Here is a post from Ed on the Subject of Night Vision
If you’ve ever had to find your way out of a large building after the power goes out you can appreciate the value of having at least a small light with you as Every Day Carry (EDC). A tiny LED on your zipper pull or key ring beats nothing. The point is to always have SOMETHING. I have Fenix EO1 single-AAA cell LED lights on the zipper pulls of all outer garments, and carry one on my key ring all the time. (I have one of these in my pocket, Howard) These are inexpensive enough that you can buy multiples and stash them everywhere, your key ring, in personal first aid or survival kits, etc.
In my Get Home Bag I keep a Petzl Tactikka Plus Headlamp and spare batteries. I prefer LED lights because they are more rugged, and have longer run time on a set of batteries, to last all night if working a 12-hour shift. In heavy use of Xenon lamps on searches you must carry both spare lamps and spare batteries. My needs these days are mostly in finding things in my pack, in the car or cockpit at night, and for walking trail illumination. You must wear protective safety glasses with side guards whenever moving around at night
The Petzl headlamp with red filter is recommended for night flying in general aviation, used at its lowest setting. Red is the only color that does not bleach out your rhodopsin and degrade night vision. Green light at very low levels has much less effect than white light. In the days before military pilots flew while wearing night vision, night training involved wearing red goggles for an hour before flying, to protect from exposure to bright lights, exclusively using red lights in flight planning rooms, keeping lights off on the flight line and avoiding flying anywhere near intense light sources. Night training flights were planned for the darkest times when the moon was not full or before it rose or after it set below the horizon. If you want the best night vision avoid bright light religiously, get plenty of rest, do not smoke, stay at low altitudes and use supplemental oxygen when at cruising altitude.
Military aviators back in the 1970s were issued a simple 2-AA cell pen light with white bulb and sliding red filter for night cockpit use. This was used mostly for writing ADC clearances on the kneeboard on night ops, but in Indian Country would be very cautiously used as an evasion light also. In the 1970s an evasion light was no light at all, or as little light as possible exposed for no longer than absolutely necessary. Safe, stealthy movement depends on staying still until your eyes are fully dark adapted, then moving slowly, quietly and cautiously, traveling at night to avoid detection and hiding in dense vegetation during the day
Movement attracts the eye, and so does any light. A moving light at night especially draws attention and gets investigated. Even a tiny LED is highly visible for a mile or more with the naked eye and several times that with FLIR or NVG. If a downed air crewman in a hostile area incautiously leaves a light unprotected for more than a few seconds and moves around. it may be seen and increases risk of detection or capture. Side shields are absolutely necessary for any evasion light.
The human eye performs poorly at night. Fatigue has great influence at night. The retina is the first and fastest part of the body to react to reduction of blood oxygen. Cigarette smokers start out with an immediate night vision problem. Complete night adaptation of the eye to darkness takes over 30 minutes and be destroyed in seconds. The cones used for color vision are centered in the eye but are slow to adapt and then only by a factor of x 100. Rods make it so we can see at night but not in color and are spread to the sides in the back of the eye. They are more sensitive at night by a factor of x 100,000. Rods take 30 minutes to recover from a bright light shock.
The oval shaped region retinal blind spot cannot see light, but binocular vision compensates for this in daytime. At night we often are unable to see objects if we look directly at them.
To see at night do not look directly at what you want to see because your central vision is inoperative at night.. Looking off center at night uses your peripheral vision which is 100,000 times more sensitive than central vision at night. Your eyes can be adapted to night vision by wearing red glasses, patching one eye and using dimmed lighting.
No matter how well you do this one muzzle flash in your face destroys it all!
Your visual adaptability to light/darkness is reduced 50% every eleven years of your life. Experience and frequency of night flight is the best compensation for this loss. Any bright light effectively reduces night vision. You might try protecting one eye from light until airborne. Try wearing sunglasses at dusk.
Vitamin A is a vital element for night vision and adaptation. Vitamin A deficiency will make a significant difference in night vision. However excessive intake of Vitamin A will not give an apparent improvement.
Ample oxygen is necessary for adequate night vision more so than day vision. Above 4000 feet supplemental oxygen improves night vision. The most dangerous aspect of this is that the pilot has no way of knowing that he is not seeing as well.
Wearing of sunglasses during the day is one way to improve your night vision. Neutral gray glasses with UV resistant coating are best . At night, red lenses will absorb blue light and aid dark adaptation. Restrict any use of bright white light at night since even a momentary flash will destroy night vision. Use blue, green or red LEDs.
Should blur interfere with the things you see at night, it may be indicative of night myopia. Squinting will help some or the use of glasses. If the eye is unable to focus on anything at a distance at night it may be having space myopia. Keeping the eyes moving can help limit these effects that are made worse by staring.
Objects are harder to see at night just because they are less well defined around the edges. This makes things appear farther away than they actually are. The requirement for corrective lenses (if you wear them) at night is much greater than during daylight.