Design Nomenclature / Light & Optics
Specular highlight
Also called hotspot, catchlight, speculars, spec
The reflected image of the source itself in a glossy surface — sharp and small on a polished one, spread and dim on a rough one, since roughness scatters the same energy across a wider lobe. Its position moves with the viewer, which is what separates it from shading.
In practice
A diffuse highlight is the brightest part of the matte shading, where the normal points at the key; it does not move when you do. Both get called the highlight.
Not to be confused with
- BloomA post-process that bleeds luminance outward from the brightest parts of an image, standing in for scattering in the lens, the sensor's cover glass, or the eye's own media. It is applied to the finished image rather than simulated in the light transport itself.
- GlareVisual impairment or discomfort caused by a luminance in the field of view far above what the eye is adapted to. Disability glare measurably reduces what can be resolved; discomfort glare merely hurts. Both depend on the ratio to the adaptation level, not on absolute brightness.
- RoughnessThe statistical spread of microfacet normals across a surface, controlling how tightly reflected light clusters around the mirror direction. Low values concentrate energy into a small bright highlight; high values spread the same energy into a broad dim one. It is a distribution width, not a quantity of reflection.