Domain: Humanities and Social Sciences — Arts
Target concept: A single-sided light gradually illuminates a face in a dark room.

Video generation prompt: In a dimly lit room, a person faces the camera, and a light positioned to their left gradually brightens.

Evaluation guide:
(i) Target concept: Directional illumination creating hemifacial contrast in controlled darkness.
Minimum mechanism: A fixed, unilateral light source must exist and increase in intensity; human face must be static, frontal, and possess inherent surface reflectance properties that yield asymmetric luminance distribution.
(ii)Storyline: [Frame 0] Room fully dark, face invisible or barely silhouetted; [Transition] Left-side light begins increasing in brightness; [Mid-sequence] Left cheek, eye, and forehead become progressively visible with coherent shading; [Stable contrast phase] Lit/unlit boundary aligns with facial midline, nose shadow points rightward, right eye remains in shadow; [Visibility constraint] Camera viewpoint fixed, no occlusion, no ambient fill light: all visibility derives solely from left-side source; [Causal transition] Brightness increase → local luminance increase → local feature revelation → stable asymmetry.

Manual:
Experimental Procedure
1. Place person facing camera in a dark room.
2. Position a single light source on the left side of the person.
3. Gradually increase brightness of the left-side light over ~10 seconds.
Observation of Experimental Phenomena
- Person remains motionless and centered.
- Left side of face progressively brightens while right side stays dark.
- Illuminated region is confined to left hemiface; no spill to right side.
- Shadow of nose and cheekbone extends rightward, sharpening as light brightens.
Summary of Experimental Principles
A single-sided light gradually illuminates a face in a dark room — demonstrating directional lighting, chiaroscuro contrast, and the role of light angle in facial modeling.

Prompt Grounding rubric:
level_1: No person facing the camera in a dark room; or no light source positioned to the person's left; or the face never receives any illumination change over the shot.
level_2: A person faces the camera in a dim room, but either the light is not clearly on the left (e.g., overhead, on the right, or ambiguous), or the light never brightens over time, or the face's brightness never changes even though a light is present.
level_3: A person faces the camera in a dark room; a light source is positioned to their left and visibly increases in brightness; as it brightens, the left portion of the face becomes progressively lit while the right portion stays comparatively dark.
level_4: Beyond the 3-point basics, the lit region on the face stays confined to the left side without crossing onto the right cheek or eye, the right side remains visibly darker for the whole shot, and the brightening itself is a smooth ramp rather than sudden jumps or flickers.
level_5: Building on the 4-point level, the person stays still and centered in frame for the whole shot, the room background shows no stray light besides the left-side source, and that source reads as a single identifiable origin (a lamp, window, or glow) rather than an ambiguous or multiple-source look.

Scientific and Causal Correctness rubric:
level_1: The face's shading contradicts the light's position entirely: e.g., the nose or brow shadow falls toward the lit side instead of away from the light source, or as the left light brightens the right cheek becomes brighter than the left.
level_2: The overall brightening direction is roughly right, but the shading logic is inconsistent: the nose or brow shadow points the wrong way for a left-positioned source, or a bright specular highlight appears on the shadowed cheek rather than the lit one, or the skin's hue/saturation shifts in a way unrelated to brightness (e.g., the face turns visibly more orange or desaturated as the light brightens with no physical cause).
level_3: Shading responds correctly to a left-side source: the shadow cast by the nose and brow falls toward the right, any specular highlight sits on the lit cheek or forehead, and the skin's hue stays the same while only its brightness changes as the light strengthens.
level_4: Beyond the correct shadow and highlight placement at score 3, brightness falls off gradually from the side nearest the light toward the shadow boundary, rather than the lit region reading as one flat, evenly bright patch with a sharp edge.
level_5: Extending the gradual falloff at score 4, the skin keeps a plausible matte, diffuse look consistent with a single soft or hard key light (no glossy specular blotches appearing out of nowhere), and the balance between the lit and shadowed sides stays physically coherent across the whole brightening ramp, with no moment implying a second, hidden light has switched on.

Spatiotemporal Consistency rubric:
level_1: The person or light source jumps position or vanishes between frames (e.g., the head snaps to a different spot, or the lit patch disappears then reappears), the room swings between fully dark and fully lit in a single frame with no ramp, the background flickers, warps, or changes appearance for no reason, or the face changes apparent size without the camera moving.
level_2: The face drifts sideways, or the lit patch's position shifts across the face during the shot even though nothing should be moving; or the brightening is non-monotonic (brighter, then dimmer, then brighter again) without cause; or the shadow cast by the nose changes shape abruptly from one frame to the next for no reason.
level_3: The person stays in place and keeps facing the camera; the light stays fixed to the left and brightens without reversing; the shadow on the face grows or shifts only gradually and continuously; there is no sudden break in the face's geometry or the room.
level_4: Beyond the smooth, one-directional brightening at score 3, the camera itself never pans, zooms, or tilts during the shot, the brightening ramp has no stutters or skipped frames, and the outline of the face and its features stay aligned frame to frame.
level_5: Beyond the frame-to-frame alignment at score 4, any implied motion, such as a slight breathing movement, looks natural for a static portrait shot with no jitter inconsistent with a person simply sitting still, and the sense of depth (how far the light sits from the face, what reads as foreground versus background) stays stable and unambiguous for the whole shot.