This part of IEC 62150 specifies test and measurement procedures for wavelength channel tuning time of tuneable transmitter. It applies to laser transmitters, and the transmitter portion of transceivers. This procedure examines whether the device or module satisfies the appropriate performance specification. The method described in this standard uses optical filters to transfer the transition of the output wavelength to the transition of the optical power. This is because the transient response of the output wavelength before stabilized at steady-state of the target wavelength channel is too fast to measure using a wavelength meter or an optical spectrum analyzer. Reference optical filter sets are described in Annex A.