Also referred to as scotopic vision, is your natural ability to see in the dark.
In a dark room or outside at night, your eyes like to gather as much light as possible so that they can translate the images in front of you to your brain. Your eyes are able to do this by widening your pupils which means that more light and shapes can enter.
Want to test this? Stand in front of a mirror and switch the light off for a minute. Make sure your eyes are completely closed. Then, still with your eyes closed, switch on the light. Whilst facing the mirror, open your eyes and you will see your pupils shrink! This is because in a brighter setting your pupils have enough light for your eyes to see, so they don’t need to be bigger.
But, it’s not just the pupils that make you able to see in the dark. For that, you have to look at the microscopic cells in the back of your eyes. There are millions of rod-shaped and cone-shaped cells on every eye’s retina and without them, we wouldn’t be able to see.
Cones register bright lights, colours and fine details, and rods help you to see in darker settings because they are more sensitive to light. However, rods don’t process colour - hence why in the dark you don’t see many colours.