In this study, 15 evaluation questions about light were developed and presented to 30 middle school students, and then the theory of knowledge space was used to analyze the status of the middle school students`` knowledge about light. Not only was the state of the students`` knowledge about light intended to be measured by schematizing the knowledge hierarchy obtained; the data obtained were also intended to be used as basic materials to improve the teaching methods used. To achieve the purpose of this study, the evaluation results, the individual knowledge state, and the hierarchy of questions were analyzed. As a result, different knowledge structures were found in the individuals and groups, and it was determined that individuals and groups should be diagnosed differently. In addition, the implication that there is a connection between each question and the individual knowledge state was drawn.