Sets the ambient value for character models in the Phong lighting model.^[1]

/console characterAmbient [value]

value 

Floating-point value between 0.0 and 1.0

Allows no value to be set and disables all Ambient Lighting on M2 Models.

Notes 

Even with characterAmbient set to 0.0 it is considered to be on, and needs to be entered as /console characterAmbient to disable Ambient lighting

Default:

SET characterAmbient "0.0"

References

1. ^ Phong shading at graphics.wiki.com