\(\text { Power } P=2 \times 10^{-3} \mathrm{W}\)
Energy of one photon \(E=h\upsilon\)
\(=6.63 \times 10^{-34} \times 6 \times 10^{14} \mathrm{J}\)
Number of photons emitted per second,
\(N=P / E\)
\(=\frac{2 \times 10^{-3}}{6.63 \times 10^{-34} \times 6 \times 10^{14}}=0.05 \times 10^{17}=5 \times 10^{15}\)