Familiar with polarising filters, but no idea where polarisation stems from? Read on!
Urth HQ | AUSTRALIA
Whether you’re new to photography or a seasoned pro, you’ll probably be familiar with the word polarisation. While polarisation might seem like a modern concept, it was actually discovered many years ago.
What is polarisation?
Polarisation refers to light waves that form different properties in various directions, particularly when vibration takes place in a single plane. Polarised light is most useful after it has been filtered. In photography, polarising filters reduce polarised light, to increase contrast, darken skies, and reduce reflections and glare.
Yet, it’s not just photography where polarisation plays a vital role. Most commonly, it is used to reduce glare in sunglasses. But, it’s also used to stress test transparent plastics. You wouldn’t be able to watch 3-D movies if it wasn’t for polarising filters. Plus, radar, radio transmission, televisions, digital watches and laptop screens wouldn’t work without polarised light.
Polarisation is also important in the natural world. Bats use polarised light to help them navigate, while a zebra’s black and white stripes use polarised light to keep flies at bay.
Where it all began
Where does the story of polarisation begin? Although it’s hard to say who discovered it, it’s believed that the Vikings were able to make their way across lands, thanks to polarisation of the sky.
Early studies show that the first real hint of polarised light discovery dates back to around 1669. This was when Erasmus Bartholin noticed that a type of colourless calcite crystal, known as Iceland spar, created a double image when objects were viewed through it during transmitted light. In particular, Bartholin found that when the crystals were rotated, one image would move around the other in a circular motion, as if splitting the light into two separate beams.
Further discoveries were made in 1808 by French mathematician, Etienne Louis Malus. He observed that some images made with reflected light from calcite crystals would occasionally disappear. He concluded that polarised light was not just relevant to crystals, but could be present in reflections from a wide range of transparent or opaque substances. From this, he devised the Malus Law. This states that light intensity transmitted through a polariser varies when there is a change in the angle of the transmission.
Not long after, in 1812, scientist Sir David Brewster described the features of polarised light. He also invented something we’re all familiar with — the kaleidoscope.
With a keen interest in polarised light, French scientist François Arago developed the very first polarising filters in 1812. These filters were made by pressing glass sheets together.
Polarisation advanced further, when in 1932, Dr Edwin Land invented the first commercially available polarised materials from synthetic films. These films were sold under the name Polaroid. No prizes for guessing that Land then went on to produce Polaroid cameras.
In 1948, A. F. Hallimond coined the phrase ‘polar’ or ‘polariser’. This referred to any device that could select plane-polarised light from natural, or non-polarised, white light.
Image—Miguel Fabbris
Polarisation today
Since these early days, many further polarisation discoveries have been made. In particular, with regards to how animals and nature use polarised light for survival. Today, many photographers would be lost without polarising filters in their kit bag, proving just how versatile and dynamic polarisation is.
