Graphics Programs Reference
In-Depth Information
ing in order to see light from user-defined sources. Click Turn Off the Default Lighting to
disable default lighting. (To turn default lighting back on, open the Lights panel slideout
on the Render tab and click Default Lighting.) You should always disable default lighting
when using user-defined lights; otherwise you can end up over-lighting your model, mak-
ing it look unnatural.
The two types of user-defined lights that you can create are generic and photometric:
Generic lights:
Provide advanced control over how they emit light and are much
more complex than photometric lights
Photometric lights:
More convenient to use as they are defined to represent how
lights work in the physical world
The LIGHTINGUNITS system variable controls whether user-defined lights in
your drawing are represented as generic or photometric lights. When
LIGHTINGUNITS is set to 0, generic lights are used. When LIGHTINGUNITS is set to
1 or 2, photometric lights are used; 1 indicates American lighting units, and 2 in-
dicates International lighting units. Lights don't have to be removed and added to
switch between generic and photometric lights; you just need to switch the sys-
tem variable.
To add a user-defined light to your drawing, click the lower half of the Create Light split
button on the Lights panel of the Render tab. You can choose from four distinct types of
lights on the flyout (for the differences between the light types, see Figure 23-3):
Point light:
Emits light uniformly in all directions, but the emitted light falls
off the farther it gets from the source. A point light is similar to a candle or a lan-
tern.
Spotlight:
Emits light in a specific direction. As light travels farther from the
source, it spreads out in the shape of a cone. You can define the
hotspot
— the
brightest part of the emitted light — and the fall-off of the light.
Distant light:
Emits light along a specified vector and doesn't decay or fall
off like other user-defined lights do. A distant light is similar to the sun.
