luminous flux maintenance factor, <of an electric light source>
lumen maintenance factor, <of an electric light source>
ratio of the luminous flux of an electric light source at a given time in its operational life to its initial luminous flux, the electric light source being operated under specified conditions
Note 1 to entry: In IEC standards, “lumen maintenance” is also commonly used with the same meaning.
Note 2 to entry: The luminous flux maintenance factor has unit one and is usually expressed in per cent.