Glossary for detailled explanation - take your pick:
Effective Operating Distance Sr
The effective operating distance Sr is measured at a single proximity switch with determined conditions and amounts 0,9 Sn ≤ Sr ≤ 1,1 Sn.
The electromagnetic compatibility (EMC) indicates the desired condition that technical devices do not influence themselves reciprocally through unintended electrical or electromagnetic effects. The European EMC directives for sensors - EN 55011 and EN 61000 - describe all parameters of interference immunities and transmissions with their limit value. In their own house standards, most of the sensor producers implement these parameters with remarkable higher requirements.
Extraneous Light Limit
Extraneous light is the light that comes from external light sources and strikes the light receiver. The measured point is the intensity of illumination on the light ingress surface. Generally, the devices are insensitive against ambient light thanks to the use of modulated light. Nevertheless, there is an upper limit for the intensity of external radiation that is called extraneous light. It is defined for sunlight (unmodulated light) and halogen light (with double power frequency modulated light). For illuminances that exceed the respective extraneous light limit an exact running of the devices cannot be guaranteed anymore.