standard test conditions (STC)

Conditions under which a module is typically tested in a laboratory: (1) Irradiance intensity of 1000 W/square meter (0.645 watts per square inch), AM1.5 solar reference spectrum, and (3) a cell (module) temperature of 25 °C, plus or minus 2 °C (77 °F, plus or minus 3.6 °F).