Glossary

4

4:3

Aspect ratio of 4 units wide by 3 units high is the current standard for TVs in the United States. Can also be described as 1.33 aspect ratio (i.e., width is 1.33 times height). Amorphous Technology

A

Active Matrix TFT

The most common type of LCD used in most laptops, and projectors. A typical active matrix TFT display is a single panel of LCD glass that controls all three primary colors. TFT displays are noted for their quick response time and ability to display full motion video and animations without image ghosting.

Analog Transmission

The way information is transmitted over a continuously changing electrical wave that is similar to, or analogous with the original signal. All telephone calls used to be transmitted in an analog format. Today they are translated to digital pulses for both local and long-distance transmission. Your television at home receives analog signals.

ANSI Lumens

A standard for measuring light output, that is used to compare projectors. Unfortunately, there are enough variables, that the eye will often disagree radically with the ANSI rating. At best, ANSI lumens do fairly well comparing "apples" to "apples". If however one projector uses Halogen lamps and another metal-halide, the halogen projector will seem noticeably dimmer even if the two units rate the same. Other variables, including type of LCD technology (active matrix TFT, Poly-Si, passive), type of overall technology (LCD vs.DLP vs. CRT), contrast ratios, etc. all effect the end result.

Aspect Ratio

The most popular aspect ratio is 4:3 (4 by 3). Early television and computer video formats are in a 4:3 aspect ratio, which means that the width of the image is 4/3 times the height. Other formats are 5:4 used by the 1280x1024 SXGA resolution, 16:9 is used by HDTV, and 3:2 for 35mm slides.

Auto Balance

A system for detecting errors in color balance in white and black areas of the picture and automatically adjusting the white and black levels of both the red and blue signals as needed for correction.

B

Back Room Projector

A projector with a "long-throw" lens designed to be used from the far back of the room, often in a projection booth, balcony, or back of an auditorium. Many typical projectors have third party lenses available for "long-throw" applications.

Backlit

Refers to a remote control, or on projector control panel, that has buttons and controls that are illuminated. This is a major asset when using the projector in a darkened or semi-darkened room. Many projectors have backlit remote controls, while the number of projectors with backlit control panels is much smaller. As projectors have gotten brighter, room lights tend to stay on. So while a nice added feature, having backlit controls is no longer important to many users.

Bandwidth

The number of cycles per second (Hertz) expressing the difference between the lower and upper limiting frequencies of a frequency band; also, the width of a band of frequencies.

Bandwidth

The effective carrying capacity of a telecommunications transmission medium. Bandwidth describes how much information can be pushed through an electronic "pipe" at any given time.

Barrel

An outward bowing of the picture. A condition in which colours appear to flow into unintended areas of the image.

BRI (Basic Rate Interface)

The ISDN standard that governs how phones and other electronic devices are connected to the ISDN switch.

Bridge

A videoconference bridge is usually made up of back-to-back codecs from different manufacturers to convert signals from one proprietary system to another.

Brightness

The attribute of visual perception in accordance with which an area appears to emit more or less light. (Luminance is the recommended name for the photo-electric quantity which has also been called brightness.)

Broadband

Digital services at rates greater than 1.536 million bits (mbps), capable of supporting voice, video, and data, possibly using multiple channels.

C

Channel

A path for electrical transmission between two or more points. Also called a link, line, circuit, or facility.

Chromatic Aberration

An optical defect of a lens which causes different colors or wave lengths of light to be focused at different distances from the lens. It is seen as color fringes or halos along edges and around every point in the image.

Chromaticity

The color quality of light that is defined by the wavelength (hue) and saturation. Chromaticity defines all the qualities of color except its brightness.

Chrominance

A color term defining the hue and saturation of a color. Often confused with brightness, the two terms are not interchangeable.

CIE

Commission Internationale de l'Eclairage, the international commission on illumination.

Coated Optics

A variety of materials are put on to high quality lenses for several reasons. One of the key reasons to coat optics is to minimize the amount of light reflected back to the lamp and the amount of ambient light that mingles with the focused light leaving the lens. Generally good coatings can add 15% or more to the lenses brightness. Other coatings are used for filtering colors.

Codec

An acronym for Coder/Decoder. This device compresses (for transmission) and decompresses (once received) digital video and analog audio signals so that they occupy less bandwidth during transmission.

Colour

We often hear references to 8-bit, 16-bit, or 24-bit colour. These measurements refer to how many unique colours are used to display the image. The more colours used, the smoother the colour gradations will appear.

Colour Temperature

A method of measuring the "whiteness" of a light source. Metal halide lamps have very high colour temperatures compared to halogen or incandescent lights which tend to look red in comparison.

Component Video Connection

The output of a video device (such as a DTV set-top box or DVD player), or the input of a DTV receiver or monitor consisting of the three component signals: luminance or brightness (Y) and two-colour difference signals (PB and PR), each on a separate wire.

Composite Video Signal

The most common video output from VCR's & DVD players. The combined picture signal, including vertical and horizontal blanking and synchronizing signals.

Compressed Resolution

Anytime a projector can accept a higher resolution signal and compress the data down to fit its true resolution. Quality of compressed images varies tremendously. Most but not all projectors offer compressed resolution for handling higher

Compression

Any of several techniques that reduce the number of bits required to represent information in data transmission or storage, thereby conserving bandwidth and/or memory.

Continuous Presence

The transmission of two or more simultaneous images.

Contrast Control

An accrual control to increase the difference between black and white in an image.

Contrast Ratio

The ratio between the whitest and blackest portions of an image. The larger the contrast ratio the greater the ability of a projector to show subtle color details and tolerate extraneous room light.

Convergence

The ability of a three-panel projector to project uniform images without colour variance

D

D-Channel

The Data Channel on the ISDN circuit is used to carry control signals and customer call data at 16 kbps (BRI) and 64 kbps (PRI).

Data

Information represented in digital form, including voice, text, facsimile, and video.

Dedicated Access

A private connection between a customer's equipment and a company providing transmission services. The connection bypasses the local switched telephone network.

Dedicated Network

Sometimes referred to as a private or leased line. This transmission circuit is used exclusively by a single customer.

Diagonal Screen

A method of measuring the size of a screen or a projected image. It measures from one corner to the opposite corner.

Dichroic

A mirror or lens that reflects or refracts selective wavelengths of light. Typically used in projector light engines to separate the lamps "white" light into red, green and blue light. Also used to remove the Infrared and Ultra-violet

Digital Light Processing (DLP)

The commercial name for this technology from Texas Instruments (TI). The technology inside is often referred to as either "micro-mirrors", or DMD. It works this way: build a few hundred thousand tiny mirrors, and line them up in 800 rows of 600 mirrors each. Now attach a hinge to each of those 480,000 mirrors. Attach each of those 480,000 hinges to its own very tiny motor! Power each motor with electrostatic energy! The motors tilt their mirrors up to 20 degrees at incredible speeds. This allows the mirrors to modulate light from a lamp, and send the "modulated signal" out through a lens on to a screen. The most amazing part of DLP micro mirrors, is the scale of size. The 480,000 mirrors (actually 580,000 are used), hinges and motors are packed onto a "wafer" a bit larger than your thumbnail.

Digital Transmission

A way of sending coded information via a series of electric or light pulses through the air, over wires, or through glass fibers.

Distribution Amplifier

An amplifier used to maintain a clean noise free signal to the projector over significant distances. Even with good heavily shielded cables, range of video and computer signals is limited to a few metres before noticeable degradation. In ceiling mount situations, where the wiring may pass along side or across electrical conduits, etc. a distribution amp may be needed with shorter distances. Many distribution amps can also split the signal into 2 or more amplified signals for driving multiple projectors and monitors.

DLP Technology

Digital Light Processing

Dot Pitch

The distance between pixels in an image.

DPI

Dots Per Inch.

DS-1

The Level 1 standard for digital systems operating at 1.536 mbps (24 DS-0 channels). Also known as T1.

DS-3

Digital Signal Level 3. This term is used to refer to the 45 mbps digital signal carried on a T3 facility.

DVI

Digital Video Interface is a connection standard for linking a video card and a display that requires a digital signal, such as a LCD panel. Analogue video signals can also be used with the DVI interface. A normal DVI cable can support 1600 x 1200 resolution at 60 Hz. A special dual link version can support 2048 x 1536 or even higher resolutions.

E

Echo Cancellation

A technique used in high-speed modems and voice circuits to isolate and filter out unwanted signal energy caused by echoes from the main transmitted signal.

F

FM Based Remote

A remote control that broadcasts its instructions with an FM transmitter, normally required in large rooms, thanks to long range, and no line of site requirement.

Focal Length

The distance between the focal point of a lens or mirror in a projection device and the corresponding principle plane.

Focus

Sharpness of a pixel or series of pixels on the projection screen faceplate. Also measured as the spot size.

FPS

Frames Per Second.

Fractional T1

A service provided by carriers, where a full T1 link is leased to a customer, but the service charge is based only on the number of time slots used.

Frame

A single refresh of the entire screen as perceived by the viewer. This is two fields in an interlaced system.

Full Duplex

A system capable of transmitting and receiving signals simultaneously.

G

Gamma Correction

A variation in the input signal to provide a linear relationship between signal source and display output.

Gbps

Gigabits per second. 1 Billion bits per second.

H

H.320

An international standard designed to bring interoperability to videoconferencing.

Half Duplex

A system capable of transmitting and receiving signals in one direction at a time.

Halogen Lamps

Used in some low priced data projectors, and most Ohp's, these lamps last about 40 hours, with consistent output throughout their life. Although halogens look very white compared to a normal incandescent lamp, they are not as white as metal halide units.

Hard Wired Remote

Generally a remote control is wireless, and uses infra-red transmitter. There are situations where this is not practical: including large rooms where the speaker is 35 ft or more from the projector; Rear projection, where the screen will pass some signal, but normally has the presenter pretty much tied down. Also, the presenter has to point the remote "at" the projector which often means turning away from the audience. A couple of projectors (Epson for one) offer wireless remotes that will accept a cable (hard wiring) back to the projector, assuring range and signal getting though.

HDTV

The new High-Definition Television standard displays and broadcasts signals that use many more scan lines than normal television and a 16:9 aspect ratio rather than the old 4:3 aspect ratio of a standard TV set. HDTV also refers to the televisions that pick up these signals. HDTV does not degrade through many generations of editing; the final broadcast is crystal clear. The resulting picture is up to five times sharper than that of today's sets, with CD-quality sound.

High Gain Screen

A screen that uses one of many methods to collect light and reflect it back to the audience. This dramatically increase the brightness of the image over a white wall or semi-matte screen. Technologies used include curved screens, special metal foil screens (some polarized), and certain glass beaded screens. Prices and performance vary tremendously, but attention to the screen can make a big difference, particularly in "tough" environments such as trade shows.

Horizontal Frequency

This indicates how long it takes to scan each of the horizontal lines that make up the display. The unit of measurement is kilohertz (kHz). It is directly related to the number of lines and the vertical refresh (frequency) so that the higher the vertical refresh or the number of lines, the higher the horizontal frequency required. Illuminance

I

Infrared Remote

The traditional remote control, it transmits infra-red, just as a television remote. Typical range is limited to 30 - 35 feet. Infra-red requires line of site or a bounce off of a hard surface. The presenter must pay attention to where the remote is pointed. Some projectors have an IR sensor in both the front and rear of the projector, which can help. When working at or near the maximum distance, pointing right at the receiver is necessary. Remember "line of sight" - a person's head, directly between your remote and the projector may be enough to render it unusable. FM (radio frequency remote mousing systems, by comparison, have two distinct advantages, no line of sight requirement, and longer range.

Interlaced

Method of significantly increasing data densities at conventional horizontal scan rates. Half the image is refreshed (every other scan line) to produce a field. Two fields are refreshed at rates of 87 Hz forming one 43.5 Hz frame. Causes flicker on CRT displays.

International Power Supply

A unit that can operate under international selection of power requirements. The specs of units vary widely, but the minimum is 105-230 volts, and 50-60 cycles AC (alternating current). If you see a specification like 110v, 220v instead of a range, those ratings are usually +/- a given percent such as 10%. Some units are "self-switching" they will automatically switch to whatever power source you plug it into. Others will have to be switched (internally or externally to accommodate a different voltage or cycle range.

Interoperability

A state of compatibility between videoconferencing units that may support differing levels of compatibility.

Inverted Image

Invert image flips the image from top to bottom to compensate for ceiling mounting a projector upside down. Projectors typically ceiling-mount upside down, because most have "keystone" correction built in to compensate for the distortion created by "pointing up" from the table to the screen. Usual positioning has the projector about even with the bottom of the screen in a "table top position," or even with the top of the screen when ceiling mounted.

IP

Internet Protocol. Allows for videoconferencing over LAN or commercial Internet.

IR Communication Standard

Many new laptops have an Infra-Red transceiver that follow a recent standard for wireless communicating with peripherals (new laser printers complying with the standard) and networks or desktop systems. If you have a laptop like this, you know the pleasure of walking into a room with a configured laser printer, and printing out documents without having to "plug-in." Only a couple of projectors are available that follow this standard. This allows their remote controls to talk directly to your laptop for remote mousing.

ISDN

Integrated Services Digital Network is an international standard for digital services on the public switched telephone network.

It is also a measure of audio level.

K

kbps

Kilobits per second. 1 Thousand bits per second.

Keystone Correction

The innovation of using optics design or other methods to apply a "negative" keystone to the image, which will partially cancel the effects of keystoning. If you aim a projector with keystone correction at a screen with the lens level with the middle of the screen, you will note that the image at the bottom is wider than the top. When the projector is in normal position, pointing upward 10-25 degrees, the resulting image is fairly rectangular.

Keystoning

Keystoning is caused when the projected image is not perpendicular to the screen, making the top and bottom of the image different widths for a trapezoid effect.

L

Lamp Life Expectancy

The time that the lamp can keep its projected screen lumens higher than 50% of the initial value.

LAN

Local Area Network. A high volume data transmission signal is returned to the sending device after passing through all or part of a communications link or network.

Laser Pointer

A small pen or cigar sized pointer, that contains a small battery powered laser. The laser pointer projects a small, red (typically), high intensity beam of light that is immediately

LCD

LCD stands for liquid crystal display and comes in many forms, sizes, and resolutions. Its primary purpose is to present a digital image for viewing. A common use of LCDs is as a display on a notebook computer.

LCOS

Liquid Crystal On Silicon. This consists of mirror electrodes on a silicon substrate and transference electrodes on a glass substrate, enclosing vertically aligned liquid crystal. LCOS requires a far smaller light blocking layer that allows it to achieve a much higher aperture ratio (92% as opposed to 40-60% for conventional LCD)

Long Throw Lens

A lens designed for projection from the back of a room, or rather the back of a large room. Long throw lenses would be used in a projection booth in the back of a theater, etc. A typical long throw lens might have to be 15 to 30 from the screen to project a 120" diagonal image.

Lumens

A standard for measuring light output used for comparing projectors. However, the rating does not always match the perceived brightness. For example, if one projector uses halogen lamps and another metal-halide, the halogen projector will seem noticeably dimmer, even if the two units rate the same.

Lux

A standard for measuring light, numbers provided by manufacturers usually do not provide necessary additional information to compare one product to another.

M

Maximum Distance

Sometimes Maximum Distance refers to the distance from the screen that a projector can focus the image. Most of the time, however, it is the manufacturer's opinion of how far from a screen the projector can be to cast an image that is useable (bright enough) in a fully darkened room. Generally this is very subjective. One projector might quote a distance that allows them to produce a 25ft diagonal image, while a brighter projector might quote a distance that only equates to a 20ft image. Beware!

Maximum Image Size

The largest image a projector can throw in a darkened room. This is usually limited by focal range of the optics.

mbps

Megabits per second. 1 Million bits per second.

Metal Halide Lamp

The type of lamp used in many medium and all high-end portable projectors. These lamps typically have a "half-life" of 1000-2000 hours. That is they slowly lose intensity (brightness) as they are used, and at the "half-life" point, they are half as bright as when new. These lamps output a very "hot" temperature light, similar to mercury vapor lamps used in street lights. Their whites are "extremely" white (with slight bluish cast) and make Halogen lamp's whites look very yellowish by comparison.

Minimum Distance

The closest position that a projector can focus an image onto a screen.

Motorised Zoom

A zoom lens with the zoom in and out controlled by a motor usually adjusted from the projector's control panel and also the remote control.

Multiplexer (MUX)

A device allowing two or more signals to pass over and share a common transmission path simultaneously.

N

Network

1. An interconnected group of nodes. 2. A series of points, nodes, or stations connected by communications channels; the collection of equipment through which connections are made between data stations.

NTSC

The United States broadcast standard for video and broadcasting. An older standard and lower resolution than systems used in most of the world.

O

OHP

The common abbreviation for overhead projector.

OSD

On Screen Display.

Overhead Projector (OHP)

A device consisting of a light source, a transmissive or reflective platform, and a focusable lens assembly. An OHP is designed to project images from tranparencies onto a screen. LCD projection panels are designed to be used with transmissive OHPs and work best with OHPs that produce at least 3,000 lumens. Since 5% to 10% of the light that shines through an LCD panel gets onto the screen, a 3000 lumen OHP will produce an image of 150 to 300 lumens. Transmissive OHPs are fairly bulky (bigger than many projectors). Reflective OHPs are fairly portable but are not useful with LCD projection panels.

P

Packet

An ordered group of data and control signals transmitted through a network as a subset of a larger message.

PAL

A European and international broadcast standard for video and broadcasting. Higher resolution than NTSC.

Panel

Also known as a projection panel, LCD projection panel, or plate. The panel is the predecessor of today's projectors. It is slightly larger and heavier than a notebook computer and the LCD it uses to produce an image is very similar to that of the notebook computer. Because panels lack their own light source, they are designed to sit on top of a transmissive overhead projector (OHP). (See the definition of Overhead Projector for lumen performance.) Because of its small size, low cost, and versatility, panels have been a popular solution for education applications where an OHP is frequently available in the classroom for other instructional purposes. A few products have been built that integrated the panel and the OHP. These were some of the earliest projectors.

PanelLink

An all digital interface used to transmit computer video from a PC/Notebook to a projector. Supports resolutions from 640x480(VGA) up to 1600x1200(UXGA). This digital interface might someday replace the analog VGA interface typically used to connect projectors to computers.

Passive Matrix LCD

The original LCDs, these are controlled by a single processing system, for the whole screen, unlike active and poly-si, which have descrete circuits for each "pixel." This results in a panel with terrible color dynamics and contrast (typically 15:1). They are also incredibly slow: On passive laptop computers, the cursor (or anything else) moving on the screen, goes invisible until you stop moving it (submarining) Only one or two projectors use any type of passive matrix display.

PBX

Private Branch Exchange.

Pincushion (pillowing)

An inward bowing of the video image. Some projectors experience a slight amount of pincushion distortion. There are guidelines on what the specifications are for each model. The pincushion changes according to the size of the image. Pincushion is similar to bowing or barrel distortion.

PIP

Picture In Picture.

Pixels

The smallest element of a display that has the full-colour capacity of the display.

PnD

Plug and Display.

PnP

Plug and Play.

Poly-Si (silicon) LCD

A popular LCD technology for the top of the line LCD projectors. Monochrome Poly-Si LCDs are typically placed in each of the three color light paths inside a projector, one each for Red, Green, and Blue. This results in increased color saturation, with contrast ratios above 200:1. Poly-Si technology is also a bit faster than the Active Matrix TFT, for smooth video and multimedia.

Port

The physical interface to a computer multiplexer, for connection of terminals and modems.

Power Zoom

A zoom lens with the zoom in and out controlled by a motor, usually adjusted from the projector's control panel and also the remote control.

PRI

Primary Rate Interface is the combined signal-carrying capacity of 23 B-Channels (Bearer Channels) operating at 64 kbps and one D-Channel (Data Channel) also functioning at 64 kbps. The total capacity is equal to that of 1 DS-1 circuit.

Projection Distance

The distance between the projector lens and the screen measured in linear units (e.g., metres, feet, or inches).

Projection Panel

The panel is the predecessor of today's projectors. It is slightly larger and heavier than a notebook computer and the LCD it uses to produce an image is very similar to that of the notebook computer. Because panels lack their own light source, they are designed to sit on top of a transmitting overhead projector (OHP).

Projector

A projector is a device that integrates a light source, optics system, electronics and display(s) for the purpose of projecting an image from a computer or video device onto a wall or screen for large image viewing. There are hundereds of products available in the market and they are differentiated by their resolution, performance and features. These devices attach to a computer or video device as you would connect a monitor.

Protocol

A formal set of conventions governing the formatting and relative timing of message exchange between two communicating systems.

PSTN

Public Switched Telephone Network. The telecommunications network commonly accessed by ordinary telephones, key systems, PBX trunks, and data equipment.

Q

QXGA

QXGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. A QXGA display has 2048 horizontal pixels and 1536 vertical pixels giving a total display resolution of 3,145,728 individual pixels that are used to compose the image delivered by a projector. A QXGA display has 4 times the resolution of an XGA display.

R

Rear Screen Projection

Using an opaque screen, the projector is placed behind the screen, invisible to the audience. The image projects onto the screen which the audience sees on the other side. Good rear projection screens actually produce brighter images than some standard screens. A projector with a short throw lens is typically used to accommodate the lack of space behind the screen. Since the projector can be placed at the ideal height, without blocking anyone's view, keystoning is not a problem. Some mid-room projectors have available 3rd party short throw lenses. Since the image is projected through the screen, the image must be reversed.

Refresh Rates

An ergonomic issue that is directly related to long-term ease of use. A higher refresh rate translates to a more "flicker" free display on a CRT. Bandwidth and horizontal and vertical scanning rates depict a projector's ability to provide a higher resolution and refresh rate.

Resolution

The density of lines and dots per line, which make up a visual image. Usually, the higher the numbers, the sharper and more detailed the picture will be. In terms of DTV, maximum resolution refers to the number of horizontal scanning lines multiplied by the total number of pixels per line, called pixel density.

Reverse Image

Reverse image is a feature found on most projectors which flips the image horizontally. When used in a normal forward projection environment, text, graphics, etc, are backwards. Reverse image is used for rear projection.

RGB

Red, Green, Blue; the standard type of monitor used with computers. Examples of usage: RGB input or output often referred to as computer input or output.

S

S-Video

A video transmission standard that uses a 4 pin mini-DIN connector to send video information on two signal wires called luminance(brightness, Y) and chrominance(color, C). S-Video is also referred to as Y/C. A composite signal, typically found coming out of an RCA jack on the back of most VCRs has the Y and C information combined into one signal. The advantage of having luminance and chrominance separated is that a comb filter is not needed inside the video projector to separate the composite signal into the luminance and chrominance signals. A comb-filter can reduce the sharpness of your video image.

SECAM

A French and international broadcast standard for video and broadcasting. Higher resolution than NTSC.

Short Throw Lens

A lens designed to project the largest possible image from short distance. Most front room projectors use a short throw lens. They are often required for rear projection, where the depth behind the screen is limited. A typical short throw lens might produce a diagonal image size of 10 ft, from a distance of 7 to 10 ft.

sRGB

A new industry standard developed to ensure standard, uniform colour reproduction regardless of the type of display used. sRGB colour profile technology uses colour coordinates common to all display technologies. As a result, it eliminates the hue variations that occur between different display systems. 16:9

SVGA

SVGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. An SVGA display has 800 horizontal pixels and 600 vertical pixels giving a total display resolution of 480,000 individual pixels that are used to compose the image delivered by a projector.

SXGA

SXGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. An SXGA display has 1280 horizontal pixels and 1024 vertical pixels giving a total display resolution of 1,310,720 individual pixels that are used to compose the image delivered by a projector.

T

T1

A Level 1 digital transmission system operating at 1.536 mbps. Also known as DS-1.

TFT

Thin Film Transistor

TSS

Telephony System Specification.

U

Uniformity

Comparison of the brightness of one area to an adjacent area. In general, the brightest part of the image will normally be in the centre area. When moving out to the edges, the intensity of image will vary in a non-linear function. This means that one corner of the screen will not be the same brightness as another corner of the screen. A typical projector specification may call for up to a 30% difference between the centre area and the corners.

UXGA

UXGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. A UXGA display has 1600 horizontal pixels and 1200 vertical pixels giving a total display resolution of 1,920,000 individual pixels that are used to compose the image delivered by a projector

V

Vertical Frequency

This indicates how many times per second the graphics adapter can draw all the lines on the screen. A higher vertical frequency or refresh rate will produce less flicker.

VESA

Video Electronics Standards Association. An association whose mission is to promote and develop timely, relevant, open display and display interface standards, ensuring interoperability and encouraging innovation and market growth.

VGA

VGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. A VGA display has 640 horizontal pixels and 480 vertical pixels giving a total display resolution of 307,200 individual pixels that are used to compose the image delivered by a projector.

Voice Compression

The conversion of an analog voice signal into a digital signal using minimum bandwidth (16 kbps or less).

X

XGA

XGA is used to define a specific display resolution. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. An XGA display has 1020 horizontal pixels and 768 vertical pixels giving a total display resolution of 783,360 individual pixels that are used to compose the image delivered by a projector.

Z

Zoom Lens

A lens with a variable focal length. You can adjust the size of the image on a screen by adjusting the zoom lens, rather than making the projector closer to or further from the screen.

Zoom Lens Ratio

The ratio between the smallest and largest image that a lens can project from a fixed distance. For example, a 1.4:1 zoom lens ratio means that a 10 foot image without zoom would become a 14 foot image with full zoom. Conversely, a 10 foot diagonal image at 15 feet with no zoom would still be a 10 foot image at 21 feet at maximum zoom (15 x 1.4 = 21 feet). A zoom lens is "not as bright" as a fixed lens, and the higher the ratio, the less light output.