A common feature of many digital games is that they are played in a simulated 3D environment, a game world. Simulated illumination is the lighting designed into a game world. This thesis explores the influence of simulated illumination in digital games upon the emotion and behavior of the player. It does so within the context of game aesthetics, building upon an understanding of games as having the potential to evoke an aesthetic experience that is deeply absorbing, is experienced as whole and coherent, evokes intense feelings or emotions, and engages a sense of “make believe.” A full account of how simulated illumination affects people is gained by tracing the contributions from media practice and real-space lighting, as well as taking into account the unique possibilities of interactive media. Based upon the rich set of lighting references and possibilities that are present in digital games, this thesis offers a taxonomy of influence of simulated illumination, which is organized such that it moves from progressively simple patterns and mechanisms that work without much player awareness, towards progressively greater complexity and consciousness of light qualities.The study of simulated illumination is complex, and best conducted within a transdisciplinary framework that includes three perspectives: empirical emotion research, investigation of the lighting attitudes of creative practitioners, and formal analysis of games with the aim of articulating their use qualities related to simulated illumination. The way in which a “triangulation” study could be structured is presented through the results of the two-year Shadowplay project, with specific reference to the effects of warm (reddish) and cool (bluish) simulated illumination upon the experience of gameplay. We learned that exposure to warm light in a game prototype created more positive affect and led to better performance, and uncovered an interesting correspondence in the lighting attitudes of creative practitioners, regarding the relatively attractive versus repulsive qualities of warm and cool illumination in game environments. The (sometimes inconsistent) results of the Shadowplay project are discussed with reference to the conception of “pleasure” as it is developed within phenomenological philosophy and hedonic psychology. Considered this way, simulated illumination can create “eliciting conditions” for more complex sequences of emotions that constitute game pleasures. Within a game, we respond emotionally to exposure to qualities of simulated illumination, based upon what we bring with us into the game (whether based upon tastes, attitudes related to genre, memories or more “hard-wired” responses to light). At the same time, we implicitly learn the significance of the illumination that we encounter through our activity in the game. This means that there is no simple mapping of illumination quality to emotional outcome. Rather, designers need to learn to manipulate the unique potentials of simulated illumination in relation to the other elements of the gameplay experience.