Does the angle that the light ray hit the sensor affect its energy? Say, does a light ray in a normal direction of the sensor carry the same energy as the same light ray that is from a different direction?
I am a little confused about the other direction. Do we need an assumption that all radiant energy is received by the sensor to state that the time integral of flux is total radiant energy?
How are these (and more complex) integrals computed in practice? Fancy GPU hardware?
Why can we assume that the amount of energy received per unit time is constant?