With relatively cheap and available night vision devices, the military and police have quickly become dependent on technology.  Heck, you can’t even break into a hardware store without some day/night surveillance camera filming the whole thing.  We have even forgotten some of the things routinely taught in the Army as late as the 80’s.

Even though they lacked our technology and medical knowledge, the ancients spent a lot of time in the dark.  Since prehistory, humans fought and hunted in the dark. Warriors sought every advantage and many groups developed night fighting skills.

One of the first recorded accounts of night combat (some say the first special operations mission) was the biblical account of Gideon.   After running a selection and assessment course, he conducted a night attack on an entire army.  Carefully using light and noise to cause confusion, he persuaded the Medianites to help the effort by killing each other.  In true SF fashion, there were no friendly casualties, but Gideon’s commando team was exhausted carrying away the spoils of war.

The human eye works much like a digital camera.  The pupil is a lens which focuses light on to receptors in the retina.  The brain processes this data and turns it into the experience we call human vision.  There is an incredible amount of processing which goes on in the brain.

There two kinds of receptors, cone cells and rod cells. Cone cells see color and are dense in the center of the eye.  Our normal vision uses cones.  As light levels drop, the eye switches to rod cells. Rod cells are predominately situated in the periphery of the eye.  They see less detail and sense only shades of grey. This is experienced as a loss of color vision.

There is a spot in the back of the retina where the optic nerve enters.  There are no sensors there.  The brain generates a complete image, but you can experience this by staring at a faint light, like a dim star.  As you stare, the light disappears.  If you look off to the side, the light will reappear.

To function properly, the rods need rhodopsin, also known as visual purple.  Rhodopsin is a biological pigment that is extremely sensitive to light.  When exposed to light, the pigment immediately photobleaches, and it takes about 20 minutes to regenerate fully. This means that it takes about 20 minutes to build full night adaptation and a single exposure to bright light to lose it.  Repeat as necessary.

This does not explain the phenomenon which causes the perception of female attractiveness to shift upward sharply at closing time.  An old Green Beret trick is to make sure that your eyes are completely night adapted before approaching someone of the opposite sex in subdued light.  One advantage is the improved ability to accurately determine the sex of apparent members of the opposite sex.