Question 1

What wattage discharge lamp do I need for my venue?

Accepted Answer

The required wattage for a discharge lamp depends on your venue size, throw distance and application. For small clubs and mobile DJ setups, 150 W to 250 W metal halide lamps (10,000–22,000 lumens) are typically sufficient. Medium-sized stages and corporate events benefit from 400 W lamps (30,000–36,000 lumens), which are the industry standard for professional moving heads. Large venues, outdoor festivals and long-throw followspots require 575 W to 1,200 W lamps (45,000–110,000 lumens). Calculate your required lux level at the target distance and consult fixture photometric data to determine the appropriate wattage. LTT's technical team can advise on lamp selection for your specific application.

Question 2

How do discharge lamps compare to LED alternatives?

Accepted Answer

Discharge lamps and LED fixtures each have distinct advantages. Discharge lamps — particularly metal halide types — deliver higher peak intensity from a compact source, creating sharper beams and more vivid aerial effects, which is why they remain preferred for large-scale touring productions and long-throw applications. They also offer superior colour rendering (CRI 80–95 for quality metal halide lamps) compared to many LED fixtures. However, LED technology has advanced rapidly: modern LED moving heads eliminate warm-up and restrike delays, consume less power, generate less heat and have much longer lifespans (20,000–50,000 hours versus 750–2,000 hours for discharge lamps). For applications requiring instant on/off control, low power consumption or minimal maintenance, LED is often the better choice. For maximum punch and traditional beam quality, discharge lamps still lead.

Question 3

What ballast is compatible with my discharge lamp?

Accepted Answer

Ballast compatibility depends on three factors: lamp wattage, lamp type (metal halide, high-pressure sodium or mercury vapour) and ignition technology (pulse-start or probe-start). A ballast designed for a 400 W metal halide lamp cannot safely operate a 250 W lamp or a high-pressure sodium lamp of any wattage. Additionally, pulse-start lamps require electronic ballasts with pulse-start ignition circuits; older magnetic ballasts designed for probe-start lamps will not reliably ignite pulse-start types. Always check the lamp manufacturer's datasheet for recommended ballast specifications, and verify that the ballast voltage and frequency match your mains supply. LTT stocks compatible ballasts and ignitors from Philips, Osram and Venture Lighting, and our technical team can confirm compatibility for your specific fixture.

Question 4

How long is the warm-up time for discharge lamps?

Accepted Answer

Metal halide discharge lamps typically require 2 to 10 minutes to reach full luminous output after ignition, depending on the lamp type and ballast. Pulse-start metal halide lamps with modern electronic ballasts warm up fastest, reaching 90% output in 2–3 minutes. Older probe-start lamps with magnetic ballasts may take 5–10 minutes to stabilise. High-pressure sodium lamps warm up slightly faster (1–3 minutes) but are rarely used in stage lighting due to poor colour rendering. Once extinguished, a hot discharge lamp cannot immediately restrike; the arc tube must cool for 5–15 minutes before the ignitor can re-establish the arc. This restrike delay is a significant limitation in live event applications where instant on/off control is required, and it is one reason why LED moving heads are increasingly replacing discharge types in touring rigs.

Question 5

What is the difference between pulse-start and probe-start discharge lamps?

Accepted Answer

Pulse-start and probe-start refer to the ignition method used to initiate the electrical arc in a metal halide discharge lamp. Probe-start lamps contain a third starting electrode inside the arc tube and require a lower ignition voltage (1–2 kV); they take longer to warm up (5–10 minutes) and exhibit more colour shift over their lifespan. Pulse-start lamps eliminate the starting electrode and use a brief, high-voltage pulse (3–5 kV) to ionise the gas; they warm up faster (2–3 minutes to 90% output), maintain more stable colour temperature and offer better lumen maintenance over their rated life. Pulse-start technology requires compatible electronic ballasts — older magnetic ballasts designed for probe-start lamps cannot reliably ignite pulse-start types. When replacing lamps, always verify that your ballast supports the ignition technology of the new lamp.

Question 6

Which discharge lamp suits outdoor events and architectural lighting?

Accepted Answer

For outdoor events and architectural floodlighting, high-pressure sodium (HPS) lamps in the 250 W to 1,000 W range offer the highest efficacy (80–140 lumens per watt) and excellent lumen maintenance, making them cost-effective for large-scale installations where colour rendering is not critical. Their warm yellow-orange light (2,000–2,500 K) suits decorative facade lighting and outdoor festivals. Where accurate colour reproduction is required — such as lighting performers, stages or branded installations — metal halide lamps are the better choice. A 400 W metal halide lamp delivers 30,000–36,000 lumens with a colour rendering index (CRI) of 65–90 and colour temperatures from 3,000 K to 6,500 K. Ensure outdoor fixtures have appropriate IP ratings (IP65 or higher) and that all electrical installations comply with local codes and DGUV Vorschrift 17 where applicable.

Question 7

How often should I replace discharge lamps in touring fixtures?

Accepted Answer

Professional touring companies and rental houses should replace discharge lamps at 70–80% of their rated lamp life to maintain consistent output and avoid on-stage failures. A lamp rated for 1,000 hours should be replaced after 700–800 operating hours, even if it still lights. Implement a lamp tracking system that records operating hours for each fixture, and mark lamps with installation dates. Lamps used in high-vibration environments (truck-mounted fixtures, outdoor festivals) or subjected to frequent on/off cycling may fail earlier than their rated life. Inspect lamp sockets and connectors regularly for corrosion or carbon buildup, which increases contact resistance and accelerates failure. Keep spare lamps on hand for critical fixtures, and always test replacements before the show. Proper maintenance ensures reliable performance night after night.

Question 8

Can I dim a metal halide discharge lamp with a standard dimmer?

Accepted Answer

No, you cannot dim a metal halide discharge lamp using a standard phase-control dimmer designed for incandescent or halogen lamps. Discharge lamps require constant current to maintain the arc; reducing voltage with a conventional dimmer causes the arc to become unstable or extinguish completely. To dim a metal halide lamp, you must use an electronic ballast with built-in dimming capability, such as Philips DynaVision or Osram Powertronic models. These ballasts can dim metal halide lamps down to 50–70% of full output while maintaining arc stability, though some colour shift may occur at lower levels. Dimming below 50% is generally not recommended as the arc becomes unreliable. Most professional moving-head fixtures with discharge lamps use mechanical shutters or iris diaphragms for intensity control rather than electronic dimming, preserving colour consistency and arc stability.