How to identify GU4
- Measure pin centers.
- Check for GU4 or MR11 markings.
- Read voltage before choosing an LED.
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 GU4 base. The base code does not guarantee the bulb width, length, beam angle, or clearance.
Before you buy a replacement
- GU4 is not GU5.3.
- MR11 describes the reflector, not the electrical system.
- Check transformer and dimmer compatibility.
Quick answers
Questions about the GU4 bulb base
What is a GU4 bulb base?
GU4 uses two straight pins spaced a nominal 4 mm apart and is commonly paired with MR11 reflectors.
What size is a GU4 bulb base?
GU4 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 GU4 bulb base commonly used?
Common examples include mr11 spotlights, display lighting, landscape fixtures, compact downlights. Fixture type is only a clue; confirm the code on the bulb, socket, fixture label, or manufacturer documentation.
Can I choose a GU4 replacement by appearance alone?
No. Match the GU4 connection first, then verify voltage, actual input wattage, bulb dimensions, fixture restrictions, controls, and any enclosure or location rating required by the installation.