For years it’s been a tradition in the Carl household to sit around our fire pit on a beautiful fall night after Thanksgiving. We relax, make s’mores, and talk about getting together over the next few months.

One evening, our grandson had noticed a pair of glowing eyes peeking through the underbrush at us and scooted his chair a little closer to his grandpa. My husband explained there was nothing to be afraid because it was probably a raccoon looking for a s’more!

I wondered if cavepeople saw shining eyes watching from the darkness and were as frightened as our grandson.

I recently attended a five-day workshop at the DaVinci Center learning how to help students become thinkers when it comes to science instead of learning unrelated facts that were spoon-fed to them.

My assignment was to choose a topic to investigate for my phenomena and I decided on eyeshine. When light enters the eyes the retina processes the light as images using the photoreceptor cells in the eyes called rods and cones. The images are signals sent to the brain via the optic nerve so the brain can interpret them. Simply put, this is called “sight.”

Rods don’t distinguish colors and function best in the dark while the cones distinguish between colors and function best in bright light. Animals with the brightest eyeshine have more rods and fewer cones in their retinas. As a result, they have excellent night vision, but most are color-blind.

Eyeshine occurs when light enters the eye, passes through the rods (light receptors) and cones (color receptors) of the retina and strikes the membrane behind the retina. This causes the light to be reflected back through the eye and outward.

The glow can be attributed to a particular layer of the eye which is known as the tapetum lucidum derived from Latin meaning “bright tapestry.” Eyeshine is more common in mammals, but spiders, alligators, and frogs that also have this adaptation.

Interestingly enough, humans, primates, squirrels, kangaroos, and pigs don’t have this layer. So that made me wonder why in these instances the eyes look red?

“Red-eye” in photographs is caused because the flash travels through the pupil and hits the retina at the back of the eye.

Eyeshine coloration varies from the glowing reddish orange of the alligator to the yellows and greens of the deer and cat families. Each species has its own distinct “signature” color. Just what causes these color differences remains a mystery It varies with angles at which the light strikes the eye, the species, the type of light and the amount of light.

Common colors are green, yellow, reddish orange while blue, turquoise, or pink being the most uncommon. Some studies have attributed such minerals as riboflavin and zinc and how they are processed by various animals as an explanation for the various colors. These differences in mineral levels will vary within one species so other contributing factors include things like nourishment, age, and the number of the layers of the reflective material.

Nocturnal animals have the ability to use the available light several times, once on the way in, as it ricochets off the inside of the eyes, and on the way out giving them additional light to see by. This allows animals to see clearly using only about one-sixth the light needed for human vision.

A college professor once explained that if a barn owl could read, it could read a newspaper in almost total darkness at a distance of 300 feet.

I would never survive in the wild because I can’t see which key is which when I am standing on my deck even with the night lights on.

Jeannie Carl is a naturalist at the Carbon County Environmental Education Center in Summit Hill. The center rehabilitates injured animals and educates the public on a variety of wildlife found in the area. For information on the Carbon County Environmental Center, visit www.carboneec.org.