## 1 Introduction  
The negative anthropogenic impact on the Earth biosphere results in such serious climatic changes as the growth of atmosphere and ocean annual average temperatures, the formation of greenhouse gases in large amounts, the ozone layer depletion and consequently rises the UV radiation intensity. The impacts studying of the UV radiation shows that it affects the ecosystems' biodiversity negatively and results in migrations and/or extinction of large species of animals and plants [1; 2; 3; 4]. The ozone layer depletion and the inevitable rise of the levels of UV-A, UV-B and UV-C radiation affects negatively the organisms' physiology, increases the frequency of cancer diseases in animals and inhibits plants' vegetation and productivity [5; 6]. In many publications devoted to this problem, the influence was studied of the light spectral composition on the plants' growth and development; and the mechanisms of plant protection from the UV radiation were described including pigment synthesis and accumulation processes, the features of accumulation of the secondary metabolites and the functions of those substances [7; 8; 9; 10]. It is well-known that in small doses, UV radiation can stimulate metabolic processes, thereby inducing a strengthening effect in plants [11]. When the plants are exposed to small doses of UV radiation, some insignificant changes occur in their morphological parameters, such as the plants' fresh and dry mass, the average leaf area and the plant height. That is why the plants' mechanisms of adaptation and photoproduction are studied mainly by the following metabolic parameters: the concentration of pigments and micro- and macro-nutrients, the content of nitrates, sugars and acids in the leaves, and the fruits of the plants. Mostly, the studies on this topic are carried out in an artificial environment, where conditions are created enabling the control of UV radiation exposure doses and duration. Many papers are devoted to studying of the influence of the sulfhydryl compounds (thiourea and dithiotreitol) and other active additives on the flavonoids concentration and accumulation rates as far as the flavonoids reduce significantly the stress caused by UV radiation [12; 13; 14; 15]. First of all, the results of the studies of UV radiation's effect on plants are important for enterprises growing agricultural products in an artificial climate. After all, the addition of UV spectrum rays to the main illumination will allow obtaining green and vegetable crops with the specified characteristics in terms of the contents of acids, sugars, anthocyanins and antioxidants and thereby increasing the nutritional value and taste qualities of the products. Pigment concentration measurement by the chemical method takes quite a long time, limiting the ability to analyze a large number of samples, so sub-sampling is used instead. Modern digital technologies allow estimating the pigment concentration in a leaf by the analysis of its reflection spectra (analysis of the hyperspectral images) [16; 17; 18; 19]. Based on such data, plant stress states can be determined [20; 21; 22] as well as the content of substances of interest, for example, shikimic acid [23]. Such measurements are carried out in a non-invasive way and require much less labor. However, in cases of the analysis of the purple-leaved crop, difficulties are encountered with assessment of the chlorophyll concentration. Analysis of the published research on the UV radiation influences on green crops has revealed that only a few works are devoted to the effects of UV-A and UV-C on the purple-leaved crops. Additionally, the non-invasive methods are developed quite poorly for the pigment concentration measuring [24; 25]. Taking the above into account, it was decided to study the photo-protective reactions of the red-leaved green crops under exposure to UV-A, UV-B, and UV-C radiation in addition to the main light.