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)