LCD Acronyms and Vocabulary

The State-of-the-Art in Display Technology (September 2001 issue)


Technology
TFT--Thin Film Transistor - Used interchangeably with "active matrix"; refers to the fact that an individual thin-film transistor (an active device) drives each sub-pixel in an active-matrix LCD.

STN--Super Twist Nematic - Used interchangeably with "passive matrix"; refers to the way liquid crystal material switches light in a passive-matrix LCD. Variations include CSTN (Color STN) and DSTN (Double STN); this article lumps all of these together under the generic term "STN" because the differences aren't very relevant to outdoor color.

Construction
Aperture Ratio--The ratio of the area of a sub-pixel to its total screen area, which includes all the support structures required by the sub-pixel (e.g., the "transistor" in TFT). Larger aperture ratios allow more light to go through the LCD, which makes it appear brighter.

Pixel--A dot on a display which can be driven to a specified color. A pixel is composed of three sub-pixels (red, green and blue).

Transmissive--LCD construction in which light is only transmitted through the display.

Transflective--LCD construction in which light can be transmitted through or reflected from the display.

Reflective--LCD construction in which light is only reflected from the display.

Resolution
VGA--Video Graphics Adapter - A hardware descriptor from early PC history that today refers to a resolution of 640 x 480 pixels.

1/4-VGA--Quarter VGA - 240 x 320 or 320 x 240 pixels

1/2-VGA--Half VGA - 640 x 240 pixels

SVGA--Super VGA - 800 x 600 pixels.

XGA--Extended VGA - 1024 x 768 pixels.

SXGA--Super XGA - 1280 x 1024 pixels.

SXGA+--Super XGA Plus - 1400 x 1050 pixels.

UXGA--Ultra XGA - 1600 x 1200 pixels.

Lighting
AR Ð Anti-Reflection--A coating used on one or more surfaces of an LCD to reduce the reflection of ambient light.

Backlight--A light source and light guide mounted behind the LCD. Light goes through the LCD to illuminate it.

CCFL--Cold Cathode Fluorescent Lamp - The light source used in most portable computer color LCD backlights and frontlights; also called CFL (Cold Fluorescent Light).

Frontlight--A light source and light guide mounted in front of the LCD so that the user views the LCD through it. Light from the frontlight is reflected by the LCD.

LED--Light Emitting Diode - An alternative light source used instead of CCFL; not as bright.

Light Guide--A device used to direct the light from a light source such as a CCFL towards an LCD; can be located behind or in front of an LCD.

Nit--(Not an acronym, from Latin "nitere" = "to shine") - A unit of measure for brightness; equal to one candela per square meter (cd/m2).

Based in Silicon Valley, Geoff Walker is a consultant with Walker Mobile. Geoff has worked on the engineering and marketing of pen computers since 1990 at GRiD Systems, Fujitsu Personal Systems (now Fujitsu PC) and Handspring. He can be contacted at geoff.walker@att.net.

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