Rendering and Illumination - Autodesk AutoCAD 2013 Practical 3D Drafting and Design - page 323

Scene illumination
We are going to see how to add light to scenes, making a distinction between natural
lighting, from the Sun and sky simulation, and artificial lighting, with point lights, spot
lights, distant lights, and web lights (with IES file information).
Default lighting
Before adding any light, AutoCAD applies default lighting, consisting of two distant
lights parallel to the viewing direction. When orbiting the view, this default lighting fol-
lows. That's why if we make a render without applied lights, the model can be seen
without shadows, which is unrealistic.
When we create the first light or activate the Sun light, AutoCAD prompts for turning
off the default lighting. With lights applied, the DEFAULTLIGHTING variable controls
which illumination will be used in the current viewport: 0 to applied lights and 1 to de-
fault lighting. This variable does not affect renderings.
Generic and photometric lighting
AutoCAD can calculate indirect lighting, thus adding realism to the scene, but it takes
more time to render. We achieve this by applying photometric lights, whose intensities
are measured in real lighting units, such as candela or foot-candles.
Three options are available:
• International : Photometric lights are applied and light intensities are
measured in international units, namely candela
• American : Photometric lights are applied where light intensities are meas-
ured in American units, namely foot-candles
• Generic : Generic lights are applied without lighting units, and each light
has a generic intensity value of 1 , without correspondence to real lights
Illumination can be activated by using the following:
• The UNITS command (alias UN ): This is available on the Lighting area of
the dialog box