New Jersey Scuba Diving

Human Vision Underwater

When light travels from a less-dense medium like air to a more-dense medium like water, the rays are refracted or bent towards the normal or perpendicular of the surface between the two mediums. In crude terms, light going from air to water will tend to be straightened, while light going from water to air will tend to be ... um ... crookeded. Confused yet? Take a look at the figure below.

In this figure, you can see the light rays traveling from an object in the water to your eyes, neglecting the effect of the flat glass lens of your mask. The blue lines trace the actual path of the light rays through the water and into the air, or conversely, through the air into the water - the direction really doesn't matter. As you can see, the rays are bent toward the perpendicular of the surface on the water side, and away from it on the air side.

More: Light, Air & Water ...