The VFL source launches overfilled light that will surround the core of the bare fiber and extend into and through the cladding, flooding the inside of the connector body. This is normal and does not necessarily mean the fiber is damaged. The amount of light can vary by fiber and connector type. To visually check the quality of a termination, verify the intensity and quality of light exiting the opposite end of the cable under test. If the light is weak or non-existent, a damaged connector or fiber may exist.
Sourced through Scoop.it from: www.leviton.com