The RVR depends on the light intensity of the runway edge and center line lights as far as i know.
The system measures visibility, background luminance, and runway light intensity to determine the distance a pilot should be able to see down the runway.
https://www.faa.gov/about/office_org...vices/lsg/rvr/
Not sure if it's the same for Eurocontrol?
Maybe the question is aimed at this fact?