The basic process is straightforward: turn the meter on, set it to the correct wavelength, clean your connectors, plug in, and read the display. But getting accurate, meaningful results depends on understanding a few key details about wavelength settings, reference levels, and. An optical power meter measures the strength of light traveling through a fiber optic cable, giving you a reading in dBm (decibels relative to one milliwatt). We'll give you the basic information you need and provide some printable references. Links to videos and more. Step-by-step fiber optic cable testing guide using an optical power meter and VFL. Learn to measure loss, detect breaks, and certify links. Consistent procedures ensure accuracy.