How does a fluorescent backlight illuminate a transmissive LCD?
In nematic arrangements the crystals are randomly positioned with all their long axes pointing in essentially the same direction, given by a vector known as the director. In smectic arrangements the crystals are further constrained to parallel planes; in smectic A the director is perpendicular to these planes, while in smectic C the director is at some other angle to the planes.
In a transmissive liquid crystal display (LCD), the fluorescent backlight serves as a constant light source positioned behind the liquid crystal assembly. The display operates by using the liquid crystal layer as an electro-optical shutter between two polarizers.12
When no electric field is applied, the liquid crystal molecules are typically arranged in a twisted structure that rotates the polarization of the light passing through the assembly, allowing it to emerge through the second polarizer and appear bright. When an electric voltage is applied, the liquid crystal molecules realign with the field, losing their ability to rotate the light's polarization. Consequently, the light is blocked by the second polarizer, causing that portion of the display to appear dark. By controlling these states across a grid of pixels, the backlight is selectively transmitted or blocked to create images.2
While traditional LCDs rely on a constant backlight, some advanced systems use a colored backlight that flashes in rapid succession to produce color without the need for static color filters.3