9

Intensity/Color/Distribution Rollout 1353
Inter face
Distr ibution—Describes the directional
distribution of the light emitted by a source. There
are several different distributions:
• Isotropic (page 2–1323)
• Spotlight (page 2–1324)
• Web (page 2–1325)
• Diffuse (page 2–1323)
Note: T arget Point and Free Point lights can have
either Isotropic, Spotlight, or Web distribution.
All other photometric lights use either Web or
Diffuse distribution.
Color group
Light—Pickacommonlampspecificationto
appro ximate the spectral character of your light.
The color swatch next to the Kelvin parameter is
updated to reflect the light you select.
K elvin—Set t he color of the light by adjusting the
color temperature spinners. The color temperature
is displayed in degrees Kelv in. The corresponding
color is visible in the color swatch next to the
temperature spinners.
Filter—Useacolorfiltertosimulatetheeffectof
a color fi lter placed over the light source. For
example, a red filter over a white light source
casts red light. Set the fi lter color by clicking
the color swatch to display the Color Selector
(page 1–161). Default=white (RGB=255,255,255;
HSV=0,0,255).
Intensity group
These controls specify the strength or brightness of
photometric lights in physically based quantities.
You set the intensity of a light source using one of
the following units:
•
lm (lumen)—Measures the overal l output power
of the light (luminous flux (page 3–955)). A
100-watt general purpose light bulb has a
luminous flux of about 1750 lm.
•
cd (candela)—Measures the maximum luminous
intensity (page 3–965) of the light, usually
along the direction of aim. a 100-watt general
purpose light bulb has a luminous intensity of
about 139 cd.
•
lx at (lux)—Measures illuminance (page 3–955)
caused by the lig ht shining on a surface at a
certain distance and facing in the direction of
the source. The lux is the International Scene
unit, which is equivalent to 1 lumen per square
meter. The AS unit for illuminance is the
footcandle (fc) which is equivalent to 1 lumen
per square foot. To convert f rom footcandles to
lux, multiply by 10.76. For example, to specify
an illuminance of 35 fc, set illuminance to 376.6
lx.
To specify the illuminance of a light, you must
set t he lx value, and enter the distance at which
that illuminance is measured.
Note: You can obtain these values directly from
lighting manufacturers. A table of some common