Free · Everyday planning calculators

Light Bulb Energy and Replacement Budget

Compare bulb purchase and electricity costs over a selected operating period.

  • Formula & worked example
  • Private in your browser
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

Four hours per day at $0.20/kWh gives $7.922 annual LED cost and $19.532 reference-bulb cost.

Cost = bulb price × ceiling(operating hours / lifetime) + kWh × tariff

Worked example

Enter these known values and leave the other values blank.

Bulb type
Enter custom bulb details
Price
5 USD
Power consumption
10 W
Lifetime
10000 hrs
Price
1 USD
Power consumption
60 W
Lifetime
1000 hrs
Energy price
.2 USD / kWh
Daily usage
4 hrs
Over how many years?
1 yrs
LED total cost
7.92 USD
Regular bulb total cost
19.53 USD
Total savings
11.61 USD
Annual cost ratio × one year (descriptive proxy)
4.9 mos

Assumptions and limitations

  • Compare equal lumen output, with user-supplied purchase prices, rated lifetimes and energy tariff. Replacement counts round up. The cost-ratio interval is annual LED cost divided by annual reference cost times one year; it is a descriptive proxy, not a financial payback date. A year is 365.25 days.

Common questions

What does this estimate assume?

Compare equal lumen output, with user-supplied purchase prices, rated lifetimes and energy tariff. Replacement counts round up. The cost-ratio interval is annual LED cost divided by annual reference cost times one year; it is a descriptive proxy, not a financial payback date. A year is 365.25 days.

Can I find a missing input?

Clear the unknown field and enter compatible known values. The controls retain supported inverse calculations, while rounded counts and one-way outputs stay directional.

References

The internal hundred-year reference-bulb cost previously used ten years for replacement purchases and one hundred years for electricity. Both terms now use one hundred years, including supported inverse variants. The annual-cost-ratio interval is relabeled as a descriptive proxy rather than a payback estimate.

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