Rods are only capable of seeing shades of grey, and they are only used at night after a period of dark adaptation. Rods provide a visual acuity of 20/200. If you see any color day or night, you are using cones. Also, if you look at something directly with night vision (rods) the image bleaches out of vision after a few seconds. The object disappears! All of this is important if dealing with colors. Colors are viewed with day vision(cones). And, you don't lose visual acuity as with rods. I'm bringing this up so that there is no misunderstanding how this part of the perception issue functions.