Domain: Engineering — Communications Engineering
Target concept: An increase in the distance between the transmitter and receiver leads to a decrease in LED brightness.

Video generation prompt: An LED receiver is placed on a table, and a powered handheld radio transmitter is activated nearby and moved to a greater distance, gradually increasing the distance between the two.

Evaluation guide:
(i) Target concept: Inverse relationship between RF signal strength and distance, manifested as optical output attenuation in an LED-based receiver.
Minimum mechanism: LED receiver must be designed to convert received RF energy into proportional optical output; transmitter must emit modulated RF signal; no intervening shielding or reflective surfaces that distort free-space propagation.
(ii)Storyline: [Start] LED receiver placed on table, unlit or dim; transmitter held adjacent, inactive → [Activation] Transmitter powered on (visible cue), LED receiver immediately brightens → [Motion onset] Transmitter begins smooth, horizontal outward motion → [Causal transition] LED brightness begins decreasing synchronously with motion initiation → [Progression] Brightness declines monotonically as separation increases → [End state] Transmitter at maximum visible distance; LED remains stably dim. All events occur from fixed frontal tabletop viewpoint; no camera motion; no third-party interference; LED state must be legible at all distances.

Manual:
Experimental Procedure
1. Place LED receiver flat on tabletop.
2. Hold powered handheld radio transmitter beside it and activate.
3. Move transmitter steadily away from receiver along tabletop.
Observation of Experimental Phenomena
LED receiver brightness decreases continuously and irreversibly as transmitter distance increases.
Summary of Experimental Principles
An increase in the distance between the transmitter and receiver leads to a decrease in LED brightness.

Prompt Grounding rubric:
level_1: Neither an LED receiver nor a handheld radio transmitter appears on the table, or the scene is not a tabletop setting with two devices at all.
level_2: Both the LED receiver and the transmitter are visible on the table, but the transmitter is never switched on (no glow, screen light, or other power cue) and stays in the same spot the whole time, so the separation between the two devices never changes.
level_3: The LED receiver sits on the table and the transmitter is powered on (shown by a lit indicator or display) and is carried farther from the receiver, but its path outward is not smooth: it may reverse direction, stall, or move erratically before settling farther away.
level_4: The LED receiver stays in place on the table while the powered-on transmitter is carried steadily and only outward, away from the receiver, across the whole shot; both devices stay fully in frame the entire time with no unexplained entrances or exits.
level_5: All conditions for score 4 are met, and the transmitter starts right next to the receiver and moves away from it in one unbroken, single-direction motion to its farthest point, with both devices remaining fully visible and never blocked or repositioned by an outside hand or object.

Scientific and Causal Correctness rubric:
level_1: The receiver LED's brightness never changes throughout the video regardless of how far the transmitter travels, showing no link between distance and brightness.
level_2: The LED's brightness changes, but not in the expected direction: e.g., it gets brighter as the transmitter moves away, or it flickers with no relation to the transmitter's position, or it changes before the transmitter is switched on or after it has stopped moving.
level_3: The LED is bright while the transmitter is close and grows dimmer as the transmitter moves away, but the dimming is not smooth: it may flicker, jump between brightness levels, or pause partway through the motion.
level_4: The LED is bright when the transmitter is nearby and dims steadily and continuously as the separation grows, with no moment where it brightens again, and the dimming clearly starts once the transmitter begins moving rather than long afterward.
level_5: The LED is bright at the start when the transmitter is adjacent, begins dimming as soon as the transmitter starts moving away, fades smoothly and without reversal all the way to its dimmest point at maximum separation, and never flickers, pulses, or momentarily brightens again during the whole motion.

Spatiotemporal Consistency rubric:
level_1: The LED receiver or the handheld transmitter jumps to a different spot on the table between frames with no visible travel; either device disappears and reappears; the room's lighting or the shadows cast by either device change abruptly between frames (e.g., a shadow vanishing and then reappearing, or the scene flipping between bright and dark) with no cause; the tabletop itself changes color or texture between shots; or the transmitter's outward motion contains an impossible instantaneous jump in position.
level_2: The transmitter or receiver is hidden from view for two or more consecutive seconds without explanation; the room's ambient lighting dims or brightens on its own while the transmitter moves, in a way that could be confused with the receiver LED's own brightness change; the tabletop edge or the room background behind the devices visibly warps or bends as the transmitter moves; or the transmitter's motion freezes for a moment and then jumps ahead to a farther position.
level_3: Both the LED receiver and the transmitter stay fully visible and keep their true shape and size on the tabletop for the whole video; neither device teleports, floats, or passes through the table surface; the transmitter's outward path is a physically plausible straight or gently curved line rather than a random back-and-forth.
level_4: All conditions for score 3 are met, and the transmitter's speed across the table stays roughly even rather than lurching or stalling partway through its outward path; the tabletop stays flat and rigid with no bending or tearing near either device.
level_5: All conditions for score 4 are met, and the room's ambient illumination and the angle it falls on the two devices stay the same from the moment the transmitter is activated to the moment it reaches its farthest point (only the receiver's own LED is allowed to change in brightness), with no visible shake in either device's outline as the transmitter is moved.