What types of ballasts are there?

There are three main types of ballasts used in professional lighting: conventional magnetic ballasts (KVG), which operate at mains frequency and have relatively high power losses of 10–20 per cent; low-loss magnetic ballasts (VVG), which use improved core materials to reduce losses to around 14 per cent; and electronic ballasts (EVG), which operate at high frequency (25–50 kHz) and offer the highest efficiency, lowest losses (around 5 per cent) and additional features such as flicker-free operation, dimming capability and extended lamp life. For LED lighting, dedicated LED drivers regulate either constant current or constant voltage to power LED modules. EVG and LED drivers are the preferred choice for modern professional event lighting installations due to their superior performance and energy efficiency.

When do you need a ballast?

You need a ballast whenever you operate a gas-discharge lamp, fluorescent tube or certain types of LED modules. Discharge lamps (including HMI lamps, metal-halide lamps, sodium-vapour lamps and fluorescent tubes) have a negative voltage-current characteristic: once the arc is struck, the current would rise uncontrollably without external current limiting, destroying the lamp within seconds. The ballast limits the current to the lamp's rated value and provides the high ignition voltage required to start the discharge. Some LED modules also require a ballast (called an LED driver) to regulate constant current or constant voltage, ensuring stable brightness and preventing thermal runaway. In professional event technology, ballasts are essential for moving heads, followspots, cyclorama lighting, fluorescent work lights and many LED fixtures.

What is EVG, KVG and VVG?

EVG stands for electronic ballast (Elektronisches Vorschaltgerät), a high-frequency ballast that operates lamps at 25–50 kHz, offering high efficiency, flicker-free operation, instant start and dimming capability. KVG stands for conventional ballast (Konventionelles Vorschaltgerät), a magnetic ballast operating at mains frequency with relatively high losses (10–20 per cent) and requiring a separate starter for fluorescent lamps. VVG stands for low-loss ballast (Verlustarmes Vorschaltgerät), an improved magnetic ballast with reduced losses (around 14 per cent) but still operating at mains frequency. In professional event lighting, EVG are the preferred choice due to their superior energy efficiency, lighting quality and compatibility with modern control systems. KVG and VVG have been largely phased out in the EU due to their poor energy performance.

Can you simply replace a fluorescent tube with an LED tube?

Replacing a fluorescent tube with an LED tube is possible, but compatibility with the existing ballast must be verified. Some LED tubes (retrofit or plug-and-play types) are designed to work with existing electronic ballasts (EVG) and can be installed as direct replacements. Other LED tubes require the ballast to be bypassed, with the tube connected directly to mains voltage; these tubes have an integrated driver and are not compatible with external ballasts. A third category, hybrid LED tubes, can operate either with an EVG or with direct mains connection. Always check the LED tube specification and follow the manufacturer's installation instructions. If the existing installation uses a conventional ballast (KVG) with a starter, the starter must be replaced with a starter bridge (bypass starter) when installing an LED tube. For professional event lighting applications, consult the luminaire and lamp documentation to ensure safe and reliable operation.

How do I connect a ballast?

Connecting a ballast requires careful attention to the manufacturer's wiring diagram. For conventional magnetic ballasts (KVG), the ballast is connected in series with the lamp: mains live connects to one ballast terminal, the other ballast terminal connects to one lamp pin, and the other lamp pin connects to mains neutral. A starter is connected in parallel with the lamp for fluorescent tubes. For electronic ballasts (EVG), the mains supply (live, neutral and earth) connects to the EVG input terminals, and the EVG output terminals connect directly to the lamp holders according to the wiring diagram (which varies depending on whether the EVG is a single-lamp or multi-lamp model). Any existing starter must be replaced with a starter bridge, and power-factor correction capacitors must be removed. Always isolate the mains supply before working on electrical installations, and if you are not confident in electrical work, engage a qualified electrician. In professional event installations, ensure all work complies with DGUV Vorschrift 17 and relevant electrical safety regulations.

How to test fluorescent lamp ballasts?

To test a fluorescent lamp ballast, first isolate the mains supply and verify that the circuit is de-energised. Visually inspect the ballast for signs of damage such as burn marks, melted insulation or bulging components. For magnetic ballasts (KVG, VVG), use a multimeter to measure the resistance of the ballast winding; a reading of a few ohms to a few hundred ohms (depending on ballast size) indicates the winding is intact, while an open circuit or very high resistance indicates a failed winding. For electronic ballasts (EVG), functional testing is more reliable than resistance measurement: reconnect the ballast to a known-good lamp and mains supply, and verify that the lamp ignites and operates normally. If the lamp fails to ignite, flickers continuously or produces abnormally low light output, the ballast is likely defective. In professional event applications, replace suspect ballasts rather than attempting repair, as ballast failure can cause lamp damage and create safety hazards. Always follow the manufacturer's testing and replacement guidelines.

Do LEDs need ballasts?

LEDs require a driver (a type of ballast) to regulate the current or voltage supplied to the LED, but the driver operates on different principles from traditional discharge-lamp ballasts. High-power LEDs used in professional stage lighting require constant-current drivers that maintain a fixed current (e.g. 350 mA, 700 mA or 1050 mA) regardless of the LED's forward voltage, preventing thermal runaway and ensuring stable brightness. LED strips and modular systems often use constant-voltage drivers (12 V or 24 V DC) with current regulation performed by resistors or ICs on the LED module itself. Some LED lamps (such as retrofit LED tubes and screw-base LED bulbs) have the driver integrated into the lamp base and can be connected directly to mains voltage. When upgrading from fluorescent tubes to LED tubes, verify whether the LED tube is compatible with the existing ballast (EVG) or requires the ballast to be bypassed. In professional event lighting, always use LED drivers specified by the luminaire manufacturer to ensure optimal performance, safety and longevity.

Which ballast suits my stage lighting application?

Choosing the right ballast for stage lighting depends on the lamp type, wattage, fixture design and control requirements. For HMI discharge lamps in moving heads and followspots, use a ballast specifically rated for the lamp wattage (e.g. HMI 575 W, 1200 W, 2500 W) and capable of delivering the required ignition voltage (typically several kilovolts). For fluorescent cyclorama lighting and work lights, electronic ballasts (EVG) are preferred due to their flicker-free operation, energy efficiency and compatibility with dimming systems. For LED-based stage lighting, use constant-current or constant-voltage LED drivers as specified by the luminaire manufacturer. In professional touring and rental applications, prioritise ballasts with robust construction, TÜV certification, DGUV Vorschrift 17 compliance and compatibility with your control protocol (DALI, DMX, 0–10 V). LTT's technical team can advise on ballast selection for specific luminaire models and installation scenarios, ensuring you specify the optimal solution for reliable, high-quality stage lighting.

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