SDI Open Water Scuba Diver Practice Exam

Underwater, what is the effect of light on visibility?

1. It increases clarity

2. It enhances color contrast

3. It decreases visibility with greater depth

4. It remains consistent regardless of depth

The correct answer is: It decreases visibility with greater depth

The correct answer highlights a fundamental principle of underwater visibility and light behavior. As you descend deeper in the water, light travels less effectively due to absorption and scattering. This phenomenon leads to a decrease in visibility with greater depth, particularly because different wavelengths of light are absorbed at different rates. For example, red light is absorbed quickly, which is why underwater scenes appear more blue or green at depth. While light does indeed play a role in clarity and color contrast, these effects tend to diminish with depth rather than consistently enhance visibility. In shallow waters, light can illuminate and reveal details, improving clarity and contrast, but as you move deeper, these benefits are significantly reduced, resulting in reduced visibility. Thus, understanding how light interacts with water is crucial for divers as they plan their underwater activities and navigation.