The liquid crystal display is mainly composed of a backlight, a liquid crystal panel and a driving circuit.

You can think of the LCD panel as a sandwich structure,

That is, a layer of liquid crystal layer is sandwiched between two polarizer systems whose polarization directions are perpendicular to each other.

LCD structure diagram

Take the TN (Twist Nematic) panel as an example,

The rotation of the liquid crystal can be controlled under the action of an external electric field.

After the natural light source passes through the polarizer (one of the polarizers), it becomes polarized light in the vertical direction

After the polarized light passes through the TN liquid crystal that is not energized and maintains the original alignment state,

Due to the optical properties of liquid crystals and the arrangement of liquid crystal molecules,

As a result, the polarization direction of the light is changed from straight to horizontal.

The polarized light in the horizontal direction is consistent with the transmission axis of the analyzer and is transmitted out of the liquid crystal cell.

This type of liquid crystal display mode in which incident light can be transmitted when no electric field is applied to both ends of the liquid crystal is called "NormalWhite" (NW)

Similarly, if a voltage is applied to the liquid crystal,

TN type liquid crystal is divided from the twisted arrangement state to the vertical arrangement state,

At this time, the polarization direction of the incident linearly polarized light will not change,

As a result, its polarization direction is perpendicular to the transmission axis of the analyzer and is blocked,

In the end, no light is transmitted from the liquid crystal cell.

This kind of liquid crystal display mode in which the incident light cannot be transmitted when no electric field is applied to both ends of the liquid crystal is called "NormalBlack" (NB)

Therefore, in principle, the liquid crystal display is just an optical switch that controls the ON-OFF of the transmitted light through the ON-OFF of the voltage.

The basic principle of the above liquid crystal display only shows that the incident light is either transmitted or completely cut off, that is, the emitted light has only two states (the brightest state and the dark state).

The actual application of the liquid crystal panel is through the switch function of TFT, and each pixel is inputted with different magnitudes of data signal voltage:

The state of rotation of liquid crystal molecules is different under different voltages, so the degree of rotation of linearly polarized light is also different.

The components on the transmission axis of the analyzer are different, that is, the brightness of the emitted light is different,

In this way, a multi-gray-scale picture display can be realized.