Autodesk LIGHTSCAPE, Manual

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Glossary
330
Lightscape
light
Radiant energy capable of producing a visual sensa-
tion in a human observer.
linear light
A light source that can be approximated as a straight
line segment.
LTLI file format
The luminaire photometric file format implemented
by the Danish Illuminating Laboratory, Lysteknisk
Laboratorium, in the early 1970s—used in Scandina-
vian countries.
lumen
The SI unit of luminous flux.
luminaire
A light fixture complete with one or more lamps and
housing.
luminance
The photometric quantity that describes light leaving
a surface in a particular direction.
luminance contrast
The relative difference between luminance values of
adjacent regions.
luminous exitance
The luminous flux leaving a surface of unit area.
luminous flux
The quantity of light energy per unit time arriving,
leaving, or going through a surface.
luminous intensity
The light energy per unit time emitted by a point
source in a particular direction.
luminous intensity distribution
The function that describes the directional distribu-
tion of luminous intensity of a point source.
lux
The SI unit of illuminance, equal to 1 lumen per
square meter.
magnify
A filtering operation used by texture mapping tech-
niques to determine the color of an area that covers
less than one pixel in image texture space.
material
The set of parameters assigned to a surface that are
used by the reflection model to determine how light
interacts with it.
material properties
See material .
matte surface
A surface that scatters light uniformly in all direc-
tions. It appears equally bright at any angle.
mesh
The data structure that describes the light distribu-
tion over a receiving surface. It breaks down the orig-
inal surface into a set of smaller polygonal pieces
called
mesh elements . The corners of these elements,
called mesh vertices, are shared among adjacent ele-
ments and are used to store the illumination data col-
lected during the lighting simulation.
minimize
A filtering operation used by texture mapping tech-
niques to determine the color of an area that covers
more than one pixel in image texture space.
nanometer (nm)
One billionth of a meter. A common unit for describ-
ing the wavelength of light.
normal
See surface normal .
OpenIRIS GL
An industry-standard application programming
interface for drawing 3D graphics.
orbit
A camera motion around the focus point, keeping
the same distance.
orientation
See surface orientation .
pan
A camera motion parallel to the screen. The focus
point moves the same amount in the same direction
as the camera.
penumbra
The transition region at the boundary of a shadow