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NCERT describes a polaroid as a thin plastic sheet of "long chain molecules aligned in a particular direction". That sheet exists because of Edwin Land. Before him, polarising light meant working with natural crystals. This post covers who he was, his two key patents, how a sheet polariser works, a worked example with polarised sunglasses, common mistakes, and what you can take from his way of working. For how polarisation by reflection was discovered, see our post on Etienne-Louis Malus.
Who was Edwin Land?
The National Inventors Hall of Fame, which inducted him in 1977, gives his life as 7 May 1909 to 1 March 1991. He was born in Connecticut and educated at Norwich Free Academy and Harvard. The Hall of Fame credits him with the first modern polarisers, polarised sunglasses and, best known of all, instant one-step photography from the company he founded, the Polaroid Corporation.
Optica, the optics society, says he studied chemistry in his first year at Harvard, then left for New York. He later returned but did not finish his degree. In 1932 he set up Land-Wheelwright Laboratories with his Harvard physics instructor, and it was renamed the Polaroid Corporation in 1937.
What was his first polariser?
Optica describes his breakthrough: instead of trying to grow one large polarising crystal, he made a film holding millions of microscopic crystals "coaxed into perfect alignment". His US patent No. 1,918,848, filed on 26 April 1929 with Joseph S. Friedman and granted on 18 July 1933, describes exactly this. Small needle-shaped dichroic crystals, such as herapathite (a sulphate of iodoquinine), are mixed into a liquid, lined up by a mechanical, magnetic or electric field, and then the liquid is set hard so they stay aligned.
A dichroic crystal absorbs light whose electric field points one way and lets through light whose field points the other way. One crystal is tiny, but millions pointing the same way act like one large polariser.
How did the later stretched sheet work?
His US patent No. 2,237,567, filed on 4 May 1939 and granted on 8 April 1941, describes a different method: a sheet of polyvinyl alcohol, a plastic with long chain-like molecules, stretched so the chains line up, then stained with a solution of iodine and an iodide.
That matches the NCERT Class 12 Physics chapter on wave optics. It says the electric field component along the aligned molecules is absorbed, so light comes out polarised at right angles to them, along the "pass-axis". NCERT adds that a single polaroid cuts unpolarised light to half and that polaroids are used in sunglasses, windowpanes and cameras.
In a 1951 review in the Journal of the Optical Society of America, Land described 25 years of work on sheet polarisers, the J, H, K and L types, and why special polarisers were developed for uses from optical instruments to car headlights.
Worked example: why polarised sunglasses cut glare
Light reflected off a road or a lake is partly polarised with its electric field horizontal. Take a simplified model with sample numbers: the glare is fully horizontally polarised with intensity 100 units, and light from the scene is unpolarised with intensity 100 units. The sunglasses are ideal polarisers with a vertical pass-axis.
Head upright. The glare's field is at 90° to the pass-axis: 100 × cos² 90° = 0. The unpolarised light is halved: 50. You see 50 units, all from the scene.
Head tilted 30°. The pass-axis is now 60° from horizontal, so the angle between the glare's field and the pass-axis is 60°. Glare through = 100 × cos² 60° = 100 × 0.25 = 25. The scene still gives 50. Total 75, of which a third is glare.
Lying on your side (90° tilt). The pass-axis is horizontal: glare through = 100 × cos² 0° = 100. Total 150.
This is why polarised sunglasses have a vertical pass-axis, and why the glare returns when you tilt your head.
What mistakes do students make with polaroids?
Applying cos² θ to unpolarised light. Use one half instead.
Mixing up the molecule direction and the pass-axis. NCERT says light along the molecules is absorbed; the pass-axis is at right angles to them.
Using the tilt angle as θ. θ is the angle between the light's polarisation and the pass-axis.
The JEE (Main) 2026 syllabus lists "uses of plane-polarized light and Polaroid" in Unit 16, and the section on polarisation appears in the 2026-27 reprint of the NCERT chapter. Check your own year's syllabus. For Brewster's law and more examples, see our post on diffraction and polarisation.
Polarisation is easier to grasp when you can rotate the filters yourself. The Fermi Simulation Lab has interactive simulations for ideas that are easier to see than read.
What can a student take from Land's way of working?
Change the question. Others asked how to grow big crystals. He asked how to make many small ones line up.
Keep improving the method. His 1929 crystal suspension gave way to the 1939 stretched polymer.
Write down what you learned. His 1951 review explained both the science and why each sheet type existed.
Next step: find the glare and scene intensities in the example for a 45° head tilt.
