Many students in introductory science courses at both the secondary and tertiary levels learn science as a miscellaneous collection of facts, concepts, and equations that must be memorized to pass examinations. One way to show students that they actually can "do" science is to have them use an observable event to generate a relationship that can be used as a predictive tool. In this article, the author discusses how teachers can have students investigate the inverse-square law. Through a simple experiment using readily available and inexpensive apparatus, students learn about the law by demonstrating the quantitative relationship between light intensity and distance. (Contains 3 figures.)