Design Nomenclature / Light & Optics
Shadow softness
Also called hard light, soft light, shadow diffusion, edge transfer
- Light & Optics
- Composition
- 2D & 3D
How wide a shadow's penumbra is, governed by one quantity: the angular size the source subtends from the point in shadow. A source is hard or soft only relative to a distance — the same softbox is soft at a metre and hard at twenty.
In practice
Photographers and lighting TDs say soft light as though it named a class of fixture. Diffusion helps only because it enlarges the emitting area; moving the lamp closer does the same thing for free.
Not to be confused with
- PenumbraThe graded margin of a shadow from which part of the source is visible and part is blocked. Its width grows with the source's angular size and with the distance from occluder to receiver — the whole of what is called a soft shadow is simply this region being wide.
- 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.
- Point lightAn 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.