Begin with the existing load and operating schedule, then compare a proposed layout that meets the warehouse tasks. Energy savings have little value if picking labels or vehicle routes become harder to see.
Survey before selecting replacements
Record fixture quantities, total input power including ballast losses where relevant, operating hours, failures, rack geometry, and access constraints. Identify task areas that the existing layout does not light adequately.
Calculate electricity savings explicitly
Annual kWh saved = (old watts − new watts) × quantity × annual hours ÷ 1,000. Replacing fifty 400W fixtures with 150W units over 3,600 hours gives 45,000 kWh. Multiply by the applicable energy tariff.
Keep maintenance and business assumptions separate
Add documented lamp-change costs, lift hire, labour, and downtime to the maintenance comparison. Do not count an assumed productivity increase as guaranteed cash savings.
Model controls from occupancy
Estimate hours at each light level by aisle or zone. Use measured dimmed watts and avoid counting the same unoccupied hours twice. Confirm sensor coverage and the needs of pedestrian and vehicle routes.
Review the lighting outcome
Compare floor and vertical illuminance, uniformity, glare, color quality, and emergency-lighting interfaces. Check thermal conditions and service access for the driver and controls.
Prepare a full installed-cost budget
Include equipment, wiring, access, labour, disposal, controls, commissioning, and verified rebates. Divide the resulting investment by the annual savings to calculate simple payback. Review longer-term maintenance separately.
Frequently Asked Questions
Does fixture-only payback describe the whole project?
No. Installation, access, controls, disposal, and other costs must be included in the project budget.
Can controls add a fixed percentage of savings?
Use the actual schedule and power at each operating level; there is no universal extra percentage.
