Liquid crystals are rod-shaped molecules that – like tiny compass needles – can be aligned by an electric field. They are birefringent: their refractive index depends on the direction in which light passes through them.
The trick lies in the refractive index. The polymer is chosen so that its refractive index matches the ordinary refractive index (no) of the liquid crystal. When the crystals are aligned with the field, light hitting the film head-on “sees” no difference between droplet and polymer and passes through undisturbed. Without a field, the crystals in each droplet point in a different direction; light then encounters thousands of small changes in refractive index and is scattered. Because the droplets are about the size of the wavelength of light (around 1 µm), this scattering is very effective. [4][6][9]
Alternating voltage (AC) is used, not direct voltage. With DC, ions in the film migrate, leading to stains, burn-in and a shorter lifespan. [13]