R40 bulb shape and size

Dimensions

What R40 tells you

Shape

large reflector bulb

Nominal diameter

5 in (127 mm)

Typical bases

E26

Common uses

large recessed fixtures, heat-lamp-style housings

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 R40

• Do not assume a general LED is suitable for heat-lamp service.
• Check physical depth and fixture label.

Sources

Reference method

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

• LEDVANCE guide to light bulb shapes, types, and sizes
• U.S. Department of Energy: lumens and lighting choices