Liquid Crystal Displays

Well today we will tell you guys about something that you look at everyday. They have become so common that we don’t even think about them anymore, It might be weird to be at a place where you don’t see them but never the opposite. Of course I am talking about Electronic displays but more specifically LCDs. They are all around us, in our laptops, in our phones and TVs, in airports as schedule displays, from small coffee shops to large offices. Should a person from the future be brought to the present time, he would be amazed by the progress we’ve made and would call it nothing short of magic. These magical windows with which we can display anything we want are a marvel we often ignore. In this article we will briefly describe the difference between the two most commonly used types of Liquid Crystal Displays (LCDs) namely:

· Twisted Nematic

· In-Plane Switching

What is a Liquid Crystal Display?

The most common types of displays that we see are LCDs be they TN (Twisted Nematic) or IPS (In-Plane Switching) displays. The underlying principle of liquid crystal displays is that they use polarization filters and liquid crystals to allow light to selectively pass through, ultimately displaying an image. The process is way more complicated as one might imagine because the mechanisms for the manipulation of the properties of these liquid crystals are far beyond the scope of this article.

The display is composed of many layers, the first one is a set of polarization filters that polarize light to one plane. Whether they are parallel or orthogonal depends on the type of display. The second layer consists of materials that allow the manipulation of the liquid crystals and also contains the mechanism for the application of electric fields. In the middle of all these layers is the liquid crystal. All of these are of again sandwiched between layers of glass or polymer to protect them.

That is all fine and dandy but then where do all the colors come from? Well since we can control where light can and can’t pass through and passing the light through color filters can change its color so we use this effect to the best we can. A pixel on a screen is composed of three sub divisions called sub-pixels, each of which has a filter that can display a color. Since these sub-pixels are very small so they appear as one to the human eye. By varying the amount of light passing through each of these filters, we can change the amount of red, blue and green light that is emitted by each pixel. These colors appear as one to the naked eye therefore we are able to produce a range of colors.

Now with all of that in mind, let us see how different technologies work and affect the color accuracy, brightness, color shift and response time of the panel.

Twisted Nematic or TN panel

In a twisted nematic or TN panel the two polarization filters are placed such that their plane of polarization is at 90 degrees to each other thus the light emitted by the backlight of the display does not pass through. We can allow a certain amount of light to pass through by applying an electric field to the liquid crystal. When an electric field is applied, the liquid crystal twists light by a certain amount. The amount of rotation light undergoes depends on the voltage applied. This twist in the plane of light is due to the arrangement of liquid crystals themselves. Due to this rotation, some light passes through the second polarization and can be therefore viewed by an observer. As one might imagine, the more the light is twisted, the more of it can pass through the filter.

As transparent electrodes are present on the upper and lower layers in TN panels therefore their density decreases and this allows TN panels to be brighter than IPS panels which is one of the two main advantages of TN over IPS.

The other big advantage of TN panels is their low response time, this allows them to easily support high refresh rates which is very advantageous in competitive gaming where motion blur can be a big problem. Even though IPS panels are available that have a refresh rate upto 165 Hz but they are no where near as fast as 240 Hz TN panels.

But this is where the good news ends, TN monitors, as mentioned above do support high refresh rates but where they take the cake in response time, they also lose to the color accuracy of IPS and other types of monitors. This makes them unsuitable for content creation and even, for some people, content consumption. This problem is further amplified by the effect known as color shift, what this means is that when viewed from different angles the colors displayed by the panel seem to shift/distort. This effect is most significant when the vertical viewing angle changes and is not as significant in the case of horizontal movement.

Furthermore the color accuracy of TN panels is notoriously bad as compared to its counterpart i.e. IPS. This again makes it unsuitable for content creation and professional work. Again there are some exceptions in which TN panels have a very respectable color gamut and color accuracy but this is not normally the case.

So in short, do not go for a TN panel if what you aim for is content creation because you will only get sub-par if not bad color specifications and will have no use for the high refresh rates. Though if you are a gamer and have a powerful enough setup, go for a TN panel with a high refresh rate. The higher refresh rate makes the game look much smoother as compared to a traditional run of the mill IPS, but watch out for that color shift!

In-Plane Switching or IPS panel

Well taking some context from the previous discussion we know how displays work. So the difference between an IPS and a TN panel is that the two polarization filters are oriented in a way that they have the same plane of polarization. One would think that this would result in a condition where all the light from the first filter passes through the second one, well that is true in the case where no liquid crystal is present between them. So in an IPS panel the normal state of the liquid crystal is such that it rotates the light by 90 degrees, so all the light that passes through the first filter gets blocked by the second filter. When an electric field is applied, the liquid crystals align themselves in a way that does not twist the polarization plane of light and so the light intensity is controlled.

Another great difference in the structure of IPS panels is that the transparent electrodes in IPS panels are only in one layer as opposed to TN panels, so their density increases greatly compared to their two layered opposite. This effects the brightness of the screen and therefore IPS panels are generally less bright.

As told in the comparison above, these panels have a low response times too, but what they excel in are viewing angles and color specifications. They are very less susceptible to color shift, vertical and horizontal, and generally have a higher color accuracy over a wider color gamut.

This shows that these screens are very suitable for content creators and professionals. Gamers will rarely have a problem playing games on these monitors when it comes to casual games so due to this IPS panels are generally more favored as compared to TN.

Conclusion:

We know that this might be a lot to take in but this all is what it takes to display that image of a cat your friend has and that Taylor Swift music video you’ve been waiting for. We all take this technology very lightly but this is nothing short of magical once you know what goes into making this amazing piece of technology.

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Sources:

https://imagefinder.co/photo/black-modern-minimalistic-desk/

https://siim.org/page/displays_chapter2

https://en.wikipedia.org/wiki/Twisted_nematic_field_effect