Question

Which of the following terms describes the difference between white and black in an lcd monitor

Answer 1

In liquid crystal displays (LCDs), the presentation of white and black originates from the modulation of the backlight system by liquid crystal molecules. The core differences are reflected in three aspects: optical properties, driving mechanism, and material response:

1. Differences in optical paths

White display: When the pixel needs to present white, the liquid crystal molecules are in a vertical arrangement (or nearly vertical) state under the action of the electric field. At this time, the light emitted by the backlight module (usually a white LED) is almost unblocked by the liquid crystal layer, and directly penetrates the polarizer, color filter (in color LCDs) and glass substrate, and finally reaches the human eye. In theory, the white brightness is determined by the backlight intensity, and in actual display it is affected by the transmittance of the liquid crystal layer, the efficiency of the polarizer, and the surface coating.

Black display: The presentation of black depends on the horizontal arrangement (or specific tilt angle) of the liquid crystal molecules. At this time, the liquid crystal layer acts as a light valve, deflecting the backlight light to a direction perpendicular to the output polarizer, causing the light to be absorbed or blocked. Since the liquid crystal molecules cannot completely block the light (there is light leakage), the actual black appears as dark gray, and its contrast is restricted by the liquid crystal response speed, the polarizer extinction ratio, and the backlight uniformity.

2. Driving voltage and molecular response

White drive: low voltage or no voltage is required (depending on the liquid crystal mode, such as TN, IPS or VA). In the vertical arrangement mode (such as VA technology), the liquid crystal molecules are naturally vertical when there is no voltage, and light passes directly; in the horizontal arrangement mode (such as TN technology), voltage is required to tilt the molecules to a specific angle to allow light to pass through.

Black drive: high voltage is required to drive the liquid crystal molecules to rotate to a horizontal or specific blocking position. The voltage intensity directly affects the molecular tilt angle, which in turn determines the light blocking efficiency. In dynamic scenes, the black response speed is affected by the liquid crystal viscosity, electrode design and driving waveform optimization, and the smear phenomenon is often related to the black transition delay.

3. Material and structural limitations

Liquid crystal layer characteristics: The birefringence, dielectric anisotropy and elastic constant of the liquid crystal material determine its light modulation ability. High birefringence materials can enhance the optical path difference, but may introduce dispersion; low viscosity materials improve the response speed, but sacrifice contrast.

Polarizer and filter: White display depends on the polarizer's transmission axis matching the liquid crystal arrangement, while black display requires the polarizer's extinction axis to be perpendicular to the liquid crystal blocking direction. In color LCD, black needs to be achieved by synchronously turning off sub-pixels (red, green, and blue). Any sub-pixel light leakage will reduce the black purity.

Backlight design: Traditional side-entry backlight has edge light leakage, resulting in uneven black; full array local dimming (FALD) technology can significantly improve black depth by controlling backlight brightness by partitioning, but it increases cost and complexity.

4. Performance index correlation

Contrast: The ratio of white to black brightness (such as 1000:1) directly reflects the display quality. High contrast depends on the balance between low black brightness (light leakage control) and high white brightness (backlight efficiency).

Color gamut and color accuracy: The white color temperature (such as 6500K) is determined by the backlight spectrum, while the black purity affects the performance of dark details. Wide color gamut LCDs need to optimize the arrangement of liquid crystal molecules to reduce light loss while avoiding black color cast (such as bluish or reddish).

Summary

The difference between white and black is essentially the dynamic modulation of the backlight path by liquid crystal molecules: white achieves high transmittance by minimizing light blocking, and black suppresses light leakage by maximizing light absorption or deflection. This process is jointly determined by the physical properties of liquid crystals, drive circuit design, and coordinated optimization of optical components, and is a key challenge in balancing contrast, response speed, and energy efficiency in LCD technology.

Answer 2

In a liquid crystal display, white is when the liquid crystal molecules are fully open, allowing all backlight to pass through and appearing as a mixture of various colors of light; black is when the liquid crystal molecules are tightly arranged under the action of the electric field, blocking most of the backlight from passing through, with only a small amount of light leaking out, so the display is darker. The two form a sharp contrast by controlling the amount of backlight transmitted through the different arrangement states of liquid crystal molecules.

Answer 3

In liquid crystal displays, the core term that describes the difference between white and black is "display mode", which is specifically divided into normal white mode (NW) and normal black mode (NB). The following is a detailed analysis:

1. Definition of terms and principles

Normal white mode (NW):

When there is no external voltage, the liquid crystal molecules are arranged to allow light to pass smoothly, and the screen presents a white background; after power is turned on, the liquid crystal molecules deflect, block the light, and form black text or images.

Representative technology: TN (Twisted Nematic) type liquid crystal display.

Features: It is bright (white) when there is no power, so it is called "normal white".

Normal black mode (NB):

When there is no external voltage, the liquid crystal molecules are arranged to block the light, and the screen presents a black background; after power is turned on, the liquid crystal molecules adjust their direction to allow light to pass through, forming white text or images.

Representative technology: IPS (In-Plane Switching), VA (Vertical Alignment) type liquid crystal display.

Features: It is dark (black) when not powered, so it is called "normally black".

2. Differences in display effects between white and black

Features	Normal White Mode (NW)	Normal Black Mode (NB)
Background brightness	White background (high brightness)	Black background (low brightness)
Contrast	Low (white background easily reflects ambient light)	High (black background absorbs ambient light)
Visual experience	Text/images are clear, but glare may occur due to the bright background	Text/images are sharp, black is purer, suitable for dark scenes
Applicable scenarios	Bright environments such as text processing, web browsing, office work, etc.	Low-light environments such as late-night reading, movie watching, design, etc.
Power consumption	White background requires higher backlight power, and power consumption is slightly higher	Black background relies on direct light from the chip, and power consumption is slightly lower

3. Technical association and expansion

Liquid crystal molecule arrangement:

In the normally white mode, the liquid crystal molecules form a 90° twisted structure (such as TN type) when there is no voltage, so that the polarization direction of the light rotates 90° and appears white after passing through the polarizer; after power is turned on, the molecules tend to be arranged parallel, and the light is blocked.

In the normally black mode, the liquid crystal molecules are arranged vertically when there is no voltage (such as VA type), blocking light; after power is turned on, the molecules tilt and allow light to pass through.

Relationship between display type and mode:

TN type: normally white mode, narrow viewing angle but fast response speed, often used in low-end displays.

IPS/VA type: normally black mode, wide viewing angle but slow response speed, often used in high-end displays.

4. Practical application suggestions

Choose the normally white mode:

If high brightness and wide applicability (such as office and text processing) are required, and the ambient light is sufficient, the normally white mode is more suitable.

Choose the normally black mode:

If high contrast and low glare are required (such as design, film and television production), or the ambient light is dark, the normally black mode is better.

Summary

The difference between white and black in LCD displays is determined by the display mode (normally white/normally black), which is essentially the change in light transmittance caused by the difference in the arrangement of liquid crystal molecules when there is voltage or not. The normally white mode uses white as the background and is suitable for bright environments; the normally black mode uses black as the background and is suitable for low-light scenes. The selection should be based on specific requirements (such as contrast, brightness, and viewing angle).