May
17
2010

What’s the difference between AMOLED and LCD cellphone displays?

LCD pixels (photo by chrisdlugosz - CC-BY)

Two display technologies are commonly mentioned in cellphone specifications: LCD and AMOLED. How do they differ? Is one better than the other?

An LCD is a Liquid Crystal Display. The molecules of a liquid crystal can line themselves up like a crystal, but they can also move like a liquid when an electric charge is applied. In one orientation they will let most of the light through, and in another orientation they will block most of the light. In an LCD an electric field is applied to switch the state of individual pixels so that they will transmit or block the passage of light. For a color LCD display, a white backlight is placed behind the display, and individual pixels are overlaid with red, green or blue filters.

An AMOLED display uses Organic Light Emitting Diodes as the light source. Instead of filtering the light emitted by a white backlight (as with an LCD), an OLED display generates light directly from its red, green and blue LEDs.

The “AM” in AMOLED stands for “Active Matrix”. It means that each pixel is associated with one or more transistors. However, it’s not relevant to the distinction between AMOLED and LCD, because a cellphone LCD is also an active matrix device, with thin film transistors (TFT) driving each pixel.

So which is the better technology for a cellphone display? AMOLED displays have rich, intense color. They also have lower power consumption, important in a battery-powered device, because light is only emitted when pixels are lit up (unlike an LCD where the backlight is constantly glowing).

However, LCDs can have an advantage when viewed in direct sunlight. Sunshine can leave an AMOLED display looking “washed out” or unreadable. It’s possible to put a transmissive-reflective layer (“transflective”) behind an LCD so that some of the incident sunlight is reflected back through the LCD. A transflective LCD remains readable in bright sunshine, although much of the color detail is lost.

In practice, modern AMOLED displays and LCDs can both perform impressively well, and in many cases the purchase decision will be driven by factors other than the display technology.

Thanks to Quezi reader “pretty momma” for suggesting this question.

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