Why do small and medium-sized LCD screens have two display modes: always white and always black?

     In the specifications of small and medium-sized color LCD screens, you often see "always white" and "always black" display modes. What do these specifically mean? Engineers from Shenzhen Hongjia Technology explain here. Always white and always black are two basic operating modes of an LCD monitor. Their difference stems from whether the LCD screen transmits or blocks light when no power is applied (default state).

Simply put:

Always White Mode: When no power is applied, the pixel displays white.

Always Black Mode: When no power is applied, the pixel displays black.

A Visual Comparison of Working Principles:

To better understand, we can use a simple "Venetian blind" analogy to a pixel on an LCD screen:

Liquid crystal molecules are like the slats of the Venetian blind, controlling the passage of light.

Backlight is like sunlight from outside the room, always present.

Applying voltage is like changing the angle of the Venetian blind slats.

1. Normal White Mode

 Definition: When the voltage applied to a pixel is 0 (i.e., no power), light can pass through, and the pixel displays white; when voltage is applied, light is blocked, and the pixel displays black.

 Venetian Blind Analogy: By default, a Venetian blind is open (no power, light passes through). When you apply power, it's equivalent to closing the Venetian blind (blocking light).

Common Technologies: TN technology typically uses normal white mode.

2. Normal Black Mode

 Definition: When the voltage applied to a pixel is 0 (i.e., no power), light is blocked, and the pixel displays black; when voltage is applied, light can pass through, and the pixel displays white.

Venetian Blind Analogy: By default, a Venetian blind is closed (no power, light blocks). When you apply power, it's equivalent to opening the Venetian blind (letting light through).

 Common Technologies: IPS and VA technologies typically use normal black mode.

      In short, always-black mode has an inherent advantage in image quality, making it the preferred choice for today's high-end display technologies (IPS, VA). Meanwhile, always-white mode, due to its low power consumption in specific scenarios, continues to play an irreplaceable role in certain niche areas, such as TN LCD screens.