Technology

AMOLED vs LCD: differences explained

Mobile display technology is firmly split into two camps, the AMOLED and LCD crowds. There are also phones sporting OLED branding, which is essentially the same tech as AMOLED. AMOLED and LCD are based on quite different underlying technologies, leading manufacturers to tout a number of different benefits depending on which display type they’ve opted for. Smartphone manufacturers are increasingly opting for AMOLED displays, with LCD mostly reserved for less expensive phones.

Let’s find out if really there’s a noticeable difference between these two displays technologies, if there is what sort of differences we can expect, and if the company marketing hype is to be believed.

Technology explained – AMOLED

We’ll start alphabetically with AMOLED, although to be a little broader we should probably start with a little background about OLED technology in general.

It’s hidden in the name, but the key component in these display types is a Light Emitting Diode (LED). Electronics hobbyists will no doubt have played around with these little lights before, but in a display panel these are shrunk down dramatically and arranged in red, green and blue clusters to create an individual pixel that can reproduce white light and various colors, including red, green, and blue.

The structure of an organic light emitting diode.

NovaLED The structure of an organic light emitting diode.

The arrangement of these sub-pixels alters the performance of the displays slightly. Pentile vs striped pixel layouts, for example, results in superior image sharpness, but lower pixel life spans due to the smaller pixel sizes.

The O part in OLED stands for organic. Simply put, there are a series of thin organic material films placed between two conductors in each LED, which is then used to produce light when a current is applied.

Finally, the AM part in AMOLED stands in for Active Matrix, rather than a passive matrix technology. This tells us how each little OLED is controlled. In a passive matrix, a complex grid system is used to control individual pixels, where integrated circuits control a charge sent down each column or row. But this is rather slow and can be imprecise. Active Matrix systems attach a thin film transistor (TFT) and capacitor to each LED. This way, when a row and column is activated to access a pixel, the capacitor at the correct pixel can retain its charge in between refresh cycles, allowing for faster and more precise control.

Active verses passive matrix OLED displays.

ksgvo Active verses passive matrix OLED display designs.

One other term you will encounter is Super AMOLED, which is Samsung’s marketing term for a display that incorporates the capacitive touchscreen right into the display, instead of it being a separate layer on top of the display. This makes the display thinner.

The major benefits from OLED type displays comes from the high level of control that can be exerted over each pixel. Pixels can be switched completely off, allowing for deep blacks and a high contrast ratio. Being able to dim and turn off individual pixels also saves on power and produces deep blacks. Great if you want a display capable of playing back HDR content. The lack of other layers on top of the LEDs means that the maximum amount of light reaches the display surface, resulting in brighter images with better viewing angles.

The rise of curved displays and foldable phones

OLED technology is a key driving force behind the growth of curved edge displays and the latest foldable smartphones.

The use of LEDs and minimal substrates means that these displays can be very thin. Furthermore, the lack of a rigid back light and innovations in flexible plastic substrates enables flexible OLED based displays. Flexy displays were originally very promising for wearables. Today, premium tier smartphones are beginning to make use of flexible OLED displays too. Although, there are some concerns over how many times a display can flex and bend before breaking.

Foldable smartphones based on OLED display technology include the Samsung Galaxy Z Flip, the Motorola Razr, and the Huawei Mate XS.

Technology Explained – LCD

LCD stands for Liquid Crystal Display, and reproduces colors quite differently to AMOLED. Rather than using individual light emitting components, LCD displays rely on a backlight as the sole light source. Although multiple backlights can be used across a display to help save on power consumption, but this is more of a requirement in larger TVs.

Scientifically speaking, there’s no individual white light wavelength. White light is a mixture of all other visible colors in the spectrum. Therefore, LCD backlights have to create a pseudo white light as efficiently as possible, which can then be filtered into different colors in the liquid crystal element. Most LCDs rely on a blue LED backlight which is filtered through a yellow phosphor coating, producing a pseudo white light.

The spectral content of a single "white LED" is different to producing white light from three RGB LEDs.

Power Electronics The spectral content of a single “white” LED is different from producing white light from three individual RGB LEDs.

LCD LayersThe really complicated part comes next, as light is then polarized and passed through a crystal element. The crystal can be twisted to varying degrees depending on the voltage applied to it, which adjusts the angle of the polarized light. The light then passes through a second polarized filter that is offset by 90 degrees compared with the first, which will attenuate the light based on its angle. Finally, a red, green, or blue color filter is applied to this light, and these sub-pixels are grouped into pixels to adjust colors across the display.

All combined, this allows a LCD display to control the amount of RGB light reaching the surface by culling a backlight, rather than producing colored light in each pixel. Just like AMOLED, LCD displays can either be active or passive matrix devices, and you’ll often see active TFT LCD displays in mobile phones.

Showdown: Super AMOLED vs LCD

LCD and OLED pixel structures are considerably different, leading to different visual results.

provideocoalition LCD and OLED pixel structures are considerably different, leading to different visual results.

This wide variation in the way that light is produced has quite a profound difference to the user experience. Color gamut is often the most talked about difference between the two display types, with AMOLED providing a greater range of color options than LCD, resulting in more vibrant looking images.

OLED displays are known for additional green and blue saturation, as these tend to be the most powerful colors in the sub-pixel arrangement and very little green is required for white light. Some observers find that this extra saturation produces results that they find slightly unnatural looking. LCDs typically tend to overcompensate further into the reds, with more subdued greens. Although not possessing quite such a wide gamut, LCD displays typically offer a very close match to the Standard FBG color gamut profile used by image and video media.

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A closer examination of actual smartphone displays reveals that color gamut can vary quite considerably even between the same types of display. The graphs above show that even though the Samsung Galaxy S10 Plus, Huawei P30 Pro, and LG V40 share OLED displays, they produce quite different gamut profiles. The inclusion of multiple display profiles and different manufacturer calibration targets partly explains these differences, so few displays are ever exactly alike.

Color accuracy is also another notable difference, particularly when it comes to whites. Our own testing of some of the best Android smartphones last year revealed that OLED based displays produced very accurate results, while LCD displays resulted in a slight blue tint. This isn’t so surprising though, given that LCD displays are based on a filtered blue backlight.

LCD vs AMOLED

The Z5 Premium and LG V10 (LCD) show a notable blue tint on whites compared with the Priv and Note 5 (AMOLED).

As we mentioned before, the lack of a backlight and filtering layers also weighs quite heavily in favor of OLED over LCD. LCD displays often suffer from light bleed and a lower contrast ratio as the backlight doesn’t switch off even when pixels are supposed to be black, while OLED can simply switch off its pixels. LCD’s filtering layer also inherently blocks some light and the additional depth means that viewing angles are also reduced compared to OLED.

One downside of AMOLED is that different LEDs have different life spans, meaning that the individual RBG light components eventually degrade at slightly different rates. As well as the dreaded but relatively rare burn-in phenomenon, OLED display color balance can drift very slightly over time, while LED’s single backlight means that color balance remains more consistent.

Picking a winner

There are some pros and cons to both technologies and some reasonable user preferences between the different color and contrast profiles. Although the prevalence of multiple display modes available in modern smartphones makes this somewhat less of an issue these days. However, the falling production costs and additional benefits of OLED displays has made then a more popular choice than ever across a wide range of price segments.

Major display manufacturers, such as LG Display and Samsung Display, are betting big on OLED technology for the future, making major investments into additional production facilities. Particularly when it comes to its use in flexible display technology. The AMOLED panel market is expected to be worth close to $30 billion in 2022, more than double its value today.

That said, developments in Quantum Dot LCD displays could narrow the performance gap between LCD and OLED, so certainly don’t count LCD out of the race just yet.

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