Liquid Crystal Displays (LCDs) have several key parameters that define their performance and quality, including transmittance, response time, contrast ratio, viewing angle, color gamut, and color temperature. Each of these parameters impacts how the display performs and is perceived by users.

 

Transmittance

 

Transmittance is a crucial optical parameter of LCDs, indicating how much light from the backlight passes through the LCD panel. It directly influences the overall power consumption of the display. The transmittance can be calculated using the formula:

 

Transmittance = Brightness of panel surface\text{Brightness of backlight

 

Factors affecting transmittance include the materials used, the design of the panel, and the pixel aperture ratio. To improve transmittance, materials with higher light transmission and lower light loss can be used, and designs can focus on increasing the pixel aperture ratio.

 

Contrast Ratio

 

The contrast ratio (CR) of an LCD is defined as the ratio of the luminance of the brightest white to the darkest black that the screen can produce. Common LCDs have a contrast ratio greater than 1000:1. A higher contrast ratio results in clearer images, more vivid colors, and better depth perception. Methods to improve contrast ratio include increasing the brightness in the bright state and decreasing the brightness in the dark state. This can be achieved by enhancing the polarization degree of polarizers, developing high-contrast liquid crystals, improving liquid crystal alignment, and developing high-contrast color filter materials.

 

Static contrast ratio is measured with the backlight at normal brightness, while dynamic contrast ratio measures contrast with the backlight adjusted to lower brightness in the dark state, achieving ratios over 10000:1.

 

Response Time

 

Response time (RT) measures how quickly an LCD can change from one image to another. It has two forms:

 

1. Black-to-White Response Time: The time it takes for a pixel to change from the darkest state to the brightest state and vice versa. It includes rise time (from 10% to 90% transmittance) and fall time (from 90% to 10% transmittance). Fall time is typically longer than rise time, but overdrive techniques can reduce rise time.

2. Gray-to-Gray Response Time (GTG): The time it takes for a pixel to change between different gray levels. GTG response time is often used to provide a more realistic measure of display performance.

 

Shorter response times reduce motion blur in dynamic scenes. Reducing response time can be achieved by using low-viscosity liquid crystals, decreasing cell gap thickness, and applying overdrive technology.

 

Viewing Angle

 

Viewing angle defines the range of angles from which the display can be viewed clearly without significant loss in image quality. It is measured in three ways:

 

1. Contrast Ratio-Based: The angle range where the contrast ratio is at least 10:1.

2. Gray-Scale Inversion-Based: The angle range where no gray-scale inversion occurs.

3. Color Shift-Based: The angle range where color shift remains acceptable.

 

Wider viewing angles ensure consistent image quality from various positions.

 

Color Gamut

 

Color gamut (CG) measures the range of colors an LCD can display. A wider color gamut means the display can show more colors, making the image more vibrant. Color gamut is typically represented as a percentage of standard color spaces like NTSC, sRGB, or Adobe RGB. Achieving a wide color gamut involves using backlights with broad and accurate spectra, such as BG LED chips with R phosphor, B chips with KSF phosphor, or QD film.

 

Color Temperature

 

Color temperature (CT) defines the color appearance of the display’s white light. It is measured in Kelvin (K), with lower temperatures appearing redder (warm colors) and higher temperatures appearing bluer (cool colors). Preferences for color temperature vary by region, with higher temperatures favored near the equator and lower temperatures in higher latitudes. Typical standards are 10000K for TVs and 6500K for monitors and notebooks.

 

These parameters collectively determine the performance and visual quality of LCDs, and advancements in technology continually aim to enhance these characteristics.