What quantity is measured in lux and describes how many lumens fall on each square metre of a surface?
ALuminous flux
BIlluminance
CWavelength
DAmplitude
Answer & Solution
Correct answer: B. Illuminance
1. Illuminance is the number of lumens falling on each square metre of a surface.
2. It is measured in the unit lux, written lx.
3. Luminous flux is a different quantity, measuring the total light radiated by a source in lumens, not light landing on an area.
_Source: OpenStax Physics (CC BY 4.0), Ch 15 "Light", section 15.2 The Behavior of Electromagnetic Radiation_
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