The energy flux of sun light reaching the surface of the earth is $1.388 \times 10^3 w/m^2$. How many photons (nearly) per sq.m are incident on the earth per sec ? Assume that the photons in the sunlight have an average wave length of $550 \;nm$

Question

$\begin{array}{1 1} 3.84 \times 10^{21} photons /m^2 \\ 3.84 \times 10^{20} photons /m^2 \\ 38.4 \times 10^{21} photons /m^2 \\ 38.4 \times 10^{21} photons /m^2 \end{array}$