# lux

/ˈɫəks/ (US) · /lˈʌks/ (UK) · CEFR C2 · Noun

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

## Definition

a unit used to measure how much light falls on a surface. You use it to describe how bright a room or a screen is.

For teachers: the SI unit of illuminance, equal to one lumen per square metre. Used to quantify the intensity of light as perceived by the human eye hitting a specific area.

## Examples

- The office lighting should be at least 500 lux for comfortable reading.
- The technician used a light meter to ensure the film set reached the required lux for the camera sensors.
- While a moonless night might provide only 0.0001 lux, a bright summer day can exceed 100,000 lux, demonstrating the incredible range of human visual adaptation.

## Usage notes

- The plural form is also 'lux'. Often used in technical specifications for cameras, projectors, and workplace safety standards.

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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.