Autodesk 24000-000000-9860 - Revit Architecture - PC, User Manual

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You can define the initial intensity of a light source in a lighting fixture family file (as follows). In a project,
you can change the initial intensity of an individual lighting fixture. (See
Changing the Initial Intensity of
a Light Source on page 1133.)
To define the initial intensity of a lighting fixture family
1 Open the lighting fixture family.
2 On the Design Bar, click Family Types.
3 For Name, select the family type to modify.
4 Scroll down the list to locate the Initial Intensity parameter, and click in its Value column.
5 In the Initial Intensity dialog, specify values for the parameters.
See Initial Intensity Parameters on page 1125.
6 Click OK.
The Family Types dialog displays the new Initial Intensity value.
7 Click OK.
8 Save changes to the lighting fixture family.
Initial Intensity Parameters
When defining the Initial Intensity of a light source, define the parameters as follows.
Description Parameter
A measurement of the electrical power consumed by a light source.
TIP When adjusting Wattage, it is also important to consider Efficacy. If you change
Wattage alone, you may make the light source unintentionally bright. Luminosity is defined
as Wattage (W) times Efficacy (W/lm). Luminous Efficacy for a 100 W tungsten incandescent
(110 V) is 175, while a 32 W fluorescent tube (T8) is 60.
Wattage
The amount of light (luminous flux, measured in lumens) produced by a light source as
a ratio of the amount of energy consumed to produce it (measured in watts). Efficacy
The quantity of light energy per unit of time arriving, leaving, or going through a surface.
The lumen (lm) is the unit of luminous flux in both the International System (SI) of units Luminous Flux
and in the American System (AS) of units. If you think of light as particles (photons)
moving through space, then the luminous flux of a light beam arriving at a surface is
proportional to the number of particles hitting the surface during a time interval of 1
second.
TIP In general, Luminous Flux provides more accurate lighting in rendered images than
Wattage and Efficacy.
The light energy per unit of time emitted by a point source in a particular direction. Lu-
minous intensity is used to describe the directional distribution of a light source, that is, Luminous Intensity
to specify how the luminous intensity of a light source varies as a function of the outgoing
direction. The Candela (cd) is the unit of luminous intensity.
The luminous flux incident on a surface of unit area. Illuminance measures how much
energy has fallen on a surface. This quantity is useful for describing the level of illumination Illuminance
incident on a surface without making the measurement dependent on the size of the
Creating and Modifying Lighting Fixtures | 1125