Understanding the Type of Ballast You Might Have in Your Fixture

How can I tell if the Feit Electric Linear Tubes I bought will fit and work with the lamp holders in my fixture?

Linear tube lights, such as fluorescent and LED tubes, come in different pin configurations—single-pin or two-pin—due to their design and compatibility with specific ballast types. Here’s a quick breakdown of the differences, the evolution of ballast technology, and key considerations for fixtures and retrofits.

Why Single-Pin or Two-Pin?

Single-Pin Tubes: These are commonly designed for instant-start ballasts. The single pin on each end allows for a quick electrical connection, making them ideal for setups requiring frequent on/off cycling.

Two-Pin Tubes: These work with rapid-start or preheat ballasts and require two electrical connections to preheat the cathodes before ignition. Preheating helps extend the tube’s lifespan, making these more common in residential or smaller-scale setups.

Ballast Evolution

• Preheat Ballasts (1930s-1940s): The oldest type, requiring a starter to preheat the lamp’s electrodes before ignition.
• Rapid-Start Ballasts (1940s-1950s): An improvement over preheat ballasts, these eliminate the need for a starter by providing continuous low-level heating to the electrodes.
• Instant-Start Ballasts (1950s-1960s): The newest type, designed for efficiency and ease of installation. These ignite the lamp without preheating, enabling quicker starts but reducing the lamp’s lifespan slightly.

Fixture Considerations: Shunted vs. Non-Shunted

Shunted Tombstones:

• Internal electrical contacts are joined, creating a single path for electricity.
• Commonly used with instant-start ballasts.
• Compatible with most single-ended LED tubes, simplifying wiring during retrofits.

Non-Shunted Tombstones:

• Electrical contacts are isolated, allowing separate circuits for preheating.
• Required for rapid-start or programmed-start ballasts.
• Occasionally found in single-ended fixtures that support preheat systems or have been converted for specific purposes.

LED Retrofits: What You Should Know

Most single-ended LED tubes are designed for shunted tombstones because of their simplicity and compatibility with instant-start systems. However, some LEDs require non-shunted tombstones. Always check the fixture or ballast manufacturer’s specifications to avoid mismatched components, which could lead to safety hazards.

Usage & Tips:

• Single-pin tubes are tailored for quick-start commercial applications, while two-pin tubes prioritize lamp longevity through preheating.
• Instant-start ballasts dominate modern commercial setups but preheat and rapid-start systems paved the way in earlier decades.
• Single-ended fixtures are mostly shunted but not exclusively. Always confirm the type of tombstones in your fixture when replacing or retrofitting tubes to LEDs.
• Make sure the linear tubes with two switch pins are fully pushed into place during installation to ensure they work correctly. (See image below)