For an objective assessment of behavior in neurobiological studies, the “open field” test is often used, it is an adequate method for quantifying the behavioral characteristics needed to identify individual characteristics of animals. This method objectively characterizes emotionality, research behavior, as well as behavioral features in conditions of moderate stress.  In the natural habitat of rats, mainly night activity is observed. Light is an environmental factor affecting the research behavior of both wild and domesticated animals. Usually in the laboratory, white rats are kept in a mode of illumination 12 hours light and 12 hours darkness or in natural light conditions.  The problem of the influence of the detention conditions is often not taken into account in the analysis of behavioral characteristics, in connection with this the purpose of the study was to investigate the influence of illumination on the behavior of rats in the “open field”. The experiments were carried out on male white rats weighing 130 ± 10 g. The rats were divided into two groups of 10 animals. Control group - natural light (illumination ≈ 20 lux). The experimental group - darkening for 7 days (illumination ≈ 2 lux). The behavior of the rats of the control and experimental groups was examined in the “open field” (illumination ≈ 80 lux), the following behavioral characteristics were assessed: vegetative response, horizontal motor activity, vertical locomotor activity, grooming related to displaced behavior.  Comparing the results of the control and experimental groups, it should be noted that rats that stayed for 7 days in conditions of reduced illumination become more emotional, which is manifested in an increase in vegetative reactions and grooming, characteristic for the state of emotional stress, in addition, their locomotor activity sharply decreases. This is evidenced by a sharp decline in horizontal and vertical motor activity, which characterizes the orientation and research behavior. Analysis of the obtained data allow us to conclude that light deprivation for 7 days has a generalized effect and increases the stress-reactivity of rats; Reducing the illumination of the habitat suppresses the manifestations of the research behavior of rats in the “open field”.