How do eyes perceive different wavelengths of light?

Eyes perceive different wavelengths of light through the activation of specific photoreceptor cells, namely cones and rods.

The human eye is a complex organ that allows us to perceive the world around us in a myriad of colours and shades. This is made possible by the presence of specialised cells in the retina, the light-sensitive layer at the back of the eye, known as photoreceptors. There are two types of photoreceptors: rods and cones. Rods are responsible for vision in low light conditions, while cones are responsible for colour vision and work best in bright light conditions.

The cones are further divided into three types, each sensitive to a different range of wavelengths of light: short (S), medium (M), and long (L). The S-cones are most sensitive to short-wavelength light, which we perceive as blue. The M-cones are most sensitive to medium-wavelength light, perceived as green, and the L-cones are most sensitive to long-wavelength light, perceived as red. This is known as the trichromatic theory of colour vision.

When light enters the eye, it passes through the cornea and the lens, which focus the light onto the retina. The photoreceptors in the retina absorb the light and convert it into electrical signals. These signals are then sent to the brain via the optic nerve. The brain interprets these signals and produces the images we see.

Different wavelengths of light activate the cones to varying degrees. For example, when we look at something red, the long-wavelength light is primarily activating the L-cones. The brain receives this information and interprets it as the colour red. Similarly, when we look at something blue, the short-wavelength light is primarily activating the S-cones, and the brain interprets this as the colour blue.

In summary, our ability to perceive different wavelengths of light and see the world in colour is due to the specialised photoreceptor cells in our eyes and the way our brain interprets the signals they send.