Encircled energy

Encircled energy (EE) is a concept used primarily in the fields of optics and photonics, particularly in the context of fiber optics and imaging systems. It measures the amount of light energy that is contained within a certain radius around the center of a beam or distribution. Essentially, it provides a way to quantify how much of the emitted light is contained within a defined area, which is critical for evaluating the performance of optical systems.