Quick Guide to Projection Screen Terminology

Projection Screen Definitions

A. Gain

This is the reflectivity (luminance/brightness) amount a projection screen provides and is measured perpendicular to the screen center.  It is compared to an NIST traceable lambertian white reference standard which has a 1.0 gain.  The higher the gain number, the more luminance a screen reflects back.

  1. Half-Gain: (Typically measured horizontally) The measure of off-axis degrees in which picture brightness diminishes by 50%
  2. Half-Gain Cone: Specific angular measurement of half-gain performance in a specific material
  3. High Gain: Screens with higher levels of reflectivity caused by a narrower concentration of the half-gain cone typically  >1.3 gain (also see retro reflective)
  4. Low Gain: Screens with lower levels of reflectivity caused by a broader half-gain cone typically  <1.3+ gain (also see angular reflective)

B. Format

Proportion of projection screen viewing area expressed as a ratio of height to width.

  1. Square: 1.0 to 1.0 or 1:1
  2. Cinemascope or Anamorphic Format: 1.0 to 2.35 or 2.35:1
  3. HDTV Format: 1.0 to 1.78 or 16:9
  4. Letterbox: 1.0 to 1.85
  5. NTSC or Video Format: 1.0 to 1.33 or 4:3
  6. Wide Format: 1.0 to 1.6 or 16:10

C. Viewing Angle

The Horizontal angle from perpendicular center of screen at which gain or brightness decreases by 50%. (also see Half Gain or Half Gain Cone)

  1. Off-Axis (Horizontal): Points of measurement where the viewer’s eyes are offset from the center of the projection surface to either the left or the right.
  2. Off-Axis (Vertical): Points of measurement where the viewer’s eyes are offset from the center of the projection surface to either a vertically higher or lower viewing angle

Projection Material Types and Characteristics

D. Material

  1. Acoustically Transparent
  2. Ambient Light Rejecting (ALR)
  3. Matte Grey/Gray
  4. Matte White
  5. Rear Projection

E. Reflectivity

The direction in which light reflects off the material.

  1. Angular Reflective: (Typically Low Gain) Projected light reflects off the material in a mirror-opposite direction
  2. Retro Reflective: (Typically High Gain) Light reflects back from the material  at the same angle toward the projector
  3. Rear Projection: Semi opaque material that allows projectors to present their image from behind the material to the viewer on the opposite side
  4. Diffusion Uniformity: (Typically matte white) Light reflectivity is equal regardless of measurements taken from a 0°Axis to a 180° off-axis position (see uniformity)

F. Uniformity

Light reflectivity is equal regardless of measurements taken from a 0°Axis to a 180° off-axis position from either a vertical or horizontal position.

G. Contrast

The difference between light and dark in the projected image. The “black level” performance of an image is determined both by the projector’s performance capabilities as well as the projection material’s ability to reflect or absorb various light wavelengths with a neutral color temperature.