$${R = \frac{P_{kiirg}\lambda}{hf} \\ = \frac{(100\, \mathrm{W})(590 \times 10^{-9}\, \mathrm{m})}{(6,63 \times 10^{-34}\, \mathrm{J \cdot s})(2,998 \times 10^8\, \mathrm{m/s})} \\ = \underline{\underline{2,97 \times 10^{20}\, \mathrm{footonit/s}}}}$$