**Choose a ballast that explicitly supports your exact tube type, the number of tubes it will operate, and your fixture’s supply voltage.** The old ballast’s model number is a useful starting point; confirm a replacement against its manufacturer’s lamp table and wiring diagram.

Before opening the ballast compartment, disconnect power at the breaker or unplug the fixture, and verify that it is de-energized. Use an electrician if you cannot safely identify and test the wiring. [Manufacturer safety instructions](https://ledvance.com/00_Free_To_Use/asset-13148562_led_t8_ledlescent_installation_manual.pdf)

Record these details:

| Item | What to check |
|---|---|
| **Tube designation** | Read the printing on the tube—for example, `F32T8` or `F40T12`. Match the complete lamp designation, including any HO/high-output designation. Matching length alone is insufficient. |
| **Lamp count** | Count the tubes connected to each ballast. A four-tube fixture may contain two ballasts. The replacement must list your intended lamp count. |
| **Supply voltage and frequency** | Match the actual electrical supply to the ballast’s input rating. “Universal voltage” covers only the range printed on that product. |
| **Physical fit** | Check case dimensions, mounting holes, available space, and lead lengths. |
| **Wiring and lampholders** | Check the replacement’s wiring diagram and socket requirements. Wire count and colors can differ from the old ballast. |
| **Operating conditions** | Check minimum starting temperature, particularly for garages or outdoor fixtures, and compatibility with any dimming or emergency equipment. |

Manufacturers provide selection tables organized by lamp type, wattage, and quantity. For example, [Fulham’s selection tool](https://www.fulham.com/contact-us/wiring-diagrams/) supplies the corresponding wiring diagram; [Advance’s ballast catalog](https://www.signify.com/advance/en-us/solutions/ballasts) lists lamp and input-voltage combinations.

For an upgrade, choose an **electronic fluorescent ballast** approved for your lamps. Then consider:

- **Starting method:** Programmed-start ballasts preheat the lamp electrodes and suit frequent switching, including occupancy-sensor use. Instant-start ballasts suit lamps that remain on for extended periods. Changing starting methods may require rewiring or replacing lampholders; programmed-start models commonly require **non-shunted sockets**, whose two contacts are electrically separate. [Advance starting guidance](https://www.assets.signify.com/is/content/Signify/Assets/philips-lighting/united-states/20190814-philips-lighting-sg-100-2019-full.pdf), [Fulham socket requirements](https://www.fulham.com/PDFs/SpecSheets/InstallSheet-Intelligent-Ballast.pdf)
- **Brightness and energy use:** Compare the manufacturer’s system light output and input watts for your lamp combination. Ballasts are offered with different ballast factors, so compatible replacements can produce different brightness. [Advance product options](https://www.signify.com/advance/en-us/solutions/ballasts)

**Follow the new ballast’s wiring diagram.** A T12-to-T8 conversion requires a ballast approved for the new T8 lamps and compatible fixture components. Similar-looking tubes can have different electrical requirements.

If your goal is an LED upgrade, select the LED system first. Ballast-compatible tubes require a ballast on the lamp manufacturer’s compatibility list; ballast-bypass tubes require the specified fixture rewiring. [LEDVANCE retrofit guidance](https://www.ledvance.com/en-us/professional-lighting/insights/blog/lighting-basics/do-led-lights-need-a-ballast)

For a specific replacement, provide the tube designation, old ballast model or label photo, tube count, and your country or supply voltage.