The desire to see in the dark was probably created when the first caveman awoke in the middle of the night after hearing something moving around in the brush. Technology has now made this possible.
Humans have a limited ability to see in the dark once they allow their eyes to adjust to the darkness. This is most effective when there are no sources of light, such as streetlights or nearby homes or buildings.
The goal is to allow the eye’s iris to open wider, which occurs naturally in dark conditions. As the iris opens, the pupil becomes larger, allowing more light to reach the retina, which is comprised of light-sensitive tissue and covered with two kinds of photoreceptor cells. These cells, which send signals to the brain that determine what’s seen, include rods and cones; the rods are capable of “seeing” in low-light conditions but only in black and white, while the cones that provide color work best under well-lit conditions. As a result, under very dark conditions, humans have, at best, very limited vision.
There are two ways that an object can be seen. One way is if the object produces light, such as a star in the sky, a light bulb, or a burning match. The other way that an object is visible is if it reflects light; an example is walking into a dark room and seeing nothing but perhaps a few shadows. But upon turning on the light, an array of furniture is visible as the light reflects from it, scattering across the room.
The Good Old-Fashioned Flashlight
When there aren’t any objects producing light and no light switch at hand, your best option is to use a flashlight to replace darkness with light. Handheld flashlights are the most commonly used see-in-the-dark tools, with the light output measured in lumens. While a 7,000-lumen light used by rescue personnel is ideal for illuminating a wide swath of the outdoors, if it were to be used indoors, it could be overwhelming. A flashlight capable of producing a beam of about 1,000 lumens is good for all-around use, while military and law enforcement personnel might prefer those capable of producing 3,000 or more lumens.
Newfangled Night Vision Devices
The next level of night vision is thermal imaging, which provides an image of infrared light in the form of a heat signature. This is often used by law enforcement agencies to determine if a structure is occupied and, if so, by how many people. Night vision devices (NVD) are a more technologically advanced option and can be had in two versions: traditional NVD and digital night vision.NVD systems use an image-intensifying tube to collect and then amplify both infrared and visible light reflecting from objects, displaying them in the form of a somewhat blurred green image. NVDs are bulky and used primarily by military and law enforcement agencies, which overlook the lack of clarity as well as the high expense, limited useful life, and potential for damage from knocks or drops.
Digital night vision systems, on the other hand, produce crisp, full-color images at a fraction of the cost of NVD. These systems use a digital image sensor to capture light, which is then digitally enhanced to produce a clear picture.
At a Glance: Say, Can You See?
The Eyes Have ItTo a limited degree, our eyes let us see in the dark, by adjusting to provide a black-and-white image.
Flashlights are the most commonly chosen tool to see what goes on after dark, by replacing it with light. A green LED that minimally affects normal night vision while providing better detail than red lights, is a good choice for neighborhood walks or camping.
Sionyx’s Aurora digital night vision systems provide a clear, crisp, full-color image of what goes on after dark. They’re a game changer for stargazing, too.
