The relationship is: 1mw=0dbm, that is to say, 2mw=3dbm, 10*lgmw is the dbm value. In addition to measuring optical power, optical power meters can also be used with light sources to measure optical. Ensure your power meter is calibrated for the correct wavelength. Input Value: 1 dBm Conversion Reference: Note: For power levels in dBm, positive values represent power > 1 mW, negative values represent power < 1 mW. Optical power is a measure of the rate at which light energy is emitted. While optical power meters are the primary power measurement instrument, optical loss test sets (OLTSs) and optical time domain reflectometers (OTDRs) also measure power in testing loss. TIA standard test FOTP-95 covers the measurement of optical power.