In the context of recurring heat waves, an adaptation strategy is growing worldwide to maintain the economic productivity: shifting working hours to the night. This avoids workers' exposure to high temperatures, limits the use of air conditioning, and facilitates collaborations between workers located in different continents. In this article, we warn of the existence of risks to the safety and health of people working at night during heat waves. We highlight deleterious effects on vision and on the regulation of the circadian biological clock affecting sleep, well-being, and responsible for physical and mental health outcomes. Our article proposes mitigation measures involving specific adaptations of working conditions and schedules. In addition, urban spaces and buildings should be adapted in a way that nighttime activities can be carried out safely during heat waves. Light exposure plays a big part in this adaptation: lighting installations should be designed and operated very differently in these specific conditions. At home, sleeping during the day could become unavoidable, which poses serious problems when the environment is noisy, hot, and bright. The adaptation strategy should focus on the bedroom to promote sleep: it should be kept cool, quiet, and as dark as possible with the help of windows equipped with light-proof shutters.