This is a renovation project of the Playfair library. It will no longer be a normal library, but a multi-functional "third space". First of all, it re-imagines the features and functions of the library. Recognizing the functional transformation of Playfair, it proposes a multi-purpose space with additional facilities to facilitate community and multi-disciplinary discussion. It also proposes a space configuration that can bring multiple functions and make library space and other components Parts, such as common workspace, gallery and performance space. In principle, the use of light creates a typology of architecture, which blurs the boundaries between comprehensive public institutions such as libraries and learning centres and fixed spaces such as squares and cafes. Through the device intervention, promotes human participation and creates a dynamic public sphere. Therefore, the project aims to study the role of light in abandoned public spaces and institutions by adding devices.