Energy\; of\, a \, single\, photon=\frac{hc}{\lambda }
\frac{6.626\times 10^{-34}\times 3\times 10^{8}}{450\times 10^{-9}}=4.42\times 10^{-19}J
Number\, of\, photons=\frac{Total\, Energy}{Energy\, of\, photon}=\frac{1\times 10^{-3}}{4.42\times 10^{-19}}=\, 2.26\times 10^{15}
There u go...