How to identify G4
- The two thin, straight pins are very close together.
- Measure center to center, not outside edge to outside edge.
- Read the old lamp for its voltage before buying an LED replacement.
Where it is commonly used
Common use is a clue, not proof. The fixture label and model documentation take priority over a visual match.
Bulb shapes sold with this base
You may see these shapes with a G4 base. The base code does not guarantee the bulb width, length, beam angle, or clearance.
Before you buy a replacement
- G4 and G9 are not interchangeable.
- Some LED replacements are too wide or long for the original cover.
- Transformer compatibility can affect LED performance.
Quick answers
Questions about the G4 bulb base
What is a G4 bulb base?
A G4 bulb base has two thin straight pins with nominal 4 mm center-to-center spacing. G4 identifies the connection only; it does not specify voltage, AC or DC supply, capsule size, or transformer compatibility.
What size is a G4 bulb base?
G4 has a nominal 4 mm pin spacing. Pin spacing is measured from the center of one pin to the center of the other. Use the printed base code when available because a visual estimate is not conclusive.
Where is a G4 bulb base commonly used?
Common examples include puck lights, cabinet lights, landscape lights, small desk lamps. Fixture type is only a clue; confirm the code on the bulb, socket, fixture label, or manufacturer documentation.
Can I choose a G4 replacement by appearance alone?
No. Match the G4 connection first, then verify voltage, actual input wattage, bulb dimensions, fixture restrictions, controls, and any enclosure or location rating required by the installation.
What does the 4 in G4 mean?
It identifies nominal 4 mm center-to-center pin spacing. G4 does not by itself specify the capsule dimensions, voltage, wattage, or fixture rating.