The number of photons crossing an area in a given time is given by

=Intensity of source; =Energy of a single photon.

If now, two sources have equal intensities, the number of photons emitted in a given time is dependent on the area crossed and the energy of each photon emitted from the two sources as described by the equation above. Hence, it is not always true that for two source of equal intensity, the number of photons emitted in a given time, are equal.