Can Dogs See In The Dark?
I live in the middle of the forest, in an area with no street lights and only one automatic night time light on my side of the house. Going out to my porch at night, though, I would often see two glowing orbs rise in the darkness. No matter how quietly I'd opened the door, I could see my dog looking right at me. The superior hearing of dogs certainly plays its part, but it made me wonder, can dogs see in the dark?
Understanding dog night vision
The simple fact is that dog eyes are structurally different than human eyes. In answering the question, "Can dogs see in the dark?" (or phrased somewhat more whimsically, "Do dogs have night vision?") understanding those structural differences helps demystify dogs seemingly preternatural vision in low light. Dogs have larger pupils, more rods in wider retinas, and a tissue called the tapetum lucidum behind those retinas. These are the mechanisms by which dogs appear to see in the dark.
I say "appear" because dogs cannot see in total darkness any better than we can. The secret to dog night vision is that they make much better use of whatever light is available to them, no matter how little there is. Because of the way dog eyes are constructed, they effectively use any light that's there twice, processing it as it comes into their eyes and reflecting back any excess. It means that dog vision at night, in the dark, or in low light situations may be blurrier or less distinct, but that even the smallest movements can be recognized.
Dogs have larger pupils and wider retinas
Whatever color iris your dog's eyes may have under normal circumstances, look into your dog's eyes when evening is falling and they will appear to be completely black. This is the first step to understanding how dogs can see in the dark. Their pupils dilate wider and wider as the sources of light dim, until their eyes seem to be two giant pupils. These pupils admit all available light, no matter how little there is.
The retina is a net of tissue that lines the inside of the eye and helps to form images from light input. Dog eyes have wider retinas than humans, which means they're capable of processing even very small amounts of light. If you recall your high-school biology classes, you'll know that retinas are where we find the cells that process visual input; namely, rods and cones. Dog eyes have more rods -- which make sense of light and motion -- than their human counterparts. Wider retinas with more rods means that dog eyes are far more sensitive to light, no matter how dim, and better detect movement, no matter how small.
The tapetum lucidum, or the "tapestry of light"
Just behind the retina in dog eyes, you find something that human eyes do not have at all -- a tissue called the tapetum lucidum. A rough but poetic translation from Latin for "tapetum lucidum" is the "tapestry of light." As the retinas draw in whatever light is available to dog eyes, and the rods process them as forms and movement, the tapetum lucidum reflects back whatever is left over for the dog to make use of again. Effectively, dogs can see in the dark because any available light is used twice, once coming in and again reflected back out.
How many photos have you seen or taken of your dog where the flash goes off and it looks like the dog's eyes take on an eerie yellow or green glow? That is an effect of the tapetum lucidum, and is a primary reason why dogs can see in the dark, or at least why their ability to maneuver in low light is five times better than ours. It is also the reason why I could see only my dog's eyes at night with only a single outside light, even at a distance of over 75 feet. It's not that dog eyes are better than ours, just more efficient at making use of any available light source.
Sacrificing focus for sight
What dog eyes gain in their ability to utilize light and detect motion by way of wider retinas, more rods, and the tapetum lucidum, they give up in detail and focus. If you are curious not only as to whether dogs can see in the dark but also what it is they see, it's really a matter of perception. In a letter of August 1799, William Blake, the great poet of vision, wrote that the "tree which moves some to tears of joy is, in the eyes of others, only a green thing which stands in the way."
Dog eyes have more rods than humans, but at the cost of fewer cones, the other set of cells in the retina, responsible for color and detail. I saw only two glowing dots in the dark oriented in my direction, and knew it was my dog. What did my dog see? For a close approximation, think about old grainy photos or the vast majority of pictures people post from a night out on Instagram -- images of shapes that you can just make out, but which tend to be blurry and indistinct. A rough approximation, to be certain, but it gives you some idea of what dogs see in low light.
Does your dog have night vision?
Those of you who have indoor dogs may express wonder at your dog's ability to navigate the home in the dead of night. There's no mystery here, only familiarity. Provided you aren't practicing weekly feng shui or rearranging furniture to maximize your energy, chances are your dog has had every opportunity to know the general layout of its home terrain. Knowing where things are makes it much easier for your dog to "see in the dark," given that dogs can compensate for lack of light by intimate knowledge of their surroundings.
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