|Image from US National Institutes of Health|
We have millions of photoreceptors in each eye to detect photons. A photon is exceptionally tiny, but if one photoreceptor misses it, there are plenty more to pick up on it. Lots of photons coming in, and our mind makes sense of it all.
Suppose you are an electronic engineer tasked with devising a mechanism that can translate ordinary variations of light into useful information. But here is the tricky part: It has to work inside a living person. Your engineering instincts instantly recognize the mechanism will require multiple parts—primarily a light detector and a data-processing center—working together for a single purpose.You can clearly see the rest by clicking on "Made in His Image: Living Light Detectors Declare Design".
You recall people have been sending messages to each other for centuries simply by flashing a light in a coded sequence. The people who send and receive these flashing messages must know “the code” in advance. However, light is simply a condition of nature—it is either present or it is not. It does not convey information or send instructions to organisms in and of itself. Processing data into useful information happens within the neurological center of an organism. Fortunately, the required data-processing element of the mechanism is already built into the person’s brain, saving you decades of work. All you have to do is devise a sensor to detect light and send that data to the brain. So, how would you begin your task?