I’m sorry, Gemma. But we can’t live in the light all of the time. You have to take whatever light you can hold into the dark with you. ~ A Great and Terrible Beauty
In the summer of 2022, I participated in a field trip to learn about fireflies, aka lightning bugs. My fellow students and I arrived in Elkmont (an area of the Great Smoky Mountains National Park for those who aren’t from around here), between 5:00 and 5:30 p.m. The sun was still high enough to provide considerable daylight and we strolled around the restored cabins, waiting for darkness to fall.
We eventually headed over to the Little River Road trail and walked up the low-incline, gravel path. After more than a mile we paused and waited for the night to blanket the forest. As we chatted, we took in the views from the river and the remains of homes that had provided a high-altitude escape for city dwellers more than fifty years ago.
Our instructor cautioned us about turning on flashlights or looking at our phones. We needed to let our eyes do what they do to manage the loss of light. Even after 9:00 p.m., our eyes could still discern an incredible amount of detail.
Eventually, the synchronous fireflies made their appearance and it was worth the wait, seeing those tiny little lights blinking in almost perfect unison. I have no idea how the experience would have been different if we’d walked out to our viewing location with flashlights. I only know that as impressive as the fireflies’ display was, the surprise that night was what I learned about my eyes. Their surprising ability, my friend, is the topic of this post.
How much can you see in the dark?
You can see a lot. Humans can’t see in total darkness, but how often are you in that situation? Not often. Ambient light is more useful than you might think, though it can take a little time for your ocular tool to reach its peak ability. West Texas A&M describes the process, which I’ll attempt to interpret–just after a scenario that is mine.
You are fast asleep, hours after nightfall. A noise jars you awake and you open your eyes. At first, you don’t see much, but within a few minutes, you can make out the furniture in the room. You decide your cat has the zoomies and you lie back down and try to return to peaceful slumber.
If you had stayed up for an extended time, instead of dropping back onto your pillow, you would have experienced a noticeable change in your ability to see objects in a low-light environment. This superpower occurs through changes in the pupil, cone cells, and rod cells.
As I have admitted before, I am no whiz at any type of science. I know two parts of my eyes: the pupils and the irises. That’s it. The other two parts mentioned are new to me, and proof that I should have listened better in my 7th grade science class. Sadly, while I know what pupils and irises are, I never learned how they function. Unlike learning geometry, which I believe requires a specific type of physiological wiring, I could have memorized facts about eyeballs, but I didn’t. I am remedying that now. If you’re all over this topic, you may not need to read the next section. Its terms are fairly basic.
The science explained
Maybe it’s just me, but of all the components of other people’s eyes, I notice the irises first. Color? Tint? Twinkly or stone-cold? As it happens, they aren’t just facial features, per A&M. Iris muscles control the size of the pupil. That is, the iris detects the amount of available light and expands or contracts the pupil according to need. As I’m sure you already know, the pupil lets the light in. Ironic, that, since it’s the darkest part of the eye.
The cone cells allow us to perceive colors, as they detect red, blue, and green. They also contain a number of chemicals, one of which is rhodopsin. That chemical is so sensitive to light, it is inactive unless the light is low. When levels reach low light, the cone cells aren’t helpful and rhodopsin reactivates and assists us in our efforts to see in the dark. That brings us to the rod cells.
These cells also contain rhodopsin and are the heroes of our night vision. They enable black-and-white vision, which is what you’re going to get in low light. The rods collect light slowly, and that is why it takes several minutes, maybe even a few hours, to reach maximum vision when light is scarce.
Another source I tapped for a little more context was the Cleveland Clinic. Rod cells are located along the outside edges of the retina and, in addition to supporting night vision, provide peripheral vision. That seems to be the equivalent of a security feature, since we don’t have multiple eyes like spiders do. The location of the cone cells is primarily in the macula, in the center of the eye. Recall that cone cells allow you to see in color. This makes me wonder if folks who have some degree of color blindness have an issue with one or more of their cone cells. You know, like when your printer runs out of magenta and the printed image doesn’t prove to be the visual you hoped for? Just a thought.
Some people have optical issues that seriously impact their ability to see at night. If you’re one of those people, you might want to pay attention to night vision deficiencies, as they could be a symptom of an underlying problem.
Do you see differently now?
The more I learn, the bigger my world gets, and the more I am amazed at every single thing I see. Lest you misconstrue, I still do not fully understand the way eyes work. Not even the tiny portion this post addresses, and it is but a small part of the whole. That makes the entire process all the more incredible. As with every other topic I’ve researched, learning about the gift of sight serves to diminish my inclination to take it for granted. Perhaps I shouldn’t default to a sense of entitlement about anything.
You?
This video is almost 8 minutes, but it contains some fascinating correlations between eye color and other physical abilities. Ironically, the audio matters more than the video. Listen if you have time.
Excellent blog. Thanks for the refresher on. “ Visual Purple”
When we flew night low level missions in the air force all of our lights were red in the cockpit so our rhodopsin wouldn’t dissipate and we could see terrain features.
So glad so many people know more than I do about everything. Otherwise, too many professionals would not be able to function effectively. Insert head-slap emoji.
“To go in the dark with a light is to know the light. To know the dark, go dark. Go
without sight, and find that the dark, too, blooms and sings, and is traveled by
dark feet and dark wings.”
What a lovely verse, and how appropriate! Thank you.
You can observe a lot by just looking. Yoggi Berra
Poor Yogi. I have a book of his sayings – the ones he never actually said. 😉