Which description best fits an isophase light?

An isophase light is characterized by equal periods of light and darkness. This means that the duration of the light flash is precisely the same as the duration of the eclipse. In this context, a 1 second flash followed by a 1 second eclipse fits this definition perfectly, as both phases last the same amount of time.

While other options present different sequences of flashes and eclipses, they all involve unequal durations of light and darkness, which does not align with the concept of an isophase light. The key characteristic of balance in timing isn't present in the other choices, making them inconclusive representations of an isophase light. Thus, the correct answer accurately reflects the equal interplay of light and darkness that defines this type of light.