G4 LED Bulbs — Low-Voltage Capsule

G4 bulb

G4 LED bulbs are the compact capsule replacement for halogen bi-pin lamps used in low-voltage fittings, cabinet lights, and decorative pendants. Lumination stocks G4 LED capsules from Lampfix and Magnalux in warm white (2700K) and cool white (4000K), covering 12V AC/DC and mains-voltage variants.

G4 LED Bulbs — Low-Voltage Capsule Replacements

G4 LED capsules replace the 10W–20W halogen bi-pins found in low-voltage ceiling fittings, table lamps, and recessed cabinet lights. The LED equivalent typically draws 1.5W–3W while delivering comparable light output in the 150–250 lumen range. Most G4 LED bulbs measure just 30–35mm in length, making them a direct physical swap in most fittings. Lumination recommends checking whether your transformer is dimmable before switching, as not all LED G4s are compatible with older magnetic transformers.

Dimmable G4 LED Options and Voltage Compatibility

G4 LED bulbs are available in 12V and mains 240V versions — confirm your fitting's voltage before ordering. Dimmable G4 LEDs require an LED-compatible dimmer and a suitable LED driver or transformer. Lumination's team at the Taunton and Wellington showrooms can advise on transformer compatibility and dimmer pairing for your existing low-voltage lighting installation. Warm white (2700K) G4 LEDs suit decorative and ambient fittings; cool white (4000K) suits task and under-cabinet applications. Browse our full LED bulb range for other capsule and retrofit options.

Frequently Asked Questions

G4 LED bulbs may not be compatible with all low-voltage transformers, particularly older magnetic (iron-core) transformers. Electronic transformers are generally more compatible with LED loads. Lumination recommends confirming whether your existing transformer is rated for LED use before purchasing. The minimum load rating is important — LED capsules draw only 1.5W–3W each, and some transformers require a minimum load to operate correctly. Lumination's lighting specialists at our Taunton and Wellington showrooms can advise on transformer compatibility. With 25 years of specialism in residential lighting, we help customers avoid the common pitfall of purchasing LED bulbs that flicker or fail to light on their existing low-voltage circuits.

A 20W halogen G4 capsule produces approximately 200–250 lumens. An LED G4 drawing 2W–3W typically matches this output. Lumination stocks G4 LED capsules from Lampfix and Magnalux across multiple wattage and lumen grades. The key figure to compare is lumens, not watts — a 2W LED G4 can match or exceed the output of a 20W halogen while running at 90% lower energy consumption. Our product listings confirm lumen output for each capsule so you can select the right brightness level for your fitting. Customers with 1,797+ Google reviews at 4.8 stars consistently praise the accuracy of our bulb recommendations.

Most G4 LED bulbs are designed for 12V AC or DC low-voltage circuits. However, some G4 LED capsules are available for mains 240V use — these contain an integrated driver and are slightly larger in size. Lumination's G4 LED range clearly indicates the operating voltage on each product page. Using a 12V G4 LED on mains voltage will damage the bulb immediately, so always confirm the voltage before ordering. If you are unsure whether your fitting runs on 12V or 240V, Lumination's specialists at our Taunton and Wellington showrooms can help you identify the correct bulb type for your installation before purchase.

Dimmable G4 LED capsules are available, but they require a compatible LED dimmer switch and an LED-rated transformer or driver. Not all G4 LED bulbs are dimmable — check the product specification carefully. Lumination stocks dimmable options from Lampfix and Magnalux for customers who need dimming capability in their low-voltage fittings. Standard trailing-edge LED dimmers are typically compatible; leading-edge dimmers designed for halogen may not work correctly. Lumination's team, with 25 years of specialism in residential lighting, can confirm dimmer and driver pairings for your specific installation. Free delivery is available on orders over £75.

G4 LED bulbs are available in warm white (2700K), neutral white (3000K), and cool white (4000K). Warm white (2700K) is the most popular choice for decorative pendants, table lamps, and ambient living spaces — it closely matches the tone of the halogen capsule it replaces. Cool white (4000K) suits task lighting applications such as under-cabinet lighting and kitchen worktop illumination. Lumination stocks both warm and cool white G4 options from Lampfix and Magnalux. At our Taunton and Wellington showrooms, you can view colour temperature samples in person to confirm the right tone for your room before ordering.