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Presets are starting assumptions, not product recommendations.
Use one project with the same old and replacement watts per item.
items
Enter the old lighting's actual load per item.
W / item
Check lumens, beam, color quality, controls, and fixture rating separately.
W / item
Use a bill, timer schedule, or operating-hours estimate where available.
hours / day
The model converts this schedule to annual operating hours using 365.25 days.
days / week
USD is the global default display; replace the value with the applicable rate.
$ / kWh
One-time labor or access cost belongs in Advanced.
$ / item
Leave zero when no per-item incentive applies.
$ / item
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Zero is neutral and is correct when current watts already include overhead.
%
Zero is neutral for a self-installed bulb swap.
$
This is converted to an expected annual maintenance saving using old lamp life.
$/ lamp
The default 1,000 hours is an editable incandescent example.
hours
This drives the LED-life net-savings row only.
hours
This changes the planning artifact, not the annual result.
years
Zero is neutral and reports the estimate as not supplied.
lb CO2 / kWh
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Wattage measures electrical power, not brightness. An LED upgrade comparison is meaningful only when the old and replacement lamps serve the same lighting job. Lumens, beam angle, color temperature, color rendering, dimmer behavior, fixture rating, and location suitability should be checked before lower watts are treated as a true replacement.

Energy savings depend on the difference in actual input watts and the hours the lights operate. A modest watt reduction can be valuable in fixtures that run all day, while a large reduction in a rarely used room may save little money. Electricity price converts avoided kilowatt-hours into bill savings.

  • Upfront cost includes LED purchases after per-item rebates plus one-time installation.
  • Annual benefit combines electricity savings with optional avoided old-lamp purchases.
  • Simple payback divides upfront cost by that annual benefit; it does not discount future cash flows or model changing rates.
  • Rated life is a laboratory-based planning value, not a guarantee in every enclosure, temperature, control, or electrical environment.

Ballasts, transformers, and drivers can make an old fixture draw more than the lamp rating alone. Add overhead only when the entered old wattage excludes it. Maintenance savings also need care: an avoided lamp purchase belongs in the model only when the old lamp would actually have been replaced during the comparison period.

Emissions savings require a current grid factor for the relevant location. A generic factor can make the arithmetic look precise while giving the wrong environmental estimate.

How to Use This Tool:

Compare one group of equivalent old and LED items using actual watts, a defensible operating schedule, and the applicable electricity price.

  1. Choose an Upgrade preset or enter the item count and comparable old and LED input watts, followed by the operating schedule and electricity price.
  2. Add LED purchase cost and any confirmed per-item rebate. Keep the rebate at zero when it is uncertain or unavailable.
  3. Open Advanced for old-fixture overhead, installation, avoided old-lamp cost, rated lives, the analysis horizon, or a local grid emission factor.
  4. Read annual bill savings with Payback plan and Fixture checks. Correct the first invalid field if results disappear, and verify product fit before using the financial result to approve a purchase.

Interpreting Results:

Annual bill savings reflects electricity only. Annual total benefit also includes entered maintenance savings, so the payback period can shorten when old lamps are costly and short-lived.

LabelPayback periodInterpretation
Fast payback0 through 1 yearUpfront cost is recovered within one modeled year
Solid paybackMore than 1 through 3 yearsCompare with expected service life and budget
Long paybackMore than 3 through 7 yearsHigher-use fixtures or rebates may deserve priority
Slow paybackMore than 7 yearsAssumptions and non-financial reasons need closer review
No savingsAnnual total benefit ≤ 0No positive simple payback is available

A positive multi-year net result assumes the same annual schedule, rate, and maintenance benefit for every modeled year. Confirm those assumptions and the LED's expected service in the actual fixture before treating the curve as a forecast.

Technical Details:

Annual energy is power multiplied by operating time and fixture count. The old-fixture overhead percentage is applied before comparing old and LED watts, which prevents ballast or driver losses from being omitted when they are not already included in the entered load.

Formula Core:

The main chain converts a weekly schedule to annual hours, watts to kilowatts, avoided energy to money, and annual benefit to simple payback.

Wold-effective=Wold×(1+o100) H=hday×dweek7×365.25 E=n×(Wold-effective−WLED)×H1000 S=E×r I=n×max(cLED−q,0)+cinstall P=IS+Smaintenance
SymbolMeaningUnit
nBulbs or fixturescount
W, oInput watts per item and old-fixture overheadW, %
HAnnual operating timehours/year
EAnnual energy savingskWh/year
r, SElectricity price and annual bill savingsUSD/kWh, USD/year
I, PNet upgrade cost and simple paybackUSD, years
qRebate or discount per itemUSD/item

Annual maintenance savings equal fixture count × old lamp cost × annual hours ÷ old lamp lifespan. Net savings over the selected horizon equals annual total benefit × years − net upgrade cost. LED-life net savings uses rated LED hours ÷ annual hours as its horizon.

Rule Core:

  • Payback exists only when annual bill savings plus maintenance savings is greater than zero.
  • A rebate cannot reduce modeled LED item cost below zero.
  • At zero annual operating hours, energy savings and annual benefit are zero, and rated-life years are reported as unavailable.
  • Annual avoided emissions equal annual kWh savings × the entered lb CO2/kWh factor; no default factor is assumed.

For twelve 60 W lamps replaced by 9 W LEDs at three hours per day and seven days per week, annual avoided energy is about 670.6 kWh. At $0.16/kWh, bill savings are about $107.30 per year. A $36 purchase with no installation cost has a simple payback of roughly four months.

Limitations and Accuracy Notes:

The estimate holds operating hours, electricity price, lamp failure rate, and maintenance benefit constant. It does not model discount rates, rate escalation, demand charges, cooling-load changes, taxes, disposal, or fixture replacement unless those costs are entered directly.

  • Use measured or nameplate input watts for comparable light output.
  • Confirm dimmer, ballast, transformer, enclosure, wet-location, and wiring compatibility.
  • Treat rated life as a comparison value rather than a guaranteed service interval.
  • Use a current local emissions factor and keep its geographic basis consistent with the electricity use.

References: