Light Intensity: Definition & Applications

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Light intensity is defined as the energy per unit area per unit time, expressed mathematically as d(energy)/dtdA. It can be represented as E/(A.t), where E is the energy related to the number of photons, n, and their frequency, hf. When all photons have the same frequency, this definition aligns with counting the number of photons. In cases with varying frequencies, a Fourier integral is necessary for accurate representation. Understanding light intensity is crucial for applications in fields like the photoelectric effect and electromagnetic emissions.
RavanDi
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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 :smile:
 
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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.
 

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