Yes, the rods and cones can detect a very, very small number of photons exciting it. However, the difference between a cell responding to a single photon, and the brain recognizing and processing that into a picture, is a world of difference. If nothing else, that 1 photon means that you're essentially blind in one eye.

The other problem, just practicality, of course, is that a flashlight that emitted such a small number of photons would be fairly useless because A) you can't gaurantee that the photons emitted would be reflected directly back to your eye, and B) even if they were, you'd only see the one thing it bounced off of. Meaning, you'd miss the tree in your way, only to walk off the cliff.

On the other hand... that's some pretty fancy math work!