2012

Modifies the brightness of a lamp.
Summary
Dialog box for setting the Lamp Intensity for a photometric light.
List of Options
The following options are displayed.
Lamp Intensity Represents the brightness of a lamp. More specifically, it
represents the luminous intensity, or power in a particular direction. It is
specified in candela by default (in both the SI and American units systems).
Must select from one of the following radial buttons:
■ Intensity (Candela). Specifies the number of candelas (cd) is the SI unit of
luminous intensity (perceived power emitted by a light source in a
particular direction).
■ Flux (Lumen). Represents the rate of total energy leaving the lamp. It is
specified in lumens (SI and American). Mathematically, the flux is the
integral of the luminous intensity over the sphere. The calculation of flux
depends on the distribution of intensities. For a point light with constant
intensity, the flux is simply the product of the intensity and the solid angle
of a sphere: 4 Pi * Intensity. For a spot light, the flux is the product of the
intensity and the solid angle of the hotspot cone, plus the incremental
solid angle of the fall-off region. For a weblight, there isn’t any analytical
formula. The flux is obtained by numerically integrating the intensities
provided in the web file.
■ Illuminance (Foot-candles). Represents the energy per area arriving at a
surface (Area-flux-density). It is specified in lux (SI) and foot-candles
(American). For a near light, because the light rays are diverging, you have
to talk about the illuminance at a specific distance from the lamp. So this
requires an extra control to specify this distance and an additional
affordance in the viewport to show the distance.
Intensity Input Control Controls the intensity value.
Distance When Illuminance is selected, displays the lux as a distance glyph
in the viewport for the given light. Note: the text for the illuminance radio
button will depend on the current lighting units. For the SI system, this will
be “Illuminance (Lux),” and for the American system, it will be “Illuminance
(Footcandles).” The distance field represents a world distance and should be
formatted in the current length unit corresponding to the current lighting
units. The distance field represents a world distance and should be formatted
1556 | Chapter 16 P Commands