Key Terms and Explanations

LCD display technology

Anti Smudge/ Anti Fingerprint coatings work by resisting the ability of the oil on a finger to stick to the screen. Instead they bead up, making them less noticeable and easier to clean from the screen. Learn more.

Anti-Glare coatings and glass etching processes use a material’s diffusive properties to disperse reflected light across the screen surface, making it appear fuzzy or blurred, eliminating any sharp reflections or hot spots. Learn more.

Anti-Reflective coatings and films consist of layers of material with varying refractive indexes, each of which reflects unwanted light at a different angle, thus reducing any visible reflections. Learn more.

Backlight.  The source of light for the LCD panel in a display, today a grid of light-emitting diodes, or LEDs. Edge-lit LEDs form a line around the rim of the screen with a diffusion panel to spread the light evenly. In a direct full LED array the LEDs are arranged behind the screen at equally spaced intervals. In a mini or micro LED backlight, a larger number of smaller LEDs (less than .2 mm) provide the illumination, improving contrast by showing little or no light behind black pixels. Learn more.

Bezel. The frame, or edge, around the LCD panel in a display. Zero bezel panels, with no frame around the front edges, are favored in monitor-based video walls because there is little or no gap between the displays forming an image. They are also preferred for many medical devices, as they offer fewer places for pathogens to collect.

Brightness. Typically measured in candelas per square meter (cd/m2) or nits. Displays in laptops and mobile devices usually produce between 200 and 500 nits, with many televisions higher and outdoor TVs often at 1,000 nits or higher.

Color gamut. The range of colors that a display is able to reproduce.  sRGB, the most commonly used standard, can produce 16.7 million colors, based on 8 bits or 256 shades each of red, blue, and green.

Cover glass is a protective layer of glass installed over an LCD panel to protect it from damage and to hold display enhancements, such as a touch sensor, in place. The glass used may be plain or tempered soda lime glass or a chemically-hardened glass such as Gorilla Glass or Dragontrail Glass.  Learn more.

Display Interfaces internally connect the liquid crystal display module which consists of a TFT Cell, Driver IC/Source PCB and a backlight unit. Common interfaces used today are Low Voltage Differential Signaling or LVDS, Embedded Display Port or eDP, Mobile Industry Processor Interface - Display Serial Interface (MIPI-DSI), RGB, V-by-One, I2C, Serial Peripheral Interface or SPI and MCU. Learn more.

EMI, or Electromagnetic Interference, is a disturbance generated by a nearby electromagnetic source that can affect the electrical circuits within an LCD display.  RFI, or Radio Frequency Interference, is closely related. Either or both can be generated by electrical devices including motors, microwave ovens, transformers, CRT monitors, and power supplies, and wireless devices including phones and network transmitters.

IP Rating measures Ingress Protection, the ability of the display to resist dust and water, where the first digit indicates resistance to dust and the second resistance to water. IP67 and IP 68 both include a “6” for dust, or full protection. The “7” in IP67 indicates 30 minutes of protection against water at a depth of up to 1 meter; the “8” in IP 68 indicates continuous protection against water at depths greater than 1 meter. Learn more.

Luminance Uniformity measures the display’s ability to produce brightness consistently across its surface. Typically it is measured at the center of the screen and at eight additional points around its perimeter, then calculated using the formula ΔL=[ L(MAX) / L(MIN) –1 ] X 100. 

Oleophobic Coatings repel oils and grease. They are often used on screens in medical devices to make them easier to clean and to reduce the risk of contaminants. Learn more.

Optical Bonding.  The process of bonding a touch screen and/or cover glass to an LCD panel, while at the same time filling the gap between them with an optically transparent material that eliminates internal reflections, thus improving durability, brightness and contrast. OCR, or wet bonding, uses optically clear resin to fill in the gap between the elements, creating the strongest bond and the most readable image, because it does the best job of eliminating internal reflections. OCA, or dry bonding, uses optically clear adhesive to create good durability and readability. Air Gap is the least expensive and least effective, using double-sided tape to bond the elements. Learn more.

Pixel. The “picture element” or dot formed by a single liquid diode, or LCD.  The overall image seen on an LCD display is formed by millions of pixels, blended together by the human eye into a single picture.

Polarizer. A layer of crystalline material placed between the backlight and the LCD element within a display to direct the alignment of the light waves passing through the LCDs.

Any type of wave has an alignment or directionality separate from the direction in which the wave is traveling. With light waves, this alignment or polarization varies with the light source and changes whenever the waves are reflected from a surface. A polarizer only allows light of a specific alignment to pass through.

In an LCD module, a rear polarizer, placed between the backlight and the LCD panel, forces all of the light passing through the LCD element to be aligned in one direction. Since the ambient light outside the panel will be aligned in different random directions, a front polarizer, placed on the outside of the panel, eliminates virtually all of the transmission of light into the panel.  Thus the two polarizers work together to keep ambient light from washing out the image created by the display.

Refresh Rate. A measure of how often a display updates its picture each second. Most LCD displays refresh at 60 cycles per second, or 60 Hz, but some special purpose displays, notably those used for gaming, resulting in smoother on-screen motion.

Response Time is the time it takes the display to shift from one color to another or from black to white to black again, measured in milliseconds (ms). Today most displays respond in about 10 ms, with lower response times desirable for gaming and other applications where high-speed motion is shown.

Resolution. The level of detail of a given image or display, expressed in the number of pixels in the horizontal axis by the number of pixels in the vertical. For example, VGA resolution screens are 640 x 480 pixels, XGA 1024 x 768, WUXGA 1920 x 1200, and 4K 4096 x 2160 (Digital Cinema Initiatives) or 3840 x 2160 (Ultra High Definition).

TFT LCD. Thin-film-transistor liquid-crystal display, the technology used in most displays today. There are three types commonly used. The oldest, twisted nematic (TN) displays offer extremely fast response times but originally had limited color reproduction and viewing angles. Over time, however, TN has been improved to display 8-bits per channel RGB (16.7 million colors) and relatively wide viewing angles. In-plane switching (IPS) offers deeper color depth and wider viewing but somewhat lower response times. Newer technologies, including VA (vertical alignment) panels offer various tradeoffs between color, response, viewing angles and cost.

Touch Interface. A technology to translate touches to the display to the computer or processor. Three are most commonly used: PCAP or Projected Capacitive Touch, which uses a conductive grid to recognizes changes in an electromagnetic field caused by the touch of a finger or stylus; Surface Capacitive Touch, which uses a glass overlay with a conductive layer to recognize the touch; Resistive Touch, in which the touch presses two electrically resistive layers together; and IR, which uses an array of invisible infrared LED light sources and detectors around the edges of the screen to recognize the touch of the finger or stylus. Learn more.

System on Module (SOM). A board level circuit that integrates a system function on a single module. The term can include an SoC, a system on a chip, or a COM, a computer on module. Unlike a single-board computer, a SOM or SoC typically serves a special function. Learn more.