Readings are in decibel-milliwatts (dBm), higher means stronger light, lower or negative means weaker like for example, -10 dBm is usually good while -25 dBm could show a bad connection or damaged fiber. Fiber Optic Measurement Units: "dB" and "dBm" Whenever tests are performed on fiber optic networks, the results are displayed on a power meter, OLTS or OTDR readout in units of “dB. ” Optical loss is measured in “dB” which is a relative measurement, while absolute optical power is measured in “dBm,”. Engineers use the decibel-milliwatt (dBm) to quantify the absolute power level of the optical signal on a logarithmic scale, referencing it to one milliwatt (mW). However, it is important to note that the optimal dBm level can vary based on the specific fiber optic system and network requirements.