How do Sunglasses Work?

Some say Nero watched gladiators battle in the sun through the green tint of emeralds held in front of his eyes. Like emeralds, color isn't free. If something has color, it is absorbing light, and thus that light isn't making it to your eyes. Colored lenses darken what you see.

World War II aviators learned that green sunglasses reduced the glare of high-altitude sunlight. The military also discovered that pink and rose lenses could actually improve night vision and the view across water. Dirt bike riders found that yellow lenses help define their path, increasing sharpness and detail as riders rip through a green forest trail, while the lens itself keeps passing branches from ripping their eyes out altogether.

In the 1950s, polarized sunglasses became the rage. But what does "polarized" mean? Light travels in waves, just like sound. And just as an empty room can reflect one sound again and again into a jumbled mess of echoes, one source of light can bounce around so that we see the same light from more than one angle, causing glare. A polarized filter is like a narrow slot, letting in only light that vibrates in that slot's plane, thus eliminating the "noise." Try this experiment: remove your polarized sunglasses from your face, and look through the lenses while you slowly rotate them, sideways and upside-down. Changing the angle of the slot will make certain objects, especially clouds and water, dramatically change in appearance, depending on the vibration of their original light.