IEC 61315:2019 is available as IEC 61315:2019 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.IEC 61315:2019 is applicable to instruments measuring radiant power emitted from sources that are typical for the fibre-optic communications industry. These sources include laser diodes, light emitting diodes (LEDs) and fibre-type sources. Both divergent and collimated radiations are covered. This document defines the calibration of power meters to be performed by calibration laboratories or by power meter manufacturers. This third edition cancels and replaces the second edition published in 2005. It constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) update of terms and definitions; b) update of 5.1, including Table 1 (new type of source); c) update of Annex A; d) addition of Annex B on dB conversion. Keywords: Fibre-optic power meters