How do we see? How do our eyes actually translate light into something that our brains can "see"? It all starts in the retina, the thin film of tissue that lines the inside of our eyes. Everything in the front of the eye, the cornea and the lens, focus light on the retina. It's then the job of the PHOTORECEPTORS to turn that focused light into electrical energy.
Rods are the photoreceptors for side vision and vision at night. They are very sensitive to low levels of light, and they also "fire" when there is some evidence of movement. Some night vision problems are caused by diseases of the rods. Complex chemical reactions occur when either a rod or a cone is "excited" by the energy in light, and these reactions create the electrical impulses that eventually become sight!