This thesis studies the notion of responsiveness in architectural design. It tries to make a framework for understanding the act of response in architectural body. Focusing on Light as a contextual force, it studies the way light affects the built environment and architectural body, in order to introduce a light responsive system. This light responsive system will be used to design a mediatheque in the city of Geneva. Studying a multidisciplinary thematic between architecture and building physics this study is interested primarily to the architec- tural qualities of space. In parallel, it also considers the perfor- mance and comfort metrics. Two case studies in the third chapter are based on in-situation mappings and radiation analysis. The radiation calculations are done by Diva light simulator (based on Radiance software). The case studies are ordered considering the scale that they study; Their outcomes are used for the same-scale factors in a light responsive system proposed in the fifth chapter. In the chapter four the city and the program are reduced to quanti- tative design parameters to be used in the light responsive system. The term responsiveness is widely used in different disciplines. In the first chapter after a survey on these usages in different con- texts such as biology, social science and art, this study summarises a definition of responsiveness to found a framework for a light responsive system. Focusing on climate responsive systems and particularly light, in the second chapter, different approaches to use light as a form- giver for architecture are introduced. This chapter is devoted to the 6 questions such as :What are the spatial qualities of light and how lighting concerns affect architecture and design process? For introducing a light responsive system in the third chapter two case studies in two different scales are carried out. One studying the relation of light and the public space focusing on the urban promenades and the other one studying the relationship of interior light zones and the geometry; It searches for a lighting grammar in the interior space. Chapter four is devoted to analysis of the contextual and organisa- tional design problem parameters. As this study will be used later to solve a real design problem, in this chapter the objective is to propose simplified-well-behaving models of the urban context : the city of Geneva and the program: Mediatheque for the light respon- sive system. Chapter five proposes the characteristics of a light responsive sys- tem, considering all the design problem parameters.