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Networking Fundamentals · Intermediate

Visual Fault Locator (VFL)

A pen-shaped device that shines visible red laser light into a fiber so breaks, tight bends and bad connectors glow visibly.

Definition

VFLs are useful for short runs, patch cords and identifying fibers, typically up to a few kilometers. Never look directly into a fiber carrying invisible infrared light.

Example

Red light leaking from a kinked patch cord reveals the fault.

Exam tip

VFL is a quick visual check; it does not measure loss.

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