Domain: Natural Science — Chemistry
Target concept: Red helium neon tube

Video generation prompt: A sealed gas-discharge tube filled with helium gas, connected in a closed electrical loop, is observed when electrified.

Evaluation guide:
Target concept: Element-specific atomic emission spectra, demonstrated via helium's 706.5 nm red line under electrical excitation in low-pressure gas discharge. Minimum mechanistic assumptions: (1) Electrons accelerated by electric field collide with He atoms; (2) Excited He atoms decay radiatively with nanosecond lifetime; (3) Emitted photon wavelength is determined solely by electronic energy level difference (E = hc/λ); (4) Observed color is direct perceptual proxy for λ. Phased storyline: [t=0] Operator closes switch → [t<0.05 s] Current flows through closed loop → [t<0.05 s] Electron collisions excite He atoms → [t<0.05 s] Radiative decay emits 706.5 nm photons → [t<0.05 s] Uniform deep red-orange volumetric glow appears along entire tube → [t=0.03 s after release] Glow vanishes instantly. Visibility constraints: Must be front-lit with neutral white light; tube must fill >60% of frame height; glow must be resolvable as continuous (not pixelated/strobed); no occlusion of tube body or switch action; color must read by eye as a deep red, visibly different from the warmer orange-red typical of neon tubes.

Manual:
I. Basic Demonstration Information
Demonstration Title: Red Helium Discharge Tube Glow Demonstration
Subject: Natural Science - Chemistry - Atomic Emission Spectra
Demonstration Purpose: To visually demonstrate that helium gas, when electrically excited in a low-pressure sealed tube, emits a characteristic deep red-orange light (706.5 nm); to distinguish helium’s emission from neon’s orange-red (640 nm) and confirm the principle of element-specific atomic spectra; to reinforce the causal chain: closed-circuit electrification → electron acceleration → He atom excitation → radiative decay → visible red emission.
II. Demonstration Carrier/Equipment
Core Carrier: Commercial helium discharge tube (borosilicate glass, 7 cm length, metal end electrodes, labeled "He", filled at ~5 torr He)
Auxiliary Equipment: DC power supply (0–5 kV, current-limited to 5–10 mA), insulated wires with alligator clips, series ballast resistor (50 kΩ, 5 W), tactile momentary switch, black non-conductive mounting stand, neutral-white LED illumination (6500 K)
III. Demonstration Content Description
Layout: Mount tube horizontally on stand, centered in frame. Connect wires: power supply (+) → switch → ballast resistor → tube anode; tube cathode → power supply (−). Ensure all connections are tight and visible.
State Control: Power supply OFF initially. At start, operator presses switch firmly for ≥1 s, then releases. Observe only during active conduction.
Comparison Baseline: Tube must emit *uniform* volumetric glow — not localized at electrodes — confirming gas-phase excitation, not filament or arc.
IV. Observation of Core Phenomena
Electrification Event: Clear visual of switch lever moving downward, followed immediately by circuit completion (no delay).
Glow Onset: Within 0.05 s of switch closure, intense, uniform, saturated red-orange light fills entire inter-electrode region — no blue/violet fringe, no flicker, no electrode hot spots.
Glow Color: Deep crimson (distinct from neon’s warmer orange-red); matches published He I 706.5 nm spectral line; confirmed by absence of other dominant wavelengths (no 587.6 nm yellow, no 447.1 nm blue).
Glow Termination: Within 0.03 s of switch release, glow extinguishes completely — confirming atomic (not phosphor) emission with nanosecond decay.
V. Summary of Key Knowledge Points and Principles
Core Concept: Each element emits unique wavelengths when excited electrons return to lower energy levels; helium’s strongest visible line is 706.5 nm (3³P → 2³S), appearing as deep red.
Why Not Neon?: Neon’s dominant line is 640.2 nm (orange-red); confusion arises from colloquial use of "neon light" for any gas-discharge tube — but true red helium tubes are scientifically distinct.
Critical Conditions: Low pressure (~1–10 torr) enables mean free path for electron acceleration; DC current prevents polarity reversal artifacts; ballast resistor ensures stable glow (not arc).
VI. Demonstration Precautions
— Never operate without ballast resistor (risk of tube explosion or power supply damage).
— Avoid touching electrodes while powered (high-voltage hazard).
— Use only certified He-filled tubes — do not substitute with air, argon, or neon.
— Record under neutral white light — avoid ambient red filters or colored backgrounds that distort hue perception.
— Limit ON time to <5 s per trial to prevent He depletion or electrode sputtering.

Prompt Grounding rubric:
level_1: No sealed discharge tube visible; no glass tube containing gas; no closed electrical loop shown (switch, wires, and power source absent or clearly disconnected); no glow at any point; scene shows a different object type entirely (e.g., an incandescent bulb, an LED strip, or a neon storefront sign) instead of a sealed gas tube.
level_2: A glass tube is present but its ends look open or unsealed, or wires trail off-screen without ever reaching a power source; a switch or battery may be pictured but is not shown wired into the tube's circuit; no glow appears at any point, or a colored light appears to be glued onto the tube's outside rather than glowing from within it.
level_3: A sealed glass tube with metal end-caps is wired to a power source and switch, closing a real loop; when the switch is thrown, a glow appears but stays confined to small bright spots at the electrode tips rather than filling the tube, or the glow's color looks muddy or shifts between frames; the tube carries no 'He'/'helium' marking or context cue tying it to helium.
level_4: Sealed tube, end-cap electrodes, wires, power source, and switch are all shown connected in one continuous loop; the tube or its stand carries a legible 'He' or 'helium' label; throwing the switch produces a glow that fills nearly the whole length of the tube rather than only the electrode tips; one small setup gap remains, e.g., the switch action is partly hidden by a hand, or the wire-to-electrode connection point is not clearly visible.
level_5: Every setup element from the prompt is shown unambiguously and in the correct order: a sealed glass tube labeled 'He'/'helium' with metal end-cap electrodes; a fully visible wire loop connecting tube, switch, and power source with no hidden joints; the switch action (lever or button moving) filmed in full view; immediately after switch closure, the glow fills the tube's entire length end-to-end with no dark segment remaining; nothing in the shot suggests any object other than a helium-filled discharge tube (no neon-sign lettering, no visible heated filament).

Scientific and Causal Correctness rubric:
level_1: Glow appears in a color other than red (e.g., blue, green, or golden-yellow), which would not match helium's line emission; or the tube glows before the switch is closed, or keeps glowing after the loop is opened; or the light comes from a heated wire or filament rather than from the gas filling the tube.
level_2: The tube does glow in some shade of red or reddish-orange, but the timing is decoupled from the switch: the glow starts well before or well after (more than roughly a second) contact is made, or persists for a similarly long stretch after the switch opens; or the glow sits only as bright dots at the electrodes with no sign the gas column itself is lit.
level_3: Glow onset and switch closure are clearly linked (the glow appears essentially together with the switch action, not long before or after) and the glow largely fills the gas column rather than sitting only at the electrode tips; however, the hue drifts partway through the clip (e.g., starts orange-yellow and settles into red), a faint bluish tinge mixes into the glow, or the glow lingers visibly for more than a couple of seconds after the switch opens.
level_4: Glow appears together with switch closure and disappears together with switch opening, with no lingering afterglow beyond roughly a second; the glow is a steady deep red across the full length of the gas column (not orange, not pink, not blue-tinted) for as long as the switch stays closed; only a minor issue remains, such as a slightly brighter patch near one electrode.
level_5: The causal chain is fully and consistently shown: the glow appears only while the switch is closed, essentially in step with the switch action, and vanishes essentially in step with the switch opening, with no perceptible afterglow; the glow color read across the whole clip is a deep, blood-red hue, visibly distinguishable from the warmer orange-red one would expect from a neon-filled tube, and stays that same deep red uniformly along the tube rather than concentrated at the electrodes; no other emission color (blue, violet, white) contaminates the glow at any point.

Spatiotemporal Consistency rubric:
level_1: The tube, wires, switch, or power source jump to a different position or vanish and reappear between shots; the tube appears to hover with no visible stand or support; the glow is present in one frame and simply gone in the next with no switch action shown causing the change; the camera framing or background changes entirely partway through the clip.
level_2: The tube stays roughly in place, but the wires visibly re-route (a different path or number of loops) between frames with nothing touching them; the switch lever appears in two different positions in consecutive frames with no hand or mechanism visibly causing the jump; the stand or background swaps color or texture partway through for no shown reason.
level_3: Tube, wires, switch, and stand keep the same relative arrangement throughout, and the switch's motion is shown as one continuous motion rather than jumping between positions; the only continuity flaw is a brief, roughly half-second stutter or momentary doubling of the tube or switch, and the room's overall brightness and color don't suddenly change character.
level_4: Every element (tube, end-cap electrodes, wires, switch, stand, and background) keeps a fixed position and identity across the whole clip; the switch's press-and-release is one smooth continuous motion with no skipped positions; the room's light comes from the same single source throughout, with no new lamp appearing and none disappearing; at most one brief instant of motion blur, lasting well under a second, occurs during the fastest part of the switch action.
level_5: The scene holds together with no visible seams: the tube, its electrodes, the wires, the switch, and the stand never shift position, duplicate, or flicker in and out across the clip; the hand or mechanism operating the switch moves through one continuous, physically plausible arc from open to closed; the ambient light comes from one identifiable source the entire time, with no new light appearing when the tube glows and none of the existing light vanishing; the camera's distance and angle stay fixed with no unexplained jump cuts or zoom changes.