# lumen

/ˈɫumən/ (US) · /lˈuːmɛn/ (UK) · CEFR C2 · Noun

Source: https://englishreference.com/word/lumen
Updated: 2026-08-15

## Definition

a unit that measures the total amount of light coming from a source like a bulb. The higher the number, the brighter the light looks to your eyes.

For teachers: the SI unit of luminous flux, equal to the amount of light emitted per second in a unit solid angle of one steradian from a uniform source of one candela.

## Examples

- This LED bulb produces 800 lumens of light.
- When shopping for energy-efficient lighting, consumers should compare lumens to determine brightness rather than relying on wattage.
- The architectural lighting plan specified a minimum of five hundred lumens per square metre to ensure the workspace remained functional during the winter months when natural light is scarce.

## Pitfalls

- Not "This bulb has 60 watts of brightness" but "This bulb has 800 lumens of brightness" — Watts measure power consumption, while lumens measure the actual light output or brightness.

## Usage notes

- Commonly used in the plural when describing the output of lamps or digital projectors.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.