Answer
$3.18\times 10^{15}~~$ photons are emitted each second.
Work Step by Step
We can find the energy of each photon:
$E = \frac{hc}{\lambda}$
$E = \frac{(6.63\times 10^{-34}~J~s)(3.0\times 10^8~m/s)}{633\times 10^{-9}~m}$
$E = 3.142\times 10^{-19}~J$
We can find the number of photons emitted each second:
$\frac{1.00\times 10^{-3}~W}{3.142\times 10^{-19}~J} = 3.18\times 10^{15}$
$3.18\times 10^{15}~~$ photons are emitted each second.
