Inventory the existing and proposed system
Record fixture quantities, lamp and ballast or driver power, operating schedules, space use, and condition. Compare complete system input wattage rather than only a lamp label. The proposed design should meet appropriate illumination, glare, color, controls, and safety requirements. DOE’s luminaire purchasing guidance emphasizes performance and life-cycle considerations. A lower-power fixture that leaves a work area underlit is not an equivalent efficiency improvement. Include emergency lighting and applicable code requirements in qualified design review.
Calculate energy and control effects
For a simple constant-power estimate, multiply fixture quantity by wattage reduction divided by 1,000 and annual operating hours. Occupancy or daylight controls can reduce hours, but avoid counting the same time reduction twice. Demand benefit depends on whether lighting is on during the relevant billed peak and whether a ratchet limits the saving. Reduced internal heat can affect cooling and heating differently. Model those interactions where material instead of assuming every site receives an identical extra HVAC benefit.
Compare cost over the useful life
Installed cost includes fixtures, labor, controls, access equipment, disposal, and commissioning where applicable. Verify rebate eligibility and preapproval before counting an incentive. Maintenance savings depend on actual failure rates, labor, replacement access, and product quality. Simple payback ignores financing and cash flows after recovery; a life-cycle comparison can be more suitable for a major project. Preserve warranty terms and make sure staff know how to operate and maintain the new controls.
Hypothetical lighting calculation
One hundred fixtures reduce input power from 100 W to 40 W and operate 3,000 hours annually. The modeled reduction is 100 × 60 ÷ 1,000 × 3,000 = 18,000 kWh. At an illustrative avoidable energy price of $0.10/kWh, energy benefit is $1,800 annually. A $9,000 installed cost gives five-year simple payback before maintenance, incentives, or interactions. This is a hypothetical screen, not a product recommendation or expected result for every commercial building.
Practical review checklist
- Measure complete existing fixture input power and confirm equivalent useful lighting performance.
- Verify actual hours and controls assumptions, keeping kWh and demand effects separate.
- Include installation, commissioning, maintenance, access, warranty, and confirmed incentive conditions.
- Inspect the finished lighting and verify consumption and control operation after installation.
Questions & answers
Can I estimate savings from watts alone?
Watts identify power reduction; annual kWh also requires operating hours and control behavior.
Do LEDs always eliminate maintenance costs?
No. Drivers, controls, fixtures, and access still create maintenance needs; use realistic product and operating assumptions.
Sources & scope
Primary references reviewed October 15, 2026. These sources support the stated concepts; actual tariffs, program rules and signed agreements govern the account. Decision examples and operational worksheets are original educational analysis.
- DOE FEMP: Energy-efficient luminaires
Product selection, lighting performance, and life-cycle purchasing. - DOE FEMP: Evaluating your utility rate options
Demand, ratchets, time-of-use rates, coincident peaks, and standby charges. - DOE FEMP: Light commercial heating and cooling
Equipment sizing, installation, economizers, and control requirements.