Night vision and visual illusions
How rods and cones split the work between them, and the scanning technique that compensates for the night blind spot.
14 min read · Human factors
After this lesson you can
- Explain the difference between rods and cones and why the eye needs an off-center scan at night.
- Apply the recommended night scanning technique, including timing and overlap.
- List at least four self-imposed stressors that degrade night vision, with the mechanism for each.
- Read the position lights of another aircraft to determine its relative direction of flight.
Seeing at night is not simply seeing less well; it is seeing with a different receptor, distributed differently across the retina, governed by different rules. A pilot who keeps using daytime visual habits at night will not see what is actually in front of the airplane.
The single most counter-intuitive point in this lesson is that, at night, you have to stop looking directly at the thing you are trying to see.
The rest of this lesson
- 1.Two receptors, two kinds of vision
- 2.Photopic, mesopic, and scotopic vision
- 3.The night blind spot and off-center viewing
- 4.Scanning technique
- 5.Protecting your night vision
- 6.Self-imposed stressors
- 7.Distance, depth, and the illusions that come with darkness
- 8.Reading another aircraft's position lights
These 8 sections, their figures, the checks along the way and the end-of-lesson quiz come with the PPL track. Paid once, yours for good.
Key terms
Try to recall each definition before turning the card.