The importance of nonvisible wavelengths for the study of astronomy suggests that student understanding of nonvisible light is an important consideration in astronomy classrooms. Questionnaires, interviews, and panel discussions were used to investigate 6-12 student and teacher conceptions of ultraviolet (UV) and infrared (IR). Alternative conceptions about the characteristics and human sensual perception of visible light, UV and IR, were observed in many students and in a subset of teachers. Instruction involving electromagnetic radiation should first address preexisting alternative conceptions, and conceptual questionnaires such as the one used here can help teachers to identify student ideas prior to instruction. (Contains 2 tables and 2 figures.)