This paper introduces "I Light U Up", an interactive installation that explores the use of light as input for emergent narrative powered by LLM. Through an installation with light sensors, the audience uses light to communicate with the parallel digital beings, generating a narrative experience that emerges from the interaction. This work serves as a proof-of-concept, supporting a conceptual framework that aims to open new perspectives on the participation of physical data in emergent narrative experiences. It seeks to develop a new dimension in contrast to the text-centric one-way relationship between reader and story by including agency beyond human interactivity.