This spring break I travelled to Tucson, Arizona to visit some family. Tucson does not have very many clouds and most days have a clear sky and lots of sunshine. Since the sun is always shining your eyes get accustomed to the brightly lit environment for the length of the day. But while I was there we visited the nearby Kartchner Caverns. So when I went to the caverns and entered the dark, barely lit caves I couldn’t see a thing and my vision took a few minutes to adjust. After about three minutes my eyes were finally able to adjust and I could start to see some of the caves details. But it was a slow process and I felt impatient that I couldn’t adjust to the darker environment quickly. After touring the caves we exited back out into brightly lit desert and once again I was blinded in my new environment but this time my eyes were able to adjust and adapt much quicker than before. I was able to get a strong sense of my surroundings and was able to see clearly again within a minute.

The reason that our eyes adjust to light and dark at different rates is based on the properties of the rods and cones within our retina. Rods are very sensitive to light so when we are in dimly lit and dark areas we rely more on our rods to see, while cones on the other hand are less sensitive to light and are more dominant in well lit areas. Cones and rods also differ in their ability to regenerate, which comes into play in this scenario. Cones are able to adjust quickly as the pigment within them regenerates every six minutes, but rods are much slower. It takes their pigment about a half hour to regenerate. This difference in regeneration speed is crucial to difference between light and dark adaptation.  Since we use rods in dark places, it takes longer for our eyes to adjust to those places because the pigment takes so long to regenerate in our rods. But when going back out into a well-lit area, then our cones take over and we can adjust quickly to it’s the rapid regeneration of pigment that goes on within our cones.

So when I first entered the dark caverns from the bright desert environment my eyes had to adjust from light to dark which meant a transition from cones to rods. These rods took a while to adapt and adjust which is why I had difficulty seeing clearly for a few minutes. But once the rods within my retina were able to adjust then I had no problem seeing. And as I left the caverns and went back out into the sunlight my eyes had to once again adjust and switch back to the cones being dominant. Since the cones adjust much quicker I was able to see fine relatively quickly.