How does the human eye perceive visible light?

The human eye perceives visible light through a complex process involving the cornea, lens, retina, and optic nerve. Here’s how it works:

1. Light enters the eye through the cornea, the transparent front layer that helps focus the light.
2. It passes through the pupil, whose size is controlled by the iris to regulate the amount of light entering the eye.
3. The lens further focuses the light onto the retina, a light-sensitive layer at the back of the eye.
4. The retina contains two types of photoreceptor cells:
   • Rods, which detect brightness and are active in low light.
   • Cones, which detect color and function in bright light. There are three types of cones, sensitive to red, green, and blue wavelengths.
5. When light hits these cells, it triggers electrical signals.
6. These signals travel through the optic nerve to the brain, particularly the visual cortex, where they are processed into the images and colors we see.

This system allows us to perceive a spectrum of colors in the visible range (approximately 400–700 nm) and respond to brightness and contrast, enabling detailed vision in varying lighting conditions.