The Visual Fault Locator (VFL) Pen has a visible red light source centered on 650nm. A fiber visual fault locator pen VFL for fiber optic installation, fault finding, continuity checking, polarity checking, verifying a signal path, and identifying a fiber. For single mode, multimode and plastic fibers, this is a low price fiber laser light tester that complies with the latest. DESIGNED FOR TECHNICIANS – This VFL rechargeable fiber optic visual fault locator is built for fiber technicians to quickly identify breaks, bends, and faults in fiber optic cables and patch cords.