Though our eyes aren’t as efficient during low light as a cat or raccoon, there are things you can do to maximize the capabilities that exist. First, we need to understand the physiological facts of your eyes.
The light-sensitive layer of cells at the back of the eyeball is called the retina, the equivalent of the film in a camera. This layer is comprised of two types of cells: rods and cones. The cones require a large amount light to operate and are functional during daylight but are almost useless at night.
The rod cells serve the opposite function. They incorporate Rhodopsin, sometimes called “visual purple,” a light-sensitive protein that activates the rod cells and allows you to see at night.
Rod (night) vision is not as effective as cone (daylight) vision and only allows you to distinguish black, white, shades of grey and the general outline of objects. The eye contains primarily cone cells, concentrated at the rear of the eye where most light falls. The more specialized rod cells are scattered throughout the retina.
Cone cells can be thought of as a high-quality video camera while rod cells are essentially a low-resolution black-and-white webcam.
Several factors affect night vision. Exposure to bright light quickly breaks down the visual purple and blinds the rod cells. A lack of vitamin A can decrease night vision because Rhodopsin is chemically related and deficiency will reduce production of the protein. Illness, headaches, fatigue, drugs, alcohol and heavy smoking also reduce your ability to see at night.
Night vision does not start working immediately after the lights go out. It takes about thirty minutes for the rod cell to produce enough visual purple to activate. Thus, if knowing you are going into a dangerous situation during low light, it is important to spend at least a few minutes in the dark before deploying. If you don’t hurry, by the time you finish checking your gear, your night vision will be much improved.
The problem is that most crisis situations unfold without planning. However, there are a few simple things you can do to help preserve any visual purple already present in your eyes.
Dark sunglasses are an important piece of tactical gear. There are many reasons to wear eye protection (including “looking cool”) but protection of your night vision is a relatively unknown yet important function. On a bright day when suddenly entering a dimly lit area such as a bar or dark hallway, sunglasses allow you to adjust much faster to ambient light levels in order to better detect possible threats.
One common night-vision-killer is your vehicle’s interior lights when exiting or entering. Opening a door instantly leads to a flood of white light that quickly dazzles vision but there are several workarounds. You can remove the bulbs or purchase either red bulbs/red lens tape from an automotive store. Fortunately, many newer vehicles have a switch that will disable interior lights. Leaving the interior lights disabled is standard procedure on police cars and military transports but should likewise be normal practice on private vehicles.
Aside from preserving vision, a blacked-out vehicle also prevents you from being a highly visible target to anyone outside. If you have concerns about someone hiding in the backseat, a quick flash with your pocket flashlight (which you always carry!) will resolve that concern.
All tactical lights should have a red filter to preserve night vision when searching or navigating. Unfortunately, while most weapons or larger handheld lights have some type of vision-saving bulb or filter option, most small Every Day Carry (EDC) lights do not. This falls into the category of “Do the best you can with what you have on hand.” In such cases, use a lower power setting when possible.
Even without artificial light there is usually enough ambient illumination that your eyeballs are still functional, making “off-center vision” a very useful dim-light technique. Rod cells are not located in the center of the retina; the most dark-sensitive region is located six to ten degrees off-center. Thus, if you want to better see someone’s face, you will need to look at their ear. When evaluating a landmark or object, look several feet left or right of it. It takes some practice but you will be amazed at how well this works.
You must also “scan” with your night vision. Even in dim light the visual purple eventually bleaches out within 4 to 10 seconds, causing individual rod cells to cease functioning. To compensate, simply shift your glance every few seconds and avoid staring. You have probably noticed that the harder you stare at something in the dark, the more it will seem to float and jump and finally disappear. This is due to the degradation of visual purple.
While electronic night vision devices have evolved to the point where darkness doesn’t pose any substantial hindrance, the old Mark I eyeball is still less bulky, easier and much faster to deploy. Practice these techniques and you’ll be surprised at how well you can “own the night.”