Set the Type of Lighting

AutoCAD offers three choices for lighting units: standard (generic), International (SI), and American. The standard (generic) lighting workflow is equivalent to the lighting workflow in AutoCAD prior to AutoCAD 2008. The default lighting workflow for AutoCAD 2008 is a photometric workflow based on International (SI) lighting units. This choice results in physically correct lighting. The American lighting unit provides another option. American differs from International in that illuminance values are formatted in foot-candles rather than lux.

In previous versions of AutoCAD, standard lighting was the default. You can change the type of lighting with the LIGHTINGUNITS system variable. The LIGHTINGUNITS system variable set to 0 represents standard (generic) lighting; set to 1 represents photometric lighting in International SI units; set to 2 represents photometric lighting in American units.

Photometric Lights

Photometric lights are physically correct lights. Physically correct lights attenuate as the square of the distance. Photometric properties can be added to both artificial lights and natural lights. Natural lights are the sun and the sky. The natural lighting is represented interactively by a viewport background type.

You can create lights with various distribution and color characteristics, or import specific photometric files available from lighting manufacturers. Photometric lights always attenuate using an inverse-square falloff, and rely on your scene to use realistic units.

Tone Mapping

Generally with photometric lights and especially the sun you need to perform tone mapping. Tone mapping can be adjusted with the RENDEREXPOSURE command. The Adjust Rendered Exposure dialog box provides a preview and controls to adjust the tone mapping.