Free engineering tool
LED retrofit energy savings & payback calculator
Replacing high-pressure sodium, metal halide or fluorescent lights with LED? Calculate the energy saved, the money saved each year, the CO₂ avoided and the payback period, including ballast losses and relamping costs.
What is often forgotten
- Ballast losses. A magnetic ballast adds 10–20% to the lamp wattage: a “250 W” sodium lamp draws about 290 W from the grid.
- Relamping. HPS and metal halide lamps need replacing every 2–4 years, often with a bucket truck or scaffolding. LED removes most of that cost.
- Lumen maintenance. Old lamps lose light long before they fail, so a correctly sized LED often gives more light than the installation it replaces.
To choose the LED wattage for a road or a hall properly, use the pole spacing calculator or the high bay calculator rather than a fixed replacement ratio.
Questions about this calculation
How much energy does LED save compared with high-pressure sodium?
Typically 50–65%. A 250 W HPS lamp draws about 285–290 W with its magnetic ballast, while an LED street light of 100–120 W usually gives the same or better light on the road because its optics put the light where it is needed.
What LED wattage replaces a 400 W metal halide high bay?
Usually 150–200 W of LED, depending on mounting height and the required lux. Use our high bay calculator to size it for the actual hall rather than by a fixed ratio.
What is a good payback period for an LED retrofit?
Street and industrial lighting that runs 4,000+ hours a year usually pays back in 1–3 years. Shorter running hours or low electricity prices extend the payback; maintenance savings from no relamping shorten it.
More free tools
- Solar street light calculatorBattery Wh / Ah and solar panel watts from LED power, schedule, sun hours and autonomy.
- Street light pole height & spacing calculatorRecommended pole arrangement and maximum spacing from road width, pole height and LED lumens.
- Solar battery autonomy & rainy-day calculatorHow many rainy days your solar street light battery lasts, and whether it survives your rainy season.
- Solar vs grid street lighting cost calculatorTotal cost of ownership over 5–25 years: trenching, cabling and electricity vs. solar street lights.
- High bay lighting calculatorHow many LED high bays a warehouse, factory or sports hall needs, with layout and W/m².
Next step
Ask our engineers to check your design
Calculators give planning figures. Send us the site location, drawings and quantity, and we return a photometric or solar sizing check and a quotation for the complete set.
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