When you open legacy drawings, AutoShade content can be converted to be usable in rendering.
Older drawings may contain legacy AutoShade information pertaining to lights, scene blocks, and camera blocks.
Lights and materials used in older drawings can be converted. Starting with the 2008 release, AutoCAD-based products introduced the 3DCONVERSIONMODE system variable. With the system variable set to the default value of 1, lighting and materials are automatically converted for older drawings.