Light and seeing

Eyelids and eyelashes protect the eye, and tears keep it moist. In the middle of the eye is the pupil, with the coloured iris around it. In bright light the pupil gets smaller; in dim light it gets bigger. Light reflected from an object passes through the pupil to the retina inside the eye. The retina has light-sensitive cells: cones tell colours apart, while rods work in dim light but cannot tell colours, so in the dark everything looks grey. The signal goes along the optic nerve to the brain and we see. When sunlight passes through a glass prism it splits into seven colours: red, orange, yellow, green, light blue, blue, violet. After rain a rainbow appears when sunlight passes through water drops in the air. Eye care: do not rub them with hands, do not look at screens for long from close up, read in good light, never look straight at the Sun.