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From the late twentieth century onwards we have all witnessed the revolution in TV set technology. Display screens have undergone a noteworthy evolution, in which square box television sets changed to wide rectangular ones, then to flat plasma displays although they weren’t actually flat but only labeled as such in reference to what they used to be. Plasma display panels (PDP) were succeeded by LCD technology which wasn’t much thinner than their predecessor. Only when the compact fluorescent light source got upgraded to LED, did the thickness reduce tremendously. For many years, these LED-lit, LCD panels were the flavour of the month and they increased in either brightness or resolution as new and improved models were released. With each of these technological breakthroughs our minds were blown away and the screens became more appealing every time. Even upgrades within existing technologies were impressive. The next level of display innovation has arrived and recently came to light through many well-known manufacturers at ISE2016. This new technology is known as Organic LED (Light Emitting Diode), more commonly abbreviated to OLED.
Organic LED as a display technology is nothing new. Many film and video production institutions have been experimenting with it for many years. However, it has only recently become available as residential and commercial displays. The OLED display screen is a light emitting technology and therefore doesn’t need a separate light source behind the screen as is required in LCD panels. They can thus be manufactured much thinner than ever before. LCD screens are classed as a transmissive technology, which essentially means that the LCD display merely transmits the light from a separate light source behind the LCD screen. Each pixel in the LCD panel then individually disperses the white light into the three primary RGB (Red, Green and Blue) colours at various intensities in order to display the correct mixture of light required to reproduce the image visible to the viewer. The architecture of these LCD panels requires a screen in front, as well as a light source behind it which adds to the thickness.
In contrast to conventional light sources which emit light by heating a filament until it glows while hot, LEDs are a semi-conducting, solid state light source that require far less energy to produce light. LEDs emit light when electrons are energised through specially treated solid materials that the LEDs are made of. Through this sub-atomic process, low voltage pulses initiate electron movement further away from its proton core and when the energy dissipates, the electron jolts to its original position. During this twitch, alternative energy is released in the form of light. Depending on the length of electron movement, different colours can be created based on the colour spectrum. Organic LEDs are similar to traditional LEDs but the light is produced by organic molecules. In this environment the term ‘organic’ refers to the molecules around the rings of atoms in carbon elements such as wood, plants, petroleum and diamonds. As mentioned above, OLED technology emits its own light and therefore does not require a separate light source. This enables the OLED display products to be extremely thin.
Plasma displays have finally reached the golden years and it has become increasingly difficult to purchase one. PDP is also an emissive technology as the ionized gasses inside the screen emit light. The plasma imaging technology has extremely high thermal emissions albeit very bright and therefore sufficient cooling components are required behind the plasma panel which adds to their thickness. Another downside for PDP is that they consume high levels of energy and the panels are physically very heavy to handle and install. PDP technology has each pixel subdivided into three segments. Each of these sub-pixels is filled with different colour (RGB) phosphor-coated cells which illuminate when energized. The three colours combined at 100% intensity, or variations thereof create the full colour spectrum that forms the image which the viewer can then experience. Plasma display panels have their benefits as well. Because of the panel emitting the light, the black areas were darker, delivering higher contrast between lit and unlit areas. LCD panels have a challenge in this regard as the light source at the back is present even when a pixel is blacked out. This results in black areas appearing dark grey instead of true black. Plasma displays are also capable of delivering very high brightness levels and can be produced in large sizes. However none of these benefits could save its obsolescence.
The imaging technology in OLED displays works by means of a layer of organic semiconductor between two electrodes which emits light in response to electric current. The OLED pixel composition works in a similar pattern to that of a plasma display with each pixel subdivided into three sub-pixels. These are known as RGB OLED displays and each segment contains an organic diode which produces one of the primary RGB colours. Certain manufacturers use WRGB (white, red, green and blue) technology where each pixel is divided into four sub-pixels instead of three. The fourth segment produces white light only, but in order to create white light, one requires a 100% mixture of each of the RGB colours. The architecture to achieve this white segment works somewhat differently to RGB OLED.
In the case of WRGB OLED, each segment of the pixel is created by compressing different layers of red, green and blue diodes. This sandwich of materials then creates a pixel with four segments delivering white light. A colour filter is applied to the surface area of three of the white segments creating the required RGB light and the fourth segment is left clear for the white light to be visible.
This fourth sub-pixel makes the technology even more energy efficient as it requires only one LED to produce white instead of a combination of the RGB LEDs to deliver the same objective. This results in an energy saving of roughly 60%. Another benefit of having a fourth pure white sub-pixel is the increased brightness when used in conjunction with the remaining RGB LEDs to produce whiter images. OLED displays also offer a much higher contrast as black areas can be completely switched off - as in the case of plasma technology - compared to the light leakage experienced in LCD screens. Additional benefits of OLED are lower thermal emissions and because of the properties of the organic diodes, they can be applied to all kinds of surfaces that make it possible for OLED screens to be lighter, thinner, flexible (bendable and foldable) and generally more durable. OLEDs can also operate in a wider temperature field than older technologies.
OLED products are currently still very expensive but based on the statistics around the costs of developing and producing electronics, pricing can only go one way from here and hopefully, OLED displays will be part of every video project sooner than we can imagine.
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