IEC 61300-3-53:2020 RLV contains both the official IEC International Standard and its Redline version. The Redline version is available in English only and provides you with a quick and easy way to compare all the changes between the official IEC Standard and its previous edition.

IEC 61300-3-53:2020 defines the encircled angular flux measurement of multimode waveguide light sources, in which most of the transverse modes are excited. The term "waveguide" is understood to include both channel waveguides and optical fibres but not slab waveguides. The applicable fibre types are the followings:
- A1 specified in IEC 60793-2-10;
- A3 specified in IEC 60793-2-30;
- A4 specified in IEC 60793-2-40.
This second edition cancels and replaces the first edition in 2015. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
- the scope of the applicable wave guides, and graded index multimode optical wave guide and fibre have been included;
- the structure of 5.3 has been rearranged;
- Annex C and Annex D have been added.