Design Nomenclature / Light & Optics
Terminator
Also called shadow line, light-shadow boundary
This entry has not been translated yet and is shown in English.
The locus on a surface where the light direction is tangent — where the normal is perpendicular to the incoming ray and direct illumination reaches exactly zero. It is a line of zero width; everything soft about it comes from the source's angular size, not from the boundary itself.
In practice
Renderers speak of terminator artifacts: faceting or shadow acne along this line on coarse meshes, where interpolated normals and the real geometry disagree.
Not to be confused with
- Core shadowThe darkest band within a form shadow, lying just past the terminator, where the surface has turned fully away from the key but has not yet swung around far enough to face whatever is bouncing light back. Its presence is what stops a shaded sphere reading as flat.
- Form shadowThe region of an object turned away from the light — unlit because of its own orientation, not because anything blocks the source. Its boundary is the terminator, its edge softens in proportion to the source's angular size, and almost everything in it arrives as indirect light.