Under natural conditions, daylight duration varies considerably around the globe and depends on season and latitude. High latitudes have the polar day period, when the Sun does not set below the horizon. On the Kola Peninsula, e.g., it last about 50 days, from the end of May to mid-July. Moreover, at these latitudes the period when civil twilight lasts all night (known as the white night) starts almost a month before the beginning of the polar day and continues for another month after it. During this time, the Sun does not sink low below the horizon and there is no darkness. As a result, plants in this region are exposed to continuous lighting for more than 3 months. The article summarizes and presents materials collected from archives, scientific reports and publications of researchers from the Polar-Alpine Botanical Garden (N67°38’) and other institutions who conducted research in the Arctic, studying the phenomenology and mechanisms of adaptation of crops and wild plants to the extreme light conditions of the High North.