USCG Exam Practice · Chart symbols and abbreviations (Chart No. 1)
A light is charted as 'Iso R 6s'. Which of the following correctly describes this light's characteristic?
- AA red light that flashes once every 6 seconds with a longer period of darkness than light.
- BA red light with equal periods of light and darkness, completing one full cycle in 6 seconds.✓ correct
- CA red light that is continuously on for 6 seconds, then extinguished for a variable period.
- DA red light that occultes once every 6 seconds with a longer period of light than darkness.
Why B is correct
Isophase (Iso) means equal periods of light and darkness. The period stated (6s) is the total cycle time. The colour R indicates red. Light List — light-characteristic (Iso).
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