While most power meters have ranges of +3 to –50 dBm, most sources are in the range of 0 to –10 dBm for lasers and –10 to –20 dBm for LEDs. 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,”. Because optical power levels range widely, the decibel-milliwatt (dBm) is used instead of a linear unit like the milliwatt (mW). The dBm scale is logarithmic, meaning a small numerical change represents a large change in actual light power. They are typically adaptable to various connectors, including SC, ST, FC, SMA, LC, MU, and more.