shininess
Controls globally how solid objects shine with reflected (specular)
light. Increasing values result in higher levels of object reflectance.
Decreasing values help emphasizing the objects bright spots. When
shininess is set to
0.0 no bright spots are visible.
When specular light is set to (0.0, 0.0, 0.0),
shininess has no effect.
Example: <light ... shininess="0.1"/> (default)
(defined in GAMGI_MESA_LIGHT_SHININESS)
Allowed values: 0.0 - 1.0 (optional)