Rods and cones: threats, stars and roses
What are they? Light-sensitive cells in the retina of our eye. They are called photoreceptors, which means they respond to light that hits our retina, sending signals down nerves to our brain, enabling us to see. There are about 100 million rods and 5 million cones in the retina. Why do we have two types of photoreceptors? Because they do very different jobs. Cones are sensitive to colour and don’t work well in low light. Rods don’t respond to colour but come into their own in very dim light. We see very little colour in a dark room because it’s predominantly the rods that are working then. How can rods protect us from lurking danger? Rods and cones also differ in their position on the retina: the cones are concentrated in the centre; and the rods, which are also very sensitive to objects moving in our field of vision, predominate in the periphery. So the photoreceptors that dominate in our peripheral vision are the most light- and movement-sensitive, helping us spot threats in the corner of our eye. And help us see stars? If you want to see a dim star more clearly, don’t look straight at it. Use your ultrasensitive rods to get a better view by looking slightly away from it. How can rods and cones make red roses change colour? Rods aren’t very sensitive to red light. So in bright daylight, when the colour-sensitive cones predominate, red rose petals appear bright compared to the green leaves. But when the light fades, and the rods become more effective, the red petals look dull in comparison to the leaves.