Luminosity is the total amount of electromagnetic energy radiated by a source per unit time, typically measured in units like watts. It represents the intrinsic power output of a light source and is a fundamental concept used across physics and astrophysics. Luminosity is distinct from apparent brightness, which is how intensely a source appears to an observer, as the latter is diminished by the inverse square law of distance. In the context of stellar objects, luminosity is crucial for determining the object's physical processes and evolutionary stage, as it quantifies the energy being generated, often through processes like nuclear fusion. Measuring luminosity accurately requires precise measurements of the energy flux received and careful geometric corrections based on the separation between the source and the observer.