Lighting Replacement Payback Calculator
Compare annual lamp energy and maintenance costs using your own inputs, then calculate signed savings and simple payback.
A QUICK WALKTHROUGH
How to use this tool
- Enter your own parameters in the stated units and one currency label.
- Optionally add 1–20 comparison scenarios; calculate to show every result.
- Copy the complete report or download the same report as TXT. Editing any input clears the report.
Formula and units
Annual kWh = W × lamps × hours/day × days/year ÷ 1000; energy cost = kWh × rate. Energy savings = old cost − new cost; maintenance savings = old maintenance − new maintenance. Total savings = both savings added. Net cost = project cost − rebate. Simple payback = net cost ÷ annual savings. Exact decimal inputs are retained as fractions. Parsed fields show the full numeric value and exact numerator/denominator. Results use the full available binary64 value without display rounding. Currency amounts share one label; annual and monthly periods are explicit in result names. Unrepresentable results and contributions swallowed by rounding are rejected.
Assumptions and limits
All amounts use your currency label. Optional maintenance is the total yearly amount for the whole installation. Rebate cannot exceed project cost. Payback is undefined for zero or negative savings, including zero net cost; zero net cost with positive savings gives zero years. This DOE-style simple-payback arithmetic excludes discounting, financing, tariff changes, degradation and replacement timing. It gives no advice or guarantee of actual savings. Inputs and exports stay in this browser.
GOOD TO KNOW
Common questions
What does simple payback include?
Net project cost divided by positive annual energy plus maintenance savings, following the DOE lighting retrofit financial-analysis basis. It is not discounted cash flow.
Can the savings be negative?
Yes. Higher energy or maintenance costs remain signed. Zero and negative savings have no defined simple payback.
How are examples and comparison rows used?
Examples are explanatory only and never prefill fields. Each comparison supplies its own complete installation parameters.