A modern 200 W sodium street lamp emits yellow light of wavelength 0.6 `mum`. Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is
A. `1.5 xx 10^(20)`
B. `6 xx 10^(18)`
C. `62 xx 10^(20)`
D. `3 xx 10^(19)`
