Impressions from townscape in daytime and in nighttime are usually quite different even if they are of the same place. This paper explores the environmental factors that affect to these impressions in order to find the knowledge for designing or controlling townscapes. In the previous research, the author proposed the three factors contributing to visual comfort in the environment(1). As an well known example, Waldram explores, in his classic paper, the mechanism of interior lighting and in a flow chart defines three aspects of interior lighting: Adaptation, Revealing of Form and Texture, and Emphasis(2). However, the factors contributing to visual comfort in the environment are thought to be more extensive. In order to construct a comprehensive explanation for visual comfort, three factors contributing to visual comfort are proposed by the author. The first factor is the physiological and psychological condition of the visual system. This includes not only adaptation state but also visual stress, visual fatigue, concentration or mood, etc. which are correlated with the other two factors below. The second factor is the visibility for object discrimination related to the nature of the visual task, safety issues and security issues (feeling secure).