Electrical
Lighting retrofit financial payback
Compare measured fixture watts hours maintenance and installed costs.
Your inputs
Complete the fields for your selected method. Zero means intentionally zero, not unknown. Currency selection labels amounts; it does not convert exchange rates.
How this calculation works
savings=sum((old-new W)*count*hours)/1000*rate+maintenance difference. Metered alternative: annual savings = (existing annual kWh - proposed annual kWh) × price + maintenance difference.
Use measured real electrical input kW, not volts × amps or shaft power. Hours describe time at that measured input. All rates are user supplied; no tariff lookup. An integrated kWh reading must not have duty cycle applied again. No discounting, tax credits or capacity sizing. Enter a negative maintenance difference if new upkeep costs more.
What information do I need?
Use records for the same job, equipment or accounting period. Only the fields for your selected entry method are required. An unknown amount is not zero.
Input definitions and where to find them
- How do you know the energy use?: Choose the information you actually have. Only the selected method is required.
- Existing measured fixture input (kW): Measured/rated real input PER existing fixture; identify estimate vs measurement. Used with: Measured input power and operating schedule.
- New measured fixture input (kW): Comparable proposed fixture input, not whole-building consumption. Used with: Measured input power and operating schedule.
- Fixture count (fixtures): Actual count from job, sales, production or service records for fixture count. Future counts are explicit assumptions; do not infer demand. Used with: Measured input power and operating schedule.
- Annual operation (hours/year): Use matching records or a clearly identified owner assumption for annual operation, in the displayed unit and the stated row/period scope. Used with: Measured input power and operating schedule.
- Electricity price per kWh (selected currency): Matching energy/volumetric tariff or bill component for electricity price per kwh, excluding fixed charges or other charges not modeled.
- Annual maintenance savings (negative for higher upkeep) (currency/year): Old annual maintenance expense minus proposed annual maintenance expense; negative if new upkeep costs more.
- Net installed retrofit cost (selected currency): Matching invoice, quote, statement, bookkeeping record or explicit budget amount for net installed retrofit cost. Use the stated period and exclude amounts already counted in another field. Zero means intentionally excluded/not incurred, not unknown.
- Existing lighting annual energy for the compared service (kWh): Use an isolated record or clearly labeled estimate matching this field and period. Do not substitute an unrelated whole-site total. Used with: Metered or separately estimated kWh.
- Proposed lighting annual energy for the same service (kWh): Use an isolated record or clearly labeled estimate matching this field and period. Do not substitute an unrelated whole-site total. Used with: Metered or separately estimated kWh.
Use the Where to find this value controls beside the inputs for available work-it-out helpers. Estimates remain your assumptions; a helper does not verify the source figures.
Worked example
Example amounts use US dollars (USD).
Example answer: Annual net savings is $2,800.00 for the illustrative inputs below.
Example inputs
- How do you know the energy use?: Measured input power and operating schedule
- Existing measured fixture input: 0.10 kW
- New measured fixture input: 0.04 kW
- Fixture count: 100 fixtures
- Annual operation: 3,000.00 hours/year
- Electricity price per kWh: $0.15
- Annual maintenance savings (negative for higher upkeep): 100.00 currency/year
- Net installed retrofit cost: $10,000.00
- Annual net savings
- $2,800.00
- Annual energy savings
- 18,000.00 kWh/year
- Simple payback
- 3.57 years
These illustrative values are not recommended rates or industry averages. Replace every example input with your own figures.
Use the result well
Compare measured fixture watts hours maintenance and installed costs.
Keep inputs on the same scope and time basis. Calculations retain precision internally; displayed values generally round to two decimal places, with extra precision for very small values and whole-unit rounding where required. Economic comparisons describe your supplied assumptions and do not guarantee future results.
This tool provides business arithmetic. It does not approve engineering designs, establish legal or tax treatment, select equipment or certify safe operating conditions.