A sodium lamp emits light at the power P = 100 W and at the wavelength λ = 570 nm?

A sodium lamp emits light at the power P = 100 W and at the wavelength λ = 570 nm, and the emission is uniformly in all directions. The frequency is 5.25951681*10^14 Hz, and the energy of each photon in the emission process is 3.48499271*10^-19 J. Photons are emitted from the lamp at a rate of 2.86944647*10^20 photons/second.

a) At what distance from the lamp will a totally absorbing screen absorb photons at the rate of 1.00 photon/(cm^2*s)? 

b)What is the rate per square meter at which photons are intercepted by a screen at a distance of 3.00 m from the lamp?

2017-04-11T00:37:33.809Z