Liquid-crystal display (LCD) has become one of the leading display technologies used to make TVs, computer monitors, human machine interfaces (HMIs), portable video game consoles and other devices. It lives up to its namesake by featuring an array of liquid crystals that are illuminated with a backlight to produce visual images. Aside from the use of liquid crystals, though, another unique characteristic of LCDs is polarization. Unlike light-emitting diode (LED) and other display technologies, LCDs feature a polarized filter layer. So, what’s the purpose of this polarized layer exactly?

Understanding Polarization on LCDs

The fundamental purpose of the polarized filter layer on LCDs is to create a clearer, brighter image. Without a polarized layer, the light created back the LCD’s backlight — which all LCDs have — won’t be visible to the user. By adding a cross-aligned “polarized” layer to the LCD, it allows only the illuminated liquid crystals to display.

LCDs Contain Two Polarizing Filters

Of course, that’s the short answer as to why LCDs are polarized. To better understand this feature, you must first look at the construction of a typical LCD. Normally, LCDs are designed with not one but two polarizing filters. The liquid crystals used in the LCD are sandwiched between these two polarizing filters. Like polarizing sunglasses, these filters work by only allowing light in a certain pattern or orientation to pass through. If a light doesn’t have this pattern, the filters will prevent it from displaying. The two polarizing filters of LCDs are arranged so that light becomes polarized as it passes through the first filter. After passing through the first filter, the light enters the liquid crystals. Next, the second polarized filter blocks out any “extra” light, while simultaneously only allowing the illuminated liquid crystals to display through.

What would happen if an LCD didn’t feature polarized layers? In this case, it may still produce a visual image, though it would likely feature a poor contrast ratio that results in an inferior quality image. And if the two polarized layers featured the same orientation — meaning they face the same direction — it could block all light from passing through, even the light created by the illuminated liquid crystals.

The Bottom Line on LCD Polarization

Polarization is a fundamental technology powering LCDs. Without the use of polarized layers, LCDs wouldn’t be able to create high-quality images. The polarized layers work by only allowing the light created by the illuminated liquid crystals to pass through. This light is then projected out the display, where it’s visible to the user.