Abstract Impulse and reflection jointly drive people's behavior. However, the impact of the physical environment, especially light and brightness, on reflective and impulsive behavior and the underlying processes have not been understood. We expected that light and brightness would increase self-awareness and, in turn, lead to a reflective and controlled self-regulation. Five studies confirmed our assumptions. Particularly, participants in a brightly lit room reported a higher public self-awareness than those in a dim room. Moreover, brightness triggers more controlled and reflective forms of self-regulation independent of whether lighting conditions (Study 2) or priming methods (Study 3) were used to manipulate brightness. Finally, two additional studies revealed that brightness facilitates the suppression of desires and socially undesirable impulses which signals high self-control. Overall, these results contribute to the understanding of automatic effects of light and brightness and effortless self-control. Limitations as well as practical implications for lighting design in therapeutical settings and retail spaces and are discussed.