Humans have about 100 million rods in the retina and 5 million cones
Often people describe rods as the low light, sensitive detectors to differentiate them from cones but much of the function comes from the “wiring” that connects them to the brain rather than fundamental differences between the cells. The “wiring” is configured so that 100 rods can be connected together to provide an input. This means there is a lot of sensitivity but resolution (like the number of megapixels) is lost as a result. The output of cones is not aggregated as much hence sensitivity is lower but spatial resolution is higher.
The best resolution in the retina occurs in the region called the fovea which is a bit like a small pit in the surface of the retina, this is where the highest density of cones occurs.
There are three types of cone cell each with a different peak of spectral sensitivity. Using this difference the eye and brain can derive colour vision.
Simon built an artificial eye at the National Physical Laboratory that accurately mimics the way human eyes view light (pictured). The eye will lead to a better understanding of how new lighting technologies and display systems such as projection TVs and low energy lighting affect eyesight.