The weight of LIGHT: Alvaro Siza’s triangular prism in the library of FAUP, Portugal

The word “Light” has two common meanings, one is illuminant (referred as LIGHT in this paper), and the other is something of little weight (referred as light in this paper). The “Weight of LIGHT” is an art of creating visual illusion applied in architecture design, which is a new understanding about LIGHT as well as the relationship between LIGHT and users. This study develops the concept of “the weight of LIGHT” through analyzing of the contradictions between the two concepts, and looking into several specific LIGHT designs to discuss the mediums through which LIGHT acts on buildings and occupants. The author then focuses on the library of Faculty of Architecture of Porto University (FAUP) designed by Alvaro Siza and argues that by providing a unique “Triangular Prism” inside the building, Siza conveyed “the weight of LIGHT” indirectly through the container (size, shape, material) and the relationship between the container and the surroundings (roof, wall, ceiling).