Norman Lamps, Inc.

Circular fluorescent bulbs provide efficient, even illumination in a compact, round format that fits perfectly in ceiling fixtures, wall sconces, and decorative lighting where a circular light source makes sense both functionally and aesthetically. The ring-shaped design allows for slim profile fixtures that mount close to the ceiling, making them popular in residential applications, hotel corridors, apartment buildings, and anywhere low-profile lighting is needed.

The most common sizes are designated by diameter: T9 circline bulbs (9-inch diameter), T6 circline bulbs (6-inch diameter), and smaller sizes for specialized applications. The "T" refers to the tube diameter in eighths of an inch – so a T9 has a 9/8-inch (approximately 1.1-inch) tube diameter. These bulbs typically use a 4-pin G10q base where all four pins are equally spaced around a central mounting plate. The bulb simply twists and locks into the socket.

Wattage options typically range from 20W to 40W depending on bulb size, providing light output equivalent to 75W to 150W incandescent bulbs while using a fraction of the energy. The circular design distributes light evenly in all directions, making these bulbs well-suited for general ambient lighting rather than directional or task lighting. Color temperature options include warm white (2700K-3000K) for comfortable residential lighting and cool white (3500K-4100K) for brighter, more energizing light.

Circular fluorescent fixtures require a ballast to operate the bulb, and older fixtures may have magnetic ballasts that can hum audibly and be less efficient than newer electronic ballasts. If you're experiencing flickering, humming, or difficulty starting, the ballast may need replacement along with the bulb. Some newer circular fluorescent fixtures use electronic ballasts that are quieter, more efficient, and provide instant-on operation without flicker.

The circular form factor makes these bulbs particularly suitable for certain fixture types. Ceiling-mounted fixtures for hallways, closets, and bathrooms often use circular fluorescents because the round bulb matches the round fixture opening, creating a clean, integrated appearance. Decorative fixtures in mid-century modern or contemporary styles may use exposed circular bulbs as a design element. Wall sconces with circular fluorescent bulbs provide efficient ambient lighting in corridors and common areas.

LED replacements for circular fluorescent bulbs have become increasingly available, offering the usual LED advantages: 75-85% energy savings compared to fluorescent, 25,000-50,000 hour lifespan versus 10,000 hours for fluorescent, instant-on with no warm-up, and no mercury content. However, retrofitting to LED isn't always straightforward – some LED circular bulbs work with existing fluorescent ballasts, while others require ballast bypass. Check compatibility before purchasing LED replacements.

Common Applications: Ceiling fixtures in hallways, closets, bathrooms, and bedrooms; wall sconces; apartment and hotel lighting; decorative fixtures; anywhere low-profile, efficient lighting is needed

Standard Sizes: 6-inch (T6), 8-inch (T5), 9-inch (T9), 12-inch (T9), 16-inch (T9) diameter. Most use 4-pin G10q base. Wattages typically 20W-40W.