Humans can actually see well in the dark once adjusted but generally without colour (due to using rods rather than cones in the eye). The colour is probably what makes this video appear incredible to us as its not how we are used to percieving darkness (even with eg night vision).

As to the technical question according to this you need 90 photons for a 60% chance at a human response

http://math.ucr.edu/home/baez/physics/Quantum/see_a_photon.h...