Most LED proposals hand you a payback number — 2.8 years, 3.1 years — without showing how they got there. That is a problem because the math matters more than the number.
Here is exactly how commercial LED retrofit payback works, using data from 89 real projects we have completed.
The formula is simple. The inputs are not.
Payback = Net Investment / Annual Savings
Net Investment = Total Project Cost - Rebates
Annual Savings = Energy Savings + Maintenance Savings
The formula is straightforward. The challenge is getting accurate inputs. Most proposals guess at utility rates, assume maintenance costs, and ignore rebate timing. That is where projects go sideways.
What the data actually shows
Across 89 commercial exterior retrofit projects totaling 19,364 fixtures:
These are not projections. These are actuals from completed installations with verified utility data.
Why most payback calculations are wrong
Three common errors inflate or deflate payback numbers:
**Using nameplate wattage instead of system wattage.** A 400W metal halide fixture does not consume 400W. With the ballast, it draws 450W. That 10-15% parasitic load changes the savings calculation meaningfully across hundreds of fixtures.
**Ignoring maintenance savings.** Legacy HID fixtures cost approximately $17.25 per fixture per year in maintenance — lamp replacements, bucket truck rentals, emergency calls. LED fixtures cost approximately $0.54 per fixture per year. That is a 97% reduction that most simple calculators miss entirely.
**Using a single utility rate.** Commercial buildings often have multiple meters, demand charges, and tiered rate structures. Using one blended rate instead of the weighted marginal rate can swing the payback calculation by 6-12 months.
The right way to do it
Pull every utility bill for 12 months. Calculate the weighted marginal rate across all meters. Use the IR audit data for actual fixture wattages — not estimates. Include maintenance savings based on fixture type and access difficulty. Apply confirmed rebate amounts, not estimates.
Then run the math. If the payback is under 3.0 years, the project pays for itself faster than most capital expenditures. If it is under 2.5 years, it is effectively free money.
What this means for your building
If you manage a commercial property with HID or older fluorescent lighting, the question is not whether LED saves money. It does. The question is how much — and whether the payback justifies acting now versus waiting.
Every month of delay is avoidable waste. At $139 per fixture per year in savings, a 200-fixture property loses approximately $2,317 per month by not upgrading.
We can show you the exact numbers for your building in a 30-minute call. No commitment required.