Light Intensity: Definition & Applications

[RavanDi]

Hi,
I just came to this problem when I was studying the photoelectric effect, what is the exact definition for "light intensity" ? Is it just n (the number of photons) or is it E/(A.t) where E=nhf ? The latter can be the same as the former in comparison when we suppose the frequency is the same. We use the "intensity" term with the second formula in many topics like: I (for sounds), I (for electromagnetic emission), ...
Thanks for your time

 

[Meir Achuz]

Intensity is d(energy)/dtdA, so you are right,
if all photons have the same frequency.
If there is a range of frequencies, you need a Fourier integral.