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LED bulb labels: what lumens, watts and kelvin tell you

Three packages, three numbers and a surprise: fewer watts can mean the same light output. Compare the labels, try two decisions and make a shopping note.

By Coru · Published · Updated

The lower-watt bulb can give the same light output

Imagine replacing a bulb you like: 800 lm and 2700 K. You find these three fictional options on the shelf. Which keeps both its stated light output and its colour appearance? Hold off on choosing the biggest number.

The figures are invented for practice. They compare only light output, power and colour appearance; you still need to check whether each bulb suits your fixture.

Three labels, three decisions

A   800 lm    8 W    2700 K
B   800 lm    7 W    4000 K
C   450 lm    5 W    2700 K

Fictional example. lm = lumens; W = watts; K = kelvin.

1. Follow lumens to compare light output

Lumens (lm) describe the amount of light emitted. A and B state the same output: 800 lm. C states less: 450 lm. Watts (W) describe electrical power; B requires less power than A according to these labels, although both state the same lumens.

If you only remember the wattage of a traditional incandescent bulb, the US Department of Energy gives these approximate reference points: 40 W → 450 lm; 60 W → 800 lm; 75 W → 1100 lm; 100 W → 1600 lm.

Use them as a guide to light output. “60 W equivalent” does not mean the LED uses 60 W or confirm that it suits your fixture. Whenever possible, compare the actual lumen figures on both labels.

2. Follow kelvin to choose the appearance

Colour temperature, expressed in kelvin (K), describes the appearance of white light. A lower value corresponds to a warmer, more yellow appearance; a higher value to a cooler, more blue appearance. 2700 K is a warm reference point; 4000 K looks cooler.

So B changes the appearance in this example while keeping the 800 lm. Kelvin tells you neither how much light the bulb emits nor its surface temperature. To repeat a colour appearance you already like, note its K value; to change it, decide what appearance you want.

Your first choice: keep the output and appearance

Choose an answer; explanations are also available without JavaScript.

You want the same 800 lm and 2700 K as the original example. Which label matches both?

Answers and explanations
  • A: 800 lm · 8 W · 2700 K: A matches the lumens and kelvin. Its 8 W is the stated power; you still need to check compatibility.
  • B: 800 lm · 7 W · 4000 K: B keeps the lumens and states lower power, but changes from 2700 K to 4000 K.
  • C: 450 lm · 5 W · 2700 K: C keeps the kelvin value, but states 450 lm instead of 800 lm.

Answers and explanations

  • A: 800 lm · 8 W · 2700 K: A matches the lumens and kelvin. Its 8 W is the stated power; you still need to check compatibility.
  • B: 800 lm · 7 W · 4000 K: B keeps the lumens and states lower power, but changes from 2700 K to 4000 K.
  • C: 450 lm · 5 W · 2700 K: C keeps the kelvin value, but states 450 lm instead of 800 lm.

3. Check what those numbers leave out

The same lumen figure does not promise the same result on a table: one light may concentrate its output in a beam while another spreads it more widely. For directional bulbs, compare beam angles too.

Before buying, check the package, the model specifications and the fixture instructions:

  • Base and voltage: match the type and voltage the fixture requires. Two bulbs looking alike is not enough.
  • Dimensions: check length and diameter as well as the base. The bulb must fit the available space.
  • Dimming: if you use a dimmer, look for a dimmable bulb and confirm compatibility with that dimmer.
  • Enclosed fixture: if the bulb will be fully enclosed, check that the manufacturer allows that use.
  • Use limits: follow the fixture’s maximum wattage and all other conditions for the fixture and bulb. A light-output equivalence does not replace those instructions.

Your second choice: a missing piece

Choose an answer; explanations are also available without JavaScript.

Your fixture has a dimmer and a fully enclosed cover. A package shows only 800 lm, 8 W and 2700 K. What can you conclude?

Answers and explanations
  • It is suitable because it uses only 8 W: Low wattage does not establish dimmer compatibility or suitability for a fully enclosed fixture.
  • It is suitable because 2700 K means it stays cool: 2700 K describes the appearance of the white light, not the bulb’s temperature.
  • Information about dimming and enclosed use is still missing: Check the model specifications and instructions. You need to confirm both conditions, as well as base, voltage, dimensions and use limits.

Answers and explanations

  • It is suitable because it uses only 8 W: Low wattage does not establish dimmer compatibility or suitability for a fully enclosed fixture.
  • It is suitable because 2700 K means it stays cool: 2700 K describes the appearance of the white light, not the bulb’s temperature.
  • Information about dimming and enclosed use is still missing: Check the model specifications and instructions. You need to confirm both conditions, as well as base, voltage, dimensions and use limits.

If you see the European energy label

The European light-source label uses the A–G scale and shows consumption in kWh per 1000 hours. Its QR code leads to the model information in EPREL, where you can check details such as luminous flux, colour temperature and cap type. The energy class does not replace lumens or kelvin.

The note to take shopping

Fill this in before comparing packages: “I want ___ lm and ___ K; base ___; voltage ___; available space ___; dimmer ___; fully enclosed fixture: yes/no.” Add any special conditions specified by the manufacturer.

A matches the output and appearance you wanted. If it also passes the compatibility checks, you have a choice that fits your needs.

Sources & further reading

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