Insertion loss, also known as attenuation, is the loss of optical power that occurs when light passes through a fiber optic connector. It is caused by factors such as misalignment, air gaps, and imperfections in the connector components. To be able to judge whether a fiber optic cable plant is good, one does a insertion loss test with a light source and power meter and compares that to an estimate of what is a reasonable loss for that cable plant. 10GBASE-LRM) from running on a network. A high return loss is a good thing and usually results in low insertion loss. The presence of these optical connectors makes it possible to switch conveniently from one device or system to another.