Estimating the following numbers should be interesting. The number tells you why our eye can never count photons, even in barely detetable light.
The number of photons entering the pupil of our eye per second corresponding to the minimum intensity of white light that we humans can perceive `(~10^-10 Wm^-2)`. Take the area of the pupil to be about `0.4 cm^2`, and the average frequency of white light to be about `6 xx 10^14 Hz`.