scotopic vision happens when there is not enough light for the cone cells in the eye to work. The rods, though, need much less light to function.
The rod cells are not sensitive to color, though. This is why in very dim light we see in black and white.
Scotopic vision happens with illumination levels between 10-6 and 10 cd/m2. If there is more light than that, photopic vision dominates.
Another particularity of scotopic vision is due to the fact that in center of your eyes there are not many rod cells. This is why if you want to see something at extremely low light levels it is better not to look at it directly.