Input Parameters
Results and Savings Summary
| Metric | Value |
|---|
Calculations assume constant operating profile throughout the year and do not include taxes or complex time-of-use tariffs.
Example scenario
The table below shows a typical retrofit where 20 metal halide fixtures rated at 400 W with a ballast factor of 1.15 are replaced by 150 W LED fixtures, operating ten hours per day, six days per week, all year.
| Parameter | Value |
|---|---|
| Metal halide wattage with ballast | 460 W per fixture (400 W × 1.15) |
| LED wattage per fixture | 150 W |
| Number of fixtures | 20 |
| Annual operating hours | 10 × 6 × 52 = 3120 hours |
| Annual energy use (metal halide) | 28,704 kWh |
| Annual energy use (LED) | 9,360 kWh |
| Annual energy savings | 19,344 kWh |
The actual savings for your project will depend on your exact operating hours, tariff structure, fixture performance, and maintenance strategy.
Formula used
This calculator estimates annual energy use, running cost, maintenance savings, demand savings and payback using a straightforward engineering approach.
-
Annual operating hours:
H = hours_per_day × days_per_week × weeks_per_year, or the override value if provided. -
LED operating hours:
HLED = H × (1 - controls_savings%). -
Metal halide system power (kW):
PMH = (WMH × ballast_factor × fixtures) / 1000 -
LED system power (kW):
PLED = (WLED × fixtures) / 1000 -
Annual energy use (kWh):
EMH = PMH × H,ELED = PLED × HLED. -
Annual energy cost:
C = E × rate_per_kWh. -
Annual maintenance cost:
M = maintenance_cost_per_fixture × fixtures. -
Annual demand cost savings:
Sdemand = (PMH - PLED) × coincidence_factor × demand_charge × 12. -
Total annual savings:
S = (CMH - CLED) + (MMH - MLED) + Sdemand. -
Project cost:
Capex = (LED_fixture_cost + install_cost_per_fixture) × fixtures - rebates. -
Simple payback (years):
Payback = Capex / S(when annual savings are positive). -
Net savings over analysis horizon:
NetN = S × N - Capex. -
CO₂ emissions saved:
CO₂ = (EMH - ELED) × emission_factor.
How to use this calculator
- Enter a suitable currency symbol so that cost values are clearly labeled for your region.
- Under Existing metal halide system, provide lamp wattage, ballast factor, number of fixtures, and typical annual maintenance expenditure per fixture.
- Under Proposed LED system, enter the LED wattage, expected annual maintenance per fixture, fixture cost, installation cost, and total rebates or incentives if available.
- Fill in your operating profile using hours, days and weeks, or supply an annual hours override if you already know the value.
- If your LED design includes sensors or dimming, add a controls savings percentage to reduce LED operating hours and estimate additional savings.
- Specify your electricity rate, emission factor, and any demand charge with a coincidence factor if your tariff bills for peak kW.
- Choose an analysis horizon to evaluate multi-year net savings, then click Calculate savings to generate the summary table.
- Use the CSV button to export the results into a spreadsheet, or the PDF button to generate a simple printable report for project documentation.
For more detailed analysis, you can perform multiple runs with different assumptions for operating hours, tariffs, rebate levels, LED wattages or controls savings and compare the exported CSV files side by side.
Understanding typical retrofit applications
Metal halide to LED upgrades are common in warehouses, parking lots, sports halls and large retail spaces. Long daily run hours and high ceilings make energy, maintenance and access equipment savings especially attractive for facility owners.
Key inputs that drive savings
Savings depend mainly on existing wattage with ballast, LED wattage, operating hours, tariff, and maintenance practices. Higher hours and higher electricity rates generally produce faster payback and a stronger business case for replacing aging luminaires with efficient equipment.
Linking space-level lighting design
For room-based projects such as bedrooms or small offices, you might first design the light levels using a dedicated Bedroom Lighting Calculator, then use this savings tool to compare alternative lamp wattages and control strategies at project level.
Balancing visual comfort and energy savings
When reducing wattage, confirm that the proposed LED solution still meets target illuminance, uniformity and glare limits. Consider colour temperature, colour rendering and user comfort, particularly in dressing areas that may also rely on tools such as a Dress Size Calculator.
Using controls to enhance project performance
Motion sensors, daylight dimming and scheduling can significantly reduce LED operating hours. The controls savings percentage field lets you estimate additional savings beyond wattage reduction, helping you compare simple on–off retrofits against smarter, sensor-driven designs quickly.
Documenting results for budgeting and approvals
After calculating, export results to CSV for spreadsheet analysis or create a PDF summary to attach to internal proposals. This makes it easier to compare multiple options, track assumptions and communicate payback metrics to decision makers and financial stakeholders.
Frequently asked questions
What information do I need before using this calculator?
You should know existing lamp wattage, ballast factor, number of fixtures, expected LED wattage, operating hours, electricity rate, approximate maintenance costs and any incentives, rebates or demand charges that apply to your tariff.
How accurate are the savings and payback results?
Results are indicative engineering estimates. They assume constant operating hours and simple tariffs. For final budgeting, always cross-check with manufacturer data sheets, measured run hours, detailed bills and any site-specific control strategies you plan to implement.
Can I model different operating schedules or usage patterns?
Yes. You can adjust hours, days and weeks, or directly enter known annual operating hours. The controls savings percentage also allows you to approximate reduced LED hours from sensors, dimming profiles or advanced time scheduling across your installation.
Why is ballast factor included for metal halide fixtures?
Traditional metal halide systems draw extra power in the ballast. Using a ballast factor multiplier better reflects real input wattage and prevents underestimating both current energy consumption and potential savings when you convert the system to driver-based LED luminaires.
How should I choose the correct LED wattage replacement?
Start from required light levels, lumen output and distribution rather than wattage alone. Compare manufacturer photometric data and consider mounting height, spacing and target illuminance so the selected LED fixture maintains or improves visual performance while reducing power.
What if my electricity tariff has tiered or time-of-use rates?
This calculator assumes a single blended rate per kWh. For complex tariffs, you can approximate by using an average effective rate derived from historical bills, or export results to a spreadsheet and refine the cost modelling offline.
Can I apply this tool to other lamp types, not just metal halide?
The method can be adapted for other discharge or fluorescent systems by using appropriate wattage and ballast factors. However, terminology and typical maintenance costs differ, so treat results as a guide rather than a precise calculation for non-metal-halide retrofits.