When it comes to LCDs, it is important to understand how they are able to vary light intensity. In this article, we will explore how exactly this happens and what occurs when an electric field is applied.
Understanding TN LCDs
For the purposes of this article, we will focus on TN (twisted nematic) LCDs, which are commonly used in a ‘normally white’ mode. When no voltage is applied, the orthogonal grated plates cause the director of the LC (liquid crystal) to twist and form a helical shape. This twisting turns the polarization angle of the incident light in a similar manner shown in the image below from wikipedia.
However, when the maximum electric field is applied, all of the LC molecules get tilted by 90 degrees, which ruins the helix shape and stops the turning of the polarization angle. This ultimately results in no light passing through.
The Effect of a Weaker Electric Field
Now, let’s consider what happens when a weaker electric field is applied. The naive answer is that the polarization is turned to a smaller angle, but there are a few reasons to suspect it’s not as simple as that.
For example, the gratings themselves are still perpendicular to each other – so the overall twist is still 90 degrees. It’s possible that the efficiency of the twist is simply reduced – only a fraction of the polarized light gets turned by 90 degrees causing an effective turning because of the superposition of turned and unturned light.
However, it’s important to note that because the LC is birefringent, this will induce a phase difference and cause the polarization to become elliptic. This can cause issues with the second linear polarizer, which may not block it well.
Seeking Answers and Solutions
Unfortunately, we could not find any literature on this matter. However, we would love to share an answer or a reference in which you could read about it more in depth. We hope that this article can provide a starting point for you to continue your research.
If you’re interested in the mathematical description of the LC’s jones matrix’s dependence on the applied voltage, here is a possible answer:
When an electric field is applied to an LC, the orientation of its molecular dipoles changes, which causes the refractive index tensor to be different in directions parallel and perpendicular to the field. As a result, the Jones matrix (which describes the polarization transformation of the light as it passes through an element) will also change as a function of the applied voltage. The Jones matrix for an LC is defined by:
Where is the angle between the polarization direction of the incident light and the director axis of the LC, and are the refractive indices parallel and perpendicular to the field respectively.
Conclusion
Understanding how LCDs vary light intensity is an essential aspect of their function. While there are still some questions that need to be answered, we hope that this article has provided some insights into how TN LCDs work and possible solutions to the issue at hand.
How Do Lcds Vary Light Intensity?
How LCDs Vary Light Intensity?
When it comes to LCDs, it is important to understand how they are able to vary light intensity. In this article, we will explore how exactly this happens and what occurs when an electric field is applied.
Understanding TN LCDs
For the purposes of this article, we will focus on TN (twisted nematic) LCDs, which are commonly used in a ‘normally white’ mode. When no voltage is applied, the orthogonal grated plates cause the director of the LC (liquid crystal) to twist and form a helical shape. This twisting turns the polarization angle of the incident light in a similar manner shown in the image below from wikipedia.
However, when the maximum electric field is applied, all of the LC molecules get tilted by 90 degrees, which ruins the helix shape and stops the turning of the polarization angle. This ultimately results in no light passing through.
The Effect of a Weaker Electric Field
Now, let’s consider what happens when a weaker electric field is applied. The naive answer is that the polarization is turned to a smaller angle, but there are a few reasons to suspect it’s not as simple as that.
For example, the gratings themselves are still perpendicular to each other – so the overall twist is still 90 degrees. It’s possible that the efficiency of the twist is simply reduced – only a fraction of the polarized light gets turned by 90 degrees causing an effective turning because of the superposition of turned and unturned light.
However, it’s important to note that because the LC is birefringent, this will induce a phase difference and cause the polarization to become elliptic. This can cause issues with the second linear polarizer, which may not block it well.
Seeking Answers and Solutions
Unfortunately, we could not find any literature on this matter. However, we would love to share an answer or a reference in which you could read about it more in depth. We hope that this article can provide a starting point for you to continue your research.
If you’re interested in the mathematical description of the LC’s jones matrix’s dependence on the applied voltage, here is a possible answer:
Where
is the angle between the polarization direction of the incident light and the director axis of the LC, 
and 
are the refractive indices parallel and perpendicular to the field respectively.
Conclusion
Understanding how LCDs vary light intensity is an essential aspect of their function. While there are still some questions that need to be answered, we hope that this article has provided some insights into how TN LCDs work and possible solutions to the issue at hand.