This paper addresses two problems: “What are the appropriate methods for evaluating information systems?” and “How do we measure the impact of ambient information systems?” Inspired by concepts in the social and behavioral science, we categorize the evaluation of ambient displays into two styles: intrusive and nonintrusive. Furthermore, two case studies are used to illustrate these two evaluation styles. An intrusive evaluation of MoneyColor shows that the correct disruptive order for ambient displays is animation, color, area and shape. A non-intrusive evaluation of Fisherman proposes an effectiveness measurement, and reveals three issues to improve the effectiveness of ambient displays. Keywords Ambient displays, intrusive evaluation, information visualization, human computer interaction