Electronic ballast for HMI fixtures that delivers flicker-free light above 12 fps via high-frequency current regulation (20–100 kHz), enabling smooth dimming control.
Technical Details
Modern electronic ballasts operate with switching frequencies between 20-100 kHz and achieve efficiencies of 95-98%. The ignition voltage ranges from 2-5 kV depending on the lamp type, and the operating current is regulated to within ±2%. Film-specific electronic ballasts like the ARRI EB MAX 2.5K/4K deliver flicker-free light from 12 fps through True RMS current regulation. The devices contain power transistors (MOSFET or IGBT), high-frequency transformers, and microcontrollers for regulation. Three main types are distinguished: Dimmable electronic ballasts (0-100% continuously variable), Flicker-Free electronic ballasts for slow motion, and standard electronic ballasts for continuous light.
History & Development
The first electronic ballast was developed by General Electric in 1973 for office lighting. ARRI introduced the first film-specific electronic ballast for HMI lights in 1987 – the EB 1.2K. The breakthrough came in 1994 with flicker-free electronic ballasts, which enabled constant illumination even at shooting speeds of 1000 fps. Since 2010, digital electronic ballasts with IGBT technology have dominated, offering precise dimming curves and remote control via DMX512.
Practical Application in Film
In "Mad Max: Fury Road" (2015), flicker-free electronic ballasts enabled slow-motion shots with HMI daylight simulation in the desert. Modern sets like "The Mandalorian" use dimmable electronic ballasts for LED walls to synchronize lighting frame-by-frame. Electronic ballasts eliminate the 50 Hz flicker of conventional ballasts, which leads to brightness fluctuations at 25 fps. Stepless dimming replaces scrim changes and speeds up lighting setup by up to 30%. Disadvantage: Electronic ballasts generate high-frequency interference that can affect radio microphones in the 2.4 GHz band.
Comparison & Alternatives
Conventional ballasts (KVG) with iron-core inductors operate at the 50 Hz mains frequency and cause visible flicker at variable frame rates. LED drivers are increasingly replacing electronic ballasts in film lighting, but offer less light output per unit of weight. Magnetic ballasts remain more reliable than electronic ballasts at extreme temperatures (below -20°C). Battery-powered electronic ballasts like the Dedolight DLOBML enable mains-independent HMI lighting for up to 45 minutes runtime.