How’s your night vision technique?
A sharp eye and optimal night vision can pick up that traffic sooner and increase
your margin of safety.
Optimal vision is critical to every
aspect of safe flying. We need it for the recognition and identification of
distant objects including other aircraft, structures close to the ground, and
birds. Good vision is also necessary to perceive the details of shape and colour,
to judge distances, relative object movement, and to read flight deck displays,
charts and flight plans. Night vision is unique in that it functions differently
than day vision. Effective night vision requires special skills and knowledge.
The retina is the inner most
and light sensing part of the eye. It contains a very small area called the
fovea which senses maximal visual clarity and colours. The fovea works
well under moderate to high levels of illumination. It however fails under low
intensity light such as at night.
The non-central, peripheral
part of the retina perceives light at low levels of illumination. It can actually
perceive light at one thousandth the illumination needed by the fovea. Sometimes
pilots complain that they may see an object at night only to have it disappear
as they look directly at it. What happens is that they shift from peripheral
dark- adapted vision to central day light vision. This part of the eye is not
able to detect objects at low intensity. Another location of the retina which
cannot see at all is the nearby "blind spot" where the optic
nerve enters the retina. Looking at objects off centre about 15 degrees will
correct that loss of vision in this area.
Before the peripheral part of the
eye can see efficiently, it must for undergo dark adaptation. This is a vitamin
A dependent photochemical process that occurs in each eye. It usually takes
about twenty to thirty minutes to fully dark adapt, but can be lost rapidly
when exposed to bright light.
