There are so many different solar terms, how about something like:
Solar Irradiance: The total electromagnetic radiation emitted by the sun. Typically 1367 Watts per square meter (W/m2) at the top of the atmosphere, it is reduced to approximately 1000 W/m2 when it reaches the earth’s surface. See Solar Radiation Sensor.
Solar Radiation Sensor: Instrument measuring solar irradiance. Many different types are available, the one most commonly used by weather stations measures Global Radiation - direct and diffuse solar irradiance received by a horizontal surface.