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Background. Recently, to control plants development and to better understanding the plants response to various light sources, largely due to advances in industry light-emitting diodes (LEDs), it is necessary to understand the photochemical processes carrying out under impact of different factors. At the number of works authors have established a significant impact of different intensities and light spectrum on the growth and morphometric characteristics of plants. Plants growth and development depends on photochemical activity among many other factors. The range of works were carried out to assess the influence of light intensity and spectrum on the photochemical characteristics of various crops, including rocket. However, the insufficient number of works and the lack of assessment of the photosystem operating efficiency of industrially important crops grown under high light intensities became the rationale for our work. Purpose. The main purposes of our work was to confirm the significant impact of various light treatments on the photochemical activity of plants and determine the optimal light treatments for the operating efficiency of the PSII photosystem using an industrially important crop. Materials and methods. To reach work purposes, we measured key parameters of chlorophyll fluorescence and assessed the rocket photosynthetic activity. Plants were cultivated in phytoboxes under LEDs with three monochromatic light spectra (red (R), green (G), blue (B)). Each light spectrum treatment includes six intensities (100, 300, 500, 700, 1000, and 1400 µmol/m-2 s-1). Warm white light with an intensity of 200 µmol/m-2 s-1 was used as the control. The chlorophyll fluorescence measurements in rocket leaves were conducted on the 28th day after sowing with Hansatech FMS 1+ pulsed fluorimeter in one day at phytoboxes. Fluorescence of actinic light-adapted leaves (Fs) and maximum fluorescence of actinic light-adapted leaves (Fm’) were measured. Statistical analysis was performed using the Microsoft Office Excel (USA). Results. The results obtained established that the rocket photochemical apparatus responses differently to a stressful state caused by a high irradiation level under the certain spectrum. The operating efficiency of PSII for each monochromatic light treatment and specific intensity varies. Thus, it suggests different plants responses to stress caused by the particular combination of growth conditions. The level of electron transfer has the direct linear correlation with the PPFD increase. Conclusion. Thus, irradiation intensity in the range from 100 to 500 µmol/m-2 s-1 is the most optimal for the operating efficiency of the PSII photosystem under any light spectra used in our work. The use of monochromatic blue light for rocket is probably undesirable, as it is likely caused protective mechanisms disruption of fluorescence quenching.