Seeing In The Dark
It’s official. The clocks have gone back and winter is well on its way. You will probably be travelling to and from work in the dark. The human eye is amazingly adaptive and can cope with most light levels. However, your eyes don’t work as well at night as they do in daylight.
Our retinas have two forms of light receptors …rods and cones. Rods work in low light situations and cones, which give us colour vision, in daylight. Cones tend to be densely packed together at the fovea (the centre of our retina). That’s why we have high definition vision in daylight. It’s also why we need the lights on at night if we want to read or see clearly when driving. In low light levels cones switch off and the rods kick in. Rods are spread across the retina but are densest slightly offset from the fovea. Have you ever noticed when looking at stars in the night sky you don’t see them if you look straight at them but if you look slightly off to one side they become visible? That’s because you are using your rods which are very sensitive in low light conditions. Cones only function in high light conditions. If you drive you have probably noticed at dusk you really cannot see very well. That’s because it’s too bright for rods and too dark for cones.
When we drive we use our central vision (cones) for HD vision and our peripheral retina is more for peripheral awareness and motion detection. As we age cataracts develop. These cause problems with glare from car headlights. Some of us will develop macular degeneration which reduces the clarity of our vision and our eyes take much longer to recover from being dazzled by oncoming bright lights.