How LCD and LED Screens Work

17 Jul 2019

In the years since they have become the industry standard, many of us are still unsure what the difference is between an LED and an LCD screen. From our home TVs to the bright and bold digital retail and electronic window displays that we see every day on the high street, they have become a major part of our lives, but very few of us understand them on a fundamental level.

So, how exactly do these screens work and what actually is the difference between an LED screen and an LCD screen? The answers might not be as complicated as you’d think.

How do LCD Screens Work?

An LCD (liquid crystal display) screen is composed of the display itself and the backlight which illuminates it with a diffuser placed between them in order to keep the brightness levels consistent across the entire screen. The LCD itself doesn’t actually emit any light, and actually works by filtering the backlight into a number of individual pixels and colours. 

The backlight controls the opacity of each pixel via electronic signals, so when the screen wants to show a black image it will attempt to block the light - while if it wants to show a white image, it will let more light through. For this reason, LCD screens are not able to display as complex and deep blacks as a plasma screen, but for larger applications (LCD menus and LCD billboards, for example) it’s often more than adequate.

One major benefit of LCD screens, particularly for commercial applications, is that they don’t use as much energy as their plasma counterparts. They also have the potential to be much brighter due to their backlight operation, which makes them suitable for well-lit rooms, and exterior daytime applications. 

A drawback, however, is that the viewing angle is limited due to the depth of the screen. Granted, this is nowhere near as big a problem now as it was in the early days of LCD screens - given that screens are thinner, but it’s still limited compared to plasma.

How do LED Screens Work?

There are two main types of LED display - backlit displays that use an array of LEDs to light the screen in a similar manner to an LCD display, and LED screens that work by emitting light in RGB colours directly from the face of the display. 

Both options are more cost-effective from a manufacturing perspective, as LEDs (light-emitting diodes) are cheaper to produce than the CCFL (cold-cathode fluorescent lamp) tubes used in LCD displays.

The direct display option generally offers a deeper and more complex image. In principle (and in operation) LED screens are not significantly different from their LCD cousins. In fact, the picture quality between both is almost identical. 

There are three main configurations of LED screens for domestic and commercial use:-

Direct Lit - This is the most affordable configuration and uses the least amount of LEDs. They are larger and can’t be controlled separately, which means they are able to provide less of a complex image. They are, however, perfect for larger, more affordable displays where higher definition is not that important. Note that these screens tend to be quite deep - given the space required behind the screen to fit the larger LEDs and diffusers.

Edge Lit - The most common form of LED screen. Indeed, it’s more than likely that the TV currently sitting in your living room uses this configuration. This places LEDs only at the edges of the screen, allowing the screens themselves to be that much thinner. As there are fewer LEDs than in a full array, you might have problems with dynamic lighting if your screen hasn’t been properly configured.

Full Array - Perhaps the most sought after type of LED backlighting (and also the most expensive), these methods distribute the LEDs evenly to produce a more consistent light, which allows for more dynamic colours and lighting. Some full array LED screens also use coloured LEDs, which allow for an even wider and deeper range of colours.

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