Design Nomenclature / Light & Optics
Point light
Also called omni light, omni, isotropic source
An idealized source of zero extent radiating equally in all directions from a single position. Because it has no size it subtends no solid angle, so it casts geometrically hard shadows with no penumbra whatsoever, and its illuminance obeys the inverse-square law exactly rather than approximately.
In practice
Renderers usually expose a radius on a point light. The moment it is non-zero the light is a sphere area light, and the name is a leftover.
Not to be confused with
- Area lightAn emitter with finite extent — rectangle, disc, sphere, or arbitrary mesh — radiating from every point on its surface. Because different parts of it are visible from different points in shadow, it generates penumbrae natively, and its reflection appears as a specular highlight of matching shape.
- Directional lightA source at effectively infinite distance, so its rays arrive parallel and its illuminance does not vary with position. Shadows stay the same size at any range and the inverse-square law does not apply — the falloff across a set is real but immeasurable. It models sunlight.
- Spot lightA source constrained to a cone, with a hot centre falling to a soft edge across a controllable penumbra angle. The cone is a masking of direction, not a property of the emitter: within the beam, falloff follows whatever law the underlying source already obeys.