reference to the horizon, the pilot must be prepared  to fly IFR. The human eye will see nothing outside that is dimmer than  the flight deck lighting. Always fly at night with the interior  lights as dim as possible. As the flight progesses and the  eyes adjust to the darkness, usually the interior lights can  be dimmed further, aiding the outside vision. If the interior  lights will not dim, that would increase the risk factors by  restricting the pilot’s outside vision—probably not the time  for a night flight. Although weather, terrain, airport conditions, and night versus  daylight flying each produce unique challenges, together  these factors conspire against a pilot’s senses. It is important  to understand that unwittingly these factors can create  visual illusions and cause spatial disorientation producing challenges the pilot did not anticipate.  [Figure 3-9]  Even the best trained pilots sometimes fail to recognize  problem  until it is too late to complete a flight safely. An accident involving a Piper PA-32 and an airline transport  pilot illustrates how visual illusions can create problems  that lead to an accident. In this case, the aircraft collided with terrain during a landing. The sole occupant of the  airplane was an airline transport pilot who was not injured.  The airplane owned and operated by the pilot, sus tained substantial damage. The personal transportation flight was being operated in visual meteorological conditions (VMC) in mid-afternoon. Although it was not snowing, there was  snow on the ground. Figure 3-9.  Visual illusions are easy to see when shown in the examples above. The illusion on the left represents how the brain processes  color. The “brown” square on top and the “orange” square on the side are actually the same color. The illusion on the right appears  to have red lines that curve; however, they are straight. These illusions are representative of things we see in everyday life, except we  do not see them as they really are until it is sometimes too late. Understanding that visual illusions exist is a prime ingredient to being  better prepared to cope with risk. Figure 3-8.  A  chemical stick is useful to carry onboard the aircraft  at night. It comes in various colors, intensities, and durations, and  it provides ample illumination within the flight deck. This does not  replace the regulatory requirement of carrying flashlights. • Will the flight conditions allow a safe emergency  landing at night? •  Preflight all aircraft lights, interior and exterior, for  a night flight. Carry at least two flashlights—one for  exterior preflight and a smaller one that can be dimmed  and kept nearby.  [Figure 3-8] Visual Illusions 3-7