energy for 1 photons:
[tex]E=h\dfrac{c}{\lambda} [/tex]
1.00 mW = 1 x 10⁻³ J/s
so number of photons emitted:
[tex]n=\dfrac{1\times 10^{-3}}{h\dfrac{c}{\lambda} }\\\\\tt h=Planck's\:constant(6.626.10^{-34} Js)\\\\\tt c=speed\:of\:light=3.10^8m/s\\\\\lambda=wavelength(m)
[/tex]
[tex]\tt n=\dfrac{1\times 10^{-3}\times 337\times 10^{-9}}{6.626\times 10^{-34}\times 3\times 10^8}\\\\\boxed{\bold{n=1.695\times 10^{15}}}[/tex]
