A flood light is covered with a filter that transmits red light. The electric field of the emerging beam is represented by a sinusoidal plane wave:

$E_x=36 \sin \left(1.20 \times 10^7 z-3.6 \times 10^{15} t\right) V / m$

The average intensity of the beam will be:

1.72 W/m²

I_av = $\frac{\mathrm{C} \varepsilon_0 \mathrm{E}_0^2}{2}=\frac{3 \times 10^8 \times 8.85 \times 10^{-12} \times 36^2}{2}$ = 1.72 W/m²