While most power meters have ranges of +3 to β50 dBm, most sources are in the range of 0 to β10 dBm for lasers and β10 to β20 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 βdB. β Optical loss is measured in βdBβ which is a relative measurement, while absolute optical power is measured in βdBm,β. 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. When power is measured in linear units (mW, uW or nW), dB is calculated on a log scale using this formula: Thus 1 mW = 0 dBm, 1 uW = -30 dBm, 1 nW = -60 dBm and two equal powers compared are 0dB (eg. Above 0 dBm is considered "high power", and specially adapted units may measure up to nearly + 30 dBm ( 1 Watt).
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