How the calculation works
Annual saving = kW × hours × price + maintenance saving
Payback = installed cost ÷ annual saving
Worked example
A warehouse has 200 high-bay fittings with 400 W metal halide lamps, drawing about 455 W each with their ballasts. They are replaced with 150 W LED high-bays at 250 each installed. The lights run 6,000 hours a year at 0.12 per kWh.
- Load reduction: 200 × 305 W = 61 kW.
- Energy saved: 61 × 6,000 = 366,000 kWh a year, worth 43,920.
- Investment: 200 × 250 = 50,000. Payback: about 14 months, before counting maintenance savings.
Typical replacements
| Existing fitting | Typical total input | Typical LED equivalent |
|---|---|---|
| 400 W metal halide high-bay | about 450 W | 120 to 180 W |
| 250 W high-pressure sodium | about 280 W | 80 to 120 W |
| 2 × 58 W T8 fluorescent, magnetic ballast | about 130 W | 45 to 60 W |
| 2 × 36 W T8 fluorescent, magnetic ballast | about 85 W | 30 to 40 W |
Indicative values only. Match LED fittings on delivered light (lumens) and light distribution, not on wattage, and check results with a lighting design.
Getting more from the retrofit
- Add occupancy or daylight sensors in areas that are not used continuously. LEDs, unlike metal halide, can switch and dim instantly.
- Do not simply replace fittings one for one. Older installations are often over-lit or under-lit, and a new layout can need fewer fittings.
- In air-conditioned buildings, lower lighting heat also reduces the cooling load.
Questions
How much energy does an LED retrofit save?
Replacing metal halide, sodium or older fluorescent lighting with LED typically saves 50 to 70% of lighting energy, and more with occupancy and daylight controls.
Should I include ballast losses?
Yes. Magnetic ballasts add roughly 10 to 15% to lamp power, and the saving is based on the total power drawn by the fitting.
What is a typical payback for industrial LED lighting?
For fittings running two or three shifts, one to three years is common. Lights used only a few hours a day take longer.