Question

Illuminance of a surface is measured in:
(A) Lumen
(B) Candela
(C) lux
(D) lux\[{{\text{m}}^{ - 2}}\]

Answer 1

Hint:In this question, the concept of the illuminance is used, that is, it is luminous flux per unit surface area on which the light falls. In illuminance, the light that brightens the surface which is visible to us. The luminance on a surface is the density of the luminous flux incident on that surface.

Complete step by step answer:
As we know that Illuminance is the term that describes the measurement of the amount of light falling on a surface per unit area. Illuminance is the measure of how much the incident ray illuminates the surface. We perceive the brightness of an illuminated area that is also due to the illuminance.


The illuminance of a surface is different from the luminance because luminance measures the amount of light falls on any surface, in luminance, the light travels in the given direction. In luminance light comes from the source or from an object.


To understand the difference between luminance and illuminance, we can see that the light coming from the direct source or coming from an object is luminance and the illuminance is the amount of light falling onto the given surface.

We measure illuminance of amount of light that falls on a surface in terms of foot-candles or lux
The SI unit of illuminance is foot-candles or lux.
We can calculate the illuminance \[\left( E \right)\] by the formula,
\[ \Rightarrow E = \dfrac{\phi }{A}\]
Where, \[\left( E \right)\] is the illuminance and \[\phi \] is the luminous flux that travels outward from a source, and A is the surface area on which the light falls.

Therefore, the illuminance of a surface is measured in lux. So, the option (C) is correct.

Note:In this question, do not be confused between luminance and the illuminance because in luminance the light comes from the object. And in the illuminance, the light falls on the surface.