1、Fiber Optic Test Tool: This VFL pen is specially designed for optical cables and lines maintenance, to locate defects on cables, visually search for fiber breaks. 2、Non Contact Type: The VFL pen adopts non contact connection method, no loss for optical fiber and transmitter end face, output power is not affected by voltage fluctuation. 3、USB Rechargeable: This visual fault locator is also a portable power bank, built in li ion battery, can charge for your smart devices through USB cable. 4、Lighting Function: This fiber optic cable tester comes with 4 leds, features small flashlight function, with high brightness, easy to use in dark environment. 5、Small and Portable: The fiber optic tester is small size, light weight, energy saving, portable and could stably output power, is a good tool for optical fiber testing.