# Before Einstein introduced the quantum theory of light, what was the explanation given for different intensities of light of the same frequency?

Before Einstein introduced the quantum theory of light, what was the explanation given for different intensities of light of the same frequency? How does the em theory of light explain intensity? Because intensity is amount of photons per area per second but that means you had to consider light as quanta which the em theory didn't do

• Light intensity, or irradiance is power/area. After introducing photons you can then calculate photons/area/s. And light is very well explained by Maxwell equations. Mar 8 at 10:29
• Mar 8 at 13:26

It can be defined as the Poynting vector, $$\mathbf{S}=\mathbf{E}\times\mathbf{H}$$, of the electromagnetic wave.