IEC 61280-1-3:2010 provides definitions and measure procedures for several wavelength and spectral width properties of an optical spectrum associated with a fibre optic communication subsystem, an optical transmitter, or other light sources used in the operation or test of communication subsystems. The measurement is done for the purpose of system construction and/or maintenance. In the case of communication subsystem signals, the optical transmitter is typically under modulation. NOTE - Different properties may be appropriate to different spectral types, such as continuous spectra characteristic of light-emitting diodes (LEDs), and multilongitudinal-mode (MLM), multitransverse-mode (MTM) and single-longitudinal mode (SLM) spectra, characteristic of laser diodes (LDs). This second edition cancels and replaces the first edition published in 1998. This edition constitutes a technical revision with changes reflecting new laser technology and includes a second method modified for state of the art instrumentation. Keywords: definitions and measure procedures for several wavelength and spectral width properties of an optical spectrum, optical transmitter, test of communication subsystems