Swap bulbs smarter and cut your utility bill. See savings, payback, and carbon impact fast. Plan upgrades confidently with clear, detailed results every time.
| Old W | New W | Qty | Hours/Day | Rate | Expected outcome |
|---|---|---|---|---|---|
| 60 | 9 | 20 | 5 | 0.18 | High savings with fast payback |
| 100 | 15 | 12 | 6 | 0.22 | Very high savings at heavy usage |
| 40 | 6 | 30 | 3 | 0.14 | Moderate savings with lower rates |
Lighting savings scale with run time. The calculator multiplies hours per day by days per year to estimate total operating hours. Higher hours increase both energy spend and replacement frequency, so the benefit of efficient lamps becomes more visible in corridors, kitchens, retail aisles, and outdoor fixtures. Include fixture count carefully, especially with mixed lamp types; splitting by zone or schedule gives tighter estimates and improves reporting when you export results to CSV later.
Annual energy use is computed as (wattage ÷ 1000) × hours per year × quantity. Replacing twenty 60 W lamps with 9 W lamps at five hours daily produces a 1.02 kW load drop and about 1,862 kWh fewer consumption per year. The graph compares old versus new kWh so the impact is easy to verify.
The tool converts kWh into cost using your electricity rate. At 0.18 per kWh, the 1,862 kWh reduction is roughly 335 per year in bill savings. If your tariff is time‑of‑use, enter a blended average rate to approximate seasonal variation and demand‑related charges.
Bulb purchases can rival energy savings when short‑life lamps fail often. Replacement count is (hours per year ÷ rated life hours) × quantity. A 1,000‑hour lamp running 1,825 hours yearly needs about 1.83 bulbs per socket per year, while a 15,000‑hour lamp needs only 0.12. This lowers purchasing, storage, and service calls.
Upfront cost equals new bulb price × quantity plus any labor. Payback is upfront ÷ annual savings. For longer horizons, the calculator discounts savings to compute NPV over your analysis years and estimates IRR to compare against other upgrades. Use cumulative savings to prioritize the highest‑use areas first and schedule bulk replacements when procurement budgets reset.
Lifespan determines how many replacements you buy each year. Short‑life bulbs increase purchase and service costs, which reduces net savings. Long‑life bulbs typically lower maintenance spending and improve payback.
Yes, but set realistic daily hours. Low‑use fixtures often produce modest energy savings, so payback may depend more on bulb price and lifespan. Prioritize high‑use areas first.
Use your effective average rate per kWh from a recent bill. If you have time‑of‑use pricing, estimate a blended average based on when lights operate most of the time.
Payback equals upfront cost divided by annual savings. Upfront includes new bulb purchases and optional labor. Annual savings combines energy savings and reduced replacement spending.
NPV discounts future savings to today’s value over your chosen years. IRR is the implied return rate of the upgrade. These metrics help compare lighting changes to other efficiency investments.
It is an approximation based on your emissions factor input. Use a local grid factor for better accuracy. Carbon savings will change if the power mix, usage hours, or wattage assumptions change.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.