A pilot's NIGHT VISION is impaired primarily by

Choices

• ✓ exposure to bright light (cabin overhead.correct

  flashlight, lightning) which destroys dark adaptation requiring a full 30-minute reset. Bright light destroys rod-cell dark adaptation in seconds; recovery takes ~30 minutes. Use red or low-intensity white cockpit lighting, shield eyes from outside lights (lightning, runway lights), and never look directly at the moon for long. Hydration helps vision overall, but the dramatic impairment is from bright-light bleaching of the rods.

• drinking water.

  Hydration helps but isn't the primary night-vision impair.

• altitude below 5,000 ft.

  Hypoxia degrades night vision but this answer says LOW altitude (5K) which is fine.

• wearing prescription glasses.

  Glasses don't impair vision (they correct it).