How is annual energy use calculated?

Annual kWh equals watts × number of fixtures × operating hours ÷ 1000, computed for both the old and LED fixtures. The difference is the energy saved per year.

How is the payback period found?

Simple payback is the total installed project cost divided by the annual dollar savings. A 50-fixture project costing 2,250 dollars that saves 1,800 dollars a year pays back in about 1.25 years.

What CO₂ factor does it use?

It uses the US national grid average of about 0.386 kg of CO₂ per kWh from EPA eGRID data. Grids that are cleaner (more renewables or nuclear) avoid less CO₂ per kWh; coal-heavy grids avoid more.

What operating hours should I enter?

Use realistic annual run hours. An office on 10 hours a day, 5 days a week is about 2,600 hours; a 24/7 warehouse or parking garage approaches 8,760 hours. Higher run hours dramatically shorten payback.

Does this include maintenance savings or rebates?

No. This is an energy-only simple payback. LED's longer rated life also cuts lamp replacement and labour, and many utilities offer rebates — both shorten the real payback below the figure shown here.

LED Retrofit Savings Calculator

Why an LED retrofit pays for itself

Replacing fluorescent or HID fixtures with LED cuts the wattage for the same light output, often by half or more, while the fixtures run the same hours. Because lighting in commercial buildings runs long hours, that wattage difference compounds into large annual energy and dollar savings. This calculator quantifies the saving at your own utility rate, estimates the CO₂ avoided, and — if you supply the project cost — returns a simple payback period you can put in front of a building owner or finance team.

How it works

The annual energy for a set of fixtures is:

kWh/yr = watts × fixtures × hours / 1000

computed once for the old fixtures and once for the LEDs. The difference is the energy saved. Multiplying the energy saved by your electricity rate gives the dollar savings, and multiplying by the grid emission factor (about 0.386 kg CO₂ per kWh on the US national average) gives the CO₂ avoided. If you enter an installed cost per LED, the tool multiplies by the fixture count for the project cost and divides by the annual savings to get a simple payback in years.

Example and notes

Fifty 100 W fixtures replaced with 40 W LEDs, running 4,000 hours a year at 0.15 dollars per kWh, save 60 W × 50 × 4,000 ÷ 1000 = 12,000 kWh and 1,800 dollars a year, avoiding about 4,600 kg of CO₂. At an installed 45 dollars per LED the project costs 2,250 dollars and pays back in roughly 1.25 years. Remember this is energy-only: LED’s longer life cuts re-lamping labour and many utilities offer rebates, both of which push the real payback even shorter. Verify fixture wattages from the actual product spec sheets rather than assuming a fixed ratio.