Helmet-Mounted Displays: - USAARL - The - U.S. Army

Glossary 273
Image intensifier (I 2 ): Sensor technology based on amplification of
ambient light. Photons are imaged onto a photocathode which converts
them into electrons. The number of electrons is multiplied and channeled
onto a phosphor screen.
Image overlap: The portion (usually expressed as a percentage) of the total
field of view of a biocular/binocular system that can be viewed
simultaneously by both eyes.
Image smear: An image artifact resulting from relative motion between
scene and sensor. This is caused by insufficient temporal characteristics
within the imaging system, e.g., phosphor persistence, scan rate, etc.
Interlace ratio: The number of fields per frame pertaining to displays.
Interpupillary distance (IPD): The distance between the centers of the
pupils of the two eyes.
Impact attenuation: The reduction in mechanical force through the
protective helmet.
Jitter: Small, rapid variations in a signal due to vibrations, voltage
fluctuations, control system instability, and other causes.
Just noticeable difference (jnd): A subjective difference threshold in the
perception of a variable.
Lead, lanthanum, zirconate, and titanate (PLZT): A material that can
be electronically switched rapidly in polarity such that when sandwiched
with a near infrared blocking material and a fixed polarizing material, the
visual transmittance can be varied from full open state (approximately
20%) to a full off (optical density (OD) is greater than 3.0) in
approximately 150 microseconds.
Light emitting diode (LED) display: Emissive display composed of
multiple light emitting diodes arranged in various configurations which can
range from a single status indicator lamp to large area x-y addressable
arrays.
Liquid crystal display (LCD): A type of nonemissive flat panel display
technology which produces images by modulating ambient light. The
ambient light can be reflected or transmitted light from a secondary,
external source (e.g., a backlight).
Luminance: Luminous flux per unit of projected area per unit solid angle
leaving a surface at a given point and in a given direction; measured in
footlamberts (fL).
Luminance disparity: In biocular/binocular helmet-mounted displays, the
difference in the image luminance between the two channels.
Luminance transmittance: The fraction of luminance of the outside world
seen through an optical component or system.; usually expressed as a