||Artificial light, despite its widespread and valuable use, has been associated withdeterioration of health and well-being, including altered circadian timing and sleep disturbances,particularly in nocturnal exposure. Recent findings from our lab reveal significant sleep andsleep electroencephalogram (EEG) changes owing to three months exposure to dim-light-at-night(DLAN). Aiming to further explore the detrimental effects of DLAN exposure, in the present study,we continuously recorded sleep EEG and the electromyogram for baseline 24-h and following 6-h sleepdeprivation in a varied DLAN duration scheme. C57BL/6J mice were exposed to a 12:12 h light:DLANcycle (75lux:5lux) vs. a 12:12 h light:dark cycle (75lux:0lux) for one day, one week, and one month.Our results show that sleep was already affected by a mere day of DLAN exposure with additionalcomplications emerging with increasing DLAN exposure duration, such as the gradual delay ofthe daily 24-h vigilance state rhythms. We conducted detrended fluctuation analysis (DFA) on thelocomotor activity data following 1-month and 3-month DLAN exposure, and a significantly lesshealthy rest-activity pattern, based on the decreased alpha values, was found in both conditionscompared to the control light-dark. Taking into account the behavioral, sleep and the sleep EEGparameters, our data suggest that DLAN exposure, even in the shortest duration, induces deleteriouseffects; nevertheless, potential compensatory mechanisms render the organism partly adjustable andable to cope. We think that, for this reason, our data do not always depict linear divergence amonggroups, as compared with control conditions. Chronic DLAN exposure impacts the sleep regulatorysystem, but also brain integrity, diminishing its adaptability and reactivity, especially apparent in thesleep EEG alterations and particular low alpha values following DFA.