Assessment of Lighting Uniformity as a Factor of Energy Efficiency in Greenhouse Horticulture

Abstract

Introduction. Greenhouse lighting systems are an integral part of the system for growing plants in cultivation facilities with an artificial microclimate. The uniformity of light distribution over the growing area is important to increase energy efficiency and improve plant quality, among other requirements. The aim of the work is to consider the mathematical apparatus for describing the distribution of light over the surface and to justify the choice of ways to characterize the degree of lighting uniformity. Materials and Methods. The basic concepts of the subject area such as lighting, lighting body, horizontal lighting curve, luminous intensity curve are considered in terms of theoretical photometry. To assess the energy and ecological friendliness of the greenhouse horticulture, the lighting efficiency factor was used. Various methods for determining the average lighting value are presented. The formulas for the uniformity coefficients are presented. Experimental verification was carried out on a horizontal plane simulating a surface for growing plants. A luminary with a round-symmetric light distribution was used. Results. It has been found that the lighting values calculated by the proposed method at various points of the illuminated surface correspond to the experimentally obtained values. It has been shown that the coefficient taking into account the pattern of lighting distribution over all points of the surface carries a lot of information about the uniformity. A frequency graph for the lighting distribution value has been constructed and its practical applicability has been substantiated. The relationship between the lighting efficiency and uniformity of the generated lighting has been revealed. With reduced suspension height of the luminary, it is possible to increase significantly the lighting efficiency factor, however, the lighting uniformity deteriorates sharply. Discussion and Conclusion. There is proposed a method for assessing the energy efficiency by the lighting efficiency factor, which determines the proportion of the useful lighting falling on the surface in the total lighting generated by light sources. It is suggested that this indicator can characterize the ecological quality of photoculture, since it has been established its relationship with the uniformity of the created lighting, the impact of which on photoculture is described in the literature.