Why is LCD the Most Popular Display Technology?
History of Liquid Crystal Display (LCD) As early as 1889, scientists discovered that chemicals such as cholesteryl benzoate, when melted into liquid form, refracted light like a crystalline solid and reacted to electrical charges in predicable and repeatable ways ( Timeline, 2016 ). Over the course of nearly a century, companies like RCA recognized the significance of this discovery and studied, improved and, in the 1960s, adapted these liquid crystals into a revolutionary display technology for electronic clocks and aircraft cockpit displays. The technology was adopted by Timex in 1976 to use in their watch displays. Since then, LCD technology has advanced to include color and to incorporate multi-touch functions. Despite other exotic types of display technology such as E-Ink and OLED, which promise to offer lower energy consumption or better picture quality, LCD still dominates the market due to its broad range of sizes, superior availability, energy efficiency, and its light, compact design. LCD is the most widely used display technology in touch-based user interfaces and is commonly used in the following devices: Calculators Mobile phones Point-of-sale terminals Clocks Watches Cockpit displays Instrument panels Computer monitors Tablets Signage TVs Security access panels LCD Displays in Cockpit https://commons.wikimedia.org/wiki/file:iceair_glass_cockpit_lcd_display.jpg 2
This paper compares LCD display technology to other display technologies available and discusses why LCD is still the most popular display technology for our computers, tablets, digital watches, and other mission critical devices. How LCD Works Embedded HMI LDC Display in Viking Oven http://www.cnet.com/news/luxury-design-show-reveals-whats-next-in-kitchen-appliances/ LCD works on the principles that light can be polarized, liquid crystals can change polarized light, electrical current can change the structure of the liquid crystals, and transparent substances can conduct electricity. In an LCD display, liquid crystals are placed between two layers of polarized glass called substrates. When light passes through the polarized glass, the crystals inside twist and allow light through. If an electrical charge is applied to the liquid crystals, they will untwist, causing the angle of light passing through to change so no light can reach the eye. This area appears darker than the surrounding areas (Tyson, 2000). In the simplest LCD display, a mirror placed behind one of the substrates reflects light. Two electrode planes of indium-tin oxide are placed between the two substrates at right angles to each other, forming rows and columns that either charge or ground the liquid crystals to suppress or emit light. Liquid crystals do not emit any light of their own. Some LCD displays are reflective such as those seen on solar calculators and digital watches. Other displays are backlit with LEDs such as those seen in modern flat screen televisions. 3
How LCDs work in the simplest passive matrix display http://www.circuitstoday.com/liquid-crystal-displays-lcd-working LCD displays fall into two categories: passive matrix and active matrix. Passive matrix is the simplest form of LCD. It uses a simple grid of electrodes connected to integrated circuits that send charges down the column of the negatively charged substrate and ground the corresponding row of the positively charged substrate, causing the liquid crystal in the corresponding pixel to untwist and the pixel to darken. Active matrix LCDs are often referred to as TFT displays and include variations such as in-plane switching (IPS), twisted nematic (TN), and vertical alignment (VA. In an active matrix LCD, a matrix of thin film transistors (TFT) is sandwiched between the two glass substrates surrounding the liquid crystals. When a transistor is switched on, it sends a charge to a corresponding pixel that emits a controlled amount of light. To create the brilliant colors we see today on LCD displays, a filter with three subpixels of red, green and blue is placed between the substrates. The intensity of the voltage on each subpixel of the filter determines the color our eyes will see. Color LCDs can display a total of 16.8 million colors. Active matrix LCD displays require a large number of transistors, and the larger the size of the display, the more transistors are required. This increases the likelihood that a matrix will contain a bad transistor and result in a bad pixel. 4
Active matrix (TFT) LCD display http://sustainablematerialschemistry.org/basic-page/how-stuff-works#.vy1l4tqridu LCD s Competitors Advances in new exotic display technologies such as E-Ink and OLED have failed to surpass LCD s popularity despite their impressive features. E-Ink E-Ink is primarily used in monochromatic ereaders such as the Kindle, watches, instrument panels, and heath and fitness devices. E-Ink (or electronic ink), used in Electronic Paper Displays, works much like ink on paper. However, unlike traditional ink, it contains millions of tiny microcapsules filled with pigmented chips that appear dark when the microcapsules are given a negative charge. 5
How LCDs work in the simplest passive matrix display http://www.circuitstoday.com/liquid-crystal-displays-lcd-working E-Ink is bistable, meaning that the display remains unchanged until the images are given another charge ( E-Ink History, 2016). Since it requires no backlight, E-Ink is the most energy efficient display technology, requiring power only when the display is changed. E-Ink displays emit no light, so they are easily read even in sunlight, unlike LCD and other emissive display technologies. E-Ink display was originally created to be used in an electronic book, which looked and functioned much like a traditional paper book but could change its text. This electronic book could store up to ten books that the reader could change at will. The actual technology of electronic books surpassed this vision for E-Ink, and the ink was subsequently used in the original Kindle electronic book readers released in 2007. Amazon continues to use E-Ink in their newer monochromatic ereaders such as the Kindle Paperwhite and the new Kindle Oasis. The major drawback of E-Ink is that, despite great strides in improving the technology to use colored oil drops to display color and a higher switching speed to animate images, it is still several iterations away from competing with LCD s brilliant colors and video capability, and Amazon uses an in-plane switching LCD display for their Kindle Fire tablets. 6
OLED Organic Light Emitting Diodes (OLED) has rapidly gained popularity as a next generation technology as the picture quality is better than LCD. OLED displays brighter whites and blacker blacks than LCD, resulting in a sharper picture, but it fails to compete with LCD in price, availability and reliability. OLED is fundamentally different from LCD because it emits its own light and does not require backlighting. OLED uses thin organic films made from carbon and hydrogen placed between two conductors. When a current is applied to the films, light is emitted. Since OLED does not require two substrate layers, it is thinner and lighter than LCD and can even be used in curved or flexible displays. OLED is currently used in digital cameras, Samsung s Galaxy devices, the Oculus Rift VR headset, and Google Glass. LG OLED Flexible display http://www.extremetech.com/computing/168124-lg-is-making-bendable-and-unbreakableoled-display-for-useless-curved-smartphone However, OLED s higher contrast ratio and flexible capabilities are its major advantages over LCD. Compared to OLED, LCD displays are brighter, and they are capable of achieving the same 4K resolution as OLED. LCD has a higher refresh rate and more displayable colors than OLED. In addition, LCD has a longer proven lifespan, as OLED technology is newer and has yet to prove its longevity. Due to their high availability, LCDs are cheaper and easier to replace than OLED displays. Most importantly, OLED is extremely expensive to produce, despite its simpler construction: OLED is five times as expensive as LCD and, as it is a newer technology, it has far fewer producers. Only a few companies such as LG are putting money into building OLED technology for displays, so it is primarily used for lighting solutions. 7
LCD s Advantage For the best touch-based user experience, LCD is still the most popular display technology. LCD is the tried and tested technology that we have relied upon since the 1970s. It is significantly less expensive to produce than other more exotic types of display technology. With more and more producers of LCD, the technology continues to advance, and the newer generations of LCD such as Quantum Dot are likely to rival if not surpass OLED s superior picture quality. Much like plasma display, which sunk into obscurity due to its inability to compete with LCD, more expensive, exotic technologies have yet to prove their staying power in the market. For mission critical devices, you need a trusted display technology that you can rely on. It is for these reasons that NTX Embedded features LCD displays with capacitive or resistive touchscreens and control in our embedded human machine interaction systems. For more information about our robust user interface design services and products, visit us at www.ntxembedded.com. References: E-Ink History. (2016) Retrieved from e-ink.com/history.html Jeff Tyson. How LCDs Work. (17 July 2000). Retrieved from howstuffworks.com. http://electronics.howstuffworks.com/lcd.htm OLED introduction and basic OLED information. (2016). Retrieved from http://www. oled-info.com/introduction Timeline: The Early History of the Liquid Crystal Display. (2016). Retrieved from http://spectrum.ieee.org/static/timeline-the-early-history-of-the-liquid-crystaldisplay 8