Calculating Illuminance

Choose the equation and list the knowns.

Equation: $\text{illuminance =}\frac{P}{4\pi r^2}$

P = 2,000 lm

π = 3.14

r = 2.00 m

Substitute the known values into the equation.

$$\begin{array}{ccc}\hfill \text{illuminance}& \hfill \text{=}\hfill & \frac{P}{4\pi r^2}\hfill \\ \hfill & \hfill \text{=}\hfill & \frac{\text{2,000}\text{ lm}}{4(3.14){(2.00)}^2{\text{ m}}^2}\hfill \\ \hfill & \hfill \text{=}\hfill & 39.8{\text{ lm/m}}^2\hfill \\ \hfill & \hfill \text{=}\hfill & 39.8\text{ lx}\hfill \end{array}$$