### Lighting

By default the colors assigned to pm3d objects are not dependent on orientation or viewing angle. This state corresponds to set pm3d nolighting. The command set pm3d lighting selects a simple lighting model consisting of a single fixed source of illumination contributing 50% of the overall lighting. The strength of this light relative to the ambient illumination can be adjusted by set pm3d lighting primary fraction. Inclusion of specular highlighting can be adjusted by setting a fractional contribution:

        set pm3d lighting primary 0.50 specular 0.0   # no highlights
        set pm3d lighting primary 0.50 specular 0.6   # strong highlights

Solid-color pm3d surfaces tend to look very flat without specular highlights. Since the highlights from a single source only affect one side of the surface, a second spotlight source may be desirable to add specular highlights from the opposite direction. This is controlled by "spec2 contribution". EXPERIMENTAL (details may change in a future version): The second spotlight is a pure red light source that by default contributes nothing (spec2 0.0). See also hidden_compare.dem http://www.gnuplot.info/demo_5.4/hidden_compare.html(comparison of hidden3d and pm3d treatment of solid-color surfaces)