LED lifetime savings.

LED bulbs cost more upfront (3-15 vs 1-3 for incandescent) but use 75-85% less energy and last 15-25× longer. Over the LED's lifetime (25,000 hours), total cost including energy and replacements is typically 60-80% lower than traditional bulbs. The maths are overwhelmingly in LED's favour.

50 bulbs: LED at 5 each, 10W, 25,000 hours. Traditional at 1, 60W, 1,000 hours. LED energy: 50 × 10W × 25,000h × 0.30/kWh = 3,750. Traditional energy: 50 × 60W × 25,000h × 0.30 = 22,500. Traditional replacements: 24 sets × 50 × 1 = 1,200. LED total: 250 + 3,750 = 4,000. Traditional total: 1,250 + 22,500 = 23,750. Savings: 19,750.

LED replacement is the easiest energy saving available. No lifestyle change, no infrastructure cost, drop-in replacement for existing fittings. A 50-bulb household/office switching to LED saves 700-1,500/year in energy alone. ROI measured in months, not years. Anyone still using incandescent or halogen is leaving money on the table.

A worked example

Try the defaults: number of bulbs of 50, led price each of 5, traditional price each of 1, led watts of 10. The tool returns 19,750.00. You can adjust any input and the result updates as you type — no submit button, no reload. That's the real power here: seeing how sensitive the output is to one or two assumptions.

What moves the number most

The result responds to Number of Bulbs, LED Price Each, Traditional Price Each, LED Watts, and Traditional Watts. Two inputs usually tip the answer one way or the other. Identify which ones matter most by flipping each value past a round threshold and watching whether the winning option changes.

The formula behind this

Energy = bulbs × watts/1000 × hours × price/kWh. Replacements = ceil(LED hours / traditional hours) - 1. Total = bulb cost + energy. Everything the calculator does is shown in the formula box below, so you can check the math against your own spreadsheet if you want.

Running the sensitivity

Energy prices, usage patterns, and grant availability all move the payback figure. Test at least two scenarios — current rates and a rate 20% higher — to see whether the decision holds up across plausible futures.

What this doesn't capture

Carbon reduction, health benefits, and local air quality have real value the financial figure doesn't price. The calculation gives the money side honestly; for the full picture, note the non-financial benefits alongside.