This white paper discusses how use of photorelays instead of mechanical relays can help design engineers develop systems with lower power consumption, less heat, and longer life. Photorelays are found in an increasing number of devices, especially test and measurement equipment, where even small improvements can have a significant impact on the performance of the end-use product. The paper provides a comparison of mechanical relays versus photorelays, with illustrated examples of each, and discusses the basic functions of photorelays. Various photorelay applications are noted and a list of questions to ask when specifying photorelays is provided.