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If light passing through ONE single polarizer shows variation in brightness as the polarizer is rotated, it must mean that the light is polarized.
As shown in the video, filament lamps, fluorescent lamps and the Sun emit light that is unpolarised.
The display screens of calculators, handphones and LED TV are all based on LCD (Liquid Crystal Display) technology, which produces polarized light.
xmPhysics 
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