Enable shadows

In order to enable shadows, you have to activate the option in rendering options

Then, it is possible to enable shadow for each light with the light configuration dialog box

In order to compute the light of a point, TopSolid computes the light at the face vertices and interpolates values. Result can sometimes looks “strange” when using spots if the vertices are not all under light. To solve this problem, you have to reduce the max facet size

You can change the shadow opacity:

The "Shadow tolerance" option allows to lightly "move" the shadow backward to avoid the shadow to visually overlap the front of the part.

Example: