Question

What is the illuminance on an object that is 1.50 m away from a light source with a luminous flux of 665 lumens?1) 1.87 lx2) 3.53 lx3) 23.5 lx4) 425 lx

Answer 1

Given data:

* The illuminance of an object is 1.5 m.

* The luminous flux is 665 lumens.

Solution:

The illuminance in terms of the flux and distance is,

`E=(P)/(4\pi* d^2)`

where P is the flux, and d is the distance of the object,

Substituting the known values,

`E=(665)/(4*\pi*(1.5)^2)`

By solving the above values,

`E=23.5\text{ Ix}`

Thus, the illuminance is 23.5 Ix.

Hence, 3rd option is the correct answer.