Question

What is the irradiance measured at a distance of 1 m and 2 m from a 1 W light point source

Answer 1

Using the concepto of Irradiance which is the radiant flux (power) received by a surface per unit area we have that,

$I = \frac{P}{A}$

Here,

P = Power

A = Area

The propagation of the irradiance is carried out in an area proportional to that of a sphere we will then have,

$I = \frac{P}{4\pi r^2}$

Irradiance at a distance of 1m from the source of light is

$I = \frac{1W}{4\pi (1)^2}$

$I = 0.0796W/m^2$

$I = 0.08W/m^2$

Irradiance at a distance of 2m from the source of light is

$I = \frac{1W}{4\pi 2^2}$

$I = 0.0198W/m^2$

$I = 0.02W/m^2$