Lighting Retrofit Savings Calculator

How the lighting retrofit savings calculator works

Annual electricity for each option = fixture count × input watts per fixture × annual operating hours ÷ 1,000. Fixture count is a positive whole number. Use the full device input power, including driver or ballast, and equivalent operating hours for the two options.

Each annual electricity energy charge is energy × entered flat rate, rounded half-up to cents. Energy-charge saving is existing charge minus replacement charge. Annual operating saving adds the entered maintenance saving, which rounds separately to cents and may be negative.

Simple payback years = rounded upfront project cost ÷ positive annual operating saving. A zero or negative saving has no calculated payback. Zero upfront cost with positive saving has zero payback. This is constant annual operating arithmetic without discounting, escalation, financing or asset-life analysis.

Watts alone do not establish equivalent light output, glare, color, reliability or regulatory suitability. This tool makes no product or lighting-design recommendation and excludes HVAC interactions, control changes, demand charges and tariff tiers. EIA supplies the power-to-energy relationship; the DOE report supplies the simple-payback method rather than current prices.

Worked example

40 fixtures at 100 W for 3,000 h use 12,000 kWh; at 40 W they use 4,800 kWh. The difference is 7,200 kWh. At an illustrative 0.18/kWh the annual energy-charge saving is 1,296. Adding 100 maintenance saving gives 1,396 per year. A 2,000 project cost has about 1.433 years simple payback. Replacement power of 60 W instead gives 964 total annual saving.

Sources and assumptions

The source material explains the underlying calculation or pricing structure. Entered prices, costs, schedules and scenario choices are your assumptions; this tool does not obtain supplier quotes or predict actual results.

• EIA: Measuring electricity
• U.S. DOE lighting analysis: simple-payback method