Why light

Well, it is a very interesting question that why do we only see the visible light. It is a special small range of the electromagnetic wave.

Longer

With longer wave length, it can pass the materials by bypassing the gaps between molecules. Such as radio wave, which can reach our devices through walls, buildings.

Shorter

With shorter wave length, it can pass the materials by directly going through them because of the high energy. Such as X-ray, which can go through our bodies.

Light

Light might be a perfect solution from all animals with eyes. All animals see the world in the same way, with similar wave lengths. That is possibly because we do not want to see through things. We do not expect running into something that cannot be seen by other wave lengths of electromagnetic wave.

We need to feel the world perfectly, so that all eyes chose the similar range of wave length to see, making sure that it cannot pass the objects. When it comes to the size of an eye, there is no problem that we ignore something within nanometers.

I see you without seeing through, so that I know you are there, and you always will be.