Visual performance has been a topic of study for many years. For a variety of reasons, it has been difficult to develop a completely satisfactory model of visual performance. Recently the connection has been made between reaction time experiments and realistic studies of visual performance. In this report an extensive set of reaction time data are presented which were collected over a large range of stimulus conditions relevant to interior and exterior lighting applications. An empirical model of visual performance was developed from these data. It forms the next logical step in the development of an application tool for lighting practitioners.