Ever wonder how your eyes adjust to the dark?
No one can see in total darkness. Fortunately, there’s almost always some light available. Even if it is only dim starlight that’s enough for your eyes to detect. What’s truly amazing is how little light is required for your to see. Human eyes have two main features that help us see better in low light: the pupil’s ability to change size and the eye‘S two types of light sensing cells.
Opening up to let in more light
Your pupils are the black areas at front of your eyes that let light enter.They look black because the light that reaches them is absorbed inside the eyeball. It’s then converted by your brain into your perception of the world. You’ve probably noticed that your pupils can change size in response to light. Outside on a bright sunny day, your pupils become very small. This lets less light into the eyeball since there is plenty available.
When you move to a dark place, your pupils open up to become as large as possible. This expansion allows your eye to collect more of whatever light there is.
From its tiniest size to its most wide open, your pupils can enlarge its area by a factor of only 16 times. You can wee well across changes in light level of far more than a million times. So~~~there has to be something else going on, right?
Switching to different light sensors
That’s where the photoreceptors come in. These are the light sensing cells that line your retina, the back part of your eyeball. The two kinds of photoreceptors are called cones and rods, named because of their shape.
Cones work when there is plenty of light and they are able to respond to different colors of light, providing color vision. They also allow you see fine detail and do things like read when the light is bright enough.
Rods, on the other hand, are far more sensitive to light and incapable of disseminating colors. They also pool their responses together when needed – that makes you more sensitive to light, but also means you are less able to see fine details. That’s why you cannot read a book in the dark, thought you might see its rectangular shape.
As you move from a brightly lit area to a dark one, your eyes automatically change from using the Condé to using the rids and you become far more sensitive to light. You can see in the dark, or at least in very low light.
Just how long does it take?
When you’re in bright light your rods are completely overwhelmed and don’t work. If you flip off the lights, your pupil will immediately open up (dilate). Your photoreceptors start to improve their sensitivity, to soak up whatever light they can in the new dim conditions.
The cones do this quickly – after about 5 minutes their sensitivity maxes out. After about 10 minutes in a darker place, your rods finally catch up and take over. You’ll start to see much better, and after about 20 minutes, your rods will doing their best and will see as well as possible.
Does age affect light adjustment of the eyes?
Aging eyes typically have more trouble adjusting to light changes, often taking longer to adapt when moving between bright and dim environments. This occurs because pupils become smaller and less responsive, and the rod cells, which manage lowlight vision weaken with age.
Older eyes are more susceptible to glare from headlights at night or bright sun during the day. These changes which usually become noticeable around age 40, and more pronounced after age 60, can make driving at night particularly difficult.
If you notice any changes in your vision before your yearly eye doctor visit, Schedule an eye exam
