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SI units: Identify what 'lux' measures. Lux is defined as luminous flux incident per unit area in photometry; it quantifies how brightly a surface is illuminated. Choose the correct option.

Difficulty: Easy

Illuminance (luminous flux per unit area)
Luminous intensity
Luminous flux
Radiant energy

Correct Answer: Illuminance (luminous flux per unit area)

Explanation:

Given data

Unit mentioned: lux.

Concept
In SI, lux (lx) is the unit of illuminance, equal to 1 lumen per square metre (1 lx = 1 lm·m⁻²).

Common pitfalls
Confusing illuminance (lux) with luminous intensity (candela) or luminous flux (lumen).

Final Answer
Illuminance (luminous flux per unit area)

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