How reflected light acquires a preferred direction
Light is an electromagnetic wave: its electric field oscillates across the direction the wave travels. Ordinary daylight contains a mix of oscillation directions. When light reflects from a flat, nonmetallic surface—such as water, a road, or a car hood—the reflection can become strongly polarized, meaning its oscillations favor one direction. The effect is especially pronounced when the light hits the surface at a particular slant.
That is why glare from a broad, flat surface can feel harsher than light from the sky. The reflection is not simply brighter; much of it has a shared orientation that a filter can target.
Why turning your head can change the view
Polarized sunglasses contain a thin filter whose molecules are aligned to absorb light oscillating along one axis while allowing light through along the perpendicular axis. The lenses are oriented to suppress much of the commonly horizontal polarization in reflections from roads and water. Light arriving from other directions still passes, so the scene remains visible while the reflected sheen is reduced.
The effect depends on geometry: change the angle between the sun, the reflecting surface, and your eyes, and the glare’s polarization changes too. Rotate the glasses, and more or less of that glare may get through. Polarized lenses can also make some phone or instrument screens look dim or uneven, because those displays use their own polarization. The same directional filtering that makes a watery horizon easier to see can therefore make a screen harder to read.
