Motivated light is a video-industry term for light in a scene that makes narrative sense — a visible lamp, a sunbeam casting a shadow — as opposed to light that looks arbitrarily placed. It matters for eye-direction editing (see Subject Glow via Foreground-to-Transparent Radial Gradient + Inverted Mask) because not every competing bright spot in a frame should be suppressed to zero.
When a secondary highlight — e.g., a tree catching stray light at the frame's edge — reads as lit by the same source illuminating the subject, mask it and pull down Highlights (and a touch of Exposure) partially, not all the way. Fully killing it breaks the light's narrative logic; leaving it untouched keeps it competing with the subject for attention. The target is 'enough that it stops being a distraction' while it still 'makes sense' as coming from the same light source.
This is a restraint principle layered on top of masking-based eye-direction techniques: after isolating a competing bright area, judge whether it's motivated before deciding how far to suppress it.
Из тем: Lightroom Mobile: Masking, Sliders & Simulated Light