mat_specular

mat_specular is a console variable available in all Source games. This boolean cvar enables or disable specular reflections.

Note:This console variable is flagged as "launcher"-only in Left 4 Dead and Left 4 Dead 2, so use the following command instead:
sm_cvar building_cubemaps <0 or 1> command (with SourceMod installed) or
script Convars.SetValue("mat_specular", "<0 or 1>") (using VScript).