How do humans perceive light?

Thanks to our visual organ, the eye, we can detect Light. The eye is composed by a complex system that is sensitive to light changes, capable of transforming these impulses into electrical impulses.

The interior of the eye is a dark cavity that has to avoid that light enter through and reflections and illusionary images be produced. The pupil is an opening that permits light pass into the interior of the eye. It is controlled by the iris, which is the muscle that makes the pupil dilate or contract according to light exposure. The iris at the same time is covered by the cornea, and the lens of the eye is situated behind the iris. This lens has the function of focusing the light into the retina, which acts like a screen. The retina converts these images into neurological signals.

The essential factors in the conditions that affect the vision are the distribution of the light and the contrast of the luminance.
There are two types of light sensitive cells in the retina: the cones and the rod cell. The rod cells are used for the vision in black and white, and they are concentrated in the sides of the retina. The cones are used for colour vision and are concentrated in the centre of the retina. There are three types of cones: sensitive to red, sensitive to green and sensitive to blue light.
The visibility of an object can be altered in many ways. One of the most important is the contrast of lighting due to factors of reflection, to shadows, or to the colours of the object itself and to colour reflection factors. What the eye actually perceives are the differences in luminosity between an object and its environment or between different parts of the object itself.