Keep the light useful
The FTC’s Lighting Facts guidance distinguishes brightness, shown in lumens, from energy use, shown in watts. A lower watt number alone does not prove that two bulbs provide an equivalent amount of useful light. Match the brightness you need before comparing operating costs.
Also check the appearance of the light, the bulb shape and base, and compatibility with the fixture or dimmer. The Department of Energy’s lighting guide explains why LED technology can reduce energy input compared with incandescent lighting. The exact difference in your home comes from the actual products and the hours you use them.
Calculate one bulb, then scale carefully
For this example, assume the old bulb draws 60 W and the replacement LED draws 9 W, and both provide suitable light for the task. Each is used four hours per day on 365 days at $0.18/kWh.
| Example bulb | Annual energy | Annual electricity cost |
|---|---|---|
| 60 W | 87.60 kWh | $15.77 |
| 9 W LED | 13.14 kWh | $2.37 |
The unrounded difference is $13.4028, or $13.40 per year. Five identical replacements on that same schedule would save $67.01 annually when rounded at the end. This is an arithmetic illustration, not a guaranteed household saving.
Prioritize the lamps you actually use
A hallway lamp used for a few minutes daily has a different opportunity from a desk lamp used every evening. List each bulb’s watts and realistic operating hours rather than multiplying the number of fixtures by one optimistic schedule.
In the same 60 W versus 9 W example, only one hour per day would reduce the annual saving to about $3.35. If a replacement costs an illustrative $4, its energy-only payback is roughly 3.6 months at four daily hours, or 14.3 months at one daily hour. Purchase price, use and equivalence all matter.
Check the whole arrangement
If your home already uses LEDs, replacing a working LED with another similar LED may offer a much smaller energy difference. Recalculate using the two actual wattages. Do not apply an incandescent-to-LED example to an LED-to-LED purchase.
A lamp that is unpleasant to use may lead you to switch on several others. Make the comparison at the level of the room or task when that happens. Keep comfort, glare and compatibility in the decision alongside dollars.
For a 30-day estimate, use the running cost calculator for each option. For a precise 365-day annual comparison, multiply daily consumption by 365; twelve 30-day months cover only 360 days.
Choose your next step
Continue with the question that matches your next decision:
Sources & further reading
Numerical examples are illustrative unless explicitly described as measured. This guide does not claim hands-on product testing. Read the methodology and editorial disclosure.