Glossary of Display Technology

absolute white
In theory, a material that perfectly reflects all light energy at every visible wavelength. In practice, a solid white (with known spectral data) that is used as the "reference white" for all measurements of absolute reflectance.
A neutral color (white, gray, or black) that has no hue. See hue.
American College of Radiology/National Electrical Manufacturers Association.
active matrix
A liquid crystal display structure in which switching transistors or diodes are attached to each pixel to control the on/off voltage. It produces a brighter and sharper display with a broader viewing angle than a passive matrix display. Also known as AMLCD (active matrix liquid crystal display). See TFT (thin film transistor).
additive primaries
In color reproduction, red, green, and blue. When lights in these colors are combined in equal amounts, they produce the visual sensation of white light. When these are combined at varying intensities, a range of different colors is produced. Combining two primaries at 100% produces a subtractive primary, either cyan, magenta, or yellow. See subtractive primaries.
alignment layer
A thin film layer that is applied by spin coating. This thin film is then treated to impart a desired direction at which the liquid crystal molecules will attach and align. See buffing.
amorphous silicon (a-Si)
A semiconductor material that is used to make the thin film transistors (TFTs) layer of an active matrix LCD.
aperture ratio
The ratio between the transmissive portion of the pixel and its surrounding electronics, also known as fill factor. Generally, this is a limiting factor for luminance, the higher the aperture ratio; the brighter the luminance.
aspect ratio
The width-to-height ratio of the active area of a display. Standard U.S. video has an aspect ratio of 4:3.
The light source for a transmissive LCD. Basically, two techniques are used in transmissive LCD designs, direct lighting and side lighting. Direct-lit backlights use CCFTs (cold cathode fluorescent tubes) and a diffuser panel directly in back of the LC (liquid crystal) layer. Side-lit backlights use CCFTs and a light pipe on one or more of the edges of the display.
Ideally, the complete absorption of incident light; the absence of any reflection. In the practical sense, any color which is close to this ideal in a relative viewing situation, i.e., a color of very low saturation and of low luminance.
The dimension of color that is referred to an achromatic scale, ranging from black to white, also called lightness or luminous reflectance. Because of confusion with saturation, the use of this term should be discouraged.
A technique where the alignment layer on the LCD substrate is rubbed in one or more directions. This process aligns the liquid crystal molecules parallel to the buffing direction. See alignment layer.
Candelas (cd/m2)
An international unit of luminous intensity per projected area normal to the line of observation. Luminance may be described in units of Candelas per square meter, or nits.
CCFTs (cold cathode fluorescent tubes)
These are the fluorescent tubes that provide the light for the LCD unit. These tubes are generally very thin, approximately 2 mm in diameter. See fluorescent lamp.
Perceived as having a hue; not white, gray, or black.
That part of color specification, which does not involve illuminance. Chromaticity is two-dimensional and specified by pairs of numbers such as dominant wavelength and purity.
chromaticity coordinates, CIE
The ratios of each of the three tristimulus values X, Y, and Z in relation to the sum of the three: designated as x, y, and z respectively. They are sometimes referred to as the trichromatic coefficients. When written without subscripts they are assumed to have been calculated for Illuminant C and the 2° (1931) standard observer unless specified otherwise. If they have been obtained for other illuminants or observers, a subscript describing the observer or illuminant should be used. For example, x10 and y10 are chromaticity coordinates for the 10° observer and Illuminant C.
chromaticity diagram, CIE x,y
A two-dimensional graph of the chromaticity coordinates, x as the abscissa and y as the ordinate, which shows the spectrum locus (chromaticity coordinates of monochromatic light, 380 nm-770 nm). It has many useful properties for comparing colors of both luminous and non-luminous materials.
CIE (Commission Internationale de l'Eclairage)
The International Commission on Illumination, the primary international organization concerned with color and color measurement.
CIE chromaticity coordinates
The ratios of each of the tristimulus values of a color to the sum of the tristimulus values. In the CIE systems they are designated by x, y, and z.
CIE standard observer
A hypothetical observer having the tristimulus color-mixture data recommended in 1931 by the CIE for a 2° viewing angle. A supplementary observer for a larger angle of 10° was adopted in 1964. If not specified, the 2° standard observer should be assumed. If the field of view is larger than 4°, the 10° standard observer should be used.
column driver
Small electronic circuits that provide voltages to the individual sub-pixel through the source lines. These are generally 8-bit driver circuits that provide 256 unique values per sub-pixel.
color temperature
A measurement of the color of light radiated by an object while it is being heated. This measurement is express in terms of absolute scale, or degrees Kelvin. Lower Kelvin temperatures such as 2400° K are red; higher temperatures such as 9300° K are blue. Neutral temperature is white, at 6504° K.
The level of variation between light and dark areas in an image.
contrast ratio
The ratio of intensity between the brightest white and the darkest black of a particular device or a particular environment.
Alignment of the vertical and horizontal lines in an image.
(Digital Imaging and Communications in Medicine). The DICOM standard contains a display function standard.
digital driving level (DDL)
A digital value which given as input to a display system produces a luminance. The set of DDLs of a display system is all the possible discrete values that can produce luminance values on the display system. The mapping of DDLs to luminance values for a display system produces the characteristic curve of that display system. The actual output for a given DDL is specific to the display system and is not corrected for the grayscale standard display function.
A technique used to improve the viewing angle where multiple alignment directions are produced on the same sub-pixel.
fluorescent lamp
A glass tube filled with mercury gas and coated on its inner surface with phosphors. When the gas is charged with an electrical current, radiation is produced which in turn energizes the phosphors, causing the phosphors to glow.
foot Lamberts (fL)
A unit of luminance. One foot Lambert is equal to 10.76/- (approximately 3.426) Candelas per square meter.
Screen luminance as a function of video voltage approximately follows a mathematical power function of the input video signal, the exponent of which is called gamma.
gate electrode
The "row" electrode in an active matrix LCD that controls whether a voltage is applied to a sub-pixel.
An achromatic scale ranging from black through a series of successively lighter grays to white. Such a series may be made up of steps, which appear to be equally distant from one another or may be arranged according to some other criteria such as a geometric progression based on lightness.
The main attribute of a color that distinguishes it from other colors. For example, a color may have a green, yellow, or purple hue. Colors defined as having hue are known as chromatic colors. White, black, and grays possess no hue.
IPS (In Plane Switching)
A technique of improving the viewing angle of an LCD where the liquid crystal molecules are switched in the plane of the LCD layer rather than vertical to it.
JND (Just Noticeable Difference)
The luminance difference of a given target under given viewing conditions that the average human observer can just perceive.
A page or screen orientation that is wider than it is tall.
LCD (liquid crystal display)
A display composed of liquid crystal suspended between two transparent sheets. The display is composed of pixels or other shapes which can be turned on or off with electrical stimulation. Typically, a light is passed through the LCD to illuminate the pixels.
liquid crystal
The compound found in liquid crystal displays. Liquid crystal reacts predictably when electrically stimulated. This makes it the ideal compound to turn LCD pixels "on" or "off." Liquid crystal is sometimes abbreviated as LC.
A measure of the brightness or luminous intensity of light, usually expressed in units of Candelas per square meter (cd/m2) or foot Lamberts. 1 fL = 3.426 cd/m2.
nanometer (nm)
A unit of length equal to 10-9 meter. In light measurement, the wavelength of light is measured in nanometers. The portion of the spectrum that we perceive as visible light includes wavelengths from about 380 nm to 770 nm.
A unit of luminance equal to 1 cd/m2 or 0.292 ftL.
normally black
A twisted nematic LCD design where the backlight is blocked when pixels are in the unselected state. Therefore, when no voltage is applied, the screen is black.
normally white
A twisted nematic LCD design where light is transmitted when pixels are in the unselected state. Therefore, when no voltage is applied, the screen is white.
The time it takes for the visible glow of a CRT's phosphor to darken after the scanning electron beam is removed. A long persistence means less flicker, but may create smearing when images are in motion.
PICture Element; the smallest element on a computer CRT or LCD unit.
The coating on the inside of CRTs. Phosphor glows when struck with electrons. Images appear on a CRT by controlled scanning of an electron beam.
A light filter which only allows light waves of a certain rotation through. Polarized material with perpendicular filtering is used in LCDs to enclose the liquid crystal. The liquid crystal is then used as the medium which twists the light waves 90° in order to allow the light to pass through or not.
A page or screen orientation that is taller than it is wide.
refresh rate
The number of times per second the screen is refreshed or redrawn. This number is usually stated in Hz (Hertz) or cycles per second. A rate of 60 Hz is equal to 60 times per second.
The ability of an instrument to perform as specified without premature failure.
The degree of agreement among independent measurements of a quantity under the same conditions.
Society of Motion Picture and Television Engineers.
Each pixel is made up of three independently controlled sub-pixels. In a color display these sub-pixels have red, green, or blue color filters. Or, in the case of a grayscale display, each sub-pixel will have a clear transparent filter, allowing the full grayscale range to be displayed. Each sub-pixel is capable of generating different intensities, creating a range of colors or grayscale values, which is perceived as a mixture of each sub-pixel value.
subtractive primaries
The process colors cyan, magenta, and yellow. Each absorbs or subtracts its complementary color-red, green, or blue-from the light reflecting off the paper.
TFT (thin film transistor)
Usually made from amorphous silicon (a-Si) and used as a switch to a charge storage device located below each sub-pixel on an active matrix LCD.
See active matrix.
Adjective to describe a material that transmits light without diffusion or scattering.
(1) One of the three CIE tristimulus values; the red primary. (2) Spectral color matching functions of the CIE standard observer used for calculating the X tristimulus value. (3) One of the CIE chromaticity coordinates calculated as the fraction of the sum of the three tristimulus values attributable to the X value.
(1) One of the three CIE tristimulus values, equal to the luminous reflectance or transmittance; the green primary. (2) Spectral color matching function of the CIE standard observer used for calculating Y tristimulus value. (3) One of the CIE chromaticity coordinates calculated as the fraction of the sum of the three tristimulus values, attributable to the Y value.
(1) One of the three CIE tristimulus values; the blue primary. (2) Spectral color matching function of the CIE standard observer used for calculating the Z tristimulus value. (3) One of the CIE chromaticity coordinates calculated as the fraction of the sum of the three tristimulus values attributable to the Z value.