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Question

Difficulty: EasyFog and Poor Visibility

You are driving on an unlit road and encounter thick fog. Why should you use dipped headlights rather than main beam headlights?

  1. Main beam headlights reflect off the fog and create severe glare that reduces your forward visibilityAnswer
  2. B
    Main beam headlights cause oncoming drivers to fixate solely on your vehicle rather than scanning the road ahead
  3. C
    Main beam headlights increase the thinking distance required to react to developing road hazards
  4. D
    Main beam headlights reduce tyre traction on road surfaces made damp by fog droplets

Answer

Main beam headlights reflect off the fog and create severe glare that reduces your forward visibility
In thick fog, light from main beam headlights bounces off the suspended moisture particles (backscatter), creating a wall of white glare that severely dazzles the driver and obscures the road. Dipped headlights aim light downward onto the road surface beneath the fog, providing clearer vision without reflection.

Step-by-Step Solution

1
Identify the optical effect of fog on vehicle lighting
Fog consists of millions of suspended water droplets that act like tiny mirrors.
Understanding how light interacts with moisture explains why high-angle beams create visual impairment.
2
Compare the beam angles of main beam and dipped headlights
Main beam projects straight ahead and upwards, reflecting light directly back at the driver. Dipped beam angles light down toward the road surface below the fog level.
Dipped headlights illuminate the carriageway without bouncing blinding glare back into the cabin.

Key Concept

Using dipped headlights in fog to prevent backscatter reflection and glare
Estimated Time:45s
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Topics

Fog and Poor Visibility

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