The contrast ratio of LCD displays
Feb 23, 2023| Contrast ratio is one of the main factors affecting the display performance of LCD displays. The so-called contrast ratio refers to the ratio of the bright and dark areas in the display picture of an LCD. For monochrome displays, the higher the contrast ratio, the clearer the display. For color displays, a higher contrast ratio makes the image more vivid and lifelike. There are two main contrast ratio parameters for LCD screens: typical value and maximum value. The maximum value is often a momentary value and not representative, whereas the typical value is more valuable as a reference. Currently, mainstream LCD displays typically have contrast ratios ranging from 400:1 to 600:1, with good ones reaching 1000:1 or higher. If the contrast ratio of an LCD is too low, it becomes difficult to see the displayed content.
Different application fields have different requirements for the contrast ratio of displays. The contrast ratio of a regular monitor is usually between 300:1 and 400:1, while medical equipment LCDs require higher contrast ratios, typically between 600:1 and 1000:1. The display screen used in medical equipment requires less color but rather expresses the degree of grayscale imaging between black and white. The contrast ratio of an LCD directly affects the levels of gray and color in the image. Improving the contrast ratio will make the picture more distinct with clearer bright and dark areas. Users can easily see the picture under dark conditions. There are several ways to improve the contrast ratio of an LCD, as follows:
Optimizing the voltage of the LCD screen
This is the most economical solution. Different viewing angles require different driving voltages for an LCD screen. If the voltage is too low, the LCD screen becomes dim. When the voltage is too high, the LCD screen displays non-selective segments (ghosting). Therefore, when discussing the optimal contrast ratio, the voltage needs to be determined first. The contrast ratio of an LCD screen can be improved by optimizing the voltage.
Improving the panel technology of the LCD screen
The contrast ratio of an LCD screen can be improved by improving the panel technology. LCD screens that use TN panels have low contrast ratios. However, using IPS or VA technology, that is, LCD screens with IPS and VA panels, the contrast ratio of the screens is much higher than that of TN panels.
Using better polarizing films
The higher the polarization efficiency of a polarizing film, the better the contrast ratio of the LCD screen. This effect is most apparent in negative displays. If the polarization degree of the polarizing film is changed from 98% to 99%, the contrast ratio of a negative LCD display can increase from 45 to over 1000, while the contrast ratio of a positive display can increase from 7 to 10. For environmental light, the stronger the reflectivity of the polarizer, the better the contrast ratio. For backlighting, the higher the transmittance of the polarizer, the better the contrast ratio.
Using high-quality orientation layers
The initial orientation arrangement of liquid crystal molecules in an LCD screen determines its contrast ratio, response time, viewing angle, and other performance characteristics. Orientation layer materials can induce liquid crystal molecules to uniformly orientate. The new soluble polyimide, using high-quality friction fibers and equipment, can uniformly arrange liquid crystal molecules and thus improve the contrast ratio of an LCD screen.