For CAT1 ops (UK) you can have the human observer method, no doubt other authorities will have a similar procedure. This is when a trained observer sits at a specific location in a hut/fire engine at a height of about the average cockpit eg 737. From that point (which is the same each time observations are made), the observer counts the number of runway lights in view. The controller then converts this in a table to a corresponding distance, based on the measured spacing of the runway edge lights. eg 20 lights visible=300 metres. Not all aerodromes will have this conversion table, we no longer have it as we now have full CAT3 facilities and no HOV back up.
LVP's will be put into force based on the prevailing met vis, ours start at 2300meters and ramp up in restrictions of aircraft, vehicles and personel as the met vis drops. This occurs regardless of serviceability of navaids or lighting systems. Eg, 365/24/7 UK ops airfield. No movements scheduled, at night, in fog, aerodrome lights off, LVP procedures will still be in force to protect the airfield.
In the event of total LVP transmissiometer failure we will revert to met vis which must be specifically stated to crew as 'met vis', rather than RVR. Helen49's list above of UK docs is a good starter for ten.