If a 120-W lightbulb emits 3.5 % 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 2.2 m 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 1.5 km away?
