Light is a TRANSVERSE WAVE which means that the vibration is at 90 degrees to the direction of propagation of the waves. In other words, when the wave goes forwards, the vibrations are from side to side. That means that the vibrations can have a preferred direction. They can all be up and down, or they can all be side to side. When they all vibrate in the same plane, they are said to be PLANE POLARISED. Sunlight is not polarised but reflected sunlight is polarised, provided you are looking at across the surface rather than down on it. My sunglasses are polarising filters. They will only let through light that is polarised in the right direction. In the picture of Glen Trool above, the left hand side is normal and the other two views are polarised in two different directions. The direction of the polarising sunglasses is shown below. The filter takes out some of the reflection in the middle picture making it clearer. The filter lines up with the polarisation direction in the right hand picture so all light gets through. None is filtered out so there is more glare.
