Answer
$2.96\times 10^{20}~photons/s$
Work Step by Step
We can find the photon energy:
$E = \frac{hc}{\lambda}$
$E = \frac{(6.63\times 10^{-34}~J\cdot s)(3.0\times 10^8~m/s)}{589\times 10^{-9}~m}$
$E = 3.377\times 10^{-19}~J$
We can find the rate at which photons are emitted:
$\frac{100~W}{3.377\times 10^{-19}~J/photon} = 2.96\times 10^{20}~photons/s$
