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Pool Journal · Word of the Week
Refraction: Why Water Bends the Light
by Larry Szulc, Spectrum Pool Care
Dip a straw into a glass of water and it seems to snap at the surface. Look down into a pool and the floor seems closer than it is. Both are the same quiet trick of light.
Refraction comes from the Latin refringere, “to break up,” from re-, “back,” and frangere, “to break,” the same root that gives us fragile and fraction. It’s a fitting name: a straw in a glass of water looks broken at the surface.
What’s really happening is a change of speed. Light travels about a quarter slower in water than in air, and when it crosses the surface at an angle, that change bends its path. The rule for how much it bends was first written down around the year 984 by Ibn Sahl, a scholar in Baghdad, and rediscovered in Europe more than six centuries later by Willebrord Snell, whose name it usually carries today.
Water doesn’t just hold light. It bends it, slows it and scatters it across the pool floor in shifting lines.
The Pool
Light in Your Pool
Shallower than it looks
Seen from above, a pool floor appears at roughly three quarters of its true depth. A deep end that looks 6 feet may be 8.
The dancing lines
Ripples act like moving lenses, focusing sunlight into the shimmering bright lines that dance across the pool floor.
Bent legs and arms
A swimmer standing in the shallow end seems to have shorter legs, the straw-in-a-glass effect, life-size.
Pool lights
Underwater lights spread and soften through the water, which is why a single light can glow across a whole pool at night.
From our routes: clear, balanced water shows refraction at its loveliest, with crisp lines of light on the floor on a sunny afternoon. It’s one of our favorite sights when we finish a cleaning and the water settles.
Written by Larry Szulc, owner of Spectrum Pool Care, a family-owned company serving the San Fernando Valley, Westside, Santa Monica and Malibu since 1999.
