characterizing the response of a plant to the level of illumination. Results. A significant gradient of illumination was observed on the working surface. With the same range of illumination, the number of containers with plants for a given zone is different and is sufficient to test statistical hypotheses. The values of the average illumination by zones provided the range of illumination change by 2.5 times. The standard deviations of illumination by zones were 97–163 lux and were practically no correlated with the values of the average illumination. Discussion and Conclusion. The developed mathematical model of a gradient experiment in horticulture lighting makes it possible to determine the possible number of replicates during the experiment, the average illumination value, the standard deviation, the coefficients of variation and uniformity in each zone of plant placement, based on the lighting and layout parameters of the lighting installation. It has been experimentally found that the use of a luminaire with a cosine light distribution provides an illumination gradient on a horizontal surface, the average values of which in individual zones form a linear illumination scale. Coefficients of illumination variation in individual lighting zones with the parameters set in the example were 3.0–11.5%. The coefficients of variation of the optical density of the leaves of pepper plants grown under the conditions of the gradient experiment on illumination were 6.0–11.6%. The differences in the mean values of the optical density of plant leaves in different zones of gradient illumination are statistically significant. This allows us to recommend the use of the proposed method for searching experiments on horticulture lighting.