How does an LCD screen turn light into a picture?

A bright picture on a typical color LCD begins with light behind the screen, because the liquid crystal controls transmission rather than producing light. A grid of small regions regulates how much backlight passes through optical layers, including polarizers and liquid crystal, toward your eyes.

Polarization describes the orientation of light's electric-field oscillation. A polarizer passes a selected component. Liquid-crystal molecules have an ordered arrangement that changes how polarized light travels through their layer. An electric field can change that arrangement. Between appropriately oriented polarizers, the change can let more or less light through. This is an electrically controlled light valve, not a tiny moving shutter or a glowing crystal.

Electrodes apply the field to each small region, and transistors help select and hold its setting. Color filters then leave red, green or blue contributions in neighboring subpixels. Allowing red and green through while keeping blue dark gives a yellow-looking combination. Intermediate transmission settings produce intermediate brightnesses and mixtures. The sequence is therefore light supply, controlled transmission and color selection.

LCD designs arrange and drive their molecules differently, so more voltage does not always mean greater brightness. Their shared mechanism is electrical control of light supplied elsewhere, represented generally in the enlarged drawing. An OLED supplies a useful comparison: its emitting regions generate their own light rather than controlling a common backlight. Similar-looking pictures can therefore arise through different light-producing arrangements.