It is very important that a pilot fully understand the minimum requirements in order to be "legal" to land from an instrument approach. What has not been said here is:

Visibility is CONTROLLING and must be equal to or above the authorized landing minimum (governed by Ops Specs etc). IF RVR is reported, it has a higher priority than prevailing visibility and is controlling. (Reported RVR trumps visibility every time)

A reported ceiling (i.e. 200, 250 etc) IS NOT CONTROLLING. If Tower advises ceiling 100 and visibility 1/2 mile, if you are shooting a "normal" CAT I ILS (200 & 1/2) then you are legal to shoot the approach.

In Summary, Ceiling is advisory and VISIBILITY is controlling.

Hope this helps!