Glossary - Stewart


Above Finished Floor (AFF)

This is an acronym commonly used in dimensioning. If you see a note saying 8' 0” AFF, it means that whatever is being referenced is eight feet and zero inches above the surface of the finished floor — whatever you walk on, e.g. the surface of the tile — not the underlay of that room.

ALR Screen

An ALR screen selectively reflects light back to the audience. This effect is achieved by positioning the projector and screen in such a way that the projector's light is bounced towards the audience while the other ambient light in the room is selectively absorbed by the screen. ALR screens only work if the ambient lighting is not hitting the screen from the same direction as the projector. 

Ambient Light

The light surrounding an environment or subject is called ambient light. It is the light that is already present in a room or venue before any projected light is added. Ambient light usually refers to the natural light that exists in a room or venue that cannot be controlled.

CIE Chromaticity Diagram
The International Commission on Illumination (abbreviated CIE for its French name) is the international authority on light, illumination, color and color spaces. The chromaticity diagram, established in 1931, represents the mapping of human color perception in terms of two CIE parameters x and y.  It allows all other colors to be defined as a weighted sum of the three primary colors.  

SMPTE Color Bars

Society of Motion Picture and Television Engineers color bars is a television test pattern used where the NTSC (National Television Systems Committee) video standard is utilized. Comparing this pattern as received to the known standard gives video engineers an indication of how an NTSC video signal has been altered by recording or transmission and what adjustments must be made to bring it back to specification. The pattern is also used for setting a television monitor or receiver to reproduce NTSC chrominance and luminance information correctly.

Color Space 

A range of colors can be created by the primary colors of light (RGB —Red, Green, Blue) and these colors then define a specific color space.

Digital Keystone Correction 

Digital keystone correction is a function that allows projectors that are not positioned perpendicular to the horizontal centerline of a screen (either too high or too low) to manipulate the projected image vertically and/or horizontally so that the image appears as close to an even rectangle as possible. It is performed digitally before the image passes through the lens and is accessed by projector's on-screen menu function or via a dedicated control button on the projector or remote control.


Digital Cinema Initiatives, LLC (DCI) is a joint venture of major motion picture studios, formed to establish a standard architecture for digital cinema systems. Digital cinema refers to the use of digital technology to distribute or project motion pictures. A digital movie can be distributed to cinemas in a number of ways: over the Internet or dedicated satellite links or by sending hard drives or optical discs such as Blu-ray discs. Digital movies are projected using a digital projector instead of a conventional film projector. Digital cinema is distinct from high definition television and does not use television or high definition video standards, aspect ratios, or frame rates. In digital cinema, resolutions are represented by the horizontal pixel count, usually 2K (2048×1080 or 2.2 megapixels) or 4K (4096×2160 or 8.8 megapixels).

Dispersion of Light

Half gain performance of screen fabrics is accomplished by broad band diffusion of projected light. If diffusion is not done skillfully, the artifact encountered can be dispersion which is what we define as color shift. Many poorly engineered screens will color shift or disperse light instead of diffusing light.

Fixed Frame Screen

Fixed frame screens are aluminum perimeter framed screens made with flexible material and typically hang on a wall or may be suspended.


Gain is a measurement of the reflectivity of any screen or projection surface. The gain number represents a ratio of the light that is reflected from the screen as compared to the light reflected from a standard white TPFE disc called a reflectance standard. Therefore, a screen with a gain of 1.0 will reflect the same amount of light as that from a reflectance standard. A screen rated at 1.5 gain will reflect 50% more light on axis, as the standard. A gray screen with a 0.8 gain factor will reflect 80% of the light on axis, as compared with a gain standard. Gain standards also have very controlled diffusion performance. The standards we use for screen measurement are Lambertian, having perfect ability to diffuse a single ray of projected light into a hemispheric distribution.  


See Color Space

Gray Screens

Gray screens or high contrast screens boost contrast when using digital projectors in viewing rooms that are not entirely dark. A gray screen absorbs ambient light, improving black floor performance and retention of contrast. In the same setting with similar ambient lighting, a white screen would be more washed out.

If the projector has ample lumen output, whites remain white while blacks are a deeper black. The net effect is an increase in the contrast range of the screen image.

High Dynamic Range (HDR)

HDR or high dynamic range, provides better contrast, greater brightness levels and a wider color space in order to make display images look more like real life. Your eyes can perceive brighter whites and darker blacks – greater dynamic range – than traditional formats. 

HDR content preserves details in the darkest and brightest areas of a picture that are lost using old standards such as Rec.709. The luminosity of HDR allows for more natural, true to life colors that are closer to how we see them in real life.

Half Gain

Half gain is the standard used to measure the brightness performance of a projection screen when the viewer is looking at the screen from an angle. A projection screen’s peak brightness occurs when the viewer is perpendicular to the center of the screen. As the viewer moves to the side, away from the center of the screen, the brightness of the image will decline. When the brightness drop off reaches 50% of peak gain, that measurement is called the half gain.
Half gain is how we define the viewing cone. Expressed in degrees of arc from the centerline of an image, half gain is a key consideration in screen fabric selection. The half gain measurement is commonly used to describe the limits in a planned viewing area where excellent performance can be expected.

The wider the viewing cone, the more susceptible to loss in contrast due to ambient light influence on black levels. When projector power is limited, the use of an elevated gain surface may have a consequence in limiting the viewing cone.

InfoComm ANSI Standard-DISCAS

Display Image Size for 2D Content in Audiovisual Systems (DISCAS) established a standard practice for calculating image size to viewing distance based on visual acuity. The DISCAS standard encompasses a systematic approach to display size that incorporates content, aspect ratios, image size as well as resolution. With this knowledge, the seats of viewers can be placed in relationship to the screen image to achieve maximum enjoyment.   

Incident Light Meter

Incident light meters measure the amount of light falling on a subject. The incident meter is aimed at the light source and measures the light source falling directly on an object and is not influenced by the reflectance of the object.

Lace and Grommet Screen

Lace and grommet screens are usually large, permanently tensioned screens. They are furnished with reinforced webbing on all four sides along with grommets on 4" to 6" centers. The screens attach to frames with lacing cords, springs or shock cords. The frames are available in wood, aluminum or steel for wall or suspended mounting.

Solid State Illumination

Replaces a traditional projection lamp with an LED array. LED and laser array, laser phosphor array (aka hybrid light source) or a pure RGB laser light source.  

Lens Shift

Lens shift is the ability to move the projected image up or down, left or right, while keeping the projector stationary. Having the ability to shift the projected image without having to move the projector can sometimes help to overcome unique installation challenges.

LED Display

An LED display is a flat panel, direct view display which uses an array of light-emitting diodes (LED) as pixels to show video.

Long Throw Projection Lens

All short throw and long throw lens measurements are categorized by the range of the projector in relation to the screen to create a 100" image. Long throw projectors have telephoto lenses that can create a much smaller picture from longer throw distances. Long throw lenses allow projector placement at greater distance than short throw lenses. The light is spread to a lesser degree, keeping the illuminated area smaller as a ratio of the distance to the projector location.  


Screen masking creates a sharp black border when an image is narrower or shorter than the screen surface area. Masking defines the image on the screen and creates the perception of greater contrast. Having a continuous variable masking screen system is the best way to ensure that all content is seen in the correct aspect ratio and with the sharpest possible image.


The nit is a unit of the intensity of visible light commonly used to specify the brightness of a flat panel display or direct view LED display. One nit is equivalent to one candela per square meter. The conversion factor for nits to foot-lamberts is 1 nit of illumination for 3.426 foot-lamberts.

A photometer is a device used to measure diverse aspects of the intensity of light. Color photometers measure the amount of light falling on an object along with the intensity of color coming from it. 

Projection Lamp

A modern projector lamp is an ultra-high pressure mercury vapor ARC lamp. Projector lamps are categorized as either metal halide lamps or ultra-high pressure mercury vapor lamps. Xenon lamps are also commonly used in high powered projectors.

Short Throw Projection Lens


Short throw projectors have lenses that can create a much larger picture from shorter throw distances. Typical short throw projectors can project a 100” image under less than 5 feet.

Spot Meter

A spot meter, or spot photometer, measures a small, localized area of an illuminated object. Spot meters are useful for measuring multiple areas of a screen surface and measuring the angularity of a screen’s performance.


The Society of Motion Picture and Television Engineers (SMPTE) is an international professional association, based in the United States of America, of engineers working in the motion imaging industries. An internationally recognized standards organization, SMPTE has more than 600 standards for television production, filmmaking, digital cinema, audio recording, information technology and medical imaging. 

Snapper Mounted Screen

A fixed frame screen that uses snap fasteners to attach to the square tube frame.

Tab-Tension Projection Screen

Tabs containing tensioning wires are located on each side of a retractable screen and ensure a smooth and completely flat screen surface.


When projector manufacturers talk about the throw capabilities of a projector, they are referring to the amount of distance needed to “throw” an image between the projector itself and the screen to get the display size desired.

Ultra Short Throw Projectors (UST)

Ultra short throw projectors can create an image of up to 100″ from as close as 15 feet away. Typically any lens with a focal length of 0.4:1 or shorter, is considered a UST lens.


This refers to the consistency of brightness over the entire image. For example, if a projector has a uniformity rating of 90% and is projecting a pure white or single color image on the entire screen, there will be no more than a 10% variation in intensity across the entirety of screen’s surface. Better quality projectors have a higher percent of uniformity and therefore produce a more accurate image.

Viewing Angle

In displays, viewing angle is the maximum angle at which a display can be viewed with acceptable visual performance. In a technical context, this angular range is called viewing cone, defined by a multitude of viewing directions. Many manufacturers of projection screens define the viewing angle as the angle at which the luminance of the image is exactly half of the maximum (called peak gain).

Zoom Lens

A lens allowing a projector to change smoothly from a telephoto to a close-up or vice versa by varying the focal length. Zoom lenses allow the size of the projected image to be adjusted without physically moving the projector.