Expressive inquiry is a process of exploration and discovery within an artistic medium that supports both intuitive play and iterative experimentation. Glowdoodle is a system that enables people to paint with light using objects in their environment, see the results as they paint, and share their creations on the web. I describe properties of systems that support expressive inquiry, illustrate them with glowdoodle as an example, and describe diverse examples of glowdoodle creations. Author Keywords Light-painting, expressivity, inquiry ACM Classification Keywords J.5 Arts and Humanities. K.3.1 Computer Uses in Education. General Terms Design, Human Factors