Which light pattern has equal periods of light and darkness (2 seconds each)?

• A. Occulting
• B. Flashing
• C. Isophase
• D. Fixed

Answer: (C)

Isophase lighting is defined by equal lengths of light and darkness in each cycle. If the pattern has 2 seconds of light followed by 2 seconds of darkness, then the light-and-dark intervals are equal, which is exactly what isophase describes. This makes the signal steady and rhythmic, easy to recognize at a distance.

In contrast, occulting means the light stays on for most of the cycle and only briefly darkens, so the dark interval is shorter than the light interval. Flashing has a brief, bright flash followed by a longer darkness, so the dark period is longer than the light period. Fixed is continuous light with no dark interval at all.