G4 LED bulbs

Among [LED bulbs], the G4 format is used especially in furniture, display cabinets, decorative lamps and 12 V systems, where compatibility with the transformer is just as important as the base itself. Manufacturers now offer specific G4 LED bulbs designed for 12 V low-voltage power supplies.

What is a G4 base

The G4 base uses two thin metal pins spaced approximately 4 mm apart. The bulb pushes directly into the lamp holder, with no screw thread or twist-lock mechanism.

This format originated from small halogen capsules used in compact light fittings. For this reason, many existing G4 installations operate at 12 V through a transformer positioned between the mains supply and the bulbs.

It should not be confused with G9. Although both light sources can have a capsule-like appearance, a G9 uses loop-shaped contacts spaced approximately 9 mm apart and is usually found in installations connected directly to mains voltage. G4 uses two straight pins positioned much closer together and is particularly associated with low voltage.

When replacing a G4 halogen bulb with LED, three details should be checked before installation: base, voltage and accepted power supply type. There are models designed for 12 V, and exact compatibility with the power supply equipment must be checked in the specifications of each bulb.

The transformer: the critical point

The transformer is one of the most critical factors when replacing G4 halogen bulbs with LED, because even if the bulb fits physically, the original power supply may not operate correctly with such low loads.

For example, an 80 W halogen installation may drop to just 8 W with LED, which can leave the transformer outside its operating range. Electronic transformers may be compatible in some cases, but many require a minimum load, which can cause flickering or start-up failures. A similar issue can occur with toroidal or ferromagnetic transformers: compatibility depends on the load, voltage and specific characteristics of the G4 LED bulb, so universal operation cannot be assumed.

When problems occur, the most reliable solution is usually to replace the transformer with a 12 V driver specifically designed for LED, correctly sized for the total power of the circuit. In some cases, using several G4 bulbs may help reach the minimum load required by the equipment, but this is not an ideal or always stable solution, so for complete upgrades it is preferable to use a system designed for LED.

It is also essential to check whether the bulb operates on 12 V AC, DC or both, as the G4 base alone does not guarantee electrical compatibility.

Axial or side pins

Although all G4 bulbs maintain the characteristic spacing between contacts, the position of the pins relative to the bulb body can vary depending on the design.

On some models, the pins extend along the longitudinal axis of the capsule. The bulb is therefore positioned facing directly away from the lamp holder. This is a common configuration when there is sufficient depth behind the light fitting.

Other models use a construction in which the luminous body is positioned differently in relation to the contacts. This geometry may be better suited to flat light fittings, furniture or small spotlights where the available space extends sideways rather than backwards.

The difference may seem minor, but in a furniture light fitting with only a few centimetres of depth it can be decisive. A bulb may have the correct G4 base and still fail to fit inside the housing because of the orientation or dimensions of its body.

Before replacing a halogen bulb, it is advisable to check how the original bulb is positioned and measure the available space from the lamp holder to the glass, reflector or cover.

Where G4 bulbs are used

G4 bulbs are found especially in applications where a small light source and a low-voltage installation are required. They are common in display cabinets, furniture, shelving, small decorative lamps, lighting hoods, caravans and certain 12 V systems.

In furniture and display cabinets, their small dimensions make it possible to integrate points of light without using bulky bulbs. The arrangement of the LEDs is particularly important here: a model with wide light distribution spreads the light more effectively in open fittings, while other designs concentrate more of the luminous flux in one direction.

When switching from halogen to LED, the thermal behaviour changes: energy consumption is lower, but the electronics still generate heat that must be dissipated. In enclosed fittings, it is advisable to avoid oversized models to prevent excessive temperature and shortened service life.

The amount of light should be assessed in lumens, not watts, taking into account the total luminous flux when several G4 bulbs are installed in the same fitting.

Colour temperature makes it possible to adjust the atmosphere: 2700–3000 K reproduces the warm appearance of halogen, while 4000 K provides a more functional neutral white for display cabinets or work areas.

Frequently asked questions

The main questions when replacing a G4 relate to the 12 V power supply, the existing transformer and the small dimensions of the light fittings in which this format is commonly used.

Do all G4 bulbs operate at 12 V?

The G4 format is strongly associated with low-voltage systems, and there are LED ranges specifically designed for 12 V. Even so, the rated voltage and whether the model supports AC, DC or both should always be checked before connection.

Can I use a G4 LED bulb with the transformer from a halogen lamp?

It may work, but it is not guaranteed. Some transformers require a certain minimum load, and the low power consumption of the LED may fall below that value.

What should I do if my G4 LED bulbs flicker?

One of the first components to check is the transformer. If it does not operate correctly with such a low LED load, it may need to be replaced with a 12 V power supply compatible with LED. It is also necessary to check that the AC or DC output of the equipment is suitable for the installed bulbs.

Can I solve the minimum-load issue by connecting several G4 bulbs?

With some transformers, yes, because the combined power of several bulbs may exceed the minimum load. However, when upgrading the entire installation, it is usually preferable to use a power supply specifically sized for LED.

Why does a G4 LED bulb not fit even if the pins match?

Because the base only defines the connection. The LED body may be longer, wider or oriented differently in relation to the pins.

This is especially common in furniture spotlights, display cabinets and light fittings where the glass is positioned very close to the bulb.

What is the difference between G4 and G9?

G4 uses two straight pins spaced approximately 4 mm apart and is commonly associated with low voltage. G9 uses two loop-shaped contacts spaced approximately 9 mm apart.

Which light colour is closest to a G4 halogen bulb?

To reproduce the warm appearance of a halogen capsule, around 2700 K or 3000 K is usually the best choice.