ST816B 650nm visual fault locator or vfl has the function of fiber identification and faults locator of SM or MM fiber, it is a helpful assistant to dead zone of OTDR, visual fault locator is also a basic maintenance tool for fiber network, LAN, ATM fiber system and telecom network system.VFL Visual Fault Locator is a testing equipment in Fiber Optic field. It is also called Visible Laser/Light Source, Visible Red Light Source and etc. No matter what it is called, the point is the light it launched and transmitted in a fiber is visible by human eyes. Normally the central wavelength is 650nm, so the light can be seen as a bunch of red light. ST816B is small size, easy to field test, high quality pen type visual fault locator. It’s easy to operate identification of fiber break, bend, you can protect the fiber layer.