Answer
$1.51\times 10^{19}~photons~~$ are emitted each second.
Work Step by Step
We can write an expression for the energy of each photon:
$E = \frac{h~c}{\lambda}$
We can write an expression for the photon emission rate:
$R = \frac{P}{E}$
$R = \frac{P~\lambda}{h~c}$
We can find the number of photons emitted each second:
$R = \frac{P~\lambda}{h~c}$
$R = \frac{(5~W)(600\times 10^{-9}~m)}{(6.626\times 10^{-34}~J~s)(3.0\times 10^8~m/s)}$
$R = 1.51\times 10^{19}~photons/s$
$1.51\times 10^{19}~photons~~$ are emitted each second.
