When Light Becomes Glare

A motorist driving over a highway, with the sun in front of him, finds himself squinting in order to see better. A bather at the seashore shades his eyes even on overcast days. In both cases their eyes are being hit by about 10 times as much light as they need, a painful amount. Such concentrations of light, called glare, may result simply from intense sunlight, but more often glare is caused by sunlight reflecting off surfaces like water, snow or sand. Instead of diffusing the light in many directions, these surfaces absorb some of it and reflect the rest—especially the waves which vibrate in a horizontal pattern. Scientists have a word for this selective light-filtering process: polarization.
Polarized glare can be virtually eliminated by sunglasses fitted with polarizing lenses. Such lenses contain a tinted plastic filter with tiny crystals that have been “stretched” into a series of lines, like the slats of a picket fence. The annoying horizontal light is blocked by these lines, but enough of the vertical light vibrations get through the filter so that the sunglass wearer can see to drive or even read. However, if a second set of polarizing lenses is superimposed on the first, so that their lines cross at right angles, so much light is blocked that the wearer is virtually blind. Such an arrangement is often used in space capsules to shield Astronauts from the sun’s glare during their naps.


Life Science Library - Light and Vision