Creating learning environments that integrate arts, sciences, and computing in education can improve learning in these disciplines. In particular, transdisciplinary integrations of these disciplines can lead to expansive alterations or dissolutions of epistemological, ideological, and methodological boundaries. We wish to support teachers in the creation of transdisciplinary learning environments that draw on art, science, and computing. We developed a classroom project genre, Luminous Science, that was designed to bridge disciplinary materialities, epistemologies, and representations through students' construction of computationally-rich representations of physical phenomena. We present a study of a multidisciplinary group of teachers co-designing a Luminous Science unit for their classrooms using sculptural lanterns with programmable media for both investigations and expressions of classroom gardens. We present a framework for examining what disciplinary understandings teachers drew on, how these ideas were utilized, and why they were brought together. We found teachers engaged in richly metarepresentational discussions wherein they applied values, epistemic criteria, and practices from all three constituent fields of study in their design work. We show how teachers developed units that simultaneously overlapped and diverged due to the pressures of navigating disciplinary and school structural challenges. Qualitative analysis of teacher discourse reveals how teachers liberated disciplinary boundaries, actively and critically explored synergies and tensions in disciplinary integration, and traversed goals that focused on both disciplinary improvement and holistic learning. Our study sheds light on how we can both study teachers who are designing for disciplinary integration and support them through professional development opportunities to encourage more transdisciplinary interactions that can expand what it means to do or teach art, science, and computing.