Question

Lux is the SI unit of:

• A. Intensity of illumination
• B. Luminous efficiency
• C. Luminous flux
• D. Luminous intensity

Hint:

Lux equals lumen per square metre, think about which quantity that ratio describes.

Answer 1

The Correct Option is A

Step 1: List the related quantities.
In photometry, luminous intensity, luminous flux, and illuminance are three separate but related quantities, each with its own SI unit.
Step 2: Match the units.
Luminous intensity, how bright a source looks in one direction, is measured in candela. Luminous flux, the total light output of a source as seen by the eye, is measured in lumen.
Step 3: Define illuminance.
Illuminance, also called intensity of illumination, tells how much luminous flux falls on a unit area of surface, and it is given by \(E = \dfrac{F}{A}\), where \(F\) is luminous flux and \(A\) is area.
Step 4: Identify the unit.
Since illuminance equals lumen per square metre, this combined unit is given the special name lux.
Final Answer: A) Intensity of illumination.