Off grid lighting load calculator

Understanding your lighting load

The direct answer for a typical setup

With 12 LED fixtures running 4 hours a day, lighting adds about 432Wh to a daily load. The same fixture count and usage with incandescent bulbs would add 2,880Wh, nearly 7 times more, and CFL bulbs would land in between at 672Wh. Bulb type alone makes a bigger difference to lighting load than almost any other single choice. You can check the knock-on effects with the federal ITC calculator.

Why LED bulbs use so much less power

LED bulbs convert far more of their input power directly into visible light rather than wasted heat, compared to incandescent bulbs which lose most of their energy as heat. This efficiency difference is why a 9-watt LED can produce roughly the same brightness as a 60-watt incandescent bulb, a wattage reduction of about 85% for equivalent light output. The Department of Energy's Energy Saver guide has the current version, so check there before you rely on a summary.

Why isolating lighting from total load is worth the extra step

Lighting is one of the easiest loads to cut significantly with a low-cost swap, unlike a refrigerator or well pump where the load is largely fixed by the equipment itself. Seeing lighting's contribution in isolation, rather than buried inside a total daily load figure, makes it obvious how much a bulb upgrade alone could shrink overall system requirements before considering more expensive hardware changes.

What dimmers and motion sensors change

Both reduce actual energy use below the full-wattage, full-hours estimate this calculator gives. Motion sensors cut runtime by only lighting occupied spaces rather than leaving fixtures on continuously, while dimming reduces power draw directly, with the effect more pronounced on dimmable LED fixtures than on incandescent bulbs, which dim less efficiently. ENERGY STAR's product efficiency data is a good reference for comparing specific bulb models before buying.

What to do with your lighting load figure

Put the lighting total next to the rest of your loads in your total load list, and if you're still using incandescent or CFL bulbs, this calculator puts the LED swap case in concrete watt-hours rather than a vague general recommendation. The quick output estimator in our performance and output tools is a fast way to see how much smaller your solar array could be after a full LED swap, and the federal ITC calculator in our rebates and incentives tools is worth checking if a smaller lighting load shifts your overall system size and budget. the Department of Energy's Energy Saver guide covers the broader case for LED beyond just the off-grid angle. Your inverter has to handle the biggest load you will run at once. The solar inverter size calculator in our Inverters & Equipment section can help you size it for your actual appliances.