OWL fiber optic visual fault locators (VFL) are specially designed to couple a maximum of optical energy into multimode and singlemode optical fibers by using a bright red fiber optic laser.  Breaks, microbends, and other anomalies in optical fibers and connectors cause the intense bright red laser light to escape, thus revealing the presence of a fault.

In addition to visual fault location, OWL VFL can be used as a visual optical fiber identifier.  A visual fiber optic identifier eliminates much of the guesswork during testing by identifying the fiber under test.