# luc

/ˈɫuk/ (US) · CEFR C2 · Noun

Source: https://englishreference.com/word/luc
Updated: 2026-05-06

## Definition

a unit of light that measures how much light hits a surface. You use it to talk about 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.

## Usage notes

- The plural form is also 'lux', though 'luxes' is occasionally found in older technical texts.

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