LED Lighting Conversion Calculator

This calculator weighs keeping your old light bulbs against switching to LED. Enter how many bulbs, how many hours a day they are on, the watts of the old and new bulbs, the price of a new bulb and what you pay for electricity. It works out the yearly energy use and cost of each, the yearly saving, the cost of the new bulbs, the paybacks, and the cost over the years you choose of keeping the old bulbs, switching now, or switching as they burn out.

Every bulb figure is yours to enter; the federal limits on lamp wattage are shown as a guide, and default electricity prices come from the EIA. You set the price of the new bulbs; the opening example uses an illustrative one, not a quote or a current price.

Purpose and model boundary

This calculator compares keeping your old light bulbs with switching to LED bulbs. It multiplies the number of bulbs by each bulb's watts and the hours a day they are on, prices that at your electricity rate, adds the cost of replacing bulbs as they burn out when you enter their price and life, and sets the yearly saving against what the new bulbs cost. Over the number of years you choose, it compares keeping the old bulbs, switching now and, when you say how many years the old bulbs have left, switching when they burn out.

Every figure on this page is computed by the spreadsheet; the page adds nothing to it. The model covers running cost and purchase cost only. It does not judge light quality, colour, dimming or fit, and it does not price financing, warranties or your own time.

Inputs and units

• The bulbs: how many (1 to 500), the hours a day they are on (0 to 24), the type of the old bulbs (incandescent, halogen incandescent, compact fluorescent or other), and the watts of an old bulb and of a new LED bulb, from the bulbs themselves or their packaging.
• Brightness, optional: the lumens of the old and new bulbs, used only to warn when the new bulb is dimmer.
• Bulb prices and lives: the price of a new LED bulb, more than $0 and at most $500, which is always yours to set; and, optionally, the price of a replacement old bulb and the rated life in hours of each kind.
• Electricity price, optional: the state, which sets the default price, or your own price in dollars per kWh.
• Purchase: installation, sales tax on the price and verified rebates. Each is optional and counts as zero when left blank.
• The comparison: the years to compare (1 to 30), the yearly change in electricity prices, the discount rate, and, optionally, the years the old bulbs have left.

Power is in watts per bulb, light in lumens, life in hours, energy in kWh a year and money in dollars.

Governing relationships

Energy. Each kind of bulb uses bulbs × watts × hours a day × 365 ÷ 1000 kWh a year; a plain bulb draws nothing when off.

Replacing bulbs as they burn out. When you enter an old bulb's price, the yearly cost of replacing old bulbs is bulbs × price × hours a year ÷ the old bulb's rated life, counted from the first year. The rated life is yours; left blank for a halogen or CFL bulb, it is the federal minimum rated life, 1,000 or 6,000 hours, which real bulbs may exceed, so the cost of replacing them may be overstated. For an old-style incandescent or other bulb with no life entered, replacements are not counted. New bulbs are bought again only after their rated life has run out; with a long-lived LED that is often after the years compared, and with no new life entered they are not bought again.

Value left at the end. The new bulbs' life in years is their rated hours ÷ the hours they are on in a year; the value left in them at the end is counted on a straight line over that life. With no new life entered, no value is counted.

Federal limits as a guide. There is no federal list of individual bulbs. As a guide to old bulbs, under the limits phased in from 2012 to 2014 a general service incandescent lamp may draw at most 72 W for 1490-2600 lumens, 53 W for 1050-1489, 43 W for 750-1049 and 29 W for 310-749; older bulbs commonly drew more.

Yearly cost. For each bulb, the yearly running cost is its yearly kWh times the electricity price; adding yearly upkeep gives its yearly cost, and the yearly saving is the old bulb's yearly cost less the new one's.

Electricity price. Your own price, when you enter one, is used; otherwise the average residential price for the state you choose.

Purchase cost. The capital cost is the number of bulbs × the price per bulb × (1 + sales tax rate) + installation − rebates; there is no disposal cost or sale value for bulbs.

Payback. Simple payback is the net initial cost ÷ the first year's saving, when the saving is positive; otherwise there is no payback. Discounted payback is the first year in which the cumulative discounted net benefit of replacing now reaches zero within the years compared.

The three paths over the years compared. Electricity prices change each year by the rate you enter; upkeep stays flat; costs fall at the end of each year and are discounted at your rate.

• Keep: the old unit's yearly cost every year.
• Replace now: the net initial cost today, then the new unit's yearly cost, less the value left in the new unit at the end.
• Replace at end of life (when you enter the years the old unit has left and they are fewer than the years compared): the old unit's yearly cost until it fails, then the capital cost in that year, then the new unit's yearly cost, less the value left in the new unit at the end.

The net present value of switching now is the present cost of keeping the old bulbs less the present cost of switching now: positive means switching now costs less.

Calculation sequence

The spreadsheet first checks the inputs, then works out each kind of bulb's yearly kWh and replacement cost at your hours, the yearly costs and the saving. The purchase cost, the paybacks, the present values of the three paths and the year-by-year cash flow follow. The sensitivity table uses the same per-bulb figures, so it cannot disagree with the main result. A block of consistency checks, including that the discounted cash flow reaches the same net present value as the closed-form formula, runs before the status is returned.

Outputs and interpretation

The headline is the yearly saving from switching, with the simple payback and the net present value of switching now. For each kind of bulb the results give its watts, its yearly kWh, and its yearly energy, replacement and total cost, with the electricity price actually used, the life hours used and a note on where the price came from. The decision results give the net initial cost, the discounted payback year, the total and present cost of keeping, of switching now and of switching at end of life, and a plain verdict on each.

The cash-flow table shows each year from 0 to the years compared: the cost of each path, the net benefit of replacing now, and its cumulative, discounted and cumulative discounted values. The sensitivity table shows the yearly saving at 1, 2, 3, 4, 6, 8, 12 and 24 hours a day, and at 0.5, 0.75, 1, 1.25 and 1.5 times the electricity price used.

The first chart, “Cumulative net benefit of replacing now, by year”, shows Undiscounted and Discounted by year. The second chart, “Cost over the years compared”, shows Total and Present value by option. The third chart, “Running cost in year 1”, shows Electricity and Replacement bulbs by bulbs, stacked.

Validation and status logic

The workbook returns one status, chosen in this order: NOT VALID, then CHECK, then OK.

• NOT VALID names the first problem: old watts missing or not above 0 and at most 500; an old bulb price outside 0 to $500 or an old life outside 100 to 100,000 hours; new watts missing or not above 0 and at most 200; a new life outside 1,000 to 100,000 hours; a bulb count that is not a whole number from 1 to 500, hours a day outside 0 to 24, an old bulb type that is not one of its options, or a lumen figure outside 0 to 20,000; no electricity price, or your own price outside $0.01 to $2.00 per kWh; a new bulb price that is missing, not above $0 or above $500; another money or rate input outside its range; years to compare that are not a whole number from 1 to 30, or a growth or discount rate outside its range; years left for the old bulbs that are not a whole number from 0 to 30. NOT VALID is a refusal, not a numeric answer: every figure reads zero and is withheld.
• CHECK accompanies a computed result that needs the stated review: a new bulb that draws as many watts as the old one, or more; a new bulb that gives less than 0.9 of the old bulb's light; zero hours a day; a new unit that does not cost less to run than the old one at your use, so there is no payback; or an old unit with fewer years left than the years compared, so the end-of-life path is the realistic one.
• OK otherwise.

Assumptions and limitations

• Every figure for a bulb is yours. There is no federal list of individual bulbs: the ENERGY STAR light bulb data could not be obtained, so the watts, lumens, lives and prices are what you enter.
• Hours are yours. No federal figure for household lighting hours was found; the opening example uses 3 hours a day as an illustration.
• Replacement bulbs are counted on average. The cost of replacing bulbs is spread evenly over the years by their rated life, not bought on the exact day each one fails.
• Federal minimum lives are floors, not typical lives. The 1,000-hour halogen and 6,000-hour CFL figures are the least a bulb sold under 10 CFR 430.32(dd) had to be rated for; enter your bulb's rated life if you know it.
• The default electricity price is an average. It is the EIA's annual average residential price for the state, not your tariff. Enter your own price from your bill for a better answer.
• One price change rate applies to electricity in every year. The future purchase in the end-of-life path is priced at today's price.
• There is no loan, no depreciation other than the value left in the new unit at the end, and no resale other than the old unit's sale value when it is replaced now.

Data and vintage

The federal limits on lamps and the default electricity prices are reviewed reference figures, refreshed from their federal publishers; their version is shown in the result details.

• Lamp limits: the federal maximum rated watts of general service incandescent lamps by brightness from 10 CFR 430.32, and the 45 lumens per watt sale prohibition from 2022-07-25, read 2026-10-28.
• Default electricity prices: EIA 2025 annual average residential electricity prices by state (Form EIA-861).

Worked examples and prices

Prices are not part of the reference data: the price of the new unit is an input you set. The opening example and the five worked examples each use an illustrative price for the new unit, so that the example computes, and each says so: “Illustrative price for this example, not a quote or a current price. Prices vary: check current prices online or enter your own.”

Restrictions and non-computing states

The calculator enforces its numeric and choice limits before it accepts a result. A bulb with no watts, a count or hours outside their limits and a missing price for the new bulb are refused by the workbook.

Errors and warnings

A request rejected by the page's input limits is not a computed result. A transport or service failure, a timeout or a cancelled run cannot establish a fresh workbook answer, and the last result stays on the page marked as out of date. Check the watts printed on your bulbs and your own bill before relying on a result for a purchase.

Sources and further reading

The calculator reads its default electricity prices from a reviewed reference table inside the workbook, with its version shown in the result details. Every table comes from a US federal source. The sources below publish the data and the rules the model applies. They do not endorse this calculator.

• DOE energy conservation standards, 10 CFR 430.32 (eCFR) sets the federal limits on general service lamps (430.32(dd), formerly (x)): the maximum watts of incandescent lamps by brightness, and the 45 lumens per watt sale prohibition from 2022 (retrieved 2026-10-28).
• EIA, Detailed state data (Form EIA-861) gives the average residential electricity price by state, used here for 2025 (retrieved 2026-10-28).

This is an educational estimate of running and purchase costs for the bulbs and prices you enter, not a product recommendation or a quote.