Variac

Technical Details

Standard variacs for film sets operate with capacities between 2.5 kW and 20 kW at 230V input voltage. The core component is a toroidal transformer with a movable wiper contact, controlled by a crank or a knob. Professional models like the Strand Century 2513 achieve a control accuracy of ±2% and weigh approximately 25 kg at 5 kW. Mobile units feature CEE connectors and integrated fuses up to 63A.

History & Development

In 1934, the General Radio Company developed the first commercial variac for laboratory purposes. By the late 1940s, Hollywood studios adapted the device for film lighting, as it allowed for smoother transitions than mechanical dimmers. Mole-Richardson began producing the first film-specific variants with more robust housings in 1952. In the 1980s, European manufacturers like Strand Lighting established themselves with more compact designs for mobile productions.

Practical Use in Film

For candlelight scenes in "Barry Lyndon" (1975), Stanley Kubrick used variacs for micro-fine adjustment of light intensity without color shift. On set, the variac typically controls 2K and 5K Fresnel lights for facial illumination, as mechanical dimming creates shadows that are too harsh. For sunset sequences, it enables smooth brightness transitions across multiple takes. The disadvantage: at low voltage, the color temperature drops from 3200K to as low as 2800K, requiring color correction.

Comparison & Alternatives

Unlike electronic dimmers, the variac does not generate high-frequency interference and does not affect camera electronics. While modern LED panels with DMX control offer constant color temperature, they do not achieve the warm red shifts of dimmed tungsten light. Thyristor dimmers are more efficient but can flicker at low levels. For authentic candlelight or campfire ambiance, the variac remains unrivaled, whereas HMI lamps are generally not variac-compatible.