LED Savings & Payback Calculator
Enter the existing lamp, LED, hours, rate, labor and rebate to see annual savings, payback and 10-year return.
Step-by-step
- Enter valid values to begin.
Wattages and lives are typical catalogue values (including ballast losses) for the presets; lamp life is a rated figure, so use your own data for a firm case. Labor is charged once per fixture for the LED installation and again for each avoided replacement of the existing lamp. Cooling credit = saved kWh × cooled-space factor ÷ COP, and the heating penalty is extra heating energy priced at the same rate as electricity (use a lower figure for efficient heat pumps or cheap gas). LED replacements inside the 10-year horizon are included if the LED life is shorter. No discounting, tariff escalation, lumen depreciation or light-level change is modelled, so verify light output (IES LM-79 test data) and the design illuminance before you count the saving.
LED Retrofit Savings: Energy, Maintenance and the Heat You No Longer Make
Core Engineering Principles
A lighting retrofit saves money in three ways, and energy is only the first. We take the system watts, including the ballast, on both sides, subtract, and multiply by hours and tariff. A 400 W metal halide lamp is really about 455 W once the ballast is counted. Maintenance is the second line. A metal halide lamp lasts around 15,000 hours, so at 3,600 hours a year it is changed every four years, and each change costs a lamp, a lift and a person. An LED rated at 50,000 hours can run about fourteen years without a visit.
The third effect is thermal. Nearly all lighting power becomes heat in the room. Remove 12 kW of lighting and the air conditioning has less heat to reject, so we credit the saved kWh multiplied by the share that falls in cooled space and divided by the cooling COP. In a cold climate the sign flips, because the heating plant must replace that heat, so we allow a heating penalty. In an unconditioned warehouse the credit is zero. Simple payback hides the time value of money, so read the 10-year figure and ROI beside it.
Payback (mo) = 12 × net cost / annual saving • ROI = (10 × saving − cost) / cost
NEC & Standard References
IEC 62612 sets performance requirements for self-ballasted LED lamps for general lighting. IES LM-79 is the test method for electrical and photometric measurement of solid-state lighting, so the watts and lumens on the data sheet should come from an LM-79 report. IES LM-80 and TM-21 give the method for lumen maintenance and for projecting L70 life, which is how the rated hours are derived. Rebates usually require a DesignLights Consortium or ENERGY STAR listing, and luminaires are safety-listed to UL 1598.1. Hours = 12 × 300 = 3,600. Saved = 305 W × 40 = 12.2 kW, so energy = 43,920 kWh = 5,270.40.
2. Cooling credit = 43,920 × 0.5 / 3.0 = 7,320 kWh = 878.40.
3. Old lamp changes = 40 × 3,600 / 15,000 = 9.6 a year × (30 + 25) = 528.00.
4. Annual saving = 6,676.80. Net cost = 40 × 205 − 2,000 = 6,200.
5. Payback = 6,200 / 6,676.80 × 12 = 11.1 months; 10-year net = 60,568, ROI 977%.
- Verify the light, not just the watts. A 150 W LED may give fewer lumens than the old lamp gave when new, so confirm foot-candles against the design target.
- Mind the old ballast. Bypass or remove it as the LED manufacturer directs.
- LED drivers have inrush. Limit the fixtures per breaker or the first switch-on may trip it.
- Heat shortens driver life. A hot ceiling space can push a driver past its rated temperature.
- HID lamps contain mercury. Handle and recycle removed lamps as universal waste.