A fluorescent-to-LED lighting retrofit in offices is typically analysed under IPMVP Option A: meter the kW of a representative sample of the new luminaires, estimate hours of use from a field audit or BMS occupancy data, and compare against the rated draw of the legacy lamps.

Option A (retrofit isolation with key parameter measurement) fits this ECM because the lighting load is well characterised and stable, so only one variable really needs to be measured. The key parameter is the post-retrofit LED kW, captured on a stratified sample (around 10 percent of the fleet covering each luminaire type and zone). Hours of use are estimated rather than measured continuously, drawing on BMS occupancy logs, scheduling tables or a typical-week audit, and savings are then computed as (kW_fluo - kW_LED) * hours * days. Continuous monitoring (Option B) would be over-engineering for tens of thousands of luminaires in commercial buildings.

Document the sampling plan and the assumed hours of use in the M&V Plan before the retrofit starts: arguing about operating hours after the fact, with no agreed baseline, is the number one cause of disputed lighting savings.