A modern 200 W sodium street lamp emits yellow light of wavelength 0.6 $\mu$m. 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

  $62\times {10}^{20}$

• B

  $3\times {10}^{19}$

• C

  $1.5\times {10}^{20}$

• D

  $6\times {10}^{18}$