Compare the complete lighting product
DOE distinguishes LED source efficacy from luminaire efficacy. The fixture, power supply and other design choices influence the electricity consumed by the finished product. [1] Editorial purchasing procedure: request complete-product input power and light output for the proposed configuration. Keep drive current, optical option and controls consistent in comparisons. A component claim should remain a component claim. Ask the designer whether the proposed output and distribution meet the same visual task before describing a lower wattage as an equivalent replacement.
Power and time make the energy ledger
Illustrative arithmetic: 100 luminaires drawing 40 W each create a 4 kW connected load. At 3,000 equivalent full-power hours, that load uses 12,000 kWh. A comparison of 25 W at the same hours gives 7,500 kWh, a calculated difference of 4,500 kWh. These are invented inputs, not a product guarantee. The simple calculation assumes constant power during the stated hours and excludes standby consumption. Actual dimming schedules should use measured power at each operating state; a command percentage alone is not an energy measurement.
Controls change the operating profile
FEMP identifies occupancy sensing, task tuning and daylight-responsive dimming as strategies to consider for further savings where appropriate. Its acquisition requirements apply to identified federal purchasing categories, rather than setting a universal lighting design target. [2] Editorial analysis: put each control state into the energy ledger with its duration. Avoid adding independent advertised saving percentages, because strategies can act on the same operating hours. Compare the resulting combined profile with the baseline and document the assumed occupancy and daylight behavior.
Decide how savings will be verified
DOE's Uniform Methods Project offers distinct protocols for commercial and industrial lighting and for lighting controls evaluation, supporting consistent savings assessment. [3] Editorial project preparation: agree on the baseline inventory, meter boundaries, sampling approach and observation period before changing the installation. Preserve enough information to distinguish a technology improvement from reduced occupancy or a changed schedule. If the measured period is unusual, record that limitation explicitly. A transparent result explains both the measurement and the conditions under which it was obtained.
Make the business case reproducible
Editorial financial worksheet: show installation cost, electricity assumptions, controls setup, inspection, replacements, service access and any incentive separately. Calculate simple payback only after stating what is included; do not present it as a complete life-cycle analysis. An assumed energy tariff should include its date and identify whether demand charges are modeled. Archive the original inventory and revised schedule so another reviewer can reproduce the calculation. Report visual performance alongside energy performance: a saving is more meaningful when the installation still delivers the intended service.