lighting
Light-source spectrum for stop-motion
Lighting
Definition
Light-source spectrum for stop-motion is the distribution of wavelengths a fixture sends onto puppets and sets, and therefore the range of reflected colour the camera can record. Tungsten produces a smooth thermal spectrum with a warm bias; LED spectra are engineered and may range from uneven phosphor output to broad, multi-emitter systems with excellent colour rendition. The choice cannot be reduced to “tungsten natural, LED artificial”: the actual fixture, dimming level, camera sensor, gels, and puppet materials must be tested together.
Overview
A surface has no fixed photographed colour independent of its illumination. Paint, fabric, silicone, resin and wood each reflect some wavelengths more strongly than others; the camera records the product of that material response, the light source's spectral power distribution, and the sensor's own red, green and blue sensitivities. White balance can remove an overall warm or cool cast, but it cannot make two different spectra equivalent. If a wavelength needed by a pigment is strongly underrepresented in the source, there is little reflected signal for grading to recover.
A tungsten filament is a thermal radiator. Its output forms a smooth spectrum across the visible range rather than a small set of isolated peaks, which is why cinematographers describe it as full-spectrum and why coloured materials and gels tend to behave predictably under it. “Full-spectrum” does not mean neutral daylight: cinema tungsten is warm, with much more red energy and less blue than daylight, and it becomes warmer as voltage is reduced for dimming. Its other penalties are substantial electrical load and heat -- serious constraints around miniature sets, adhesives, clay, silicone skins and animators working close to the lamps.
A white LED is an engineered source, not one fixed spectrum. A basic phosphor-converted LED may show a strong blue pump and uneven output elsewhere, while a modern multi-emitter cinema fixture can build a much smoother distribution and excellent colour rendition. This is why one average number such as CRI cannot settle the choice by itself; systems such as IES TM-30 examine fidelity, gamut and hue-specific shifts in more detail. LED also brings benefits that matter directly to stop motion: lower heat at the subject, lower power demand, compact fixtures, repeatable electronic control and, in suitable cinema units, stable output. The useful distinction is therefore not tungsten versus LED in the abstract, but a known tungsten lamp versus a specific LED fixture at the intended colour and dimming settings.
Pinocchio provides a valuable production example, but also a warning against inventing motives after the fact. Passingham said that studios were selling tungsten equipment, allowing him to stretch the lighting budget; he then used tungsten principally for key light, converted some tungsten housings to LED, and used LED for indirect, fill and bounce light. The interview establishes that division of labour and the budget context. It does not say that continuous spectrum was his reason for assigning tungsten to the key. A reasonable craft interpretation is that the direct key has the greatest influence on modelling, shadow and visible surface colour while efficient, cool LEDs scale well across numerous indirect sources -- but that remains interpretation, not Passingham's stated explanation. The rigorous lesson is to test the exact sources on the exact puppet materials, rather than turn one production's equipment plan into a universal hierarchy.
Workflow
- Photograph a grey target, a colour chart, and the actual puppet and set materials under every proposed key, fill and practical fixture using the production camera and working colour pipeline.
- Test each source at the exact colour-temperature and dimming settings intended for the shot. Tungsten warms as it is dimmed; an LED's spectrum and control behaviour depend on the specific fixture and mode.
- Repeat the test through any gels, diffusion and bounce surfaces. A filter can only subtract or reshape wavelengths already present; it cannot create a wavelength the source does not emit usefully.
- Compare full-resolution captures, not only the live-view monitor. Check neutral balance, saturated paints, skin materials, fabrics, deep reds and cyans, and any pair of materials that must match across replacement parts.
- Run a timed still sequence to test frame-to-frame stability and flicker, then record fixture model, mode, output, colour setting, DMX value, camera white balance and exposure with the shot lighting plan.