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

Glossary 271
Design eye position: The midpoint of the line segment of the open nosed
vision line connecting two points which represents the predicted eye
positions of the extremes of the aircrew population.
Display lag: The time delay in a display measured from the time when the
imaging data are received and the time they are presented.
Distortion: An unwanted variation in magnification or a prismatic
deviation with angular distance from the center of an optical component or
system; any undesired change in the frequency or amplitude of an
acoustical signal.
Dynamic retention: When pertaining to helmets, the condition of
preventing the loss of a helmet during a crash sequence.
Dynamic range: In a system or a transducer, the difference, measured in
decibels, between the overload level and the minimum acceptable level.
The minimum level is commonly fixed by any or all of the following: noise
level, low-level distortion, interference, or resolution level.
Egress: The process of exiting the cockpit.
Electroluminescence (EL): A flat panel display technology in which a
layer of phosphor is sandwiched between two layers of a transparent
dielectric (insulator) material which is activated by an electric field.
Electrophoresis (EP): A nonemissive flat panel technology based on the
movement of charged particles (of one color) in a colloidal suspension (of
a second color) under the influence of an electric field. The application of
the electric field changes the absorption or transmission of light through the
solution.
Exit pupil: The region where the observer’s eye(s) must be located in order
to view the total field of view. In optics, it is the image of the aperture stop
as formed from the image side of the optics.
Eye clearance distance: The minimum clearance from the closest display
system component to the cornea of the eye. This parameter is important in
determining system compatibility with add on devices, e.g. corrective
lenses, protective masks, etc. (Also referred to as physical eye relief.)
Fast Fourier transform (FFT): An algorithm that allows quick,
economical application of Fourier techniques to a wide variety of analyses.
Field emitting display (FED): An emissive flat panel display technology
which consists of a matrix of miniature electron sources which emit the
electrons through the process of field emission. Field emission is the
emission of electrons from the surface of a metallic conductor into a
vacuum under the influence of a strong electric field.
Field of view (FOV): The maximum image angle of view that can be seen
through an optical device.