| Scenario | Fixtures | Current W | Upgrade W | Hours | Rate/kWh | Year 1 savings |
|---|---|---|---|---|---|---|
| Pathway lights | 12 | 20 | 6 | 6 | $0.18 | $71.80 |
| Garden accents | 18 | 35 | 8 | 5 | $0.22 | $250.47 |
| Mixed zones | 24 | 15 | 5 | 7 | $0.14 | $140.16 |
- Annual energy (kWh) = Fixtures × Watts × Hours/night × Days/year ÷ 1000
- Annual energy cost = Annual kWh × Rate per kWh
- Annual total cost = Energy cost + Maintenance cost
- Annual savings = Current total cost − Upgrade total cost
- Net upgrade cost = Fixtures × (Fixture cost + Install cost) − Rebates
- Discounted savings (Year y) = Savings ÷ (1 + Discount rate)y
- NPV = −Net upgrade cost + Σ Discounted savings
- Enter how many landscape fixtures you operate and how long they run nightly.
- Fill in current and upgrade wattage to reflect your bulb or fixture choices.
- Add your electricity rate and expected annual escalation if applicable.
- Estimate yearly maintenance for both setups, then add upgrade costs and rebates.
- Choose analysis years and a discount rate to evaluate long-term value.
- Press Calculate and review savings, payback, and the year-by-year table.
- Use the CSV or PDF buttons to export your results.
Energy
Landscape lighting energy depends on fixture count, wattage, and runtime. A system with 12 fixtures at 20 watts running 6 hours for 365 days uses about 525.6 kWh annually. Switching to 6‑watt LEDs drops usage to about 157.7 kWh, cutting consumption by roughly 70 percent. Your results table separates current versus upgrade kWh so you can verify assumptions quickly against bills.
Costs
Cost is modeled as electricity plus maintenance. Electricity cost equals annual kWh multiplied by your local rate, then escalated each year if you expect price growth. Maintenance captures bulb replacements, labor, transformer checks, and occasional fixture swaps. If current maintenance is 45 per year and upgrade maintenance is 10, the maintenance gap alone contributes 35 per year of savings before energy is considered.
Payback
Simple payback answers how many years of savings recover the net upgrade cost after rebates. If net upgrade cost is 335 and year‑one savings are 72, payback is near year 5, depending on escalation. ROI in this calculator is a simple ratio using total undiscounted savings over the analysis period. Use it to compare lighting upgrades to other home efficiency projects.
Value
NPV converts future savings into today’s money using your chosen discount rate. A positive NPV suggests the upgrade beats your required return, while a negative NPV suggests the capital could be used better elsewhere. Discounting matters when you compare long analysis horizons, higher discount rates, or uncertain maintenance assumptions. The year‑by‑year table shows both raw savings and discounted savings to make this transparent.
Checklist
To use the calculator well, start with reliable inputs: count active fixtures, confirm wattage from labels, and estimate average nightly runtime by season. Then enter a realistic electricity rate per kWh from your bill, include any rebates, and set analysis years to match expected fixture life. Finally, review the chart to see trends in costs, annual savings, and cumulative savings over time. Validate outputs using last year's kWh and costs.
1) Should I enter bulb wattage or fixture wattage?
Use the wattage that actually draws power for each light point. If you are swapping whole fixtures, use fixture wattage. For retrofit lamps, use lamp wattage and ensure driver or transformer losses are reflected in maintenance or costs.
2) What maintenance costs should I include?
Include bulb replacements, labor time, fixture repairs, transformer checks, and occasional cable or connector fixes. If you hire service, use the annual service cost. If you do it yourself, estimate parts plus a reasonable value for your time.
3) Why does my payback differ from my neighbor’s?
Payback is driven by electricity rate, runtime, wattage reduction, and upgrade cost after rebates. A higher local rate or longer nightly runtime increases savings. Higher fixture or install costs, or smaller wattage reductions, generally slow payback.
4) What discount rate should I use for NPV?
A practical choice is your personal required return or borrowing cost. Many homeowners use 5–10 percent. Use a higher rate if you prefer faster returns or have uncertainty about runtime and maintenance. Use 0 percent for simple totals only.
5) Does this calculator account for dimmers or smart controls?
Indirectly, yes. If controls reduce average runtime, lower the hours per night to match expected use. If controls add purchase or subscription costs, add them to install cost or maintenance. The model will reflect the revised savings automatically.
6) How should I treat rebates and bulk discounts?
Enter all rebates as a single total. For bulk discounts, reduce the fixture cost per unit. If rebates depend on completion dates, consider a conservative estimate. You can run multiple scenarios to see best‑case and worst‑case outcomes.