In short
- An incandescent bulb turns 90% of its electricity into heat, according to ENERGY STAR. An LED giving the same light uses far less: in our example, 84% less.
- Choose an LED by lumens (the light it gives), not watts: to replace a 60 W bulb, look for at least 800 lumens. Among those that give it, pick the one with the lowest watts.
- An LED doesn’t suddenly burn out: it slowly dims. Its life is counted until it gives 30% less light; ENERGY STAR required at least 15,000 hours.
- The more hours a bulb is on, the faster an LED pays off: start with the living room or kitchen.
How much you save
The traditional incandescent bulb makes light by heating a filament until it glows white hot. According to ENERGY STAR, the U.S. government’s efficiency program, that way it releases 90% of its energy as heat. An LED makes light in a different, far more efficient way, and uses a fraction of the power for the same light.
The sum is the same as for any appliance: (bulb watts − LED watts) × hours a day × 365 ÷ 1,000 = kWh a year you stop using.
- 4 bulbs of 60 W on 5 hours a day, swapped for 9.4 W LEDs: (60 − 9.4) × 4 × 5 × 365 ÷ 1,000 = 369 kWh a year less.
- 1 of 100 W, 3 hours a day, for an 18.8 W LED: (100 − 18.8) × 3 × 365 ÷ 1,000 = 89 kWh a year less.
- In total, 458 kWh a year: 84% less on those bulbs. At 0.20 per kWh that’s about 92 a year in your currency; if each LED costs 3, the five pay for themselves in about 2 months.
Run the numbers with your own bulbs, hours and prices in the LED savings calculator. The rule is simple: the more hours a bulb is on, the more you save and the sooner it pays off. Start with the living room, kitchen or porch, not the storage room.
How to choose an LED: by lumens, not watts
Watts tell you what a bulb uses; lumens, the light it gives. With LEDs it’s worth telling them apart: two 9 W LEDs can give different amounts of light, depending on how efficient each one is. ENERGY STAR advises finding the lumens you need and then choosing the bulb with the lowest wattage. This is its equivalence table:
| Old incandescent bulb | Minimum LED lumens |
|---|---|
| 40 W | 450 |
| 60 W | 800 |
| 75 W | 1,100 |
| 100 W | 1,600 |
| 150 W | 2,600 |
The box often also says “60 W equivalent” or similar: that’s the same comparison.
What a bulb’s label says
In the United States, the box carries the Federal Trade Commission’s “Lighting Facts” label, with the lumens, estimated yearly energy cost, life, light appearance (its colour) and watts. Since summer 2023 it has been illegal to sell inefficient bulbs there, which is why ENERGY STAR stopped certifying light bulbs at the end of 2024: according to the Environmental Protection Agency, it was no longer needed.
In the European Union, since 1 September 2021 bulb labels run from A to G and the letter comes from the lumens per watt. Consumption is given in kWh per 1,000 hours switched on: a 9.4 W LED uses 9.4 kWh every 1,000 hours.
| Class | Lumens per watt | An 800-lumen LED uses |
|---|---|---|
| A | 210 or more | 3.8 W or less |
| B | 185 to 210 | 3.8 to 4.3 W |
| C | 160 to 185 | 4.3 to 5 W |
| D | 135 to 160 | 5 to 5.9 W |
| E | 110 to 135 | 5.9 to 7.3 W |
| F | 85 to 110 | 7.3 to 9.4 W |
| G | under 85 | over 9.4 W |
That’s why, for a 60 W bulb, the calculator suggests a 9.4 W LED: the most a class F LED with 800 lumens would use. If yours has a better letter, it uses less and you save more. (The rules also apply a small factor depending on the type of bulb; for ordinary screw-in bulbs it’s 1.)
How long an LED really lasts
An LED rarely burns out suddenly like old bulbs: it slowly loses brightness. That’s why its life is counted differently: according to ENERGY STAR, it’s the point at which it gives 30% less light than when new. ENERGY STAR required at least 15,000 hours of the LEDs it certified (and 10,000 of compact fluorescents). On 5 hours a day, that’s 15,000 ÷ (5 × 365) = 8.2 years.
Its enemy is heat: ENERGY STAR explains that the higher the temperature it runs at, the faster it loses light and the shorter its life. LEDs have a part that gets rid of the heat; if the box says it isn’t suitable for enclosed fixtures, follow that.
If you have compact fluorescent bulbs
Compact fluorescents (CFLs) already use little, but an LED with the same lumens usually uses less still, and the U.S. Environmental Protection Agency (EPA) notes that LEDs are more efficient and last longer. Check the watts of both on their boxes and run the sum in the calculator.
CFLs contain a very small amount of mercury: about 4 milligrams, according to the EPA. If one breaks, the EPA advises:
- Have people and pets leave the room and air it out for 5 to 10 minutes by opening a window or door to the outside. Turn off central heating or air conditioning if you have it.
- Don’t vacuum: it can spread the powder and mercury vapour. Pick up the pieces with stiff paper and sticky tape, and wipe with a damp paper towel.
- Put everything in a jar with a lid or a sealed bag, take it outside and check with your local council or municipality how to dispose of it: some places require taking it to a recycling point.
Before you swap them
Changing a bulb doesn’t need anyone: switch it off and, if the old one was on, wait for it to cool. If you want to replace the whole light fitting, add a dimmer or touch the ceiling wiring, that’s a job for an electrician.
Sources and references
- ENERGY STAR (U.S. Environmental Protection Agency). Learn About Brightness, Learn About LED Lighting and Program Requirements for Lamps, Version 2.1 (revised June 2020).
- U.S. Environmental Protection Agency (EPA), 13 March 2023. ENERGY STAR Lighting Sunset Memo.
- European Commission. Light sources and Delegated Regulation (EU) 2019/2015, energy labelling of light sources, Annex II.
- U.S. Environmental Protection Agency (EPA). What are the Connections between Mercury and CFLs? and Cleaning Up a Broken CFL.
Frequently asked questions
What LED do I need to replace a 60 W bulb?
One giving at least 800 lumens, according to the ENERGY STAR table. Among those, pick the one with the lowest watts: an LED rated class F on the European label uses at most 9.4 W for that light, and better-rated ones use less.
How long does an LED bulb last?
What its box says: ENERGY STAR required at least 15,000 hours of the LEDs it certified. On 5 hours a day, that’s about 8 years. It doesn’t suddenly burn out: it’s considered worn out when it gives 30% less light.
Is it worth replacing CFLs with LEDs?
Usually, though you save less than when replacing an incandescent, because CFLs already use little. Compare the watts of both at the same lumens and run the sum in the calculator. If a CFL breaks, don’t vacuum it up: it contains a little mercury.
