Updated: August 13, 2025

TL;DR: When metal halide lighting flickers, buzzes, fails to start, runs hot, or burns out early, the ballast is often the root cause. Match the lamp and ballast by ANSI code, verify line conditions, and replace aging components to restore stable output and lamp life.

What a Metal Halide Ballast Does

A metal halide ballast regulates voltage and current so the arc inside the lamp can start and operate safely. HID ballasts are evaluated to UL 1029 for HID ballasts, which covers ballasts and starting circuits for HID lamps, including metal halide. See the scope in UL 1029, High‑Intensity‑Discharge Lamp Ballasts.

5 Common Metal Halide Ballast Problems and Fixes

1) Flickering, dimming, or cycling

Flicker or repeated on‑off cycling often appears near end of lamp life or when the ballast cannot maintain proper lamp voltage. It can also indicate a weak capacitor, loose wiring, or a mismatch between lamp and ballast. Confirm that the lamp and ballast share the correct ANSI “M‑code” pair and tighten all terminations. Replace swollen or out‑of‑tolerance capacitors or the ballast as needed. Background on lamp–ballast interchangeability is in ANSI C78.380 overview (RPI Lighting Research Center) and a practical primer on ANSI codes and matching.

2) Long warm‑up or failure to ignite

If a lamp never strikes or takes much longer than normal to reach full output, test the ignitor on pulse‑start metal halide systems and verify open‑circuit voltage (OCV) from the ballast. Replace a failed or mismatched ignitor. If the ballast shows out‑of‑spec OCV or visible heat damage, replace it with a compatible, listed assembly. See manufacturer procedures in OSRAM SYLVANIA HID Troubleshooting Guide.

3) Loud buzzing or humming

Magnetic HID ballasts produce audible sound because of magnetically induced vibration. Excessive noise can point to loose mounting or aging parts. Tighten hardware, verify the fixture is secured, and consider a quieter design such as a potted F‑can or an electronic HID ballast, both of which are engineered for reduced noise and cooler operation compared with open core‑and‑coil units. See examples in the Philips Advance HID brochure and GE’s summary of Electronic UltraMax HID ballasts, as well as F‑can notes on quiet operation in GE F‑can spec sheet.

4) Overheating ballast

A ballast that is too hot to touch or that shows charring or bulged capacitors is at risk of failure. Check ambient temperature in the gear compartment, confirm the case temperature rating, and improve airflow. Replace thermally stressed ballasts and any swollen capacitors. If line voltage is consistently high or low, correct it at the supply. For small adjustments, a buck‑boost transformer can bring voltage back into spec. See the Eaton buck‑boost design guide and a plain‑language primer on buck‑boost applications.

5) Short lamp life or frequent burnouts

Frequent burnouts often trace back to a ballast delivering the wrong wattage or a poor lamp–ballast match. Confirm the ANSI codes, verify capacitor value against the ballast specification, and replace aging gear. CWA ballasts regulate wattage but still track line voltage, so off‑spec supply can shorten life. See the regulation discussion in the Advance HID technical brochure. To reduce rupture risk, use lamps and luminaires per their ratings. For open fixtures, use lamps marked for open use as outlined in GE’s protected metal halide brochure.

When to Replace the Ballast

Replace the ballast when any of the following are persistent after basic checks and lamp replacement:

• Cycling that returns after lamp replacement.

• Failure to ignite after ignitor and OCV testing.

• Audible noise that remains after securing the fixture.

• Case overheating or visible damage such as charring or swollen capacitors.

• Out‑of‑spec open‑circuit or operating voltage.

Choose a listed replacement that matches the lamp ANSI code and wattage. Record the fixture label and wiring diagram for future service.

Safety and Code Notes

• Follow the listing and labeling. Install listed equipment in accordance with the manufacturer’s instructions. See NEC 110.3(B) summaries at IAEI and Electrical License Renewal.

• Luminaire disconnects. In the 2023 NEC, the disconnecting‑means rule that was in 410.130(G)(1) was relocated to 410.71 and expanded to LED luminaires with double‑ended lamps and serviceable gear. See overviews from Electrical License Renewal and IAEI Magazine. Always verify adoption and enforcement with your AHJ.

• Qualified work only. De‑energize, lock out, and use appropriate PPE before opening gear compartments. See OSHA 29 CFR 1910.333 and your company’s NFPA 70E program for details.

Need parts fast?

Use a listed, compatible metal halide ballast kit matched to your lamp’s ANSI code and wattage. For small line‑voltage corrections, choose a properly sized buck‑boost transformer per the design requirements.

About Revco

Since 1978, Revco Lighting & Electrical Supply has been helping professionals bring their projects to light—literally. As a go-to source for lighting and electrical products across Long Island, NY and nearby areas, we specialize in supporting contractors, builders and industry experts with practical solutions and dependable service. Whether it’s a complex commercial build or a simple residential upgrade, we’re here to make sure you have what you need, when you need it.