Differences in Transmittance Between TN and IPS LCD Glass

     Many hardware engineers, when consulting about displays, often ask why TN LCD screens are brighter than IPS LCD screens when using the same backlight brightness. Today, engineers from Shenzhen Hongjia Technology will explain this. First, TN (Twisted Nematic) and IPS (In-Plane Switching) LCD glasses have fundamental differences in transmittance, which directly leads to differences in their display effects (such as contrast, color, and viewing angle). The differences are as follows:

1. TN (Twisted Nematic) LCD Glass

• Basic Structure: The polarization directions of the upper and lower polarizers are perpendicular to each other. Under natural conditions, the liquid crystal molecules will form a 90-degree twisted alignment under the influence of the upper and lower substrate alignment layers.

• No Power On (Normal White Mode):

Light entering through the upper polarizer becomes linearly polarized. As this polarized light passes through the twisted liquid crystal layer, its polarization direction rotates 90 degrees due to the twisting of the liquid crystal molecules. When the light reaches the lower polarizer, its polarization direction is exactly aligned with the transmission axis of the lower polarizer, allowing the light to pass through smoothly → the screen displays a bright (white) state, with the highest transmittance.

• Power On Mode:

When voltage is applied, the liquid crystal molecules stand upright along the electric field direction, losing their twisted structure and no longer able to rotate the polarization direction of the light. Light from the upper polarizer retains its polarization direction. When it reaches the lower polarizer, because its polarization direction is perpendicular to the lower polarizer, it is completely blocked → the screen displays a dark (black) state.

• Key Characteristics of Transmittance:

• Advantages: In the bright state (white screen), the theoretical transmittance is relatively high. This is one of the reasons why TN screens usually appear "brighter," and also because of their lower manufacturing cost.

Key Features of Transmittance:

Advantages: In the bright state (white screen), the theoretical transmittance is relatively high. This is one reason why TN screens usually appear "brighter," and also because they have lower manufacturing costs. • Disadvantages: In dark conditions (black screen), because the liquid crystal molecules cannot align perfectly, some light will always leak out, resulting in an impure black, appearing as a "grayish-black." This makes the contrast ratio of TN panels typically low (possibly only 1000:1 or lower).

2. IPS (In-Plane Switching) LCD Glass

• Basic Structure: The polarization directions of the upper and lower polarizers are parallel. The liquid crystal molecules always rotate within the substrate plane, unlike TN which "stands up."

• No Power Activation:

The liquid crystal molecules maintain their initial alignment, changing the polarization direction of the incident light. Because the upper and lower polarizers are parallel, the light, after being "incorrectly" modulated by the liquid crystal layer, cannot pass through the lower polarizer → the light is blocked → the screen displays a dark (black) state, at which point the transmittance is lowest.

• Power-on state:

• When voltage is applied, the liquid crystal molecules rotate in the plane, aligning the polarization direction of the incident light with that of the lower polarizer, allowing light to pass through smoothly → the screen displays a bright state (white).

• Core characteristics of transmittance:

• Advantages: Excellent light-blocking effect in dark states (black screen), producing very pure and deep blacks. This allows IPS panels to achieve extremely high contrast ratios (typically 1500:1 or even higher, with higher in high-end models).

• Disadvantages: Because it requires driving the liquid crystal molecules to rotate in a planar manner within the viscous liquid crystal material, stronger voltage and longer response time are needed. Furthermore, to achieve the same brightness, stronger backlighting or higher driving voltage is required, which increases power consumption to some extent. Early IPS panels had lower transmittance in bright states than TN panels, but modern technologies (such as AHVA, PLS, and other IPS variants) have greatly improved this.

      Shenzhen Hongjia Technology has been specializing in the R&D, production, and sales of 1.14-inch to 12.1-inch displays and matching touchscreens for 12 years. They offer both TN and IPS LCD screens in a full range of sizes and with multiple interface options. The fundamental difference in transmittance between TN and IPS LCD glass determines that IPS is superior to TN in overall image quality (especially contrast, color, and viewing angle). TN's only major advantage lies in its extremely fast response time, which still gives it a market in professional e-sports where extreme frame rates are crucial. However, for the vast majority of everyday users, image processing enthusiasts, movie viewers, and gamers, IPS panels provide a much better visual experience.