A new dedicated luminometer PLUME, based on registering Cherenkov light produced in quartz material by particles coming upstream from the collision region, is designed for the LHCb operation in Run 3. It will deliver online luminosity and number of visible interactions per bunch crossing measurements for the luminosity levelling, also per bunch, measure the radiation background induced by the accelerator or poor quality vacuum, produce alarms, measure the level of the ghost charges, cross-check the LHC filling scheme in real time, contribute to the centrality determination in the fixed-target programme, and provide accurate offline luminosity determination.