Pool Refractions and Reflections
July 25, 2003
The above photo shows the interesting shadow pattern made by the circular chlorine dispenser in this hot tub. This is an example of a caustic network or catastrophe optics. The water surface acts to both focus and defocus light onto the bottom of the pool. When areas are in crude focus, they appear as bright blotches. As a result of absorption and scattering of light on and in water, this phenomenon is best seen when the water's depth is about 5 times the waves crest to crest distance -- conditions almost always met in swimming pools and hot tubs.