LED Bulbs by Base Type

LED bulbs by base type: identify yours and get it right first time

The base is the part that connects the bulb to the lampholder, and it is what decides whether a model fits your light fitting or not. If you are looking for a bulb by base type, this category has the full catalogue sorted by connection: E27, E14, GU10, AR111, G4, G9 and the installation accessories. On screw bases, the letter E stands for the Edison system and the number is the diameter in millimetres: an E27 large screw bulb has a 27 mm thread, and an E14 small screw bulb or narrow base bulb has a 14 mm thread.

How to identify the base on your lamp

Switch off the light, wait for the bulb to cool down and take it out. Then look at the base:

• Spiral thread: it is an E type base. Measure the diameter with a ruler: 27 mm is E27 and 14 mm is E14.
• Two thick pins with a head that push in and twist to lock: this is a GU10 bayonet base, typical of spotlights.
• Two thin straight pins set close together: this is a bi-pin. Short pins with a round section are usually G4; flat, looped pins are G9.
• Long cylinder with a contact at each end: this is a linear R7S base, common in old halogen floodlights.
• Wide base with a mirrored reflector and two pins: that is an AR111, for large diameter spotlights.

Quick tip: almost every bulb has the base code printed on the neck or the base itself, next to the wattage and voltage. If you still have the old one, the answer is right there with no measuring at all.

Narrow or wide thread: the difference between E14 and E27

These are the two most common bases in the home and they are not interchangeable. The E27 takes larger, higher output bulbs, so it is the one used when you want to light a whole room. The narrower E14 is reserved for smaller fittings and for candle or golf ball bulbs, where the aim is supporting light or a decorative detail.

Which base each type of fitting usually takes

• Ceiling lights and flush mounts: mostly E27; on multi-arm models, E14.
• Wall lights: E14 and G9 when the fitting has a slim profile.
• Desk lamps and task lights: E27 on the classic ones and E14 on compact models.
• Table lamps: E14 or E27 depending on the shade diameter.
• Recessed spotlights and track lighting: GU10, and AR111 on large format downlights.
• Cabinet, display case and cooker hood lighting: G4 and G9.

Why switching to LED while keeping the same base makes sense

The great advantage of a retrofit LED is that you do not have to touch the wiring: you pick the same base you already had and swap the bulb. From there you gain in service life (between 15,000 and 25,000 hours compared with the 1,000-2,000 hours of an incandescent or halogen) and in consumption, because you get the same lumens from a fraction of the wattage. Set the colour temperature to suit the room as well: 2700-3000K warm white for living rooms and bedrooms, 4000K neutral white for kitchens and bathrooms, and 6000K cool white for work areas. And if the fitting is wired to a dimmer, check that the model is dimmable before you buy it.

Find your base, filter the category and compare everything at FactorLED: we have E27, E14, GU10, AR111, G4 and G9 LED bulbs with the wattage, beam angle and colour temperature you need for every light point in your home or business.

Frequently asked questions about LED bulbs by base type

How do I know which base I need?

Take out the current bulb and look at the base. If it is a screw type, measure the diameter: 27 mm is E27 and 14 mm is E14. If it has two pins that twist into place, it is GU10; if it has two thin pins, it is G4 or G9. The code is usually printed on the bulb itself too.

Which is the narrow base bulb and which is the wide one?

The narrow one is the E14, with a 14 mm thread, and the wide one is the E27, with 27 mm. These are the two most common screw sizes in home lighting.

Can I fit an E14 bulb into an E27 lampholder?

Not directly, because the threads have different diameters. You can do it with a base adapter, as long as the final bulb still fits in the space available inside the fitting.

Which base do recessed spotlights use?

The most common is GU10, a bayonet type with two pins and a direct 230V connection. Larger diameter downlights use AR111, and in cabinets and tight spaces you will find G4 and G9 bi-pins.