PointLightSource

Normalised here rather than trusted, because an un-normalised direction scales the cosine the cone is compared against and shows as a cone of the wrong width — which reads as the angle having been set wrong rather than as the vector.

A narrow cone is not free, and the cost is the shadow rather than the shading. A spot's shadow takes a layer of the same octahedral array a point light's does, and that layer covers the whole sphere — so a 45 degree cone uses about 15% of it, roughly 0.38 of the linear resolution, and a 10 degree cone about 0.13. Comfortable for a lamp; visibly coarse for a stage spotlight, which is the measurement that would justify giving spots a perspective map.

Applies to a point light as well as a spot. A bare bulb has a measured distribution too, and a fixture's own profile is usually a better description of it than any cone. Absent, or negative, is a light with no profile.

A light whose radius is animated invalidates its own map every frame — matchesSource compares the range, because the range is the cube's far plane — so it is perpetually stale and takes bake budget forever. With a fixed budget of a couple of faces a frame, a handful of those starve every real lamp in the world, and only the one nearest light ever finishes a bake.

That is not hypothetical: pulsing floor markers animate a squared fade into radius every frame, and a courtyard full of them left exactly one lamp casting. They are floor lighting 35 cm off the deck and were never meant to cast at all.

Then the lit shader shades it exactly only where the choice is complete and lets the field's summed light take over past it, so the light is never counted twice. Carried to the shader as the sign of the light's weight, which both light paths already have: no new storage on a part whose uniform budget has none to spare.