How are the moving light patterns at the bottom of the pool formed?
In: Physics
The water is acting like a wobbly, constantly shapeshifting lens. The peaks of the water are where the light gets most concentrated and is projected from.
So, light bends when it hits the density change of the waters surface, yes? The angle of that change is pretty constant, but if the surface is not flat (ie theirs ripples), then the light will be bent unevenly, which creates the light patterns you see as areas get more or less light.
They’re called “caustics”, unrelated to the chemical term. It’s the same idea as a magnifying glass in the sun creating a central bright spot surrounded by a dim shadow. The difference is the surface of the water doesn’t have a perfectly steady, focused lens shape, so the light and dark spots all shift around with the waves.
When light transmits between one medium and another, such as air to water, it bends its path. (The physical phenomenon is called refraction, and is a consequence of light changing its speed.) This can be seen by looking at a straw in a glass of water.
Water in a pool is not perfectly still. There are waves from people swimming, and these waves continually change the surface between the water and the air. This means the angle that the light hits the surface is also changing, which bends the light in different ways.
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