Connect a visible light source (such as a fiber optic flashlight) to one end of the cable. Take an LED flashlight and shine the light into one of the fiber. The three standard methods for testing fiber optic cabling are a visible light source, power meter and light source, and optical time domain reflectometer (OTDR). Because fiber optic transmissions work in the infrared portion. FiberLert is a fast, accurate, and safe non-contact solution for verifying fiber activity, polarity, and connectivity. First, aim your smartphone camera at the connector; most phone sensors detect the otherwise invisible 85.