P Polarising Filter 194 Polarising filters work with the physical characteristics of light, not colour. They are used to control reflections from non-metallic surfaces and to darken skies at 90 degrees to the sun. Light waves reflecting from a smooth surface tend to be oriented in the plane of that surface. The polarising filter has a molecular or crystal structure that lets light through at only one angle. It can be rotated to block most of that reflected light. Neutral in colour, polarising filters have some effect on contrast and colour