The correct answer is: A. intensity of illumination.
Lux is the SI unit of illuminance, which is a measure of the amount of light that is incident on a surface. Illuminance is equal to the luminous flux per unit area, and is measured in lux (lx).
Luminous efficiency is a measure of how efficiently a light source emits visible light. It is defined as the ratio of the luminous flux to the radiant flux, and is measured in lumens per watt (lm/W).
Luminous flux is a measure of the total amount of visible light emitted by a light source. It is measured in lumens (lm).
Luminous intensity is a measure of the strength of a light source in a particular direction. It is defined as the luminous flux per unit solid angle, and is measured in candelas (cd).
In brief, lux is a measure of how much light is falling on a surface, while luminous efficiency is a measure of how efficiently a light source emits visible light. Luminous flux is a measure of the total amount of visible light emitted by a light source, and luminous intensity is a measure of the strength of a light source in a particular direction.