It used to be dark at night and light during the day, which is far from the case now. Light pollution and excessive use of light, especially in cities, negatively affects the health of not only humans, but also insects, animals and plants... The main topic of the documentary film Sleep Thieves is the issue of light pollution and the effect of light on sleep. We are accompanied through the film by two main experts, a chronobiologist, who mainly contributes knowledge about sleep and the effect of light on sleep, and a lighting engineer, who introduces us to wrong and right lighting. The next part is dedicated to e.g. the explanation of circadian rhythms, hormones associated with sleep, the importance of alternating light and dark, the effect of light on sleep, the issue of light pollution and correct and incorrect lighting both outdoors and indoors.