The power meter will display the measured power level, showing how much light has been lost from the light source to the power meter. They provide the data necessary to quantify signal loss and pinpoint issues that could impact network performance. Here's how they work: A power. How to measure fiber loss with optical power meter and light source? What is optical power? Simply put, optical power is the "brightness" or "intensity" of light. In optical fiber networks, the units of optical power are often expressed in milliwatts (mw) and decibel milliwatts (dbm). The. In order to test “insertion loss” or the direct loss of a fiber optic cable or cable plant using a light source and power meter (LSPM in most international standards or optical loss test set – OLTS – in many articles), one must make an initial measurement to determine the “0 dB” reference point. When calculating the power budget for a new link it is necessary to allow a margin above the minimum light level required by the receiver to allow for the changes that occur during the life of the link, including equipment aging and optical path changes.