LED Bulb Savings Calculator
Compare wattage only after matching brightness in lumens and checking fixture compatibility. The calculator models electricity savings and simple purchase payback; replacement labour, lamp failures, dimmer changes and cooling/heating interactions are excluded.
Quick answerReplacing ten 60 W lamps with ten same-brightness 9 W LEDs used four hours/day saves 744.6 kWh and $126.58 per year at $0.17/kWh. At $3 per LED, the $30 purchase has a simple energy-only payback of about 2.84 months.
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Results
Purchase cost ÷ annual electricity saving × 12. No finite payback when the entered LED uses equal or greater power.
Compare compatible LED replacements
Match lumens first, then verify the exact base, voltage, colour, fixture, enclosure and dimmer requirements before buying a multipack.
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How it works
Annual kWh for each option = bulb watts × bulb count ÷ 1,000 × hours/day × 365. Saved kWh = old annual energy − LED annual energy. Annual dollar saving = saved kWh × rate. Simple payback months = total LED purchase cost ÷ annual saving × 12.
LED replacement savings examples
Every row uses four hours/day and $0.17/kWh. Lamp pairs must provide suitable comparable lumens; watts alone do not prove equivalent light output.
| Replacement scenario | Annual kWh saved | Annual saving | $3-per-LED payback |
|---|---|---|---|
| 1 × 60 W to 9 W | 74.5 kWh | $12.66 | 2.84 months |
| 5 × 40 W to 6 W | 248.2 kWh | $42.19 | 4.27 months |
| 10 × 60 W to 9 W | 744.6 kWh | $126.58 | 2.84 months |
| 10 × 75 W to 12 W | 919.8 kWh | $156.37 | 2.30 months |
| 20 × 60 W to 9 W | 1,489.2 kWh | $253.16 | 2.84 months |
| 10 × 18 W to 9 W | 131.4 kWh | $22.34 | 16.11 months |
Payback repeats current hours and rate and excludes replacement labour, maintenance, lamp life, dimmer/fixture changes, rebates, tax and space-conditioning interactions.
Worked example: ten 60 W lamps to ten 9 W LEDs
The old lamps use 60 W × 10 = 600 W; the LEDs use 9 W × 10 = 90 W. The difference is 510 W or 0.51 kW. At four hours/day for 365 days, 0.51 × 4 × 365 = 744.6 kWh saved.
At $0.17/kWh, annual saving is $126.582, displayed as $126.58. Ten LEDs at $3 cost $30, so simple payback is $30 ÷ $126.582 × 12 = 2.84 months.
Match lumens before comparing watts
DOE explains that watts measure electrical input while lumens measure visible light output. Its current federal purchasing guide shows the range of LED watts that can provide lumen output comparable with common incandescent ratings.
Choose the required lumens, beam shape and distribution first. A lower-watt LED that produces materially less useful light is not an equivalent replacement and can exaggerate the apparent saving.
Check fixture, base, dimmer and temperature compatibility
An LED must fit the physical base and enclosure and be suitable for the fixture orientation, enclosed rating, voltage and ambient temperature. Dimming also requires a compatible lamp and control; visible flicker, poor low-end dimming or buzzing can result from a mismatch.
DOE notes that LED lamps can be physically larger because of their drivers. Confirm dimensions and manufacturer compatibility before buying a multipack.
What simple payback leaves out
This model counts electricity and entered purchase price only. It does not assign a universal lamp lifetime or replacement-frequency saving because actual products, thermal conditions, switching, controls and operating hours differ.
For a commercial or high-access installation, add labour, lift/equipment cost, maintenance schedules and disposal. For a home, compare the exact product warranty, rated life, colour quality and return policy rather than buying on watts alone.
Sources used for assumptions: U.S. Department of Energy FEMP — comparable lumens, LED watts and cost-effective bulb purchasing; U.S. Department of Energy — consumer guide to energy-efficient lighting and Lighting Facts; U.S. Department of Energy — LED basics, efficacy and controls.
Frequently asked questions
How much does switching to LED save?
Subtract LED watts from old watts, multiply by bulb count and annual hours, then multiply saved kWh by your rate. The answer depends on matched brightness and actual use.
What LED replaces a 60 W incandescent?
Match lumens, not watts. DOE’s federal guide lists about 5.9–10.5 W for certified general-purpose LEDs around the 800-lumen output associated with a 60 W incandescent comparison.
Why is payback shown in months?
The calculator divides total entered LED purchase cost by annual electricity saving and multiplies by 12. It is a simple, undiscounted energy-only payback.
What if LED watts are higher than old watts?
There is no positive electricity saving and therefore no finite energy-only payback. Recheck that the lamps provide comparable useful light and that the inputs are correct.
Does the calculation include longer LED life?
No. Lamp life, failure rate, replacement labour and maintenance savings are excluded because they vary by product and operating conditions.
Will every LED work with my dimmer?
No. Confirm that both the LED and dimmer are compatible and suitable for the load range. Also check base, voltage, fixture enclosure, orientation and dimensions.
Should I replace working efficient lamps immediately?
Compare the actual watt difference, hours, purchase cost and disposal. A small watt reduction at low use can have a much longer payback than replacing incandescent lighting.
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