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Tubular shapes

T4 bulb shape and size

T4 is the narrow tubular bulb designation. Its nominal maximum diameter is 0.5 inches. T4 products use several unrelated bases and voltages. The base, voltage, light output, and exact overall length come from the individual lamp specification.

Representative family profile and nominal maximum diameter only. Overall length is not to scale, and the base is intentionally omitted.

Dimensions

What T4 tells you

Shape
narrow tubular bulb
Nominal diameter
0.5 in (13 mm)
Typical bases
G4, G9, E12
Common uses
cabinet lights, appliances, display fixtures

The diameter is part of the naming system, not a full dimension drawing. Individual models can differ in overall length, neck profile, optics, and manufacturing tolerance. Use the maker's drawing when the fit is close.

At the fixture

Four other details to record

  1. Read the base code and voltage on the old lamp or fixture label.
  2. Compare the published maximum diameter and overall length with the available space.
  3. Record lumens, beam angle where relevant, color temperature, and dimming behavior.
  4. Look for the enclosure, location, temperature, or vibration rating required by the fixture.

Easy to miss

Notes for T4

  • T4 products use several unrelated bases and voltages.
  • Match length and base, not tube diameter alone.

Sources

Reference method

BulbMatch uses the U.S. eighth-inch naming convention as a nominal shape reference and keeps model-specific dimensions separate.