Problem: If a 110-W light bulb emits 2.5% of the input energy as visible light (average wavelength 550 nm) uniformly in all directions.
Part A) How many photons per second of visible light will strike the pupil (4.0 mm diameter) of the eye of an observer 1.6m away?
Part B) How many photons per second of visible light will strike the pupil (4.0 mm diameter) of the eye of an observer 1.2km away?
I need help for the above question.