[john !!]

(Original post by AntiMagicMan)
I would say amount of photons. Because the energy of a wave is proportional to the amplitude squared, and the energy of photons is proportional to the frequency, a bigger amplitude means more energy and hence more photons are required in a given volume, or area.

So basically i'm voting in favour of Willa's explanation.

won't a bigger amplitude also indicate photons with higher frequencies as that also leads to more energy?

[habosh]

(Original post by mik1a)
won't a bigger amplitude also indicate photons with higher frequencies as that also leads to more energy?

no according to this low e=Hf the energy only depends on the frequancy while number of photons per sencond depends on the intensity