How to use the lighting retrofit savings calculator
Swapping fluorescent troffers, HID high bays or incandescent lamps for LED typically cuts connected lighting load by half or more while holding the same light level. Savings scale with the watts removed per fixture multiplied by fixture count and annual burn hours, so warehouses, parking structures and corridors that run 10 or more hours a day pay back fastest. Enter the fixture count and the before and after wattage and the tool returns annual kWh, dollar savings and simple payback.
Always include ballast loss in the existing wattage. A two-lamp 32 W T8 fixture draws roughly 59 to 62 W at the fixture input, not 64 W of lamp rating, and magnetic ballasts are worse, so using lamp-only wattage understates the savings. For the new value use total luminaire input watts including driver loss. Where existing footcandle levels are above the IES recommended range, reducing fixture count as part of the retrofit adds further savings.
Avoided CO2 uses 0.85 lb per kWh, close to the EPA eGRID national average output rate; substitute your regional eGRID subregion rate for a tighter number. A full project analysis should also credit reduced lamp and ballast replacement labor, lower cooling load, occupancy sensor and daylight dimming controls, and any utility prescriptive rebate.
Frequently asked questions
Phase the work and start with the highest burn-hour spaces. Utility prescriptive rebates, custom incentives and ESCO financing all shorten the effective payback considerably.
Compare delivered lumens and beam distribution rather than watts, then verify maintained footcandles on the work plane against the IES recommended range with a light meter after installation.