How displays make colors
Liquid crystal display (LCD) and organic light-emitting diode (OLED) play key roles in modern displays. Nowadays, one of the ways we interact with computers is by viewing the display. However, do you know how it works?
There are several types of displays, but the most commonly used today is LCD. This type of display uses a backlight, liquid crystals, and polarizers. The backlight is the primary source of light and color in LCD displays. Typically, the backlight color is white because it is a mixture of all colors. Which allows for the creation of different colors by selectively eliminating some. You can think of it as similar to stained glass artwork. In this analogy, sunlight acts as the backlight, and the liquid crystals, polarization filter, and color filter perform similar functions to stained glass (Wikipedia Contributors, 2019).
Liquid crystals are the difference between liquids and solids. When electricity passes through them, their alignment can change. Polarizers, similar to the lenses in 3D glasses, only allow specific directions of light waves to pass through.
In an LCD display, light from the backlight passes through the first polarizer, allowing only horizontally or vertically oriented light to pass through. Next, the light passes through the liquid crystals. By applying voltage, the liquid crystals align in a particular manner, altering the amount of light that can pass through the second polarizer. Normally, light that passes through the first polarizer doesn’t pass through the second polarizer since they are tilted 90 degrees toward each other. However, when the liquid crystals align in a specific shape, causing a 90-degree rotation of the wavelength direction, the light can pass through the second polarizer (Woodford, 2007).
After that, the light is divided into three colors—red, green, and blue—using a color filter, similar to colored stained glass. These colors can be combined to produce a wide range of colors. The color filter is arranged in a checkered pattern, with each square being called a pixel. An LCD pixel consists of sub-pixels, which are red, green, and blue color filters. This arrangement allows the LCD display to show text and information to the user. However, LCD displays have limitations. They struggle to display black because some of the light always passes through since the backlight is always on, even when the polarization filters and liquid crystals block the light. As a result, even when the LCD display appears black, it is not truly black (Harding, 2022).
In contrast, OLED displays offer several advantages over LCDs. OLED displays can produce a wider variety of contrast, colors, and brightness. They are also lighter, thinner, and more durable compared to previous LCD technology. Unlike LCDs, OLED displays do not require a backlight or polarization filters. Instead, each OLED pixel performs all the necessary functions (LG, 2016; LG, 2023a).
An OLED display consists of two simple layers: the TFT (thin film transistor) layer and the OLED cathode layer. TFT stands for Thin Film Transistor, and this layer provides signals to turn each pixel on or off. The OLED cathode layer itself does the job of the display. OLED technology uses organic materials to emit light. Before, it was believed that organic materials were insulators and incapable of emitting light. However, in 1987, Ching Wan Tang and Steven Van Slyke from Kodak discovered that certain organic materials, when extremely thin (around 100 nm), have conductivity and emit light. By using these thin films, light can be produced pixel by pixel in OLED displays, which makes them energy efficient, accurate in color, and high in contrast (LG, 2023a).
Reference list
Harding, S. (2022). LCD vs. LED vs. Mini LED vs. OLED: A quick guide. [online] Ars Technica. Available at: https://arstechnica.com/gadgets/2022/06/lcd-vs-led-vs-mini-led-vs-oled-a-quick-guide/ [Accessed 1 July 2023].
LG (2016). LCD, Direct View LED, and OLED Explained 2 LCD, Direct View LED, and OLED Explained. [online] Available at: https://www.lg.com/us/business/commercial-display/resources-hub/pdfs/LG-ebook-LCD-Direct-View-LED-and-OLED-Explained.pdf [Accessed 1 July 2023].
LG (2023a). OLED vs LED – what’s the difference? – LG EXPERIENCE. [online] LG UK. Available at: https://www.lg.com/uk/lg-experience/up-coming/oled-vs-led-what-s-the-difference-lg/ [Accessed 1 July 2023].
LG (2023b). The history of the OLED TV – LG EXPERIENCE. [online] LG UK. Available at: https://www.lg.com/uk/lg-experience/inspiration/the-history-of-the-oled-tv/ [Accessed 1 July 2023].
Morrison, G. (2021). LCD vs. OLED: TV display technologies compared. [online] CNET. Available at: https://www.cnet.com/tech/home-entertainment/led-lcd-vs-oled/ [Accessed 1 July 2023].
TechTarget Contributor (2019). What is LCD (Liquid Crystal Display)? [online] WhatIs.com. Available at: https://www.techtarget.com/whatis/definition/LCD-liquid-crystal-display [Accessed 1 July 2023].
Wikipedia Contributors (2019). Liquid-crystal display. [online] Wikipedia. Available at: https://en.wikipedia.org/wiki/Liquid-crystal_display [Accessed 1 July 2023].
Wikipedia contributors (2023). OLED. [online] Wikipedia. Available at: https://en.wikipedia.org/w/index.php?title=OLED&oldid=1161461771 [Accessed 1 July 2023].
Woodford, C. (2007). How do LCDs (liquid crystal displays) work? [online] Explain that Stuff. Available at: https://www.explainthatstuff.com/lcdtv.html [Accessed 1 July 2023].
