| Summary: | In this study, we investigated the effects of additional ultraviolet radiation (UV) on the main growth fluorescent lamp light on pigment content and essential oil accumulation in sweet basil (<i>Ocimum basilicum</i> L.). Three different UV light sources from light-emitting diodes and discharge lamps, which emit UV in the UV-A (315–400 nm), UV-B (280–315 nm) and UV-C (100–280 nm) ranges, were tested for basil plant growing. The plants, growing under additional UV-A and UV-B from mercury lamps, on the 60th growing day were higher than control plants by 90% and 53%, respectively. The fresh leaf mass of the UV-A irradiated basil plants was 2.4-fold higher than the control plant mass. The dry mass/fresh mass ratio of the UV-A and UV-B irradiated plants was higher by 45% and 35% in comparison to the control plants. Leaf area was increased by 40% and 20%, respectively. UV-C affected the anthocyanin content most strongly, they increased by 50%, whereas only by 27% and 0% under UV-A and UV-B. Any UV addition did not affect the essential oil total contents but altered the essential oil compositions. UV-A and UV-B increased the linalool proportion from 10% to 20%, and to 25%, respectively, in contrast to UV-C, which reduced it to 3%. UV-C induced the eugenol methyl ether accumulation (17%) and inhibited plant growth. Moreover, UV increased the proportion of α-guaiene, β-cubebene and α-bulnesene and decreased the proportion of sabinene and fenchone. Thus, we concluded that UV (except UV-C) used jointly with main light with PPFD 120 ± 10 μmol photons·m<sup>−2</sup>·s<sup>−1</sup> for sweet basil cultivation may be justified to stimulate basil growth and optimize the essential oil accumulation.
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