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Red cockpit lighting also helps preserve your night
vision, but red light severely distorts some colors, and
completely washes out the color red. This makes reading
an aeronautical chart difficult. A dim white light or
carefully directed flashlight can enhance your night
reading ability. While flying at night, keep the instrument
panel and interior lights turned up no higher than
necessary. This helps you see outside visual references
more easily. If your eyes become blurry, blinking more
frequently often helps.
Your diet and general physical health have an impact
on how well you can see in the dark. Deficiencies in
vitamins Aand C have been shown to reduce night acuity.
Other factors, such as carbon monoxide poisoning,
smoking, alcohol, certain drugs, and a lack of oxygen
also can greatly decrease your night vision.
NIGHT SCANNING
Good night visual acuity is needed for collision avoidance.
Night scanning, like day scanning, uses a series
of short, regularly spaced eye movements in 10° sectors.
Unlike day scanning, however, off-center viewing
is used to focus objects on the rods rather than the fovea
blindspot. When you look at an object, avoid staring at
it too long. If you stare at an object without moving
your eyes, the retina becomes accustomed to the light
intensity and the image begins to fade. To keep it
clearly visible, new areas in the retina must be exposed
to the image. Small, circular eye movements help
eliminate the fading. You also need to move your eyes
more slowly from sector to sector than during the day
to prevent blurring.
Focus on

Fovea
Cones Active
Night Blindspot
Rods Active
Figure 13-3. The best vision in daylight is obtained by looking
directly at the object. This focuses the image on the
fovea, where detail is best seen.
Figure 13-4. In low light, the cones lose much of their visual
acuity, while rods become more receptive. The eye sacrifices
sharpness for sensitivity. Your ability to see an object directly
in front of you is reduced, and you lose much of your depth
perception, as well as your judgment of size.
13-3
AIRCRAFT LIGHTING
In order to see other aircraft more clearly, regulations
require that all aircraft operating during the night hours
have special lights and equipment. The requirements
for operating at night are found in Title 14 of the Code
of Federal Regulations (14 CFR) part 91. In addition to
aircraft lighting, the regulations also provide a definition
of nighttime, currency requirements, fuel reserves,
and necessary electrical systems.
Position lights enable you to locate another aircraft, as
well as help you determine its direction of flight. The
approved aircraft lights for night operations are a green
light on the right cabin side or wingtip, a red light on
the left cabin side or wingtip, and a white position light
on the tail. In addition, flashing aviation red or white
anticollision lights are required for night flights. These
flashing lights can be in a number of locations, but are
most commonly found on the top and bottom of the
cabin. [Figure 13-5]
VISUAL ILLUSIONS
There are many different types of visual illusions that
you can experience at any time, day or night. The next
few paragraphs cover some of the illusions that commonly
occur at night.
AUTOKINESIS
Autokinesis is caused by staring at a single point of
light against a dark background, such as a ground light
or bright star, for more than a few seconds. After a few
moments, the light appears to move on its own. To prevent
this illusion, you should focus your eyes on
objects at varying distances and not fixate on one target,
as well as maintain a normal scan pattern.
NIGHT MYOPIA
Another problem associated with night flying is night
myopia, or night-induced nearsightedness. With nothing
to focus on, your eyes automatically focus on a
point just slightly ahead of your aircraft. Searching out
and focusing on distant light sources, no matter how
dim, helps prevent the onset of night myopia.
FALSE HORIZON
A false horizon can occur when the natural horizon is
obscured or not readily apparent. It can be generated by
confusing bright stars and city lights. [Figure 13-6] It
can also occur while you are flying toward the shore of
an ocean or a large lake. Because of the relative darkness
of the water, the lights along the shoreline can be mistaken
for the stars in the sky. [Figure 13-7]
White
Red
Green
Your Helicopter
White
Green
Red
Red Green
　
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