A pyrheliometer, such as the CHP1-L, has a window through which sunlight enters. The sunlight, or incident solar short-wave radiation, is directed onto an electronic device called a thermopile. Using the thermoelectric effect, the thermopile acts as a large thermocouple that measures the temperature of a particular body—in this case, the sun. The thermal energy is converted into a voltage output signal that can be recorded by Campbell Scientific data loggers.