The first way
The normal eye, unlike the false porcelain eye, has light receptors (cone-shaped and rod-shaped cells). The former are responsible for color perception during the day, while the latter provide the twilight vision you need. "Most bacilliform cells are located on the periphery of the retina," notes Peter Grott, professor of ophthalmology at Houston Medical College. Using that knowledge, it's easy to find a Black Square reproduction in a dark room, and you just use your peripheral vision. You should not so much stare as scan the room.
The second way
It takes an hour for the eye to fully adjust to darkness. However, the most intense adaptation occurs in the first ten minutes. When you know you are about to enter a dark tunnel, prepare for it in advance by closing one eye (or two if you have three) for a few minutes. When darkness envelops you, you will meet it fully armed by opening your clenched eye and closing the other.
By the way, while in the tunnel, avoid looking at any light sources, no matter how dim they may be. "If a direct beam hits the pupil, it will be much harder for the eye to adjust to the darkness again," Peter warns.
The third way
Electric lighting contains the entire visible part of the spectrum, from red to violet. And all of them, starting with yellow, can impair your night vision. But red, according to Peter, is the color that your darkly accustomed eyes are least sensitive to.
If your job requires you to occasionally run out of a lighted gatehouse and peer into the darkness to see if a thief is on the premises, wear glasses with red or orange lenses. It will help your eyes, already adapted to the gloom, not to adjust to night vision all over again. The fourth way.
You can also stimulate night vision with grated carrots with sugar: glucose and carotene increase eye sensitivity. And before this light snack is desirable to perform a couple of gymnastic exercises. Small muscle exercises accelerate the adaptation of the eyes to the dark.